UHF circular arrays incorporating open-loop null steering for communications

The paper describes an experimental wideband antenna and adaptive signal processing system which has the ability to exhibit an omnidirectional azimuth radiation pattern which can be modified in real time to minimize the effects of unwanted interference. The philosophy behind the use of circular antenna arrays for this system and brief details of their directional properties are given. To enable the adaptive signal processing system to be used in existing communication links, with standard receivers and no extra-special encoding of wanted signals, a simple form of open-loop adaptive control has been devised. This concept has been implemented in an experimental system based upon a four-element circular array and capable of electronically steering a single directional null against high-level interference. Finally, results from an experimental array operating over the 200-400 MHz band are presented to illustrate and qualify the concepts and theoretically predicted results.