Complex Input Impedance of the Rectangular Microstrip Antenna in a Wide Frequency Range

An analysis of the rectangular microstrip patch antenna is presented, taking into account the influence of the microstrip feeding line. The theoretical evaluation of the input impedance as a function of frequency, antenna geometry and the feed position has been accomplished by means of an equivalent magnetic-wall model, treating the antenna as a lossy cavity. A series expansion in resonant modes yields to an approximation of the properties of the antenna. The comparison between measured and calculated data of the input impedance shows good agreement both in amplitude and phase over a wide frequency range from 2 GHz to 18 GHz for all antenna geometries and feed positions under test.