Microstrip Antenna Resonating at Ku-band frequency Report

MICROSTRIP PATCH ANTENNA RESONATING AT Ku-BAND

DEPARTMENT OF ELECTRONIC SCIENCE, BUB 1

ABSTRACT

Microstrip antenna is an electrical antenna which consists of a metallic patch on a grounded

substrate. Microstrip antennas were primarily used for space borne applications which uses

frequencies of the microwave range. The main objective of this project is to design and characterize

Rectangular Microstrip antenna to operate at Ku-band frequency of 15GHz. In this project,

aRectangular Microstrip antenna resonating at 15GHz frequency has been designed and

characterized using HFSS(High Frequency Structural Simulator) software. The parameters of the

antenna like the bandwidth, radiation pattern, and return loss have been found out using the HFSS

software[1].

The specific frequency chosen here is used for space communications, radar applications, amateur

radio, other terrestrial communications and networking. Microstrip antenna at this frequency ranges

are of great importance nowadays wherein the dimensions of the patch, transmission line and the

feed becomes very small. Considerable effort has beentaken to optimize the width and length of the

conducting patch and the feed. It has taken quite a lot of time in designing to get 50Ω impedance at

the port-feed contact in order to get the power transferred to the conducting patch which is an

essential requirement for proper radiation of the antenna[1].



CHAPTER-1

INTRODUCTION TO ANTENNAS

Antennas



1.1 History of antenna

James Clerk Maxwell formulates the mathematical model of electromagnetism (classicalelectro-dynamics), “A Treatise on Electricity and Magnetism”, 1873.He shows that light is anelectromagnetic (EM) wave, and that all EM waves propagate through space with the samespeed, the speed of light.

Heinrich Rudolph Hertz demonstrates in 1886 the first wireless EM wave system: a /2λ-dipole isexcited with a spark; it radiates predominantly at λ≈8 m; a spark appears in the gap of a receivingloop some 20 m away. In 1890, he publishes his memoirs on electrodynamics, replacing allpotentials by field strengths.

May 7, 1895, a telegraph communication link is demonstrated by the Russian scientist, AlexanderPopov. A message is sent from a Russian Navy ship 30 miles out in sea, all the way to his lab in St.Petersburg, Russia. This accomplishment is little known today.

In 1892, Tesla delivers a presentation at the IRE of London about “transmitting intelligencewithout wires,” and, in 1895, he transmits signals detected 80 km away. His patent on wirelesslinks precedes that of Marconi.

Guglielmo Marconi sends signals over large distances and successfully commercializes wirelessCommunication systems. In 1901, he performs the first transatlantic transmission from Poldhu inCornwall, England, to Newfoundland, Canada. He receives the Nobel Prize for his work in 1909.

The beginning of 20th century (until WW2) marks the boom in wire-antenna technology (dipolesand loops) and in wireless technology as a whole, which is largely due to the invention of theDeForest triode tube, used as radio-frequency (RF) generator. Radio links are realized up to UHF(about 500 MHz) and over thousands of kilometers.

WW2 marks a new era in wireless communications and antenna technology. The invention ofnew microwave generators (magnetron and klystron) leads to the development of themicrowave antennas such as waveguide apertures, horns, reflectors, etc.

1.2 Introduction

An antenna or aerial is defined as “A means for radiating or receiving radio waves”. In other wordsthe antenna is the transitional structure between free space and a guiding device, the guiding device



or transmission line may take the form of a coaxial line or a hollow pipe (waveguide) and it is used totransfer electromagnetic energy from the transmitting source to antenna or from the antenna toreceiver.

Antennas are basic components of any electric system and are connecting links between thetransmitted and free space or free space and the receiver. Thus antennas play very important role infinding the characteristics of the system in which antennas are employed. Antennas are employed indifferent systems in different forms. That is in some system the operational characteristics of thesystem are designed around the directional properties of the antennas or in some others systems,the antennas are used simply to radiate electromagnetic energy in an omnidirectional or finally insome systems for point –to- point communication purpose in which increased gain and reducedwave interference are required.

Transmission and Reception of Antenna

A guided wave traveling along a transmission line, which opens out as in figure 1.2, will radiate asfree space wave. The guided wave is a plane wave while the free space wave is a sphericallyexpanding wave. Along the uniform part of the line, energy is guided, as a plane wave with little loss,provided the spacing between the wires is a small fraction of a wavelength. At the right, as thetransmission line separation approaches a wavelength or more, the wave tends to be radiated sothat the opened-out line acts like an antenna, which launched the free space wave. The currents onthe transmission line flow out on the transmission line and end there, but the fields associated withthem keep on going. To be more explicit, the region of transition between the guided wave and thefree space wave may be defined as an antenna.



Figure1.2 Antenna as Transmission device

In this vast and dynamic field, the antenna technology has been an indispensable partner of thecommunication revolution. Many major advances that took place over the years are now in commonuse. Despite numerous challenges, the antenna technology has grown with a fast pace to harass theelectromagnetic spectrum, which is one of the greatest gifts of nature.

1.3 Types of antennas

Various forms of antennas have been developed in last few decades. There has been a vigorous anddynamic change in the field of antennas, which has been an indispensable partner of thecommunications revolution. The various forms of antennas are.

a) Wire Antennasb) Aperture Antennasc) Microstrip Antennad) Array Antennase) Reflector Antennasf) Lens Antennas



Though there are different types of antennas available, we have selected the microstripantenna..Since Microstrip antennas became very popular in the 1970s primarily for space borneapplications. Today they are used for government and commercial applications. These antennasconsist of a metallic patch on a grounded substrate. The metallic patch can take many differentconfigurations. However, the rectangular and circular patches, shown in Figure 1.3, are the mostpopular because of ease of analysis and fabrication, and their attractive radiation characteristics,especially low cross-polarization radiation.

