Frequency Band Name Frequency Range Wavelength (Meters) Application

Extremely Low Frequency (ELF) 3-30 Hz 10,000-100,000 km

Underwater Communication(submarines

because ELF penetrate water and follow the earth

surface)

Low Frequency (LF) 30-300 kHz 1-10 km AM Radio

Medium Frequency (MF) 300-3000 kHz 100-1,000 m AM Radio

High Frequency (HF) 3-30 MHz 10-100 m Shortwave Radio

Very High Frequency (VHF) 30-300 MHz 1-10 m FM Radio

Ultra High Frequency (UHF) 300-3000 MHz 10-100 cm Television, Mobile Phones,

GPSSuper High Frequency

(SHF) 3-30 GHz 1-10 cm Satellite Links, Wireless Communication

Extremely High Frequency (EHF) 30-300 GHz 1-10 mm Astronomy, Remote

Sensing

Visible Spectrum 400-790 THz (4*10^14-7.9*10^14) 380-750 nm (nanometers) Human Eye

An antenna is a specialized transducer that converts radio-frequency (RF) fields into alternating current (AC) or vice-versa.

There are two basic types: 1) Receiving antenna, which intercepts RF energy

and delivers AC to electronic equipment. 2)Transmitting antenna, which is fed with AC from

electronic equipment and generates an RF field. The idea of using an antenna was developed by

Guglielmo Marconi (c.1897). They are used in systems such

as radio and television broadcasting, two-way radio, wireless LAN, mobile telephony, radar, and satellite communications

Frequency :The basics of sinusoids (sine and cosine waves), wavelength, frequency and the speed of light.

Radiation Pattern :A radiation pattern defines the variation of the power radiated by an antenna as a function of the direction away from the antenna.

Directivity :Directivity is fundamental to antennas. It is a measure of how "directional" an antenna's radiation pattern is.

Efficiency and Gain :An antenna's efficiency is a measure of how much power is radiated by the antenna relative to the antenna input power. Antenna Gain, which is real power radiated in a particular direction.

Bandwidth :The bandwidth of an antenna is the frequency range over which the antenna radiates. This describes the range of frequencies over which the antenna can properly radiate or receive energy.

Effective Aperture :Effective aperture is a basic antenna concept that is a measure of the power captured by an antenna from a plane wave. Effective aperture can be expressed as a function of the antenna gain and the wavelength of interest.

Antenna Temperature :Antenna Temperature is a property of an antenna and the environment it operates in. It is a measure of the noise received by the antenna due to thermal (or temperature) effects.

Isotropic Antenna Dipole Antenna Directional Antenna Omni-directional Antenna Sectorized Antenna

Isotropic antenna or isotropic radiator is a hypothetical (not physically realizable) concept, used as a useful reference to describe real antennas.

Isotropic antenna radiates equally in all directions. Its radiation pattern is

represented by a sphere whose center coincides with the location of the isotropic radiator.

Property of R Struzak 7

Source: NK Nikolova

An omnidirectional antenna is an antenna which radiates power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often described as "donut shaped“

that this is different from an isotropic antenna, in which the gain is uniform in all directions ("spherical"). Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted.

Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radios, walkie-talkies, Wifi, cordless phones, GPS as well as for base stations that communicate with mobile radios, such as police and taxi dispatchers and aircraft communications.

Produces omnidirectionalradiation pattern ofequal strength in alldirections

Vector A and B are of equal length

Omnidirectional Antenna

Antenna location

AB

Radiates most power in oneaxis (direction) radiates less in other direction vector B is longer than vector A : more power radiated along B than A directional along X

A BX

A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other (in line with each other), with a small space between them.

The radio frequency voltage is applied to the antenna at the center, between the two conductors.

The most common dipole antenna is the type used with televisions, often colloquially referred to as "rabbit ears" or "bunny ears". While in most applications the dipole elements are arranged along the same line, rabbit ears are adjustable in length and angle.

Another common place one can see dipoles is as antennas for the FM band - these are folded dipoles. The tips of the antenna are folded back until they almost meet at the feed point, such that the antenna comprises one entire wavelength. This arrangement has a greater bandwidth than a standard half-wave dipole..

