Theory and experiment on microstrip patch antennas with shorting walls

Experimental and calculated results based on the finite-difference time-domain method are presented on the impedance and radiation characteristics of the classic shorted quarterwave patch. It is found that, for foam substrates with relative permittivity close to unity, the bandwidths of the quarterwave patches are significantly larger than the halfwave patches. On the other hand, for microwave substrates with relative permittivites equal to 2.32 and 4.0. the bandwidths of quarterwave patches are less than those of halfwave patches, owing to the excitation of surface waves. The maximum gain in the case of foam substrate is in the range of 2-3.5dBi, occurring 0-45 degrees from broadside, depending on the substrate thickness. The use of a partial short, while reducing the resonant frequency, also decreases the bandwidth. The paper also describes the application of the shorting-wall principle to realise a compact wideband L-probe patch antenna.