Patch antenna with integrated bandpass filter

This paper presents a novel antenna that includes filtering functionality. The design approach is based on direct-coupled resonator filter theory. In this approach, the filter can be integrated into the antenna itself using the antenna resonant elements as the resonators of the filter. The design principle can be applied to any desired frequency and physically realised using different types of antenna structures. In this example, a rectangular patch antenna integrated with four conventional square open-loop resonators is designed using a single layer microstrip to verify this antenna-filter design approach. In order to preserve the filter´s characteristic, the radiation quality factor of the patch antenna is chosen the same as the external quality factor of the filter, and the coupling between the patch antenna and the last open-loop resonator is calculated using the theory for two conventional coupled resonators. The simulation results demonstrate this filter antenna design approach works well.