Rectangular Patch

Circular Patch

Figure1.3 Typical Microstrip Antenna



1.4 Radiation mechanism of Antennas

Radiation mechanism of antennas clearly explains “how the Radiation accomplished?” In otherwords, how are the electromagnetic fields generated by the source, contained and guided within thetransmission line and antenna, and finally “detached” from the antenna to form a free-space wave?These can be illustrated by examining some basic sources of radiation.

1.4.1 Radiation Mechanism in Single Wire

The fundamental relation of electromagnetic radiation simply states that to create radiations, theremust be a time-varying current or an acceleration (or deceleration) of charge.

Where, l – Length of the wire (mm)

az– Acceleration (m/ss)

ql- Charge per unit length (c)

We usually refer to currents in time-harmonic applications while charge is most often mentioned intransients. To create charge acceleration (or deceleration) the wire must be curved, bent,discontinuous, or terminated. Periodic charge acceleration (or deceleration) or time-varying currentis also created when charge is oscillating in a time-harmonic motion. Therefore:1. If a charge is not moving, current is not created and there is no radiation.2. If charge is moving with a uniform velocity:a. There is no radiation if the wire is straight and infinite in extent.b. There is radiation if the wire is curved, bent, discontinuous, terminated, or truncated.3. If charge is oscillating in a time-motion, it radiates even if the wire is straight.

1.4.2 Radiation Mechanism in Two Wires

Let us consider a voltage source connected to a two-conductor transmission line which is connectedto an antenna. This is shown in Figure 1.4.2(a). Applying a voltage across the two-conductortransmission line creates an electric field between the conductors. The electric field has associatedwith it electric lines of force which are tangent to the electric field at each point and their strength isproportional to the electric field intensity. The electric lines of force have a tendency to act on thefree electrons (easily detachable from the atoms) associated with each conductor and force them tobe displaced. The movement of the charges creates a current that in turn creates magnetic fieldintensity. Associated with the magnetic field intensity are magnetic lines of force which are tangentto the magnetic field.

Magnetic field lines always form closed loops encircling current-carrying conductors because



physically there are no magnetic charges. The electric field lines drawn between the two conductorshelp to exhibit the distribution of charge.

Figure 1.4.2Source,

transmissionline, antenna, and

detachment ofelectric field

lines.

W e remove parto f the antenna

structure, asshown inF i g u r e1 . 4 . 2 ( b ) ,f r e e - s p a c ewaves can beformed by“connecting”

t h e open ends oft h e electric lines

( s h o w ndashed) .Thef r e e - s p a c ewaves are alsoperiodic but ac o n s t a n tphase point

P 0 m o v e so u t w a r d l y

with the speed of light and travels a distance of λ/2 (to P1) in the time of one-half of a period. If theinitial electric disturbance by the source is of a short duration, the created electromagnetic wavestravel inside the transmission line, then into the antenna, and finally are radiated as free-spacewaves, even if the electric source has ceased to exist (as was with the water waves and theirgenerating disturbance).



Figure 1.4.2 Electric field lines of free-space wave for bi-conical antenna.

If the electric disturbance is of a continuous nature, electromagnetic waves exist continuously andfollow in their travel behind the others. This is shown in Figure 1.4.2 (c) for a bi-conical antenna.When the electromagnetic waves are within the transmission line and antenna, their existence isassociated with the presence of the charges inside the conductors. However, when the waves areradiated, they form closed loops and there are no charges to sustain their existence. This leads us toconclude that electric charges are required to excite the fields but are not needed to sustain themand may exist in their absence.

1.5 Microstrip Antenna

Microstrip patch antennas are the most common form of printed antennas. They are popular fortheir low profile, geometry and low cost. A microstrip device in its simplest form is a layeredstructure with two parallel conductors separated by a thin dielectric substrate. The lower conductoracts as a ground plane. The device becomes a radiating microstrip antenna when the upperconductor is a patch with a length that is an appreciable fraction of a wavelength (λ), approximatelyhalf a wavelength (λ / 2). In other words, a microstrip patch antenna consists of a radiating patch onone side of a dielectric substrate which has a ground plane on the other side as shown in Fig. 1.5(a).



Figure 1.5(a)– Typical microstrip patch antenna

Microstrip patch antennas radiate primarily because of the fringing fields between the patch edgeand the ground plane. Microstrip patch antennas have many advantages when compared toconventional antennas. As such, they have found usage in a wide variety of applications rangingfrom embedded antennas such as in a cellular phone, pagers etc. to telemetry and communicationantennas on missiles and in satellite communications.

Patch

The patch is generally made of conducting material such as copper or gold and can take anypossible shape.

Some of the typical patch shapes are shown in Fig. 1.5(b).

The radiating patch and the feed lines are usually photo etched on the dielectric substrate.



Figure 1.5(b)– Different shapes and sizes of patch

Substrate Material

The dielectric substrate material of a microstrip patch antenna can be of any type like RT Duriod ,Quartz, FR4 Epoxy, Silicon etc..,

The Dielectric Substrate Material we are using in our Design is FR4 Epoxy

Where “FR” means Flame Retardant and type 4 indicates Woven Glass reinforced Epoxyresin.

The Range of the dielectric constant of FR4 Epoxy typically depends on glass resin.

This material is popular and cost effective Compared to other PCB material.

FR4 is most Commonly Used as an electrical insulator possessing considerable mechanicalStrength.

FR4 is also used in the construction of relays, switches, standoffs, busbars, washers,transformer and screw terminal strips.

