Advantage And Disadvantage Of Antenna

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CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
Antenna is an essential component of all equipments that use radio and they are employed in system such as radio broadcasting, broadcast television, satellite communication etc. Antenna is an electronic device that converts electrical power into radio waves and radio waves into electrical power. Antennas also use to radiate or receive electromagnetic waves. Antennas are basic components of any electric system and are connecting links between the transmitter and free space and receiver. Thus antennas play very important role in finding the characteristics of the system in which they are employed. The important properties of an antenna is given in some terms like radiation pattern, radiation intensity,
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1.2.2 Random Wire Antenna: It is simple and has a very long wire with one end connected to radio and other in free space. But a random wire antenna has a disadvantage that it requires an antenna tuner, because it has a random impedance that varies in non-linearly manner with frequency.
1.2.3 Isotropic Radiator Antenna: It is a hypothetical antenna having no physical existence but very useful for theoretical model for the purpose of comparison with other antennas. It measures in dB. It is considered as a point in space with no dimensions and no mass. This antenna does not exist physically.
1.2.4 Yagi Uda Antenna: These are the most high gain antennas; they consist of driven element, a reflector and one or more directors. They also consists of parasitic elements which are added with functionality similar to adding a reflector and lenses to focus filament light bulb, they are also known as super directive antenna .If more directivity is required then more elements can also be added for this
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It has been fabricated by etching the element of antenna which bonds to dielectric substrate (insulating) along with metal layer bonded to opposite side of substrate called ground plane, it is not necessary to always fabricate on dielectric substrate. But it can also be done by mount metal plane above ground plane with the help of dielectric spacers and it results in wide bandwidth but its structure is not so robust. Microstrip patch antennas are mostly operated on high frequency bands like UHF and also provide satisfactorily directive gain of nearby 6 to 9 dB, also much higher gain is achieved by just adding patch array which can be added at a little high cost. These antennas are introduced in many shapes like rectangular, circular, triangular

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