FEED ANALYSIS FOR MICROSTRIP ANTENNAS

The input impedance of a circular microstrip antenna excited by a coaxial probe or a microstrip transmission line is computed. A distinguishing feature of the present analysis is the incorporation of the boundary conditions on the feed into the formulation.The circular patch antenna excited by a microstrip transmission line is also analyzed. Boundary conditions are enforced on a portion of the microstrip feed line as well as the patch antenna. The integral equation for the unknown currents on the antenna and the feed is solved by applying the Galerkin method of moments in the Fourier transform domain. A method designed to accelerate the convergence of the resulting spectral integrals is outlined and discussed. Extensive input impedance data are presented for the case of the electromagnetically coupled circular patch.Accuracy of the presented computational techniques is verified experimentally.In the case of the coaxial probe feed, the analysis utilizes the framework of the cavity model. The fields under the patch are expanded in a set of modes satisfying the boundary conditions on the eccentrically located probe, as well as the cavity magnetic wall. A mode matching technique is used to solve for the electric field at the junction between the cavity and the coaxial cable. The reflection coefficient of the TEM mode incident in the coaxial cable is determined, from which the input impedance is computed.