Ground Plane

The ground plane is part of the antenna. Ideally, the ground plane should be infinite as for amicrostrip patch antenna. But, in reality, a small ground plane is desirable. The radiation of amicrostrip antenna is generated by the fringing field between the patch and the ground plane, theminimum size of the ground plane is therefore related to the thickness of the dielectric substrate.Generally speaking, a λ/4 extension from the edge of the patch is required for the ground plane,whereas the radius of a monopole ground plane should be at least one wavelength.



Feed Techniques for Patch Antennas

Microstrip antennas are fed by a variety of methods that are broadly classified into two maincategories, namely, contacting and non-contacting. In the contacting method, the RF power is feddirectly to the radiating patch using a connecting element such as a microstrip line. In thenon-contacting method, electromagnetic field coupling is done to transfer power between themicrostrip line and the radiating patch.The four most popular feed techniques used are the microstrip line, coaxial probe (both contactingschemes), aperture coupling and proximity coupling (both non-contacting schemes).

a) Microstrip Line Feed

This type of feed technique excitation of the antenna would be by the Microstrip line of the samesubstrate as the patch that is here can be considered as an extension to the Microstrip line, andthese both can be fabricated simultaneously. This conducting strip is directly connected to the edgeof the Micro strip patch. , As known the conducting strip is smaller than that of the patch in width.This type of structure has actually an advantage of feeding the directly done to the same substrateto yield a planar structure as said above. The coupling between the Microstrip line and the patch isin the form of the edge or butt-in coupling as shown in the figure. Or it is through a gap betweenthem.

A Type of Microstrip feed and the corresponding equivalent circuits, Microstrip feed at a radiatingedge

b) Coaxial FeedThe coaxial feed or probe feed is a very common contacting scheme of feeding patch antennas. Theconfiguration of a coaxial feed is shown in Fig. below. As seen from Fig. 3.8, the inner conductor of



the coaxial connector extends through the dielectric and is soldered to the radiating patch, while theouter conductor is connected to the ground plane.

Coaxial Feed

The main advantage of this type of feeding scheme is that the feed can be placed at any desiredlocation inside the patch in order to match with its input impedance. This feed method is easy tofabricate and has low spurious radiation.

As we are using only probe feed and linefeed techniques in our design, we do not discuss furtherabout other remaining methods of feeding here.

1.6 RADIATION MECHANISM IN A MICROSTRIP ANTENNA

In microstrip antennas, the radiation is from the periphery of the patch, where the fringing field ismaximum. Portions of the patch act like slots, with respect to the ground plane. The exciting dipolelaunches guided modes in the parallel plate region under the patch. The surface current distributionscan be computed on the conducting and dielectric surfaces of the antenna to understand theirbehavior. The radiation from microstrip antennas occurs from the fringing fields between the edgeof the microstrip antenna conductor and the ground plane. For a rectangular microstrip antennafabricated on thin dielectric substrate and operating in the fundamental mode, there is no fieldvariation along the width and thickness. The fields vary along the length, with a period of half awavelength. The radiation from a microstrip patch is shown in figure 1.6.



Figure 1.6 Radiation on microstrip patch

The radiation mechanism can be explained by resolving the fringing fields at the opencircuited edges into the normal and tangential components with respect to the ground plane. Thenormal components are out of phase (as the patch is half wavelength long) and hence the far fieldsproduced by them cancel each other. The tangential components are in phase and the resultingfields are combined to give maximum radiation in the broadside direction.



CHAPTER-2

FUNDAMENTALPARAMETERS OF

ANTENNAS

parameters of Antennas

2.0 Introduction

The History of a basic antenna, its working, radiation mechanism and its types, microstrip antennawere outlined in the previous chapter. Here we are discussing about the essential parameters of anantenna in brief with its formulae.

2.1 Gain



The gain of the antenna is closely related to the directivity. In addition to the directional capabilitiesit accounts for the efficiency of the antenna.Gain does not account for losses arising from impedance mismatches (reflection losses) andpolarization mismatches (losses).Gain is the ratio of the intensity, in a given direction, to theradiation intensity that would be obtained if the power accepted by the antenna were radiatedisotropically.

Gain = 4π = 4π (dimensionless).

2.2 Efficiency

The total antenna efficiency e0 is used to take into account losses at theinput terminals and within the structure of the antenna.e0 is due to the combination of number ofefficiencies:

е0= er ec ed Where, е0 = total efficiency,

er = reflection efficiency

ec= conduction efficiency, ed= dielectric efficiency,

2.3Directivity

Directivity of an antenna is defined as “The ratio of the radiation intensity in a given direction fromthe antenna to the radiation intensity averaged over all directions. The average radiation in intensityis equal to the total power radiated by the antenna divided by 4 . If the direction is not specified,

the direction of maximum radiation intensity is implied.”

The directivity of a non-isotropic source is equal to the ratio of its radiation intensity in a givendirection over that of an isotropic source.

Directivity is defined as

D

If the direction is not specified, It implies the direction of maximum radiation intensity (maximum



directivity) expressed as

Dmax=Do

Where, D=directivity (dimensionless) Do=maximum directivity (dimensionless) U=radiation intensity (w/unit solid angle)

Umax=maximum radiation intensity of isotropic source (W/unit solid angle)

Uo=radiation intensity of isotropic source (W/unit solid angle) Prad=total radiated power (w)

2.4 Bandwidth

Another important parameter of any antenna is the bandwidth it covers. Only impedance bandwidthis specified most of the time. However, it is important to realize that several definitions ofbandwidth exist impedance bandwidth, directivity bandwidth, polarization bandwidth, and efficiencybandwidth. Directivity and efficiency are often combined as gain bandwidth.

This is the frequency range wherein the structure has a usable bandwidth compared to a certainimpedance, usually 50Ω.The impedance bandwidth depends on a large number of parametersrelated to the patch antenna element itself (e.g., quality factor) and the type of feed used. The plotbelow shows the return loss of a patch antenna and indicates the return loss bandwidth at thedesired S11/VSWR (S11 wanted/VSWR wanted). The bandwidth is typically limited to a few percent.This is the major disadvantage of basic patch antennas.

