What are Log Periodic Antennas?

A log-periodic antenna is a group of dipole antennas of varying sizes strung together and fed alternately through a common transmission line. The dipole antennas diminish in size from the back to the front. The element at the back of the array which is the largest, acts as a half wave dipole at the lowest frequency and that at the front is a half wavelength at the highest frequency of operation. This unique configuration, enables Log-periodic antennas to have wide bandwidths.

Not all the antennas are active at any given frequency. The active region, i.e. the sections of the antenna that are contributing to the transmission or reception vary with frequency. The length and spacing of elements in a log-periodic antenna increase logarithmically from one end of the dipole to the other.

The radiation pattern of Log-Periodic Antennas broadly stays the same over the whole operating band as do parameters like the radiation resistance and the standing wave ratio.