Antenna Fundamental

 Antenna: It may be defined as a metallic device for radiating & receiving radio waves. Antennas are broadly classified as;

1. Wire Antenna

2. Aperture Antenna

3. Microstrip Antenna

4. Reflector Antenna

5. Array Antenna

6. Lens Antenna

• Wire Antenna: A wire antenna is a radio antenna consisting of a long wire suspended above the ground whose length does not bear a relation to the wavelength of the radio waves used but is typically chosen more for convenience.

• Aperture Antenna: An antenna with an aperture at the end can be termed as an aperture antenna. The edge of the transmission line when terminated with an opening, radiates energy. This opening which is an aperture makes it an aperture antenna.

• Microstrip Antenna: Microstrip antenna is also known as a printed antenna. This antenna usually means a printed circuit which is made by using microstrip technology on PCB. It types an internal antenna and it is mostly used in microwave frequency.

• Reflector Antenna: An Reflector antenna is a device that reflects electromagnetic waves.

• Array Antenna: An Array antenna is a set of multiple connected antennas which work together as a single antenna to transmit & receive.

• Lens Antenna: Lens antennas are microwave antennas constructed with a single or multiple lenses. Lens antennas are the 3-dimensional electromagnetic device which has refractive index other than unity.

Parameter of Antenna
       1.Radiation pattern: Radiation pattern is graphical representation of radiation of             antenna as a function of space co-ordinate.
      2.Radiated power density: It is simply transmitting power divided by surface                 area of sphere at that distance.
      3.Radiated intensity: It is power radiated by antenna per unit solid angle.
      4.Directivity: Maximum directive gain is called as directivity. It is denoted by D. It is ratio of radiation intensity in given direction from antenna to rradiatio intensity averaged in all direction.
     5.Beam efficiency: It can be defined as ratio of main lobe area to total beam area.
     6.Antenna radiation efficiency: It is defined as ratio of power radiated to total input ppowe supplied to antenna it is denoted by η.
    7.Gain: Gain of antenna is always less than directivity Gain is defined as ratio of maximum radiation intensity in given direction to maximum radiation intensity from reference aantenn produced in same direction with same power input.
    8.Directive Gain (Gd): it is ratio of radiation intensity in particular direction to average radiated power.
    9.Power gain (Gp): It is defined as power density radiated in particular direction by subject antenna to power density radiated in same direction by isotropic antenna.
   10.Antenna aperture: It may be defined as ratio of power received at antenna load terminal to the power density of incident wave.
   11.Aperture efficiency: It is denoted by gap It is ratio of effective aperture to physical aperture.

   12.Polarization: Polarization refers to physical orientation of waves in space. The polarization of wave transmitted or received by antenna is a locus of the tip of the instantaneous electric field vector E traces out with time at a fixed observation point.
   13.Input impedance: It represents kind of load antenna presents to its transmission line.
   14.Radiation resistance: It is a fictitious resistance which when substituted in series          with antenna will consume same amount of power as it is actually radiated by antenna. All power delivered to antenna is not radiated but very small fraction of it is dissipated in form of heat depending upon ohmic resistance of antenna.
    15.Bandwidth: It is a range of frequencies within which the performance of antenna w.r.t. some characteristics such as power pattern, beam width, directivity, gain etc. confirms specific standards.
    16. Beam-width: Antenna beam width is angular width in degree measured on radiation pattern (main lobe) between two points.

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