BW = X 100 %

Where, fH = upper cut-off frequency (GHz) fL = lower cut-off frequency (GHz) and fc = centre frequency(GHz)



2.5 Radiation Pattern

An antenna radiation pattern or antenna pattern is defined as “a mathematical function or agraphical representation of the radiation properties of the antenna as a function of spacecoordinates. In most cases, the radiation pattern is determined in the far field region and isrepresented as a function of the directional coordinates. Radiation properties include power fluxdensity, radiation intensity, field strength, directivity, phase or polarization.”

Various parts of a radiation pattern are referred to as lobes, which may be sub classified into majoror main, minor, side, and back lobes.

A radiation lobe is a “portion of the radiation pattern bounded by regions ofrelatively weak radiation intensity.” Figure 2.5(a) demonstrates a symmetrical three dimensionalpolar pattern with a number of radiation lobes. Some are of greater radiation intensity than others,but all are classified as lobes. Figure 2.5(b) illustrates



Figure2.5(a) Radiation lobes and beamwidth of an antenna pattern.

Figure2.5(b) Linear plot of power pattern and its associated lobes and beamwidth.

i) Major Lobe: A major lobe (also called main beam) is defined as “the radiation lobe containing thedirection of maximum radiation.” In Figure 2.5(b) the major lobe is pointing in the θ= 0 direction. Insome antennas, such as split-beam antennas, there may exist more than one major lobe.

ii) Minor Lobe: A minor lobe is any lobe except a major lobe. In Figures 2.5(a) and (b) all the lobeswith the exception of the major can be classified as minor lobes.

iii) Side Lobe: A side lobe is “a radiation lobe in any direction other than the intended lobe.” (Usuallyside lobe is adjacent to the main lobe and occupies the hemisphere in the direction of the mainbeam.)

iv) Back Lobe: A back lobe is “a radiation lobe whose axis makes an angle of approximately 180 withrespect to the beam of an antenna.” Usually it refers to a minor lobe that occupies the hemispherein a direction opposite to that of the major lobe.



2.6 Beamwidth

• The beamwidth of an antenna is a very important figure of merit and often is used as a trade-offbetween it and the side lobe level; that is, as the beamwidth decreases, the side lobe increases andvice versa.• The beamwidth of the antenna is also used to describe the resolution capabilities of the antennato distinguish between two adjacent radiating sources or radar targets.

Half-Power Beamwidth (HPBW)-In a plane containing the direction of the maximum of a beam, theangle between the two directions in which the radiation intensity is one-half value of the beam.

First-Null Beamwidth (FNBW)- Angular separation between the first nulls of the pattern.

Beamwidth of an Antenna

Resolution

• The most common resolution criterion states that the resolution capability of an antenna todistinguish between two sources is equal to half the first-null beamwidth (FNBW/2), which is usuallyused to approximate the HPBW.• That is, two sources separated by angular distances equal or greater than FNBW/2 ¼ HPBW of anantenna with a uniform distribution can be resolved.• If the separation is smaller, then the antenna will tend to smooth the angular separation distance.



2.7 Polarization

The polarization of an antenna is the polarization of the wave radiated from the antenna. A receivingantenna has to be in the same polarization as the transmitting antenna otherwise it will notresonate. Polarization is a property of the electromagnetic wave. It describes the magnitude anddirection of the electric field vector as a function of time, with other words “the orientation of theelectric field for a given position in space”. A simple strait wire has one polarization when mountedvertically, and different polarization when mounted horizontally figure2.7. Polarization can beclassified as linear, circular, and elliptical.

In linear polarization the antenna radiates power in the plane of propagation, only one plane, theantenna is vertically linear polarized when the electric field is perpendicular to the earth’s surface,and horizontally linear polarized when the electric field is parallel to the earth’s surface. Circularpolarization antenna radiates power in all planes in the direction of propagation (vertical, horizontal,and between them). The plane of propagation rotates in circle making one complete cycle in oneperiod of wave.

Figure 2.7 - Polarization of electromagnetic wave

2.8 VSWR (Voltage Standing Wave Ratio)

The VSWR (also known as the standing wave ratio, SWR) is defined as the ratio of the magnitude of

the maximum voltage on the line to the magnitude of the minimum voltage on the line, as shown in

Figure Below. Mathematically, it can be expressed as

VSWR ( )

The VSWR is just another measure of how well a transmission line is matched with its load. Unlike

the reflection coefficient, the VSWR is a scalar and has no phase information. For a non perfect



transmission line, the VSWR is a function of the length of the line ( ) as well as the load impedance

and the characteristic impedance of the line. But for a lossless transmission line, the VSWR is the

same at any reference point of the line.

Return loss as a function of the line length

2.9 Return loss

The bandwidth of an antenna over which the return loss is acceptable is directly proportional to thevolume the antenna occupies, so very small antennas can produce inadequate bandwidth, especiallyin the 850 MHz band where the effective volume is smallest relative to the frequency of operation.The efficiency of a typical embedded antenna can range from about 40 to 75%. Greater than 75%efficiency is challenging to obtain from a fully embedded antenna and lower than 40% efficiency willtypically cause certification failures. In most cases, the efficiency goal should be 60%, with 40% as anabsolute minimum. It is important to understand that good return-loss performance can beinadvertently achieved at the expense of efficiency. An extreme example of this concept is a 50 ohmresistor: the resistor has an excellent return loss but has virtually 0% efficiency, and is obviously notan antenna. Therefore, an understanding of the return loss and efficiency concepts is critical to goodantenna design.

