BASIC ANTENNA THEORY : BASIC ANTENNA THEORY DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
RAJESH RAKSHIT DEB
7TH SEM What is an ‘antenna’? : What is an ‘antenna’? An antenna is a device that is made to efficiently radiate and receive radiated electromagnetic waves.
An antenna is an electrical conductor or system of conductors.
Transmission - radiates electromagnetic energy into space
Reception - collects electromagnetic energy from space.
In two-way communication, the same antenna can be used for transmission and reception. Antenna charecteristics. : Antenna charecteristics. There are several important antenna characteristics that should be considered when choosing an antenna for our application as follows:
• Antenna radiation patterns
• Power Gain
• Polarization Antenna Radiation Patterns : Antenna Radiation Patterns An antenna radiation pattern is a 3-D plot of its radiation far from the source. Antenna radiation patterns usually take two forms, the elevation pattern and the azimuth pattern.
•The elevation pattern is a graph of the energy radiated from the antenna looking at it from the side.
• The azimuth pattern is a graph of the energy radiated from the antenna looking at it from directly above the antenna. Antenna Radiation Patterns : Antenna Radiation Patterns Figure 1. a) Generic Dipole Elevation Pattern b) Generic Dipole Azimuth Pattern c) 3-D Radiation Pattern. Power Gain : Power Gain The power gain of an antenna is a ratio of the power input to the antenna to the power output from the antenna.
This gain is most often referred to with the units of dBi, which is logarithmic gain relative to an isotropic antenna. An isotropic antenna has a perfect spherical radiation pattern and a linear gain of one. Directivity : Directivity The directivity or directive gain of an antenna is a measure of the concentration of the radiated power in a particular direction.
It may be regarded as the ability of the antenna to direct radiated power in a given direction. It is usually a ratio of radiation intensity in a given direction to the average radiation intensity. Polarization : Polarization Polarization is the orientation of electromagnetic waves far from the source.
There are several types of polarization that apply to antennas. They are Linear, which comprises, Vertical, Horizontal and Oblique, and circular, which comprises, Circular Right Hand (RHCP); Circular Left Hand (LHCP), Elliptical Right Hand and Elliptical Left Hand.
Polarization is most important if you are trying to get the maximum performance from the antennas. For best performance we need to match up the polarization of the transmitting antenna and the receiving antenna. Antenna Types : Antenna Types Dipole Antennas
Multiple Element Dipole Antennas
Flat Panel antennas
Parabolic Dish antennas
Microstrip Antennas Dipole antenna : Dipole antenna A dipole antenna, created by Heinrich Rudolph Hertz around 1886, is an antenna that can be made by a simple wire, with a center-fed driven element for transmitting or receiving radio frequency energy.
These antennas are the simplest practical antennas from a theoretical point of view; the current amplitude on such an antenna decreases uniformly from maximum at the center to zero at the ends. Dipole antenna : Dipole antenna A schematic of a half-wave dipole antenna. Multiple Element Dipole Antennas : Multiple Element Dipole Antennas Multiple element dipole antennas have some of the same general characteristics as the dipole. We see a similar elevation radiation pattern, as well as a similar azimuth pattern. The biggest differences will be the directionality of the antenna in the elevation pattern, and the increased gain that is a result of using multiple elements.
By using multiple elements to construct the antenna, the antenna can be configured with different amounts of gain. This allows for multiple antenna designs with similar physical characteristics. Multiple Element Dipole Antennas : Multiple Element Dipole Antennas Multiple Element Dipole Elevation Pattern Yagi Antennas : Yagi Antennas Yagi antennas consist of an array of independent antenna elements, with only one of the elements driven to transmit electromagnetic waves.
The number of elements (specifically, the number of director elements) determines the gain and directivity. Yagi antennas are not as directional as parabolic dish antennas, but more directional than flat panel antennas. Yagi Antennas : Yagi Antennas Yagi Antenna Construction, Yagi-Uda Antenna Yagi Antennas : Yagi Antennas Yagi Antenna Elevation Radiation Pattern Flat Panel Antennas : Flat Panel Antennas Flat panel antennas are just that, configured in a patch type format and physically in the shape of a square or rectangle.
Flat panel antennas are quite directional as they have most of their power radiated in one direction in both the vertical and horizontal planes.
Flat panel antennas can be made to have varying amounts of gain based on the construction. This can provide excellent directivity and considerable gain. Flat Panel Antennas : Flat Panel Antennas High Gain Flat Panel Elevation Pattern Flat Panel Antennas : Flat Panel Antennas High Gain Flat Panel Azimuth Pattern Parabolic dish antennas : Parabolic dish antennas A parabolic antenna is a high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (radar), on the UHF and SHF parts of the electromagnetic spectrum.
The relatively short wavelength of electromagnetic radiation at these frequencies allows reasonably sized reflectors to exhibit the desired highly directional response for both receiving and transmitting. Parabolic dish antennas : Parabolic dish antennas A parabolic antenna for Erdfunkstelle Raisting, the biggest facility for satellite communication in the world, based in Raisting, Bavaria, Germany. Parabolic dish antennas : Parabolic dish antennas Main types of parabolic antennas Parabolic dish antennas : Parabolic dish antennas Elevation Pattern of a Parabolic Dish Antenna Slotted Antennas : Slotted Antennas The slotted antenna exhibits radiation characteristics that are very similar to those of the dipole. The elevation and azimuth patterns are similar to those of the dipole, but its physical construction consists only of a narrow slot cut into ground plane.
Slotted antennas provide little antenna gain, and do not exhibit high directionality, as evidenced by their radiation plots and their similarity to the dipoles.
Their most attractive feature is the ease with which they can be constructed and integrated into an existing design, and their low cost. Slotted Antennas : Slotted Antennas Microstrip Antennas : Microstrip Antennas Microstrip antennas can be made to emulate many of the different styles of antennas explained above.
In telecommunication, there are several types of microstrip antennas (also known as printed antennas) the most common of which is the microstrip patch antenna or patch antenna. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate with a continuous metal layer bonded to the opposite side of the substrate which forms a groundplane.
Microstrip antennas are also relatively inexpensive to manufacture and design because of the simple 2-dimensional physical geometry. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonance frequency. Microstrip Antennas : Microstrip Antennas Conclusion : Conclusion From this very basic introduction to antennas, we can come away with a better understanding of how to choose the right antenna for an application.
1. Dipole antennas, while not providing a large amount of gain offer the best flexibility as far as orientation of the antenna.
2.The flat panel antenna offers greater directionality and would be suited for a fixed installation.
3.The parabolic dish antenna with its high gain and sharp directionality would be best suited to providing a point to point link over a long distance, with permanently installed antennas.
4.Finally, the slotted antenna and the microstrip antenna are well suited for moderate performance applications that need to integrate the antenna and radio into OEM applications. Antenna Comparison : Antenna Comparison THANKS FOR GIVING ATTENTION : THANKS FOR GIVING ATTENTION