ELECTROMAGNETICALLY COUPLED MICROSTRIP PATCH ANTENNAS • THEORETICAL AND EXPERIMENTAL INVESTIGATIONS

Abstract

In recent years microstrip patch radiators have been. playing an increasing role in antenna design. The light weight, low profile and conformability of microstrip antennas make them very attractive for aircraft, missile and satellite applications. One of the promising method of feeding energy to the radiating element that was suggested recently is to couple the feedline electromagnetically to the patch radiator. This novel feed mechanism has the advantages of effective coupling, ease of fabrication, reduced spurious radiation from the feed network and large bandwidth. This method provides for flexibility in choosing the substrates which best meet the conflicting requirement of dissimilar substrates for feed network and patch radiator. In this thesis, an improved model is proposed for accurate evaluation of an electromagnetically coupled (EMC) rectangular patch antenna. In the proposed model, the antenna is viewed as a planar waveguide which is excited by a magnetic surface current. The equivalent circuit for the feed line and waveguide transition is developed. Effects of the stored energy and radiated energy are incorporated in the equivalent circuit. Numerical results for the input impedance and the return loss of the EMC patch antenna are obtained from the proposed model and from the two other existing models. The results were compared with the measured data (experiments were conducted in the Electrical Engineering laboratory). The proposed model is found to have a better agreement than the existing models with respect to the return loss and the input impedance of an EMC microstrip antenna.