A broadband experimental null-steering antenna system for mobile communications

The paper describes a novel and particularly simple form of null-steering antenna suitable for the base station of a mobile communication system which is subject to high levels of directional interference. The antenna provides omnidirectional coverage in the horizontal plane and has the facility of introducing a directional null which may be electronically steered through 360° of azimuth. This can therefore be used to minimize an interfering signal without affecting communication in other directions. The antenna employs a 4 or 5 element circular array and a simple null steering network requiring only one phase changer to steer the null. Various configurations of this antenna are examined theoretically and supported by experimental measurements on a system operated at 153 MHz. Experimental values of null depth lie in the range of 25¿50 dB when operating over a bandwidth of ±30% of the centre frequency. Null widths (measured at the ¿ 10 dB points) may be electronically varied within the range 28°¿68°. Applications for such a null-steering antenna and methods to increase the operating bandwidth are also discussed.