RL (dB) = 10 log(Pi/Pr)

Where, RL (dB) - Return Loss in dB Pi – Incident Power (w) Pr – Reflected Power (w)

Return Loss is related to both standing wave ratio (SWR) and reflection coefficient (Г). Increasing



return loss corresponds to low SWR. Return loss is measure of how well devices or lines arematched. A match is good if the return loss is high. A high return loss is desirable and results in alower insertion loss.

12.10 Input Impedance

The input impedance of an antenna is defined as “the impedance presented by an antenna at itsterminals or the ratio of the voltage to the current at the pair of terminals or the ratio of theappropriate components of the electric to magnetic fields at a point”. Hence the impedance of theantenna can be written as given below.

Zin = Rin + jXin (Ω)

Where, Zin is the antenna impedance at the terminals Rin is the antenna resistance at the terminals Xin is the antenna reactance at the terminals

The imaginary part, Xin of the input impedance represents the power stored in the near field of theantenna. The resistive part, Rin of the input impedance consists of two components, the radiationresistance Rr and the loss resistance RL. The power associated with the radiation resistance is the

power actually radiated by the antenna, while the power dissipated in the loss resistance is lost asheat in the antenna itself due to dielectric or conducting losses.

If we assume that the antenna is attached to a generator with internal impedance

Zg = Rg + jXg (Ω)

Where, Rg is the resistance of generator impedance. Xg is the reactance of generator impedance.

2.11 Effective Aperture

The effective aperture Aw is a parameter that is defined especially for receiving antennas. It is ameasure of the maximum received power Pr which the antenna can obtain from a plane wave ofpower density S:

Prmax = S . Aw (w)

Although the effective aperture can definitely be thought of as a real aperture that is perpendicularto the direction of propagation of the incident wave, it is not necessarily identical to the geometricaperture Ag of the antenna. The relationship between the two apertures is described by the



aperture efficiencyq = Aw / Ag (c)

The effective aperture and the gain can be converted from one to the other with the aid of theequation:

Aw



CHAPTETR - 3

DESIGN OF MICROSTRIPANTENNA

Designing of Microstrip Antenna

3.0 Introduction

The discussion on basic antenna, Its types, Radiation mechanism, Study of microstrip antenna,Fundamental parameters of antennas were outlined in the previous chapters. In this chapter we arediscussing about the design specifications, Software tool required to design a microstrip patchantenna.

3.1 Design Specifications

The three essential parameters for the design of a rectangular Microstrip Patch Antenna are:



Frequency of operation (fr): The resonant frequency of the antenna must be selectedaccording to our applications. We use the resonating frequency as 22 GHz for our design.

Dielectric constant of the substrate (εr): Glass Epoxy is used in our design with dielectricconstant of 4.4.

Height of dielectric substrate (h): Height of dielectric substrate controls the bandwidth. Thevalue of h used in our design is 1.6mm.

Step 1: Width of Patch

The width of the patch element (W) is given by

W (mm)

Where, C is the speed of light(c= 3 x m/s)

is the resonant frequencyis the dielectric constant of the substrate

Step 2: Effective Dielectric Constant

The effective dielectric constant (εeff) is an important parameter which arises because part of thefields from the microstrip conductor, exist in air. It is calculated as

Ԑreff



Step 3: Effective Length

The effective length (Leff) is given

Leff (mm)

Step 4: Length Extension

Because of the fringing effects, electrically the patch of the antenna looks larger than its physicaldimensions. Thus length extension (∆L) is given by

∆L (mm)

Step 5: Length of PatchThe actual length (L) of patch is obtained by

L=Leff - 2∆L (mm)

Step 6 : Length, Width of Ground Plane

Calculation of the ground plane Lg and Wg: Usually the size of the ground plane is greater than thepatch dimension by approximately six times the substrate thickness all around the periphery

Lg= 6h + L (mm)

And,

Wg = 6h + W (mm)

Step 7 : Length of the feed

The Length of the feed

Lf (mm)



Where λg = c / fr (m)

Step 8 : Width of the feed

The width of the feed (Wf) is given by

for < 2 (mm)

Where,

A (mm2)

For example :

If fr = 22GHz,εr=4.4, h=1.6mmC=

The width of the patch element W

W

W

W = 4.14mm

Effective Dielectric Constant

Ԑreff

Ԑreff

Ԑreff



Ԑreff 2.805

Effective Length

Leff

Leff

Length Extension

∆L

∆L

∆L

Length of Patch

L = – (2 x

L =

Length of Ground Plane

Lg = 6 x 1.6 +

Lg = 12.33mm

Wg = 6 x 1.6 +

Wg = 9.6 +



Wg = 13.74mm

Lf

Lf

Lf

λg = 3 x 108 / 22 x 109

λg = 0.3 x 109 / 22 x 109

λg = 0.0136 (m)

Wf x

Wf

A

A

A = 0.834 x 1.7624

A = 1.4697 (mm2)

3.2 Software Tool Used: HFSS

In order to design a microstrip rectangular patch antenna to operate in a Ku band frequency range,Although there are various simulation software available for example FEKO, IE3D, HFSS, CST…, etc.

We are using HFSS (High Frequency Structural Simulator) to design a MSA. It is more commonly usedsoftware because of its friendly user interface and better accuracy for complicated geometries.Therefore, in the present work, we have used HFSS Version 13.0



HFSS software is considered the industry standard for 3D electromagnetic structure simulator. It isconsidered as an essential tool for high speed and high frequency component designs. HFSS offerssolver technologies based on either integral equation method or finite element method.

HFSS solver is equipped with automated solution methods so all we need to do is to specify thegeometry, the properties of material and output. From here onwards HFSS will take charge and willgenerate a mesh for solving the problem.