A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element (typically a dipole or folded dipole) and additional parasitic elements (usually a so-called reflector and one or more directors).

A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish.

The main advantage of a parabolic antenna is that it is highly directive; it functions similarly to a searchlight or flashlight reflector to direct the radio waves in a narrow beam, or receive radio waves from one particular direction only.

Parabolic antennas are used as high-gain antennas for point-to-point communication, in applications such as microwave relay links that carry telephone and television signals between nearby cities, wireless WMAN/LAN links for data communications, satellite and spacecraft communication antennas, and radio telescopes. Their other large use is in radar antennas, which need to emit a narrow beam of radio waves to locate objects like ships and airplanes. With the advent of satellite television dishes, parabolic antennas have become a ubiquitous feature of the modern landscape.

The largest "dish" antenna in the world, the radio telescope at Arecibo Observatory, Puerto Rico, 1000 feet (305 meters) in diameter. It has a gain of about 10 million, or 70 dBi, at 2.38 GHz.

Several directional antenna combined on a single pole to provide sectorized antenna each sector serves receivers listening it its direction

3 sector antenna

Antenna arrays made up of hundreds or even thousand elements are often slotted waveguides.

A measure of the directionality of an antenna

The antenna gain, or power gain of an antenna is defined as the ratio of the intensity (power per unit surface) radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by the intensity radiated at the same distance by a hypothetical isotropic antenna.

• Antenna gain is dependent on effective area of an antenna.– effective area is related to the physical size of the antenna and

its shape– Antenna Gain is given by

whereG = antenna gainAe = effective area f = carrier frequencyc = speed of lightλ = carrier wavelength

2

2

2

44c

AfAG ee

Transmission range: receiver receives signal with an error rate low enough to be able to communicate Detection range: transmitted power is high enough to detect the transmitter, but high error rate forbids communication Interference range: sender interferes with other transmissions by adding to the noise

transmission

sender

detection

interference

Radio waves exhibit three fundamental propagation behavior Ground wave (< 2 MHz) : waves with low

frequency follow earth’s surface can propagate long distances Used for submarine communication or AM radio

Sky wave (2-30 MHz) : waves reflect at the ionosphere and bounce back and forth between ionosphere and earth , travelling around the world Used by international broadcast and amateur

radio

transmitter receiverearth

sky wave propagation (2 - 30MHz)

ionosphere

Signal propagation

Line of Sight (> 30 MHz) : emitted waves follow a straight line of sight allows straight communication with satellites or

microwave links on the ground used by mobile phone system, satellite systems

Signal propagation

transmitterreceiver

earth

Line of Sight (LOS) propagation (> 30 MHz)

• Transmitted signal attenuates over distance because it is spread over larger and larger area– This is known as free space loss and for isotropic antennas

Pt = power at the transmitting antennaPr = power at the receiving antennaλ = carrier wavelengthd = propagation distance between the antennasc = speed of light

2

2

2

2 )4()4(cfdd

PP

r

t

– For other antennas

Gt = Gain of transmitting antenna

Gr = Gain of receiving antenna

At = effective area of transmitting antenna

Ar = effective area of receiving antenna

trtrr

t

AAd

GGd

PP 2

2

2 )()4(

Receiving power additionally influenced by fading (frequency dependent) shadowing reflection at large obstacles refraction depending on the density of a

medium scattering at small obstacles diffraction at edges

Signal propagation in free space almost follows a straight line ,like light.

But in real life, we rarely have a LOS between the sender and receiver of the signal.

An extreme form of attenuation is Blocking or Shadowing of radio signals due to large obstacles.

The higher the frequency of a signal , the more it behaves like a light, even small obstacles like a simple wall, a truck on the street, or trees may block the signal.

Reflection: If an object is large compared to the wavelength of the signal e.g. huge building, mountains, the signal is reflected.

Refraction: The velocity of the electromagnetic waves depends on the density of the medium through which it travels.

Scattering: If the size of an obstacles is in order of the wavelength or less the waves can be scattered.

Diffraction: Occurs at the edge of an impenetrable body that is large compared to the wavelength of the signal

Wireless signal can arrive at the receiver through different paths LOS Reflections from objects Diffraction

Multipath Propagation (source: Stallings)