Report-luu-types-of-antenna

TYPES OF ANTENNA

Lucile D. Salvani BS ECE 5 Transmission Media and Antenna

Overview • Antenna • Properties of Antenna • Types of Antenna – Log Periodic Antennas – Wire Antennas – Travelling Waves Antenna – Microwave Antennas – Reflector Antennas – Aperture Antenna

Antenna What is Antenna? - is a structure affiliated with the region of transition between the “guided wave” and “free space” - is an electrical device that converts electric power into electromagnetic waves (or simply radio waves) and vice-versa. - sometimes called Aerial - provide a simple way to transfer signals (or data) where other methods are impossible.

Properties of Antenna • Antenna Gain – measures the degree of directivity of antenna’s radial pattern is known as gain. The higher the gain, the more effective in its radiation pattern.

G = (power radiated by anatenna)/ (power radiated by reference antenna)

Properties of Antenna • Aperture – known as the effective aperture of the antenna that actively participate in transmission and reception of electromagnetic waves. – The power received by the antenna gets associated with collective area. This collected area of an antenna is known as effective aperture.

Pr = Pd*A watts A=pr/ pd m2

Properties of Antenna • Directivity & Bandwidth – the measure of concentrated power radiation in a particular direction – considered as the capability of an antenna to direct radiated power in a given direction. – the ratio of the radiation intensity in a given direction to the average radiation intensity.

Bandwidth - the range of frequencies over which an antenna can properly radiates energy and receives energy.

Properties of Antenna • Polarization – An electromagnetic wave launched from an antenna may be polarized vertically and horizontally. If the wave gets polarized in the vertical direction, then the E vector is vertical and it requires a vertical antenna. If vector E is in horizontal way, it needs a horizontal antenna to launch it. Sometimes, circular polarization is used, it is a combination of both horizontal and vertical ways.

Properties of Antenna • Effective Length – the parameter of antennas that characterizes the efficiency of the antennas in transmitting and receiving electromagnetic waves – The ratio of EMF at the receiver input to the intensity of the electric field occurred on the antenna is known as receivers’ effective length. – The effective length of the transmitter is the length of the free space in conductor, and current distribution across its length generates same field intensity in any direction of radiation.

Effective Length = (Area under non-uniform current distrbution) /(Area under uniform current distribution)

Properties of Antenna • Polar Diagram – The most significant property of an antenna is its radiation pattern or polar diagram. – In case of a transmitting antenna, this is a plot that discusses about the strength of the power field radiated by the antenna in various angular directions as shown in the plot below. A plot can also be obtained for both vertical and horizontal planes – and, it is also named as vertical and horizontal patterns, respectively.

Types of Antenna 1. 2. 3. 4. 5. 6.

Log Periodic Antennas Wire Antennas Travelling Waves Antenna Microwave Antennas Reflector Antennas Aperture Antenna

1. Log Periodic Antennas – also named as a log periodic array. – It is a multi-element, directional narrow beam antenna that works on a wide range of frequencies – made of a series of dipoles placed along the antenna axis at different space intervals of time followed by a logarithmic function of frequency – used in a wide range of applications where variable bandwidth is required along with antenna gain and directivity.

1. Log Periodic Antennas

1. Log Periodic Antennas Bow-Tie Antennas Log-Periodic Dipole Array

1. Log Periodic Antennas  Bow-Tie Antennas • also known as Biconical antenna or Butterfly antenna • an omnidirectional wide-band antenna • According to the size of this antenna, it has low- frequency response, and acts as a high-pass filter

1. Log Periodic Antennas  Bow-Tie Antennas

This antenna will have a similar radiation pattern to the dipole antenna, and will have vertical polarization. A L=76.5mm Bow Tie antenna with width W=36mm (so that the angle D=2*atan( 76.5/36 )= 130 degrees). This antenna was mocked up as shown in figure above.

1. Log Periodic Antennas  Log-Periodic Dipole Array – most common type if antenna used in wireless communication technology – Comprises a number of dipole elements – These dipole-array antennas reduce in size from the back end to the front-end

1. Log Periodic Antennas  Log-Periodic Dipole Array

2. Wire Antennas – Linear or curved antennas – Very simple, cheap and are used in wide range of applications

2. Wire Antennas Dipole Antenna Short-Dipole Antenna Monopole Antenna Loop Antenna

2. Wire Antennas Dipole Antenna • One of the most straight forward antenna alignments • This consists of two thin metal rods with a sinusoidal voltage difference between them • It also consists of a radiating element that splits the rods and make current flow through the center by using a feeder at the transmitter out that takes from the receiver. • Different types of dipole antenna used as RF antennas include half wave, multiple, folded non-resonant, and so on.

