Compact Rear-Radiating Circularly Polarized Feeds for Front-Fed Reflector Antennas

Unique backward radiation properties of compact four-arm Archimedean spiral antennas are explored and investigated. Conventionally, an active zone in the order of one wavelength is required to have the spiral antenna work in its first mode of operation, producing broadside radiation patterns. In this letter, it is shown that a reflector-backed four-arm spiral antenna with a diameter of much less than the conventional active zone is capable of effectively directing the same broadside radiation into the backward region with an opposite sense of polarization. The antenna such developed is well suited as a primary feed in small front-fed parabolic reflector antennas. The circular polarization performance of the proposed antenna is investigated including the circularly polarized gain, axial ratios, beamwidths, and cross polarization. Furthermore, the performance of the compact rear-radiating antenna as a primary feed in parabolic reflector antennas is investigated, proving the promising applications of the proposed compact feeds with backward radiation patterns.