Prof. Satendra Sharma

8/12/2019 Prof. Satendra Sharma

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CHAPTER -1

INTRODUCTION

The increasing demand for wireless communication systems spurs on the need for

antennas capable of operating at a wide frequency band. Owing to their attractive

merits such as simple structure, pure polarization, and omnidirectional radiation

pattern, the conventional monopole and its variants have been widely used in wireless

communications. However, their inherent narrow bandwidth has been a setback to be

overcome in broadband applications. Moreover, the vertical monopole antenna has a

relatively large height of /4, thus it is not recommended when a low profile is desired.

To realize a monopole-like radiation pattern with low profile and relatively wide

bandwidth an alternative approach that makes use of the higher order modes of circular

or annular-ring microstrip antennas has been developed .The microstrip antenna

designs usually suffer from a narrow impedance bandwidth (typically 50%) because of

its high-Q resonant feature. Recently, another approach that makes use of the directions

of surface waves at the ground plane boundary is proposed to obtain a monopole-like

pattern. This type of surface wave antenna only requires a low profile of thickness


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The meaning of Energy Harvesting (also called energy scavenging or power

harvesting), is the process by which energy from different sources is captured and

stored. Generally, this definition applies when we talk about autonomous devices that

require a low amount of energy to function.

Currently, energy harvesters do not provide sufficient amount of power to produce

mechanical movements or temperature changes (cooks, refrigerators, etc) because there

are not technologies that capture energy with great efficiency. But these technologies

do provide the amount of energy needed for low-power devices that can operate

autonomously.

Another advantage of this type of technology is that, unlike the production of large-

scale power, we can consider that the energy source is free if you take into account the

electromagnetic energy of transmitting mobile stations and radio and TV broadcasting

antennas.

The use of batteries has two disadvantages: the lifetime of the batteries is very limited

even for low-power batteries, requiring impractical periodical battery replacement, the

use of commercial batteries usually overkills the power requirements for uW sensor

nodes, adding size and weight while creating the problem of environmental pollution

due to the deposition of these batteries, as well as increases significantly the cost

overhead of disposable nodes.

1.1GOAL

The project guidelines are to design and fabricate an antenna that transmits or receives

UWB signals. An antenna is a transducer between a guided wave propagating in a

transmission line, and an electromagnetic wave propagating in an unbounded medium,

like air. All wireless systems have a transmitting antenna and a receiving antenna. The

transmitting antenna is the antenna that obtains the signal from the source. The

receiving antenna is the antenna that outputs the desired signal to a receiver. Antennas

are used for many applications; one of the more recognizable applications is radio. The

receiving antenna on a car collects the signal from the radio station and outputs the

signal into the receiver. Music can now be heard in the car. Over the designated

bandwidth of UWB system (3.1-10.6 GHz). So the main goal of the project is to design

an antenna that is used for UWB applications.


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1.2 WHY ULTRA-WIDEBAND

The concept of Ultra-Wideband (UWB) was formulated in the early 1960s through

research in time-domain electromagnetic and receiver design, both performed primarilyby Gerald F. Ross. Through his work, the first UWB communications patent was

awarded for the short-pulse receiver which he developed while working for Sperry

Rand Corporation [1]. Throughout that time, UWB was referred in broad terms as

carrierless or impulse technology. The term UWB was coined in the late 1980s to

describe the development, transmission, and reception of ultra-short pulses of radio

frequency (RF) energy. Even though the knowledge has been in existence for over

thirty years, UWB technology is an emerging research topic in the wireless

communications field for a variety of reasons. For communication applications, high

data rates are possible due to the large number of pulses that can be created in a short

time duration. Due to its low power spectral density, UWB can be used in military

applications that require low probability of detection. Other common uses of UWB are

in radar and imaging technologies, where the ability to resolve multipath delay is in the

nanosecond range, allowing for finer resolution, whether it be from a target or for an

image.

After recognizing the potential advantages of UWB, the FCC developed a report to

allow UWB as a communications and imaging technology. A UWB definition was

created as a signal with a fractional bandwidth greater than 0.2 or which occupies more

than 500 MHz of spectrum. The fractional bandwidth is defined as

FBW=2*(fH-fL) / (fH+fL) (1.1)

Where fH and fL are the upper and lower frequencies respectively measured at -10 dB

below the peak emission point. To allow government and industry to conduct UWB

testing, frequency spectrum from 3.1GHz to 10.6GHz was allocated for

communications use below specified power levels while imaging was limited to below

960MHz as seen in Figure 1.1 below.


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Figure 1.1: Comparison of different wireless communication systemsIn the frequency domain.

Although the FCC has regulated spectrum and power levels for UWB, there is currently

no standard for industry to follow. Discussions have developed on the use of two

standards specifically, multiband orthogonal frequency division multiplexing (OFDM)

and direct sequence spread spectrum (DS-SS) which is based on impulse radio

technology.

Each of these schemes OFDM and DS-SS has their advantages in a communications

system although OFDM is currently a more popular technology. Impulse radio has

many advantages over OFDM, with its ability to penetrate through materials and

resolve multipath with path length differences on the order of a foot or less. Impulse

radio also allows for lower power consumption with a low duty cycle, making it very

beneficial in low probability of detection applications. Numerous multiple access

techniques such as time-hopping and direct sequence are commonly applied to impulse

radio, giving it the ability to service many users in a network. There are three primary

drawbacks to current implementations of impulse radio, namely lack of high data rates,

lack of long communication range, and analog components are necessary to construct

the system.


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1.3 CONSEQUENCE OF UWB ANTENNA AND PROJECT OUTLINE

Ultra Wide Band, a wireless communications technology that can currently transmit

data at speeds between 40 to 60 Mbps and eventually up to 1Gbps. UWB transmitsultra-low power radio signals with very short electrical pulses, often in the pico second

range, across all frequencies at once. UWB receivers must translate these short bursts

of noise into data by listening for a familiar pulse sequence sent by the transmitter.

Secondly, UWB systems operate at extremely low power transmission levels. By

dividing the power of the signal across a huge frequency spectrum, the effect upon any

frequency is below the acceptable noise floor.

For example, 1 watt of power spread across 1GHz of spectrum results in only 1 nano

watt of power into each Hertz band of frequency. Thus, UWB signals do not cause

significant interference to other wireless systems.

After the FCC approved for commercial use of ultra wideband in 2002, the feasible

design and implementation of UWB system has become a highly competitive topic in

both academics and industrial communities of telecommunications. In particular, as a

key component of the UWB system, an extremely broadband antenna will be launched

in the frequency range from 3.110.6 GHz, which has attracted significant research

power in the recent years. Challenges of the feasible UWB antenna design include the

UWB performances of the impedance matching and radiation stability, the compact

appearance of the antenna size, and the low manufacturing cost for consumer

electronics applications.

It is noted that the UWB antenna design remains to be the main challenge in the

progress of UWB technology. This is primarily attributed to the fact that antennas act

as a band pass filter and limit the transmission bandwidth. It is claimed that, as a rule of

thumb, antennas with a bandwidth such that the ratio of the maximum to minimum

frequency is more than two are not easy to build practically. A UWB signal spanning

the frequency range 1 GHz to 10 GHz has a ratio of 10 and, therefore, an antenna

providing this bandwidth is very difficult to construct.

From a compatibility point of view it would be useful to have information on the

radiation patterns associated with UWB antennas. Little information on this was found

in the references obtained, although the specific topic was not pursued in its own right.

In many of the compatibility studies it is either assumed that the UWB devices radiate


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omnidirectionally or that their maximum radiated power is directed towards the

receiver.

This thesis focuses on UWB antenna design and analysis. Studies have been undertaken

covering the areas of UWB fundamentals and antenna theory. Extensive investigations

were also carried out on two different types of UWB antennas.

The type of antenna studied in this thesis is Omega shape monopole antenna. The

vertical disc monopole originates from conventional straight wire monopole by

replacing the wire element with a disc plate to enhance the operating bandwidth

substantially.

Based on the understanding of vertical disc monopole, two more compact versions

featuring low-profile and compatibility to printed circuit board are proposed and

studied.

In this monopoles, fed by a micro-strip line. The proposed antenna has been

successfully designed and simulated and showing broadband matched impedance,

stable radiation patterns and constant gain.


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CHAPTER -2

UWB TECHNOLOGY & ANTENNAS THEORY

2.1. BACKGROUND

UWB systems have been historically based on impulse radio because it transmitted data

at very high data rates by sending pulses of energy rather than using a narrow-band

frequency carrier. Normally, the pulses have very short durations, typically a few

nanoseconds (billionths of a second) that results in an ultra wideband frequency

spectrum.

