Highly Directive 100 to 300 MHz Super Gain Antenna

The Air Force currently has a strong need to conduct antenna gain tests over the 100-300 MHz frequency band. It is desirable to conduct these tests indoors utilizing an anechoic chamber, to control the environment and reduce EMI from external sources. Unfortunately, the walls of anechoic chambers at these low frequencies have relatively high reflectivity that can cause unacceptable levels of multi-path. This issue is compounded by the fact that commonly available source antennas at these low frequencies (i.e. log-periodic antennas) have wide beamwidths and high sidelobes that heavily illuminate the chamber walls. Use of a more directive source antenna with reduced sidelobes and backlobes will help alleviate the mult-path problem. Toyon recently designed, built, and delivered a 300-1500 MHz, dual-polarized source horn for the Bistatic Anechoic Chamber at the Radar Reflectivity Laboratory at Pt Mugu. This design achieved a VSWR of less than 2:1, polarization isolation greater than 35 dB, and reduced sidelobes. The reduced sidelobes were achieved by utilizing a resistive film inside the horn to provide an amplitude taper across the aperture. Under this Phase I SBIR, Toyon proposes to re-optimize its dual-polarized, low sidelobe horn design specifically for the Air Force requirements.