Designing of Log Periodic Dipole Antenna and Its Performance

The introduction of broadband system to communication and radar technologies has demanded the design of broadband antennas. As economically and practically it is not possible to make antenna for each band of frequency, Log-Periodic antennas are widely used for applications where a large frequency band is needed. At any frequency, only a small part of the whole structure is active. Electrical properties of a log- periodic antenna such as input impedance, pattern, directivity, side lobe level, beamwidth variations are periodic with the logarithm of the frequency. Antennas obtained from this principle are called log-periodic. Successive dipole lengths, dipole diameters and distance of the successive dipoles from the apex angle α of the antenna are related by the design constant τ. If τ is selected very close to 1, the variations over the frequency band will be small. In practice, even with τ which is not very close to 1, good frequency-independent characteristics are observed. Horn antennas and spiral antennas are the other examples for wide band antennas.