The concept of impulse radio initially originated with Marconi, in the 1900s, when

spark gap transmitters induced pulsed signals having very wide bandwidths [2]. At that

time, there was no way to effectively recover the wideband energy emitted by a spark

gap transmitter or discriminate among many such wideband signals in a receiver. As a

result, wideband signals caused too much interference with one another. So the

communications world abandoned wideband communication in favour of narrowband

radio transmitter that was easy to regulate and coordinate.In 1942-1945, several patents were led on impulse radio systems to reduce

interference and enhance reliability [3]. However, many of them were frozen for a long

time because of the concerns about its potential military usage by the U.S. government.

It is in the 1960s that impulse radio technologies started being developed for radar and

military applications.

In the mid 1980s, the FCC allocated the Industrial Scientific and Medicine (ISM) bands

for unlicensed wideband communication use. Owing to this revolutionary spectrum

allocation, WLAN and Wireless Fidelity (Wi-Fi) have gone through a tremendous

growth. It also leads the communication industry to study the merits and implications

of wider bandwidth communication.

2.1

Shannon-Nyquist criterion (Equation 2.1) indicates that channel capacity(C) increases

linearly with bandwidth (B) and decreases logarithmically as the SNR decreases. This

relationship suggests that channel capacity(C) can be enhanced more rapidly by

increasing the occupied bandwidth than the SNR. Thus, for WPAN that only transmits


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over short distances, where signal propagation loss is small and less variable, greater

capacity can be achieved through broader bandwidth occupancy.

In February, 2002, the FCC amended the Part 15 rules which govern unlicensed radio

devices to include the operation of UWB devices. The FCC also allocated a bandwidth

of 7.5GHz, i.e. from 3.1GHz to 10.6GHz to UWB applications [1], by far the largest

spectrum allocation for unlicensed use the FCC has ever granted.

According to the FCC's ruling, any signal that occupies at least 500MHz spectrum can

be used in UWB systems. That means UWB is not restricted to impulse radio any more,

it also applies to any technology that uses 500MHz spectrum and complies with all

other requirements for UWB.[1]

2.2 POWER TRANSMISSION BY RADIO WAVES.

When we talk about power transmission by radio waves, we mean a complex process

that can be divided into three stages: 1) to transform the DC power in RF power, 2) RF

transmit this RF power through a wireless medium from one point to another; and 3)

turn back the received RF power to DC power. Then, we can conclude that the overall

system efficiency is directly dependent on the efficiency of each of these stages. The

modern history of power transmission studies, in many respects, has focused on

improving and developing the elements of the transmitting and receiving ends of this

system, focusing on high efficiency, low costs, reliability and low mass.

2.2.1 The Early History

Power transmission dates back to the early work of Hertz [1], He wasnt only the first

who showed the propagation of electromagnetic waves in free space, he was also the

first to experiment with parabolic reflectors at both the transmitter and receiver ends.

At the end of the 19th century, Nikola Tesla, a genius in the area of generation and

power transmission became interested in their studies applied to power transmission

from one place to another without wires. His first attempt was carried out in 1899 in

Colorado, USA, with the support of the Colorado Springs Electricity Company. He

built a giant coil over which rose a mast of 70 meters with a copper sphere at the end.

However, there is no record of how many energy was radiated to the space and whether

there was any collected energy at any other place. From today's perspective, we can say

that Teslas attempts of efficient power transmission were ahead of the developed

technology of this time. 30 years later, in 1934, H. V. Noble, this time in a laboratory,


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using two 100 MHz dipoles separated by 8 meters, collected several hundred of watts.

With this experiment, he laid the basis for power transfer demonstrations.

The main cause of the lack of interest to develop this area was that several experts had

determined that to achieve high efficiencies, concentrations of electromagnetic energy

in a narrow band were needed. During the first 35 years of the 20th century, there were

no devices that have these capabilities, but in the late 30's, the development of the

velocity-modulated beam tube (Klystron tube) and the microwave cavity magnetron,

allowed the generation of microwave power dedicated to this new technology.

2.2.2 The Modern History of Free-Space Power Transmission.

The modern history of power transmission, as far as microwaves are concerned, not

only includes the development of technologies for microwave power transmission

(MPT), the approach also includes various applications, whose achievements

contributed to the development of new ideas and new technologies. This history of

free-space power transmission will be divided in the early period beginning in 1958 and

the period beginning in 1977 with the assessment study, by the DOE / NASA, of the

concept of the solar-power satellite.

2.3- ULTRA WIDE BAND

Wireless communication technology has changed our lives during the past two decades.

In countless homes and offices, the cordless phones free us from the short leash of

handset cords. Cell phones give us even more freedom such that we can communicate

with each other at any time and in any place. Wireless local area network (WLAN)

technology provides us access to the internet without suffering of unsightly and

expensive cable.

As we know UWB technology has been used in the areas of radar, sensing and military

communications during the past 20 years. A substantial surge of research interest has

occurred since February 2002, when the FCC issued a ruling that UWB could be used

for data communications as well as for radar and safety applications. Since then, UWB

technology has been rapidly advancing as a promising high data rate wireless

communication technology for various applications.

Ultra Wide Band is a radio technology based on the generation of very short Pulses of

electromagnetic energy. These pulses, being short in the time domain, give rise to

spectral components covering a very wide bandwidth in the frequency domain, hence


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the term Ultra Wide Band. It is claimed that the spectral components fall within

existing regulations designed to control the unwanted emissions associated with

conventional radio technologies and therefore should cause no problems to existing

radio services.

2.3.1- ADVANTAGES OF UWB

Power Consumption

The Federal Communications Commission power requirement for UWB systems is -

41.3dBm/MHz (75nW/MHz) Such a power restriction allows UWB systems to live

below the noise floor of a typical narrowband receiver and enables UWB signals to

coexist with current radio services with minimum interference. UWB radio offers

short-range communication that uses 1/1000 of the power required for equivalent

conventional transmission methods. Low battery power consumption is a constraint for

many wireless communication systems, especially in the transmission devices.

Furthermore, since UWB signals use such low powers, they are less harmful to human.

High Security

Because of their low average transmission power, UWB communications systems have

an inherent immunity to detection and interception. UWB pulses are time-modulated

with codes unique to each transmitter and receiver. The time modulation of extremely

narrow pulses will add security to UWB transmissions, because detecting Pico-second

pulses without knowing when they will arrive is next to impossible. Such security is a

critical need for military operations.

Resistance to Interference

Unlike the well-defined narrowband frequency spectrum, the UWB spectrum covers a

vast range of frequencies. UWB signals then, are relatively resistant to intentional and

unintentional jamming, because it is almost impossible to jam every frequency in the

UWB spectrum at once. Thus, even though some of the frequencies are jammed, there

will still be a range of frequencies that remain signal coding. UWB provides less

interference than narrowband radio designs. Because of their low power spectrum

density, unlicensed UWB radios will cause no interference to other radio systemsoperating in dedicated bands.


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High Performance in Multipath Channels

The phenomenon known as multipath interference is unavoidable in many wireless

communications channels. When signals are transmitted between transmitter and

receiver, they scatter; reflect from objects and surfaces along the path. At the receiver

end, the receiver sees the superposition of delayed versions of the original signal. When

signals are continuous-waves or sinusoidal waveforms, these replicas may cancel the

original signal due to the phase difference of the signals. UWB communication uses

pulse waveforms and they tend not to overlap in time because of the extreme

narrowness of the pulse. Because the transmission duration of a UWB pulse is shorter

than a nanosecond in most cases, the reflected pulse has a small window of opportunity

to collide with a line-of-sight (LOS) pulse and cause signal degradation.

Strong Penetration Ability

Unlike narrowband technologies, UWB systems can penetrate effectively through

different materials. The low frequencies included in the broad range of the UWB

frequency spectrum have long wavelengths, which allow UWB signals to penetrate a

variety of materials, such as walls. This property makes UWB technology viable for

through-the-wall communications and ground penetrating radar. This is a great

advantage for sealed space and body implant wireless communication.

2.4- ADVANTAGES OF USING UWB FOR MEDICAL IMPLANT

In transmitting the information signals from inside the human body, a wireless

technology is necessary. UWB can deliver the following benefits. First, because of the

power requirement of UWB communication systems, it does not need to transmit a

high-power signal to the receiver. Hence, the UWB transmission device can have a

longer battery life or be smaller to reduce the implant size. Furthermore, since UWB

signals are required to have low powers, they are less harmful to human bodies.

