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N I . S E T Antennas-Different O N U T K Downloaded from Ktunotes.in types

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Classifications • Many Types of antennas . The choice of antenna depends on • Frequency of operation • Radiation Pattern • Polarization, N • Gain requirements I . S E T O • Application TUN K I. Isotropic Directional Omnidirectional Point Source Star antenna Dipole Horn Parabolic Half wave Dipole Marconi Circular Loop Downloaded from Ktunotes.in

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Classifications II. Resonant Non Resonant • Length is in exact multiples of /2. • Length is other than in multiples of /2. • Open at both ends • Open end is excited • Not terminated in any resistance • The other end is terminated in characteristic impedance • Used at a fixed frequency • Forward/incident and backward/reflected waves exist • Standing waves exist N U T K • Radiation patterns are multi directional • Voltage and current are not in phase • Has distributed L and C and act as resonant circuit • Known as periodic antennas • Used at a range of frequencies and has a wider bandwidth N I . S OTE • No reflected waves exist • No Standing waves exist • Radiation patterns are uni directional • Pattern is not symmetric about =90 • It is a travelling wave antenna • Also called directional antennas • Known as aperiodic antennas • Egs: Long wire, V antenna, Rhombic antenna Downloaded from Ktunotes.in

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Classifications III. Standing Wave Travelling Wave • Nothing but a resonant Antenna • Standing wave is defined as the wave in which the ratio of the instantaneous value of any component of the wave at one point to that at any other point does not vary with time N U T K • Nothing but a non resonant antenna • An antenna that is associated with radiation from a continuous source • Travelling wave is defined as a wave whose frequency component have exponential variation of amplitude and linear variation of phase with distance. • A progressive phase pattern is associated with current and voltage distributions • Aperture antennas like Horn and Reflector antennas can be treated as Travelling Wave antennas N I . S OTE Downloaded from Ktunotes.in

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