A class of notched omnidirectional antennas

A class of antennas featuring a steerable notch in an otherwise omnidirectional pattern is described. This type of antenna presents an alternative to a narrow beam antenna for certain applications; it is attractive when a small antenna capable of pattern rotation is desirable. The notch characteristic is obtained by combining in a single antenna three basic modes of radiation. One mode is omnidirectional, the other two are figure-8 patterns that are crossed in space. By controlling the amplitude and phase of these radiation modes, a family of patterns exhibiting different notch characteristics may be realized. The notch can be steered a full in azimuth by a single phase-shifter. An experimental model of a notch-omnidirectional antenna has been fabricated and tested at X-band. Notch pattern synthesis and rotation techniques have been demonstrated.