An improvement of input characteristics in a Slot-Coupled Patch Antenna with a strip

In the Triplate line fed Slot-Coupled Patch Antenna (TSCPA), the generation of the parallel plate mode becomes a minimum at the resonant frequency of the radiating patch. However, the resistive part of the input impedance (input resistance) at this frequency is extremely low. In this paper, a method is proposed to raise the input resistance at the resonant frequency of the patch. By means of the equivalent circuit of the TSCPA, it is made clear that the input resistance at the resonant frequency of the patch is reduced due to the inductive effect of the slot. A design guideline for the slot is discussed for relaxing the reduction of the input resistance due to the inductive effect. Further, it is shown that the input resistance can be increased by placing a strip shorter than the resonant length between the patch and the slot so that the inductive effect can be canceled.