Synthesis of a single null response in an otherwise omnidirectional pattern using a circular array

The paper discusses a method for designing an antenna array having an omnidirectional pattern in the horizontal plane plus a single steerable null. Such a system has applications in communications when it is required to reject interfering signals from an unwanted source, while maintaining communication coverage in other directions. Parameters such as null width, null depth and the gain ripple in the directions of coverage are defined in order to make sensible comparisons between performance of various null patterns. An efficient and simple method for the synthesis of such a pattern, using a circular array, is presented. It involves the appropriate combination of a beamcophasal pattern with that of an omnidirectional pattern, and it is shown that by choosing a phase-sequence omnidirectional pattern for this purpose, a narrower `single-zero¿ null may be obtained. The calculated results show that attractive pattern characteristics can be achieved through this method of synthesis.