Ansoft HFSS can be used to calculate parameters such as S-Parameters, Resonant Frequency, andFields. Typical uses include:

Package Modeling – BGA, QFP, Flip-ChipPCB Board Modeling – Power/ Ground planes, Mesh Grid Grounds, BackplanesSilicon/GaAs-Spiral Inductors, Transformers EMC/EMI – Mobile Communications –Patches, Dipoles, Horns, Conformal Cell Phone Antennas, Quadrafilar Helix, SpecificAbsorption Rate ( SAR), Infinite Arrays, Radar Section (RCS), Frequency Selective Surface(FSS) Connectors – Coax, SFP/XFP, Backplane, TransitionsWaveguide – Filters, Resonators, Transitions, CouplersFilters – Cavity Filters, Microstrip, Dielectric

Features of HFSS Software

High speed, High Frequency component modeling.

Solver Technologies are based on several methods.

Can select the appropriate method amongst integral equation method or finite element method.

Equipped with automated solution methods.

Automatic Adaptive Meshing

Advanced Finite Array Simulation Technology

Mesh Element Technologies

Advanced Broadband SPICE Model Generation

Optimization and Statistical Analysis

EDA Design Flow Integration

High-Performance Computing

Powerful Post-Processing Capabilities



CHAPTER-4



RESULTS ANDDISCUSSIONS

RESULTS AND DISCUSSIONS

4.0 Introduction

The Microstrip patch antenna is designed to resonate at ku-band (12-18 GHz) using HFSS Softwaretool and fabricated on FR4 Epoxy Substrate Material, The design and fabricated results obtained arediscussed in this chapter.

4.1 Simulation of 15 GHZ Patch Antenna

The project is based on designing a microstrip antenna using edge feed technique which resonatesat 15GHz and then vary the parameters of the antenna such that the working of the patch isoptimized. Simulations are divided into three basic groups:

1) To start with, the length of the transmission line is varied. The gain of the antenna varies greatlyas we vary the feed point. We get best gain when the transmission line is located at the 50Ωimpedance line. In this case the return loss curve dips the maximum.

2) The dimensions of the wave port are varied in order to match the impedance to 50Ω.



3) The dielectric substrates are changed and its effects on the performance of the patch are observed.

All the dimensions of patches are calculated with help of equations given previously. The simulationresults for the patches are given in the following sections.

4.2 Design of MSA with FR4 Epoxy Substrate Material

Height of substrate = 1.6 mmDielectric constant = 4.4Length of ground plane = 30 mmWidth of ground plane = 30 mmLength of the patch = 3.7 mmWidth of the patch = 5.8 mmLength of Feed =13.15 mmWidth of Feed =1.5 mmFrequency = 15.00 GHz

FR4 Epoxy Model (as designed using HFSS)



Figure 4.1: Structural design of MSA

The structural design of Microstrip rectangular patch antenna is as shown in Figure 4.1 andsimulated to resonate at 15GHz of frequency. It can be seen from figure 4.2 that the gain of the MSAis found to be 5.289dB. The impedance bandwidth over return loss less than -10dB is measured from12 to 18 GHz of frequency. The variation of return loss versus frequency is shown in figure 4.3.

From figure 4.3 it is seen that the antenna resonates at 15.240 GHz of frequency, with minimumreturn loss of -18.193 dB. It can be seen from figure that lower cut-off frequency (fL) is 14.730 GHz,upper cut-off frequency (fH) is 15.840 GHz and CENTRE frequency (fC) is 15.240 GHz. As given insectio n 2.4 the impedance bandwidth (BW) of MSA is found to be BW=7.283%. Though it wasdesigned to resonate at 15 GHz, but from the frequency response it is resonating at 15.240 GHzwhich is very close to the expected value.

Gain Plot



Figure 4.2: Gain Plot of MSA

Return Loss Curve

Figure 4.3: Variation of Return loss versus Frequency



Radiation Pattern

Figure 4.4: Radiation Pattern of MSA

3D Polar Plot



Figure 4.5: 3D Polar Plot of MSA4.3 MEASUREMENT RESULTS

Fabricated Design of MSA

Figure 4.3(a): Fabricated Microstrip Patch Antenna (Ku - Band)

The Fabricated design of Microstrip rectangular patch antenna is as shown in Figure 4.3(a) andsimulated to resonate at 15GHz of frequency. The impedance bandwidth over return loss less than-10dB is measured from 12 to 18 GHz of frequency. The variation of return loss versus frequency andVSWR versus frequency as shown in figure below.

Radiation Plot



VSWR Plot

Far Field Amplitude of MSA



Figure 4.3(b):Far Field

Amplitude RadiationPattern

The Far Field Amplitude Radiation Pattern of an Microstrip Patch Antenna is as shown in the figure4.3(b).This graph shows the narrow bandwidth and Theta is taken as 90o

Far-field Cut Analysis: Avg value: -14.035 dB -3. dB beam width: 38.934 deg, Peak from 3dB pts: -44.1744 deg

4.4 DISCUSSIONS ON SIMULATION RESULTS

Based on the simulation results the effect of changing h and εr on antenna dimensions andperformance is observed. The results are presented in table below assuming a fixed frequency ofoperation (15 GHz).

Parametervariation

Length of thegroundplane(Lg)

Width of thegroundplane(Wg)

Length of thepatch(Lp)

Width of thepatch(Wp)

h increased Increases Increases Increases Remains



constanth decreased Decreases Decreases Decreases Remains

constantεr increased Decreases Decreases Decreases Decreasesεr decreased Increases Increases Increases Increases

Table 4: Effect of variation of h and εr on patch dimensions

cHAPTER – 5ADVANTAGES,



DISADVANTAGES ANDAPPLICATION OF MSA

ADVANTAGES, DISADVANTAGES AND APPLICATION OF MSA

5.1 Advantages and Disadvantages of Microstrip Patch Antenna

Microstrip Patch Antenna has number of advantages compared to other antennas. Some of theirmajor advantages are given below

Low Weight

Low Profile

Low Fabrication cost. Hence can be manufactured in large quantities.

