Log Periodic FM Antenna for 88-108 MHz
Model: PAFM-LPA4 - Log Periodic Antenna
The PAFM-LPA4 antenna is a horizontally or vertically polarized log periodic antenna covering the 88-108 MHz spectrum. The antenna is composed of stainless steel and is mounted via the rear mounts at the back of the antenna, called "cantilever mounting".
The antenna can be tuned for a VSWR of less than 1.10:1 for 10 MHz of band width or less than 1.15:1 across the entire band from 88-108 MHz. In addition, log periodic antennas have a very high front-to-back ratio, exceeding 20 dB and approaching 30 dB for mult-element arrays.
Gain of the antenna system can be increased by adding multiple log periodics stacked both vertically (one on top of another) and horizontally (multiple logs oriented around the tower) to increase coverage and gain of the array. A stack of 2 PAFM-LPA4's, for example, is a 2 bay array.
Log Periodic antennas that are multi-element are considered phased arrays. The elements are positioned in-phase in the forward lobe so that each additional element reinforces and adds forward gain and directivity in the direction the log periodic is oriented. Likewise and in so doing, the elements are out of phase to the rear, or behind the antenna, where each additional element reduces gain to the rear. Since the elements are out of phase to the rear, the log periodic antenna has a high ratio of signal in the forward lobe as compared to rear lobe, called high "front-to-back ratio". If protection to the rear is required at a particular site, either from a co-channel or adjacent channel carrier, the log periodic is probably the best antenna choice that will provide phased isolation to the rear by virtue of the design of the log periodic antenna.