Second, the human body has several tissues absorb signals at certain frequencies.

Narrowband systems will suffer from transmission losses as the signals are blocked at

particular frequencies. Because of the frequency bandwidth of UWB, some of the

transmission signal will still pass through the tissues with minimal losses. Third,


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transmission security is also important for medical implants. Because of low powers

and narrow pulses in the time domain, UWB provides high security.

2.5 PRESENT SCENARIO OF UWB

The developers of UWB have already achieved an advanced level. UWB radios can be

used for handheld radios with low power and long distance, and be developed for

wireless remote with high-speed data rate and wide range. Short-range navigation and

positioning systems have attracted more and more attention. Short range positioning

can be implemented in mobile UWB communication systems, such as UWB tags, for

multiple access communication, and high-accuracy positioning system, such asprecision geolocation, can help for storage houses with 3-D position control. There are

several UWB radars using in different areas. First, collision avoidance backup sensor is

made for auto-security. UWB intrusion detection radar can be used for detecting

through the wall and also be used for security with fuze avoidance radar

2.6- ANTENNA SPECIFICATION FOR UWB APPLICATIONS

To understand the challenges faced when designing antennas it is necessary to provide

some background information on some of the key parameters and performance metrics.

There are many antenna types with differing geometry but there are certain

fundamental parameters that can be used to describe all of them.

2.6.1-FUNDAMENTAL ANTENNA PARAMETERS

The most fundamental antenna parameters are;

1. Impedance Bandwidth

2. Radiation pattern

3. Directivity

4. Efficiency

5. Gain

6. Polarisation

All of the parameters mentioned above are necessary to fully characterise an antenna,

and to establish whether the antenna is optimised for its purpose.


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2.6.1.1-Impedance Bandwidth

The term impedance bandwidth is used to describe the bandwidth over which the

antenna has acceptable losses due to mismatch. The impedance bandwidth can be

measured by the characterisation of both the Voltage Standing Wave Ratio (VSWR)

and return loss (RL) at the frequency band of interest. Both VSWR and RL are

dependent on the reflection coefficient (). is defined as the ratio of the amplitude of

the reflected voltage wave (V0 -) normalised to the amplitude of the incident voltage

wave (V0+) at a load. can also be defined by using other field or circuit quantities and

is defined by the following equation.

2.2

VSWR =

or

2.3

RL = -20Log () 2.4

The maximum acceptable mismatch for an antenna is normally 10% of the incident

signal. For the reflection coefficient, this equates to = 0.3162. For the impedance

bandwidth 1< VSWR< 2, and for Return Loss its value must be greater than 10dB or

S11< -10 dB.

2.6.1.2- Radiation pattern

An antenna radiation pattern is defined in the IEEE Standard Definitions of Terms as:

A mathematical function or a graphical representation of the radiation properties of the

antenna as a function of space coordinates. In most cases, the radiation pattern is

determined in the far-field region and is represented as a function of the directional

coordinates. Radiation properties include power flux density, radiation intensity, field

strength, directivity, phase or polarisation.

Primarily, when measuring the radiation pattern, the property of most interest is the

energy radiated relative to the antennas position. This is usually measured using

spherical coordinates.


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Fig. 2.1 Coordinate system, for antenna analysis

The antenna under test is placed at the origin and is rotated through = 0 - 360 and

= 0 - 180 while the power is measured in the far-field. As shown in Figure 2.1 the x-z

plane is considered the elevation plane. This is normally aligned with the electric field

vector and is called the E-plane. The x-y plane is normally aligned with the magnetic

field vector and is termed the H-plane.

2.6.1.3-Directivity

The ratio of the radiation intensity in a given direction from the antenna to the radiation

intensity averaged over all directions. The average radiation intensity is equal to thetotal power radiated by the antenna divided by 4. If the direction is not specified, the

direction of the maximum radiation intensity is implied.

Essentially, this means that the directivity of an antenna is the ratio of the radiation

intensity in a given direction over that of a isotropic source. This can be written as:


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D =

2.5

=

2.6

Where,

U = radiation intensity (W/unit solid angle)

U0= radiation intensity of an isotropic source (W/unit solid angle)

Prad= total radiated power (W)

If the antenna was to radiate in all directions (isotropic radiator) then its directivity

would be unity. As an isotropic radiator cannot be realised practically, the most

comparable antenna is a short dipole, which has a directivity of 1.5. Any other antenna

will have a higher directivity than 1.5, which means their patterns are more focused in a

particular direction.

2.6.1.4- Antenna Efficiency

Like other microwave components, antennas can suffer from losses. The total antenna

efficiency takes into account the losses at the input terminals, and within the structure

of the antenna itself.

The mismatch or reflection efficiency (r) is directly related to the return loss () andcan be defined as:

r= 1-|

|2 2.7

The radiation efficiency () is a measure of how much power is lost in the antenna due

to conductor and dielectric losses. These losses reduce the radiation in any given

direction and can be expressed as:

= Prad/Pin 2.8

2.6.1.5- Gain

The ratio of the intensity in a given direction, to the radiation intensity that would be

obtained if the power accepted by the antenna were radiated isotropically, the radiation

intensity corresponding to the isotropically radiated power is equal to the power

accepted by the antenna divided by 4.This can be expressed as;


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G = 4U(,)/Pin 2.9

Unless specified, it is assumed that the antenna is receiving a signal in the direction of

maximum gain. It is also common for the gain to be expressed in decibels and

referenced to an isotropic source (G = 1), as shown;

G (dBi) = 10 Log (G/1) 2.10

2.6.1.6- Polarisation

The property of an electromagnetic wave describing the time-varying direction and

relative magnitude of the electric-field vector; specifically, the figure traced as a

function of time by the extremity of the vector at a fixed location in space, and the

sense in which it is traced, as observed along the direction of propagation.

Polarisation is the curve traced by the tip of the electric field vector viewed in the

direction of propagation. Figure 2.2 shows a typical trace as a function of time.

The polarisation of the wave may be linear, circular, or elliptical. The instantaneous

electric field of a plane wave, travelling in the negativez direction, may be written as:

E (z, t) = E x (z, t) x + E y (z, t) y 2.11


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The instantaneous components are related to their complex counterparts by:

Ex (z, t) = Ey cos (t + z + x) 2.12

andEy (z, t) = Ex cos (t + z + y) 2.13

WhereEx andEy are the maximum magnitudes and xand yare the phase angles of

the x and y components respectively, is the angular frequency, and is the

propagation constant.

2.7-MICROSTRIP LINE TECHNOLOGY

Planar monopole antennas are becoming increasingly useful because they can be

printed directly onto a circuit board. Planar monopole antennas are becoming very

widespread within the wireless communication industry because of low cost, low

profile and are easily fabricated. Recently, the design of branched monopole antennas

has received the attention of antenna researchers. Numerous designs of single and dual

frequency monopole antennas have been demonstrated, including the use of a

combination of two parallel monopoles excited by a coplanar waveguide (CPW)

feedline, microstrip excited triangular monopole with a trapezoidal slit , monopole

antenna based on tapered meander line geometry , and parallel line loaded monopole

antenna etc. Most of the monopole antennas reported in the literature are mounted

above a large ground plane which increases the complexity of the system. Simulation

results demonstrate that the impedance matching of the proposed antenna depends upon

the ground plane dimensions and frequency tuning can be achieved by tuning the two

resonant lengths. Parameters of the antenna are experimentally optimized and reflection

characteristics of a prototype suitable for digital communication system (DCS)/2.4-

GHz WLAN application are presented. Details of the design and experimental results

are also presented and discussed.

HFSS (High Frequency Structure Simulator) software is the industry-standard

simulation tool for 3-D full-wave electromagnetic field simulation and is essential for

the design of high-frequency and high-speed component design. This software

automatically divides the geometric model into a large number of tetrahedron, where a


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single tetrahedron is a four-sided pyramid. This collection of tetrahedron is referred to

as the finite element mesh. Each element can contain a different material. Therefore,

the interface between two different materials must coincide with element boundaries.

The value of a vector field quantity (such as the H-field or E-field) at points inside each

tetrahedron is interpolated from the vertices of the tetrahedron. By representing field

quantities in this way, the system can transform Maxwell's equations into matrix

equations that are solved using traditional numerical methods. With HFSS, engineers

can extract scattering matrix parameters (S, Y, Z parameters); visualize 3-D

electromagnetic fields (near- and far-field). Each HFSS solver is based on a powerful,

automated solution process where you are only required to specify geometry, material

properties and the desired output. From there HFSS will automatically generate an

appropriate, efficient and accurate mesh for solving the problem using the selected

solution technology.