Required no cavity backing.

Supports both linear and circular polarization.

Capable of dual and triple frequency operation range.



Feed lines and matching networks can be fabricated simultaneously.

A Single patch antenna provides a maximum directive gain of around 6-9dBi.

Some of their disadvantages are given below

Low Efficiency

Low Gain

Large ohmic Loss in feed structure

Low Power Handling Capacity.

Excitation of surface waves.

Polarization Purity is difficult to achieve.

Complex feed structures require high performance arrays.

5.2 Applications

Microstrip patch antenna has wide range of application some of major applications are given below

Mobile and satellite communication System

Global Positioning System(GPS)

Direct Broad Cast Television(DBS)

Radio Frequency Identification (RFID)

Worldwide Interoperability for Microwave Access (WiMax)

Wireless Local Area Network’s



cHAPTER - 6

CONCLUSIONSAND FUTURE

SUGGESTIONS



6.1 CONCLUSIONS

The rectangular microstrip antennas (RMSA) were successfully designed, simulated andcharacterized using HFSS software for X-band frequency of 15GHz for substrates of varying height (h)and permittivity (εr).

SubstrateMaterial

RelativePermittivity

(εr)

Height Inmm(h)

ResonatingFrequency

(GHz)

Bandwidth(GHz)

Gain(dB)

ReturnLoss(dB)

FR4 GlassEpoxy

4.4 1.6 15.240 0.7283 5.289 -18.193

The above table gives resonating frequency (fr), bandwidth, gain and return loss of the designedRMSA for different substrates.

In earlier literatures this antenna was designed using inset feed techniques whereas in this projectwe have used the edge feed technique which comprises of a quarter wave transformer to match theimpedance. Very few literatures show the use of edge feed most of which operates at C-bandfrequencies (4-8GHz) of microwaves.

In this project we have improved the gain of the RMSA. It is found that the obtained frequency (fr) is≈15GHz. High return loss indicating a good matching.

6.2 FUTURE SUGGESTIONS

It is very important to choose the appropriate substrate for your microstrip antenna design. As saidin this project different substrates affect the performance of the antenna. Proper position toterminate the Feed line also affects the performance of the antenna. The performance of themicrostrip antenna with substrate- FR4 (glass epoxy) is shown in this project work, Further thisantenna can be designed with other substrate materials like RT-Duroid, Quartz, Silicon etc..,

In this project only transmission line feed technique is used. In future other different type of feedtechniques can be used to calculate the overall performance of the antenna. Further, work can bedone by focusing on the area of different design methods especially in enhancing the impedance,bandwidth, and the efficiency.



APPENDIX



APPENDIX I

Substrate Material Used:FR4 Epoxy

FR-4 (or FR4) is a grade designation assigned to glass-reinforced epoxy laminate sheets, tubes, rodsand printed circuit boards (PCB). FR-4 is a composite material composed of woven fiber glass clothwith an epoxy resin binder that is flame resistant (self-extinguishing).

FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate grade with goodstrength to weight ratios. With near zero water absorption, FR-4 is most commonly used as anelectrical insulator possessing considerable mechanical strength. The material is known to retain itshigh mechanical values and electrical insulating qualities in both dry and humid conditions. Theseattributes, along with good fabrication characteristics, lend utility to this grade for a wide variety ofelectrical and mechanical applications.

ApplicationsPrinted circuit boards

FR-4 is the primary insulating backbone upon which the vast majority of rigid printed circuitboards (PCBs) are produced. A thin layer of copper foil is laminated to one, or both sides of an FR-4glass epoxy panel. These are commonly referred to as "copper clad laminates."

FR-4 copper-clad sheets are fabricated with circuitry etched into copper layers to produce printedcircuit boards. More sophisticated and complex FR-4 printed circuit boards are produced in multiplelayers, also known as "multilayer circuitry".

FR-4 is also used in the construction of relays, switches, standoffs, busbars, washers, arc shields,transformers and screw terminal strips.

PropertiesTypical physical and electrical properties of FR-4 are as follows. LW (length wise, warp yarn direction)and CW (cross wise, fill yarn direction) refer to the fiber orientations in the plane of the board(in-plane) that are perpendicular to one another. The through-plane direction is also referred to asthe z-axis.

http://en.wikipedia.org/wiki/Printed_circuit_board

http://en.wikipedia.org/wiki/Printed_circuit_board



Parameter ValueSpecific gravity/density 1,850 kg/m3 (3,120 lb/cu yd)Water absorption −0.125 in < 0.10%Temperature index 140 °C (284 °F)Thermal conductivity, through-plane 0.29 W/m·K, 0.343 W/m·KThermal conductivity, in-plane 0.81 W/m·K, 1.059 W/m·KRockwell hardness 110 M scaleBond strength > 1,000 kg (2,200 lb)Flexural strength (A; 0.125 in) – LW > 440 MPa (64,000 psi)Flexural strength (A; 0.125 in) – CW > 345 MPa (50,000 psi)Tensile strength (0.125 in) LW > 310 MPa (45,000 psi)Izod impact strength – LW > 54 J/m (10 ft·lb/in)Izod impact strength – CW > 44 J/m (8 ft·lb/in)Compressive strength – flat wise > 415 MPa (60,200 psi)Dielectric breakdown (A) > 50 kVDielectric breakdown (D48/50) > 50 kVDielectric strength 20 MV/mRelative permittivity (A) 4.8Relative permittivity (D24/23) 4.8Dissipation factor (A) 0.017Dissipation factor (D24/23) 0.018Dielectric constant permittivity 4.70 max., 4.35 @ 500 MHz, 4.34

