PEC cavity for a ring array of spiral antennas

The design of a low-profile PEC cavity for a ring array of spiral antennas is presented. The goal of the design is to determine the configuration of a finite cavity to provide maximum front-to-back ratio (FBR) while keeping a good reflection coefficient for an octave bandwidth. Wall height and distance from the base of the cavity to the antennas are varied. It is shown that a wall height smaller than the distance of the antennas to the base of the cavity provides the best option of FBR (up to 6 dB at low frequencies).