A number of techniques have been reported by researchers to enhance the gain

Antennas are generally classified as either balanced or un-balanced depending on their

configuration and operation, and this has implications for how they are fed. dipole is a

balanced antenna with an identical element connected to each of its two terminals, and

therefore should be fed by a balanced source.

A monopole antenna is an un-balanced antenna given that it consists of a single

element with reference to a ground plane, A monopole must therefore be fed by an un-

balanced feed such as a co-axial cable (which is unbalanced because it consists of a

single conductor and a shield that is connected to ground), A monopole on a finite

ground plane can be considered less un-balanced than an ideal monopole on an infinite

ground plane.

Un-balanced feeds can be converted to balanced feeds using impedance matching

networks such as a balun (balanced un-balanced) transformer. Connecting an

unbalanced feed such as a coaxial cable to a balanced antenna such as a dipole would

create unpredictable results. This dipole could be considered, as a monopole antenna

with a very thick narrow .ground plane (i.e. the clement of -the dipole connected to the

coaxial shield). An unbalanced feed connected to a balanced antenna such as a dipole

would result in uneven currents in each of the elements, and therefore a net current

flow in the transmission line feeding it, causing spurious radiation from the feedline,

with unpredictable parameters of gain, pattern and cross polar performance. A printedplanar monopole antenna with die ground plane in the same plane as the monopole


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element may be considered slightly differently. This form of antenna behaves like a

hybrid monopole-dipole antenna in some ways. This is evident in the radiation pattern

characteristics of the printed planar 'monopole, where the radiation is more dipole like

than monopole with equal or greater radiation (depending on groundplane

configuration) in the lower hemisphere than the upper.

2.7.1 Printed Antenna Feeds

A microstrip feedline can be employed on a printed monopole antenna where the

ground plane is in the same plane as the monopole element. This can be done by

passing a microstrip feedline along the length of the ground plane from the edge of the

antenna to the monopole element (Figure 2.10) or via a co-planar waveguide through

the ground plane where the ground plane is on the same side of the substrate as the

monopole element. Microstrip feedlines are typically matched to the 50ohm co-axial -

able. however in, some cases mismatched CPW feedlines were found to be effective in

enhancing aspects of the antennas performance.

Figure 2.3- Microstrip feed line on a dielectric substrate.

Figure 2.4- Coplanar Waveguide (CPW) feed on a dielectric substrate

.

The principle characteristics of a monopole antenna such as impedance and radiation

pattern where presented in this chapter using a wire dipole antenna as a reference.

Planar monopole antennas were introduced and related to cylindrical wire monopole

antennas. These characteristics are used as a foundation to help understand the

operation of the antennas.


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2.8. BROADBAND MICROSTRIP ANTENNA TECHNIQUES

Some of them used to enhance the gain are, loading of high permittivity dielectric

substrate , inclusion of an amplifier type active circuitry and stacked configuration. Use

of substrate loading technique helps in increasing the radiation efficiency. Amplifiercircuits can also be integrated with the radiating patch to give rise to an active

integrated antenna. In a stacked configuration, two patches, driven and parasitic, are

used with the desired feeding technique. The narrow impedance bandwidth of the basic

microstrip element is ultimately a consequence of its electrically thin ground plane-

backed dielectric substrate, which leads to a high Q resonance behavior. Bandwidth

improves as the substrate thickness is increased, or the dielectric constant is reduced,

but these trends are limited by an inductive impedance offset that increases with

thickness. A logical approach, therefore, is to use a thick substrate or replacing the

substrate by air or thick foam with some type of additional impedance matching to

cancel this inductance. A thick substrate introduces surface wave excitation. Another

method reported for the bandwidth enhancement is by loading the suspended microstrip

antenna with a dielectric resonator. Besides impedance matching, another very popular

bandwidth extension technique involves the use of two or more stagger tuned

resonators, implemented with stacked patches, parasitic patches, or a combination of

dissimilar elements. Three dimensional patches like V-shaped patch, or wedge -shaped

patch can also be used to enhance bandwidth. Various feeding methods other than co-

axial feeding, also enhances the bandwidth. Other reported methods use proximity feed

, L-probe/ L-strip and Z-shaped feed. The patch loaded with slots like U-slotted Patch,

E- Patch , parasitic patches aside or on the top also have effect on bandwidth

enhancement. The stacked patch arrangement is very popular, with reported

bandwidths ranging from 10% to 20%. In this thesis, single-layered microstrip patch

antenna on a relatively thin substrate are presented, which is based on multiple

resonances without significantly enlarging the size.

2.9. BASIC PRINCIPLES OF BROADBAND DESIGN

The fundamental and basic principles of broadband design of microstrip and printed

antennas are often discussed in the related papers and reports which are quite general

and incomplete in true sense. The basic principles are sometimes achieved using some


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other principles, which are in the phase of very rapid development. Thorough

discussions are beyond the scope of this thesis and hence the main points are

highlighted. The basic principles and their corresponding antenna geometries can be

listed as:

1. Low Q-factor of the

magnetic wall

Low dielectric constant or wall cavity under

the patch larger thickness of the substrate.

2. Multiple resonances Parasitic patches in stacked or planar

geometry, Reactive loading by shaped slot,

notch, cuts, pin or post.

3. Impedance matching of the

feed

Probe compensation using series capacitor, L-

shape probe or any reactive loading

4. Optimization of patch

geometry

Very irregular and unconventional patch shape

optimized using Genetic Algorithm.

5. Suppression of surface

waves

Periodic patterns on the ground plane or in a

thick substrate: on any substrate produces

Photonic Band Gap (PBG) Structure on one

face of which microstrip element or arrays are

printed.

6. Frequency dependent

substrate

Multiple layers of Frequency Selective or

ground plane: Surfaces (FSS) can reflect at

respective frequency bands. For closely

spaced frequency bands, the FSS combination

acts over a larger frequency range as a pass

band

7. Various combinations of (2)

and (3).

2.10- KEY REQUIREMENTS FOR UWB ANTENNAS

The key requirements that should be considered are as follows:


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1. All of the parameters described above i.e. pattern, gain efficiency etc. must be

considered when designing any type of antenna that is part of a RF-front end.

However, UWB antennas have additional design challenges. For example, as

the name suggests, the antenna must operate over a large bandwidth when

compared to narrowband antennas. The bandwidth is specified by the FCC is

3.1 to 10.6 GHz; hence the antenna must achieve an impedance bandwidth of

7.5 GHz.

2. Another important requirement is group delay. Group delay is defined as the

rate of change of the total phase shift, , with respect to the angular frequency,

, as shown in Equation 2.14.

Group delay =

2.14

If the phase is linear throughout the bandwidth then the group delay is constant

throughout the bandwidth. Group delay can then be used as an indicator to show

how well a pulse will be transmitted with consideration of distortion and

dispersion. Normally, group delay is not considered in narrowband antennadesign because linear phase is normally quite easy to achieve over a narrow

band. Generally, if the group delay is in the tens of nano-seconds range, or less

the performance is acceptable.

3. The radiation pattern is an extremely important requirement for UWB antennas.

For wireless sensor network applications, it is desirable to have an Omni-

directional pattern so orientation of the transmitter/receiver is not as important.As the antenna operates over a large bandwidth, its pattern at the low frequency

cut-off (3.1 GHz) is different to that of the pattern at the higher frequency end

(10.6 GHz), although good design can minimize this effect.

4. There are several other key requirements that are desirable for UWB antennas

and are summarised below:

CompactnessSize is critical in terms of cost, as well as achieving the ultimate

aim for this project.


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PlanarEase of integration into monolithic circuits.

Good VSWR (


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CHAPTER -3

ANTENNA DESIGN

3.1 INTRODUCTION

Some of modification has to be made to the planar monopole antenna which provide

wider bandwidth lower profile and improved omnidirectional radiation patterns. These

modifications included altering the geometry by cutting tapered sections or folding the

elements, and changing the electrical characteristics by employing a short-circuit

between the monopole and the ground plane. However, the nature of a monopoleantenna, with a vertical radiating element situated above a horizontal ground plane,

makes it difficult to integrate into many handheld applications in this form. Ideally,

antennas of this order of size need to be completely planar structures to conform with

the slim form: factor of modem portable devices. In this chapter further modifications

of the planar monopole antenna are presented, so that the monopole element lies in the

same plane as the ground plane, enabling better integration possibilities, lower cost and

easier manufacture using printed circuit board (PCB) techniques. Furthermore some of

the printed antennas achieve wider 1.0dB bandwidths in lower frequency ranges when

compared to equivalent planar monopoles.

