Analysis and network modeling of an aperture-coupled microstrip patch antenna

This paper describes a method for analyzing an aperture-coupled microstrip patch antenna in order to develop an improved transmission-line model that reflects the effects of structure parameters, including inclination angles and offset distances of the aperture with respect to the feed line or the patch. The equivalent circuit consists of three ideal transformers, extended slotlines terminated by a short circuit, and microstrip transmission lines with open stubs. Two transformers are introduced to take account of the interaction between the aperture field and two orthogonal patch modes, while the third transformer reflects the coupling between the aperture and the feed line. The turn ratios of the transformers are calculated efficiently. The microstrip open stubs in the patch are then replaced by well-known capacitance and radiation conductance equivalents. The proposed transmission-line model is then applied to several variations and shown to produce accurate antenna impedances