A filtering waveguide aperture antenna based on all-resonator structures

In recent years, there has been a large amount of attention focused on the design of filtering antennas to reduce the front-end size of modern wireless communication systems. Although numerous design approaches are presented in the literature, they are usually applicable to a certain microwave circuit structure. Additionally, their implementations demand extra matching circuits or a structure which leads to an increase in the filtering antenna size. In this paper, the design of a 3rd-order filtering antenna operating at the X-band frequencies is presented utilizing the coupling matrix approach. It is based on 3rd order coupled-resonators filter without employing any extra structure. For the physical configuration, three inline coupled rectangular waveguide cavity resonators operating at TE101 mode are employed. The output of the last resonator is coupled to free space via a rectangular aperture. The dimensions of the aperture are manipulated to control the radiation quality factor (Q(r)). To validate the simulated results, the design has been fabricated using the Computer Numerical Control technique. Excellent agreement between the simulation and measurement results has been obtained. The fractional bandwidth (FBW) is more than 10% when the reflection coefficient S-11 = -20 dB. The gain response is very flat (7.54 +/- $\pm \phantom{\rule{}{0ex}}$0.2 dBi) from 9.5 to 10.5 GHz. The proposed filtering antenna is compact and low profile which may be of interest in radar applications.