Realisation of an automatic null steering antenna array at 10.5 GHz

This thesis describes the successful realisation of a prototype automatic null steering antenna operating at 10.5 GHz. The aim of this antenna system is to emulate the interference cancelling capability of the well known adaptive antennas without resorting to expensive ancillary microwave hardware such antennas require. A study was carried out on the problems of antenna radiation pattern synthesis with null placement and that of resolving the amplitude and the direction of arrival of the incident signals on a linear antenna array. Detailed discussion and some new solutions to these problems are proposed and presented in this thesis. Based on the knowledge gained in the work done in these two areas, an experimental automatic null steering antenna array system operating at 10.5 GHz. was successfully designed and constructed. The development of the antenna system required the design of a novel complex weighting circuit which could alter both the in phase and the quadrature phase signal paths of an input signal at 10.5 GHz independently under microprocessor control. Other relevant digital and microwave hardware were also developed. Detailed experimental verification of the antenna array performance is also included.