The low dispersion coaxial cavity as an ultra wideband antenna

A coaxial cavity antenna, patent pending, has been developed by Raytheon. It exhibits low dispersion over a wide field-of-view (FOV) and multiple octaves or ultra wideband. This antenna has essentially a flat phase and amplitude response over a /spl plusmn/60 degree FOV. The design is scaleable over multiple frequency ranges and antennas have been built covering frequency ranges from 200 MHz to 44 GHz with bandwidths on the order of four and one-half octaves. The antenna is a four point feed design where the natural base polarizations are dual linear. Both senses of circular polarization can be obtained, and have been demonstrated with the addition of a hybrid. Designs have been built where any linear or circular polarization output can be switched. These antennas have been pulse tested with excellent results when compared to the input pulse for fidelity. Completed frequency measurements verify antenna performance two octaves out of band on the low side and almost one octave on the high side, for a total of four octaves of operation for a single cavity; that presents its application to ultra wideband collection. This antenna is used in interferometers and polarimeters. The flat phase and amplitude responses have proven this antenna to be an excellent choice for polarimetry. These elements are also being implemented in linear interferometers and collection systems. A typical field collection system is discussed as an application.