2. Wire Antennas Dipole Antenna

2. Wire Antennas Short-Dipole Antenna • the simplest of all types of antennas • an open circuited wire in which short denotes “relative to a wavelength” so this antenna gives priority to the size of the wire relative to the wavelength of the frequency of operation • made up of two co-linear conductors that are placed end to end, with a small gap between conductors by a feeder. • A dipole is considered as short if the length of the radiating element is less than a tenth of the wavelength

L<λ/10

2. Wire Antennas  Short-Dipole Antenna

2. Wire Antennas Monopole Antenna • half of a simple dipole antenna located over a grounded plane • the total power radiated is half that of a dipole; the field gets radiated only in the upper hemisphere region. The directivity of these antennas become double compared to the dipole antennas. • used as vehicle mounted antennas as they provide the required ground plane for the antennas mounted above the earth

2. Wire Antennas  Monopole Antenna

2. Wire Antennas Loop Antenna • The fundamental characteristics of the loop antenna are independent of its shape. • widely used in communication links with the frequency of around 3 GHz

2. Wire Antennas  Loop Antenna

3. Travelling Waves Antenna – are not resonant so they have inherently broad bandwidth – They are typically wire antennas that are multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas

3. Travelling Waves Antenna Types of Travelling Wave Antenna:

 Helical Antenna  Yagi-Uda Antenna  Spiral Antenna

3. Travelling Waves Antenna  Helical Antenna – relatively simple structures with one, two or more wires each wound to form a helix, usually backed by a ground plane or shaped reflector and driven by an appropriate feed – the radiation properties of a helical antenna are associated with this specification: the electrical size of the structure, wherein the input impedance is more sensitive to the pitch and wire size. – two predominate radiation modes: • normal mode - the dimensions of the helix are small compared to its wavelength • axial mode - used in a wide range of applications.

– Aka “helix antenna”

3. Travelling Waves Antenna  Helical Antenna

3. Travelling Waves Antenna  Yagi-uda Antenna – antenna that makes use of passive elements – Inexpensive and effective. – can be made by using an antenna with one reflector, a driven folded-dipole active element, and directors, mounted for horizontal polarization in the forward direction.

3. Travelling Waves Antenna  Yagi-uda Antenna

3. Travelling Waves Antenna  Spiral Antenna – belong to the class of "frequency independent" antennas – these antennas are characterized as having a very large bandwidth. – Circularly polarized – widely used in the defense industry for sensing applications, where very wideband antennas that do not take up much space are needed. – Spiral antenna arrays are used in military aircraft in the 1-18 GHz range. Other applications of spiral antennas include GPS, where it is advantageous to have RHCP (right hand circularly polarized) antennas.

3. Travelling Waves Antenna Spiral Antenna

4. Microwave Antenna – The antennas operating at microwave frequencies are known as microwave antennas. These antennas are used in a wide range of applications. Types of Microwave Antennas:

Rectangular Micro strip Antennas Planar Inverted-F Antennas

4. Microwave Antenna  Rectangular Micro strip Antennas – only require space for the feed line which is normally placed behind the ground plane. – low profile antennas that are used For spacecraft or aircraft applications – based on the specifications such as size, weight, cost, performance, ease of installation, etc. – major disadvantage of using these antennas is their inefficient and very narrow bandwidth,

4. Microwave Antenna Rectangular Micro strip Antennas

4. Microwave Antenna • Planar Inverted-F Antennas – the wire radiating element is replaced by a plate to increase the bandwidth. – The advantage of these antennas is that they can be hidden into the housing of the mobile when compared to different types of antennas like a whip, rod or helical antennas, etc. – The other advantage is that they can reduce the backward radiation towards the top of the antenna by absorbing power, which enhances the efficiency. – provides high gain in both horizontal and vertical states. – This feature is most important for any kind of antennas used in wireless communications.

4. Microwave Antenna Planar Inverted-F Antennas

5. Reflector Antennas Corner Reflector Antenna Parabolic-Reflector Antenna

5. Reflector Antennas  Corner Reflector Antenna – comprises one or more dipole elements placed in front of a corner reflector

5. Reflector Antennas  Parabolic-Reflector Antenna – The radiating surface of a parabolic antenna has very large dimensions compared to its wavelength. – Certain important properties of these antennas can be studied by using ray optics, and of other antennas by using electromagnetic field theory. – The various types of feeds that use this parabolic reflector include horn feeds, Cartesian feeds and dipole feed.

5. Reflector Antennas • Parabolic-Reflector Antenna

6. Aperture Antenna Slot Antenna Horn Antenna Lens Antenna Dielectric Resonator

6. Aperture Antenna  Slot Antenna – consists of a waveguide with one or more slots cut in it to emit the microwaves. – popular because they can be cut out of whatever surface they are to be mounted on, and have radiation patterns that are roughly omnidirectional – Linear polarized – Used as UHF broadcast antennas and marine radar antennas.

6. Aperture Antenna Slot Antenna

UHF Broadband TV Slot Antenna

6. Aperture Antenna  Horn Antenna – a simple antenna with moderate gain of 15 to 25 dBi – consists of a flaring metal horn attached to a waveguide. – Used for applications such as radar guns, radiometers and as feed antennas for parabolic dishes.

6. Aperture Antenna Horn Antenna

6. Aperture Antenna  Lens Antenna – consists of layer of dielectric or a metal screen or multiple waveguide structure of varying thickness in front of a feed antenna, which acts as a lens which refracts the radio waves, focusing them on the feed antenna – made up of glass, where the converging and diverging properties of lens are followed – used for higher frequency applications.

6. Aperture Antenna Lens Antenna

6. Aperture Antenna  Dielectric Resonator – consists of small ball or puck-shaped piece of dielectric material excited by aperture in waveguide Used at millimeter wave frequencies – mostly used at microwave frequencies and higher, in some compact portable wireless devices, and military millimeter-wave radar equipment. – they lack metal parts which means lower losses and more efficient than metal antennas

6. Aperture Antenna Dielectric Resonators