ETS-Lindgren's Model 3145BDP Dual-Polarized Log-Periodic Dipole Array (LPDA) is a dual linearly polarized, broadband log antenna designed to operate over the frequency range of 100 MHz to 1.1 GHz. The choice of scaling factors, the various diameters of each element, and the center-to-center spacing of the booms result in excellent VSWR characteristics throughout the operating frequency range.
The precise design of the feed and positioning of the elements on the boom yields optimum phase relationship. This causes the active region, at any given frequency, to propagate RF energy towards the smaller elements, leaving the elements behind it inactive and operating as reflectors to improve the gain. The constant gain of the antenna yields an antenna factor which varies linearly with frequency. The variation is smooth; therefore, accurate interpolation of performance between specified frequency points is simple.