3.1.1 Analytical Modeling

Analytical investigation of antennas becomes difficult once the geometries are more

complex than simple thin wire structures (e. g. straight wires, arrays of straight wires).

Empirical methods are useful for well-understood antennas, but can be difficult to

apply to new designs. For this reason computer Modeling software is used to solve for

the antennas numerically. Modeling was used extensively during this work. 3.1.2

General Background to Numerical Modeling

The concept of Modeling allows one to use previous knowledge of well-understood

simple systems to describe the behavior of unknown complex systems, providing a

better understanding. Modeling allows a relationship to be defined between the input

and output of a system, thus enabling its behavior to be simulated and predicted. Even

the best models will never completely describe a system in every aspect of its behavior,

so the intended application of the. model must be known to optimize its


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implementation. Modern computers have enabled far more complex numerical models

of systems to be implemented; which have in turn facilitated significant developments

in Modeling over the past 30 years.

Solving an antenna's impedance analytically is a difficult task and has only been carried

out for relatively simple structures. Modern antenna design is typically carried out

using computers to model and solve for the antenna's impedance and radiation

characteristics numerically. The antenna impedance is dependent on a number of

factors including its geometry, its frequency of operation, how it is excited, and its

proximity to other objects. Once the impedance is known. We radiation pattern

characteristics can be determined. The integral equation method and the finite

integration technique are of most interest here and are outlined further below.

3.1.3 Integral Equation Method

Solving an antenna's impedance can be achieved by solving an Integral Equation

where a solution is found for current density on the antenna. The antenna impedance

can then be calculated from knowledge of the current density and voltage. The Integral

Equation can be solved numerically using the Finite Element Method. In general, the

finite element method is characterized by the following process.

One chooses a grid for . In the preceding treatment, the grid consisted of

triangles, but one can also use squares or curvilinear polygons.

Then, one chooses basis functions. In our discussion, we used piecewise linear

basis functions, but it is also common to use piecewise polynomial basis functions.

Compression to the FEM

Thefinite difference method (FDM) is an alternative way of approximating solutions of

PDEs. The differences between FEM and FDM are:

The most attractive feature of the FEM is its ability to handle complicated

geometries (and boundaries) with relative ease. While FDM in its basic form is

restricted to handle rectangular shapes and simple alterations thereof, the handling

of geometries in FEM is theoretically straightforward.

The most attractive feature of finite differences is that it can be very easy toimplement.
http://en.wikipedia.org/wiki/Finite_difference_methodhttp://en.wikipedia.org/wiki/Finite_difference_method


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There are several ways one could consider the FDM a special case of the FEM

approach. e.g. -first order FEM is identical to FDM for Poisson's equation, if the

problem is discretized by a regular rectangular mesh with each rectangle divided

into two triangles.

There are reasons to consider the mathematical foundation of the finite element

approximation more sound, for instance, because the quality of the approximation

between grid points is poor in FDM.

The quality of a FEM approximation is often higher than in the corresponding

FDM approach, but this is extremely problem-dependent and several examples to

the contrary can be provided.

Generally, FEM is the method of choice in all types of analysis in structural

mechanics (i.e. solving for deformation and stresses in solid bodies or dynamics of

structures) while computational fluid dynamics (CFD) tends to use FDM or other

methods likefinite volume method (FVM). CFD problems usually require

discretization of the problem into a large number of cells/grid points (millions and

more), therefore cost of the solution favors simpler, lower order approximation within

each cell. This is especially true for 'external flow' problems, like air flow around thecar or airplane, or weather simulation.

3.1.4 Finite Element Method

The term finite element was first coined by clough in 1960. In the early 1960s,

engineers used the method for approximate solutions of problems in stress analysis,

fluid flow, heat transfer, and other areas.

- The first book on the FEM by Zienkiewicz and Chung was published in 1967.

- In the late 1960s and early 1970s, the FEM was applied to a wide variety of

engineering problems.

- Most commercial FEM software packages originated in the 1970s. (Abaqus, Adina,

Ansys, etc.)

- Klaus-Jurgen Bathe in ME at MIT FEM: Method for numerical solution of field

problems.

Description

- FEM cuts a structure into several elements (pieces of the structure).
http://en.wikipedia.org/wiki/Computational_fluid_dynamicshttp://en.wikipedia.org/wiki/Finite_volume_methodhttp://en.wikipedia.org/wiki/Finite_volume_methodhttp://en.wikipedia.org/wiki/Computational_fluid_dynamics


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- Then reconnects elements at nodes as if nodes were pins or drops

of glue that hold elements together.

- This process results in a set of simultaneous algebraic equations.

- FEM uses the concept of piecewise polynomial interpolation.

- By connecting elements together, the field quantity becomes interpolated over the

entire structure in piecewise fashion.

- A set of simultaneous algebraic equations at nodes.

Advantages of the FEM

Can readily handle very complex geometry:

Can handle a wide variety of engineering problems

- Solid mechanics - Dynamics - Heat problems

- Fluids - Electrostatic problems

Can handle complex restraints

- Indeterminate structures can be solved.

Can handle complex loading

- Nodal load (point loads)

- Element load (pressure, thermal, inertial forces)

- Time or frequency dependent loading


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Disadvantages of the FEM

A general closed-form solution, which would permit one to examine system

response to changes in various parameters, is not produced.

The FEM obtains only "approximate" solutions. The FEM has "inherent" errors.

Mistakes by users can be fatal.

Preprocess

Select analysis type - Structural Static Analysis

- Modal Analysis

- Transient Dynamic Analysis

- Buckling Analysis

- Contact

- Steady-state Thermal Analysis

- Transient Thermal Analysis

Select element type

2-D

3-D

Linear

Quadratic Beam

Truss

Shell

Solid

Plate

Material propertiesE, , , , ..

Make nodes Build elements by assigning connectivity

Apply boundary conditions and loads

3.2- DESIGN METHODOLOGY

In order to reach the primary goal of manufacturing broadband patch antenna, the thesis

is split into subtasks, which allowed for achievable short-term goals. After the initial

research regarding microstrip antennas, specific work needed to be done as shown inthe flow chart Figure 3.1


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Figure 3.1 Design Methodology

3.3- DESIGNS OF UWB ANTENNAS

For this project, we have four main parameters. Those parameters are the bandwidth,

VSWR, gain, and the radiation pattern of the antenna. These parameters will help us

Background

Determining Substrate

Determining Simulation Software

Determining the Feeding Technique

Investigate possible Broadband technique

Design Planar Monopole

Design Reconfigurable Planar Monopole


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understand if the antenna we are designing will be the optimal design for our

application.

As we know the several design methods and structures have been reported. These

UWB antennas with filtering property at the 56 GHz band have been proposed not

only to mitigate the potential interferences but also to remove the requirement of an

extra band stop filter in the system [9].

The Federal Communication Commission (FCC)s allocation of the frequency band

3.110.6 GHz [1] for commercial use has a sparked attention on ultrawideband (UWB)

antenna technology in the industry and academia. The UWB systems can be divided

into two categories: direct sequence UWB (DS-UWB) and multiband orthogonal

frequency division multiplexing (MB-OFDM). The DS-UWB proposal foresees two

different carrier frequencies at 4.104 (low band) and 8.208 GHz (high band). By the

MB-OFDM format in 802.15.3a, the interval between 3.1 and 10.6 GHz is divided into

13 sub-intervals. Each sub-interval corresponds to one band of the MB-OFDM, with

the bandwidth of 528 MHz [2], [3].

The UWB antennas proposed in the open literature mainly focus on the slot and

monopole antenna. Printed wide slot antennas have an attractive property of providing

a wide operating bandwidth, especially for those having a modified tuning stub, such as

the fork-like stub [4][7], the rectangular stub [8], [9], and the circular stub [10] inside

the wide slot. Broadband planar monopole antennas have received considerable

attention owing to their attractive merits, such as ultrawide frequency band, good

radiation properties, simple structure and the ease of fabrication.

