Behaviour of the parallel plate mode in a stripline slot-coupled patch antenna

Excitation of the parallel plate mode is a serious concern in a stripline slot-coupled patch antenna, and the paper is a study of its behaviour. The frequency dependence of the parallel plate mode power ratio to the input power of the antenna is discussed by means of an equivalent circuit of the antenna. It is found that the parallel plate mode power ratio is very small when the antenna is operated at the resonant frequency of the patch. A prototype antenna (in which impedance matching is obtained at the resonant frequency of the patch) is designed and fabricated. Measurement of the parallel plate mode power is performed to confirm the validity of the considerations. It is concluded that the antenna should be operated at the resonant frequency of the patch to minimise the unwanted effect concerning the parallel plate mode