Theory and experiment of slot-coupled cylindrical rectangular and circular microstrip antennas

Slot-coupled cylindrical microstrip antennas with rectangular or circular patches are studied theoretically and experimentally. For the theoretical analysis the cavity-model method is applied, which has the advantages of much simpler theoretical formulation and more efficient numerical computation as compared to a full-wave approach. Based on the cavity-model method incorporating an impedance transformer, similar to that used in a generalized transmission line model analysis, to transform the patch admittance into a series load seen at the slot position by the microstrip feed line, an equivalent circuit can be derived. From the equivalent circuit the input impedance of the antenna can be readily evaluated. To check the accuracy of the cavity-model solutions, experiments are also conducted. A comparison of the theoretical and measured data is presented, and the effects of the cylinder size and the coupling slot length on the input impedance are analysed.