The typical shapes of these antennas are half-disc [11], circle, ellipse [12], [13], and

rectangle [14]. Despite the approval of the FCC for UWB to operate over

3.1 to 10.6 GHz, it may be necessary to notch-out portions of the band in order to avoid

interference with the existing wireless networking technologies such as IEEE 802.11a

in the U.S. (5.155.35 GHz, 5.7255.825 GHz) and HIPERLAN/2 in Europe

(5.155.35 GHz, 5.475.725 GHz). This is due to the fact that UWB transmitters

should not cause any electromagnetic interference to nearby communication system

such as the wireless local area network (WLAN) applications. Therefore, UWB

antennas with notched characteristics in the WLAN frequency band are required. There

are various methods to achieve the band-notched function. The conventional methods

are cutting a slot (i.e., U-shaped, arc-shaped, and a pie-shaped slot) on the patch [15][19], inserting a slit on the patch [20][22], or embedding a quarter-wavelength tuning


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stub within a large slot on the patch [23]. Another way is putting parasitic elements

near the printed monopole as filters to reject the limited band [24] or introducing a

parasitic open-circuit element, rather than modifying the structure of the antennas

tuning stub [25].Yi-Cheng Lin have been discussed the design of three advanced band-

notched (56 GHz) UWB rectangular aperture antennas [8]. The antenna structure is

simple and the aperture size is compact. Broad impedance bandwidth and stable

radiation patterns are obtained, whereas the ground plane dimension is a bit large. In

practice, when integrated with the system board of different ground plane size, the

antenna might need a retuning for the optimized dimensions.

In [14] the authors propose a new ultra wide band antenna for UWB applications. The

proposed antenna consists of a rectangular patch with two steps, a single slot on the

patch, and a partial ground plane Compact size but the gain is not constant

In this thesis, a microstrip-fed planar UWB antenna is proposed. The omega-shaped

edge radiation patch causes a wide bandwidth from 3.1 to 10.6 GHz for UWB

application. The antenna has a compact size of 24 mm 35 mm 1.5 mm. The measured

10-dB return loss shows that the proposed antenna achieves a bandwidth ranging from

2.95 to over 11 GHz with a notched band of 56 GHz. The proposed antenna presents

omnidirectional patterns across the whole operating band in the H-plane.

3.4- ANTENNA DESIGN

Based on the background of the researches above, a simple and compact CPW-fed

planar UWB antenna omega-shaped is designed and fabricated. As mentioned in

earlier, many different types of antennas are currently being considered for UWB

applications. Among these antenna configurations, omega-shape monopole features

simple structure, easy fabrication, wide frequency bandwidth and satisfactory radiation

patterns [1, 2].

However, the performances and characteristics of omega-shape monopole antenna are

not analyzed in detail in either [1] or [2]. How exactly the omega-shape monopole

operates across the entire bandwidth, remains a question. It is still not clear why this

resonating type of antenna retains a seemingly omnidirectional radiation pattern with

gain variation less than 10dB over an ultra wide frequency band.

In this Chapter, omega-shape monopole antennas will be studied in the frequency

domain with an emphasis on the understanding of their operations. The important


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parameters which affect the antenna performances will be investigated both

numerically and experimentally to obtain some quantitative guidelines for designing

this type of antennas.

This antenna yields an impedance bandwidth of 3.110.6 GHz with VSWR2, The

stable radiation patterns and constant gain are also obtained.

3.2.1- Antenna design using omega-Shape ground plane

Figure 3.1 shows the geometry of the antenna without slot (antenna A1) it works over

all frequency (3.1-10.6GHz) of UWB.

A B

Fig. 3.2- Geometry and configuration of purpose antenna.

(A) Top view. (B) Back view.

The optimize dimensional of the antenna are

L =35mm W =24mm

L1=13.4mm g =1.5mm

L2=2mm R =18mm

W1=18mm


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(1) Design a 50CPW line on a substrate with permittivity r. Calculate reffusing

reff= (r + 1)/2 where reffis the effective permittivity of the substrate.

(2) Ground plane plays a major role in determining the first and second resonances. The

dimensions of the ground plane are calculated as follows:

L = (0.8c) 3.1

L1 = (0.3 c) 3.2

Where c is the wavelength corresponding to centre frequency of the operating band.

(3) Sides of the rectangle L1 and L2 are calculated using

W = (0.55 c) 3.3

2R = W1 = (0.41 c). 3.4

reff = (r+1)/2

fr= (fH+fL)/2

The width of the feed-line line is

g 120*h*/zo*r 3.5

The ground plane size is

L1 = C/2*fr*r 3.6

The antenna is Simulated on an h=1.5mm FR4 epoxy substrate with dielectric constant

r=4.4 and loss tangent tan=0.02 and thickness h=1.6mm. As shown in the figure 3.1,

a rectangle radiator is fed by a 50 CPW transmission line which is terminated with a

subminiature A (SMA) connector for measurement purpose. Since both the antenna and

the feeding are implemented on the same plane, only one layer of substrate with single-

sided metallization is used, and the manufacturing of the antenna is very easy and

extremely low cost. Both the radiating patch and the ground plane are bevelled, which

results in a smooth transition from one resonant mode to another and ensures good

impedance match over a broad frequency range.


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CHAPTER -4

RESULTS AND DISCUSSIONS

As shown in Figure 3.1, a omega-shape copper patch with a radius of R is selected as

the radiator and mounted vertically above a rectangular copper ground plane. W andL2

denote the width and the length of the ground plane, respectively. A 50 coaxial probe

connects to the bottom of the patch through the ground plane via an SMA connector. h

is the height of the feed gap between the feed point and the ground.

Simulations have shown that the performance of the antenna is mainly dependent on

the feed gap h and the dimension of the ground plane.The first parameter that we had to consider for our design is the bandwidth. The

bandwidth is basically the frequency range that the antenna is designed to radiate.

The second parameter that we take in to account for our design is the return loss (S 11)

of the antenna. The return loss(S11) is a way of calculating how well two transmission

lines are matched. The number for the VSWR ranges from one to infinity, with one

meaning that the two transmission lines are perfectly matched. In regards to antenna

design, a return loss (S11) that is as low as possible is desired because any reflections

between the load and the antenna will reduce the effectiveness of the antenna.

Fig. 5.1 shows the characteristics of the simulated return loss (S11) of antenna . It is

found that the input impedance of the antenna is well matched as the bandwidth covers

the entire UWB band (3.110.6 GHz) and goes beyond the required 10.6 GHz with (S11

-10dB). Fig. 4.2 presents the simulated gain for antenna. The antenna gain in the

UWB band is about 25 dBi.

Fig. 4.1- Simulated return loss (S11) of antenna with optimal dimensions.

0.00 2.50 5.00 7.50 10.00 12.50 15.00 17.50 20.00Freq [GHz]

-18.00

-16.00

-14.00

-12.00

-10.00

-8.00

-6.00

dB(S(1,1

))

Ansoft LLC HFSSDesign1XY Plot 2 ANSOFTCurve Info

dB(S(1,1))Setup1 : Sweep1


36/50


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Generally, if the group delay is in the tens of nano-seconds range, or less the

performance is acceptable.

Fig. 5.2 shows the group delay vs frequency, the variation in group delay is 0.50 ns.

The radiation intensity corresponding to the isotropically radiated power is equal to the

power accepted by the antenna divided by 4.This can be expressed as;

G = 4U(,)/Pin 4.3

Fig. 5.3 presents the simulated gain for antenna . The antenna gain in the UWB band is

about 3.55.5 dBi. The variation in gain in over all bandwidth is 2.5 dBi.

Fig. 4.3- Simulated gain of antenna .

It is assumed that the antenna is receiving a signal in the direction of maximum gain. It

is also common for the gain to be expressed in decibels and referenced to an isotropic

source (G = 1), as shown;

G (dBi) = 10 Log (G/1) 4.4

For the liner phase response between input and output we can see the current

distribution in the radiating patch.


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A B

C D

Fig. 4.4 shows the current distribution at different-2 frequencies of purpose antenna at 3 GHz,

(B) at 5 GHz, (C) 7 GHz (D) 10 GHz

Fig. 5.4 shows the simulated current distributions at different frequencies. In Fig. 5.4(a)

and (d), at frequencies, the current distributions mainly flow along the transmission

line, The impedance nearby the feed-point no changes acutely making less than 10 dB

reflection at the desired band.

The fourth parameter is the radiation pattern of the antenna. This parameter is highly

dependent on the application of the antenna. In the case of the antenna our group

designed, we had to have an omni-directional radiation pattern. This means that the

radiation pattern had to be spread evenly 360 degrees around the antenna. The reason

for this is because since the location of the transmitter is not fixed, you want to spread


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the radiated signal out as far as possible so the receiver will be able to pick up the

transmitted signal.

