The OBS-520 is a compact, moderate gain, moderate VSWR, a circularly-polarized cavity-backed spiral antenna designed to transmit and receive in the frequency band of 0.5 GHz to 2.0 GHz.? The antenna exhibits an excellent impedance match and radiation pattern. It is capable of receiving both linearly polarized signals and a circularly polarized signal. The linear gain (dBil) is about 3 dB lower than the circular gain (dBic). The antenna has the advantages of a low profile, a planar aperture, no phase center offset, near-constant beam width across the frequency band, normally symmetrical radiation bandwidth, extreme flexibility for carrying, and lightweight. The servant ages render the antenna a very good candidate for electronic-warfare, direction-finding, telemetry and surveillance systems, as well as flush-mounted airborne applications.? The antenna can be used as a broadband feed for reflector antennas. Its outermost dimensions are a diameter of 68mm and a height of 50mm.