@ 1 GHzGlass transition temperature Can vary, but is over 120 °CYoung's modulus – LW 3.5×106 psi (24 GPa)Young's modulus – CW 3.0×106 psi (21 GPa)Coefficient of thermal expansion -x-axis

1.4×10−5 K−1

Coefficient of thermal expansion -y-axis

1.2×10−5 K−1

Coefficient of thermal expansion -z-axis

7.0×10−5 K−1

Poisson's ratio – LW 0.136Poisson's ratio – CW 0.118LW sound speed 3602m/sSW sound speed 3369m/sLW Acoustic impedance 6.64 MRayl

APPENDIX II

http://en.wikipedia.org/wiki/Density

http://en.wikipedia.org/wiki/Relative_permittivity

http://en.wikipedia.org/wiki/Dissipation_factor



HFSS

HFSS (High Frequency Structural Simulator) software is considered the industry standard for 3Delectromagnetic structure simulation. It is considered as an essential tool for high speed andhigh frequency component designs. HFSS offers solver technologies based on either integralequation method or finite element method. It’s up to you which method to select for thesimulation to be performed.

HFSS solvers are equipped with automated solution methods so all you need to do is to specifythe geometry, the properties of material and output. From here on wards HFSS will take chargeand will generate a mesh for solving the problem.

Features of HFSS SoftwareHigh speed, high frequency component modeling.Solver technologies are based on several methods.Can select the appropriate method amongst integral equation method or finite elementmethod.Equipped with automated solution methods.

One can achieve high-frequency, high-speed component design with state-of-the-art tools fromANSYS. ANSYS HFSS delivers the most accurate EM simulation results, every time.

Since performance of electronic devices depends on electromagnetic (EM) behavior, you need a fast,accurate account of how your design will behave in real-world implementations —long before anyprototype is built. ANSYS HFSS™ simulation results give you the confidence you need: Thetechnology delivers the most accurate answer possible with the least amount of user involvement.As the reference-standard simulation tool for 3-D full-wave electromagnetic-field simulation, HFSS isessential for designing high-frequency and/or high-speed components used in modern electronicsdevices.

Understanding the EM environment is critical to accurately predicting how a component —orsubsystem, system or end product—performs in the field, or how it influences performance of othernearby components. HFSS addresses the entire range of EM problems, including losses due toreflection, attenuation, radiation and coupling.

The power behind HFSS lies in the mathematics of the finite element method (FEM) and the integral,proven automatic adaptive meshing technique. This provides a mesh that is conformal to the 3-Dstructure and appropriate for the electromagnetic problem you are solving. With HFSS, the physicsdefines the mesh; the mesh does not define the physics. As a result, you can focus on design issuesrather than spend significant time determining and creating the best mesh.

HFSS benefits from multiple state-of-the-art solver technologies, allowing users to match theappropriate solver to any simulation need. Each solver is a powerful, automated solution process inwhich the user specifies geometry, material properties and the desired range of solutionfrequencies. Based on this input, HFSS automatically generates the most appropriate, efficient andaccurate mesh for the simulation, thereby leading to the highest-fidelity solution possible.



HFSS results yield information critical to your engineering designs. Typical results include scatteringparameters (S, Y, Z), visualization of 3-D electromagnetic fields (transient or steady-state),transmission-path losses, reflection losses due to impedance mismatches, parasitic coupling, andnear- and far-field antenna patterns

Car in an echoic chamber with Test antenna and antenna fields

HFSS, part of the ANSYS high-frequency electromagnetic design port folio, is integrated with ANSYSWork bench for coupling EM effects into multi physics analyses, such as temperature anddeformation.



TDR time domain response plot of connector vs. various angles

Engineers can use HFSS with confidence, knowing that they have achieved an accurate solution setregardless of the type of EM simulation performed.

To solve the most demanding high-frequency simulations, all HFSS solvers are equipped with highperformance computing (HPC) options including domain decomposition and distributed processing.HPC decreases computation time and leverages existing computer resources to more rapidly solvevery large simulations.

References

1. “Antenna Theory, Third Edition, Analysis and design” By Constantine A. Balanis, 2005, John Wiley

and Sons Inc.

2. “Design and Analysis of Microstrip Patch Antenna Arrays” – Ahmed FatthiAlsager.

3. “Bandwidth enhancement of dual patch microstrip antenna array using dummy EBG patterns on

feedline” by MANIK GUJRAL B.Eng. (Hons.), NUS in 2007.

4. “Design and Simulation of Multiband Microstrip Patch Antenna for Mobile Communications” by

Daniel Mammo.

5. “Design of linearly polarized rectangular microstrip patch antenna using ie3d/pso” - C. Vishnu

vardhanareddy and Rahul rana.



6. Pattern Analysis of “The Rectangular Microstrip Patch Antenna” - Vivekananda Lanka

Subrahmanya.

7. “Development of a Self-Affine Fractal Multiband Antenna for Wireless Applications” - Jagadeesha

S., Vani R. M. & P. V. Hunagund.

8. “A Self-Similar Fractal Antenna with Square EBG Structure” - Jagadeesha.S, Vani R.M, P.V.

Hunagund.

9. “A Self-Affine Fractal Multiband Antenna” - Sachendra N. Sinha, Senior Member, IEEE, and

Manish Jain.

10. “A Self-Similar Fractal Cantor Antenna for MICS Band Wireless Applications” by Gopalakrishnan

Srivatsun, Sundaresan Subha Rani, Gangadaran Saisundara Krishnan.

Microstrip Antenna Resonating at Ku-band frequency Report

Engineering

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