The simulated radiation patterns of antenna in the E-plane (xz-plane) and H-plane (yz-

plane) for three different frequencies 3.5, 8 and 10 GHz are shown in Figs. 5.8 (a-c).

The patterns in the H-plane are quite omnidirectional as expected. In the E-plane, the

radiation patterns remain roughly a dumbbell shape like a small dipole leading to

bidirectional patterns.

(3GHz)

(8 GHz) (10GHz)

Fig. 4.5- Simulated radiation patterns of antenna at 3, 8 & 10 GHz E-Field and H-Field

It has been seen that this antenna has the nearly Omni-directional radiation pattern like

normal monopole antennas. However, the Omni-directional radiation properties have a

little deterioration as frequency increases. Over the entire bandwidth, its similar to a

conventional wideband monopole antenna.


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CHAPTER - 5

CONCLUSION AND FUTURE WORK

CONCLUSION

In wireless communications, ultra wideband has many advantages. Here I introduced a

compact microstrip line-fed planar UWB antenna of omega - shape has been designed

and analysed, and the results like return loss (S11), Group Delay, Current distribution,

Stable radiation patterns and constant gain in the UWB band (3.1- 10.6 GHz) areobtained and discussed.

This thesis has developed a method for improving the performance of transmitting

antenna without potential interferences with the narrowband systems. By using this

method, users can have better signal performance by better placing of the transmitting

antenna and can easily design their devices for implantation, reducing cost, and

development time.

The simulation results of the proposed antenna show a good agreement in term of the

return loss (S11), antenna gain and radiation patterns. Accordingly, this antenna is

expected to be a good candidate in various UWB systems.

FUTURE PROSPECTIVE

Based on the conclusions drawn and the limitations of the work presented, future work

can be carried out in the following areas:

Firstly, it has been shown that UWB antennas operate in a hybrid mode of standing and

travelling waves. A more detailed understanding of the travelling wave mechanism and

the impedance variations could lead to improved design of UWB antennas.

Secondly, in the future UWB systems, antenna might be embedded inside a laptop or

other devices, thus, the devices effects on the antenna performances to be investigated.


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When the antenna is built on a portable device, the impact from human body should

also be considered.

Thirdly, UWB antenna with small size is always desirable for the WPAN applications,

especially for mobile and portable devices. Future research may focus on finding out

new methods to further reducing the sizes of UWB antennas.

Fourthly, UWB systems operate at extremely low power level which limits its trans-

mission range. In order to enhance the quality of the communication link and improve

channel capacity and range, directional systems with high gain are required for some

applications. Therefore, research on UWB directional antenna and antenna array could

be carried out.

Lastly, good time domain performance is a primary requirement for UWB antennas.

Studies can be carried out to investigate the antenna effect on the transmitted signal and

improve the time domain behaviours by optimizing the antenna configuration.


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REFERENCES:

[1] Constantine A. Balanis, antenna theory analysis and design, john wiley & sons.

[2] Jeffrey H. Reed, An Introduction to Ultra Wideband Communication Systems, Prentice

Hall,

[3] Handbook of Microstrip ANTENNAS Edited by J R James & Ps Hall.

[4] J. Liang, C Chiau, X. Chen and C.G. Parini, \Study of a Printed Circular Disc

Monopole Antenna for UWB Systems", IEEE Transactions on Antennas and

Propagation, vol. 53, no. 11, November 2005, pp.3500-3504.

[5] J. Liang, L.Guo, C.C.Chiau, X. Chen and C.G.Parini, \Study of CPW-Fed circular disc

monopole antenna", IEE Proceedings Microwaves, Antennas & Propagation, vol. 152,

no. 6, December 2005, pp. 520-526.

[6] J. Liang, C Chiau, X. Chen and C.G. Parini, \Printed circular disc monopole antenna

for ultra wideband applications", IEE Electronic Letters, vol. 40, no. 20, September

30th, 2004, pp.1246-1248.

[7] T. G. Ma and S. K. Jeng, Planar miniature tapered-slot-fed annular slot antennas for

ultra-wideband radios, IEEE Trans. Antennas Propagation., vol. 53, pp. 11941202,

Mar. 2005.

[8] Y. C. Lin and K. J. Hung, Compact ultrawideband rectangular aperture antenna and

band-notched designs, IEEE Trans. Antennas Propagation, vol. 54, pp. 30753081,Nov. 2006.

[9] Y. -J. Cho, K. -H. Kim, D. -H. Choi, S. -S. Lee, and S. -O. Park, A miniature UWB

planar monopole antenna with 5-GHz band-rejection filter and the time-domain

characteristics, IEEE Trans. Antennas Propagation, vol. 54, pp. 14531460, May

2006.

[10] J. Kim, C. S. Cho, and J. W. Lee, 5.2 GHz notched ultra -wideband antenna using slot

type SRR, Electron. Lett., vol. 42, pp. 315316, Mar. 2006.

[11] W. S. Lee, D. Z. Kim, K. J. Kim, and J. W. Yu, Wideband planar monopole antennaswith dual band-notched characteristics, IEEE Trans. Microw. Theory Tech., vol. 54,

pp. 28002806, Jun. 2006.

[12] I. Pele, A. Chousseaud, and S. Toutain, Simultaneous modeling of impedance and

radiation pattern antenna for UWB pulse modulation, in Proc. IEEE AP-S Int. Symp.,

Jun. 2004, vol. 2, pp. 18711874.

[13] Applications of ultra wideband thesis; Master of Science in electrical engineering the

University of Texas at Arlington December 2006.


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[14] Seok H. Choi,1 Jong K. Park,1 Sun K. Kim,1 and Jae Y. Park2 A new ultra-wideband

antenna for uwb applications microwave and optical technology letters / vol. 40, no.

5, march 5 2004.

[15] Ansoft. Documentation. Ansoft Corp, Available from: http://www.ansoft.com;

accessed 4 October 2006.

[16] Warren L. Stutzman , Gary A,Antenna Theory and Design, New York: John Wiley and

sons Inc, 1997.

[17] Fan Yang, , Yahya Rahmat-Samii, Reflection Phase Characterizations of the EBG

Ground Plane for Low Profile Wire Antenna Application, IEEE Transactions of

Antennas and Propagation , Vol. 51, No. 10, October 2003.

[18] Li Yang, Zhenghe Feng, Fanglu Chen, and Mingyan Fan, A Novel Compact

Electromagnetic Band-Gap (EBG) Structure and its Application in Microstrip Antenna

Arrays, State Key Lab on Microwave & Digital Communications,Tsinghua University

Beijing, 100084, P. R. China.

[19] Batra et al., Multi-band OFDM physical layer proposal for IEEE 802.15 task group

3a,IEEE Document 802.15-04-0493r1, Sep. 2003.

[20] R. Kohno, M. McLaughlin, and M. Welborn, DS-UWB physical layer submission to

802.15 task group 3a,IEEE Document802.15-04-0137r4, Jan. 2005.

[21] J. Y. Sze and K. L. Wong, Bandwidth enhancement of a microstripline - fed printed

wide-slot antenna,IEEE Trans. Antennas Propag., vol. 49, pp. 10201024, Jul. 2001.

[22] X. Qing, M. Y. W. Chia, and X. Wu, Wide-slot antenna for UWB Applications, in

Proc. IEEE AP-S Int. Symp., Jun. 2003, vol. 1, pp. 834837.

[23] R. Chair, A. A. Kishk, and K. F. Lee, Ultrawide-band coplanar waveguide- fed

rectangular slot antenna,Antennas Wireless Propag. Lett., vol. 3, no. 1, pp. 227229,

2004.

[24] S. H. Hsu and K. Chang, Ultra-thin CPW-fed rectangular slot antenna for UWB

applications, inProc. IEEE AP-S Int. Symp., Jul. 2006, pp. 25872590.

[25] H. D. Chen, Broadband CPW-fed square slot antenna with a widened tuning stub,IEEE Trans. Antennas Propag., vol. 51, pp. 19821986, Aug. 2003.

[26] Y. Liu, K. L. Lau, and C. H. Chan, Microstrip -fed wide slot antenna with wide

operating bandwidth, in Proc. IEEE AP-S Int. Symp., Jun. 2004, vol. 3, pp. 2285

2288.

[27] Y. W. Jang, A circular microstrip-fed single-layer single-slot antenna for multi-band

mobile communications,Microw. Opt. Technol. Lett., vol. 37, pp. 5962, Apr. 2003.

