Antenna is a transducer which converts radio frequency electrical current into an electromagnetic wave of the same frequency. Any shape can be assigned to an antenna which is a good source and radiator of electromagnetic waves. It senses electromagnetic waves excellently. Antenna can be used as an impedance matching device. It can also be used as a temperature sensor. The network theorems associated with antenna are Thevenin’s theorem, superposition theorem, maximum power transfer theorem, compensation theorem, reciprocity theorem and reaction theorem. The three main properties of an antenna are equality of impedances, equality of directional patterns and equality of effective lengths. The main antenna parameters are antenna impedance, radiation resistance, field strength pattern, power pattern, effective length of antenna, directive gain, directivity, power gain, antenna efficiency, effective area, antenna equivalent circuit, antenna bandwidth, front-to-back ratio and polarization. The basic elements of antenna are Hertzian dipole, short dipole, short monopole, half-wave dipole and quarter-wave monopole.
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