[28] T.Yang and W. A. Davis, Planar half-disk antenna structures for ultrawideband

communications, inProc. IEEE AP-S Int. Symp., Jun. 2004, vol. 3, pp. 25082511
http://www.ansoft.com/http://www.ansoft.com/


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APPENDIX

1 SIMULATION PROCESSES

1.1 What is HFSS?

HFSS is a high-performance full-wave electromagnetic (EM) field simulator for

arbitrary 3D volumetric passive device Modeling that takes advantage of the familiar

Microsoft Windows graphical user interface. It integrates simulation, visualization,

solid Modeling, and automation in an easy-to-learn environment where solutions to

your 3D EM problems are quickly and accurately obtained. Ansoft HFSS employs the

Finite Element Method (FEM), adaptive meshing, and brilliant graphics to give you

unparalleled performance and insight to all of your 3D EM problems. Ansoft HFSS can

be used to calculate parameters such as S Parameters, Resonant Frequency, and Fields.

1.2The HFSS Interface

The main HFSS interface is shown in Figure 1, they are summarized as follows:

1-3D Modeller Window - This is the area where you create the model geometry. This

Window consists of the model view area (or grid) and the history tree as shown in

Figure 1. The history tree documents the actions that have been taken in the model

view area, and provides an alternative way to select objects in the model view area.2-Project Manager with Project Tree - The project manager window displays details

about all open HFSS projects. Each project ultimately includes a geometric model, its

boundary conditions and material assignments, and field solution and post processing

information. An expanded view of the project manager is shown in Figure 1.

3-Properties Window - The properties window consists of two tabs. The command tab

displays information about an action selected in the history tree that was performed to

either create an object or modify an object. The attribute tab displays information about

the material and display properties of a selected object.

4-Progress Window - This window is used when a simulation is running to monitor the

solution's progress.

5- Message Manager - This window displays messages associated with a project's

devel-opment (such as error messages about the design's setup).

1.3 Setting of HFSS

Before you can use HFSS for the first time, there are a couple of items that need to be

configured for efficient and accurate operation.


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1. On the Tools menu, select Options => General Options ..., click the Default Units

tab and ensure that Length is set to mm. Click OK.

2. On the Tools menu, select Options => HFSS Options..., ensure the Include ferrite

materials check box is checked. Click the Solver tab, set the number of Processors to

4. Desired RAM Limit (MB) to 6000 and the Maximum RAM Limit (MB) to 8000.

Click OK.

Fig.1

Main screen of HFSS

1.4 Ansoft HFSS flow-chart

The Ansoft HFSS provides an intuitive, easy-to-use interface for developing passive

RF device models. Creating designs, involves the following:

1. Parametric Model Generationcreating the geometry, boundaries and excitations

2. Analysis Setupdefining solution setup and frequency sweeps

3. Resultscreating 2D reports and field plots4. Solve Loop - the solution process is fully automated

1.5DESIGN PROCESSES

Open HFSS and Save a New Project

A project is a collection of one or more designs that is saved in a single *.hfss file. A

new project is automatically created when HFSS is launched. Open HFSS and save the

default project by a new name.


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1- Double-click the HFSS 10 icon on your desktop to launch HFSS.

A new project is listed in the project tree in the Project Manager window and is

named Projectby default. Project definitions, such asmaterial assignments, are stored

under the project name.

2- On the File menu click Save As.

3- Use the file browser to locate the folder in which you want to save the project, such

as C:\Ansoft\HFSS10\Projects, and then double-click the folders name.

4- Type cpwfeedin the File name text box, and then click Save. The project is saved in

the folder you selected by the file name cpwfeed.hfss.

Select a Solution Type

Now you will specify the designs solution type. As you set up the design for analysis,

available settings will depend upon the solution type. For this design, you will choose

Driven Modal as the solution type, which is appropriate when calculating mode-based

S-parameters of a passive, high-frequency waveguide that is being driven by a

source.1-On the HFSS menu, click Solution Type.

2- In the Solution Type dialog box, select Driven Modal, and then click

OK.

Set the Drawing Units

You will now set the units of measurement for drawing the geometric model.

1- On the 3D Modeler menu, click Units.

2- In the Set Model Units dialog box, click in in the Select units pulldown list, and

then click


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OK.

Draw a Box

Draw a 3D box object to represent the first section of the FR4 substrate.

1-On the Draw menu, click Box.

2-Specify the base corner of the box as (-13, -15, 0):

a. Press Tab to move to the X text box in the status bar.

b. Type 26 in the dXbox, and then press Tab to move to the Ybox.

c. Type 30 in the dYbox, and then press Tab.

d. Type -1.6 in the dZbox, and then press Enter.

The Properties window appears, with the Command tab selected, enabling you to

modify the dimensions or position of the box.

While the Properties window is open, you will use it to assign a name (sub) to the box,confirm its material assignment, and make it more transparent.

Draw the patch

1. Click Draw>Line, or click the Draw line button on the toolbar. The status bar now

prompts you to enter the first point of the polyline.


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2. Press the Tab key to move to the X box, and then select the first point of the line by

entering the following values in the coordinate boxes, pressing Tab to move to the next

coordinate text box:

3. Press the Enter key to accept this point. You can delete the last point you entered by

right-clicking in the 3D Modeller window and then clicking Back up on the shortcut

menu.

X coordinate 0

Y coordinate 0

Z coordinate 0

4. Continue with this same method to enter the following 6 points that remain:

Point X Coordinate Y Coordinate Z Coordinate

1 -x1 -y1 0

2 -x2 -y2 0

3 -x3 -y3 0

4 x4 -y4 0

5 x5 0 0

6 -x6 0 0

5- Right-click in the 3D Modeler window, and click Close Polyline on the shortcut

menu. The 2D polyline object appears in the drawing region.

6- Assign the name patch.

Similarly we should draw ground plane and assign the name gnd.

Mirror image

1-select the patch and gnd right click edit duplicate mirror.

x=0 y=0 z=0

dx=0 dy=1 dz=0

2-Unite- select the patch right click edit boolean unite.

3- Press Ctrl+D to fit the object in the drawing region.

Boundary assignment

Select the patch and gnd right click assign boundary finite conductivity

1-Select the Use Material check box, and click the material button (where the default

vacuum is displayed). The Select Definition window appears. By default, this material


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browser lists all materials in the global material library, as well as the local material

library for the current project, which is a subset of the global library.

2- Select copper from the list of materials, and then click OK. The Finite

Conductivity Boundary window reappears. The conductivity and permeability values

for aluminum are now assigned to the finite conductivity boundary.

3- Clear Infinite Ground Plane if it is selected. If selected, the Infinite Ground

Plane option simulates the effects of an infinite ground plane. This option only affects

the calculation of near- and far-field radiation during post processing. The 3D Post

Processor models the boundary as a finite portion of an infinite, perfectly - conducting

plane.

4- Click OK to accept the default name FiniteCond1 and apply the boundary

Mesh operation

Select the patch and gnd HFSS mesh operation assign on selection length

based.

Then click ok.

Assign Wave Port 1

1- Deselect the perfect E boundary you just assigned, if it is still selected.

2- In Select Faces mode, select the face of port 1.

3- On the HFSS menu, click Excitations>Assign>Wave Port. The Wave Port wizard

appears.

4- In the Wave Port: General step, accept the default name WavePort1, and then

click Next.

5- In the Wave Port: Modes step, accept the default settings, and then click Next.

6- In the Wave Port: Post Processing step, accept the default settings, and then clickFinish to complete the wave port assignment for port 1. WavePort1 is assigned to the

waveguide and now appears as a subentry of Excitations in the.

Draw the radiation box

Select vacuum click box

X=-13, y=-15, z=-6, dx=26, dy=30, dz=-12 enter.

Click ok.

Right click on the box assign boundary radiation ok.HFSS radiation far field setup infinite sphere.


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Click ok.

Analysis setup

Perform the following steps to set up the analysis options:

1- Right click on Analysis in the Project Tree, and select Add Solution Setup"

2- Under the General tab:

(a) Set the solution frequency to 6.86 GHz

(b) Set the maximum number of passes to 6(c) Set maximum Delta S to 0.02

3- Under the Options tab:

(a) Set the Maximum Refinement per pass to 20%.

(b) Set the Order of Basis Functions to Second Order

Perform the following steps to set up the frequency sweep:

1- Under the Analysis item in the Project Tree, right-click on Setup1

2- Select Add Frequency Sweep...

3- Set start frequency to 3 GHz

4- Set stop frequency to 11 GHz

5- Set step size to 0.02 GHz

6- Click OK.

Result

HFSS result create report

Prof. Satendra Sharma

Documents

Transcript of Prof. Satendra Sharma