SIW-Based Input-Reflectionless Filter/Filtenna Using Complementary-Diplexer Architectures

In this article, a class of input-reflectionless filter/ filtenna on substrate-integrated-waveguide (SIW) technology that exploits complementary-diplexer design principles is proposed. By extracting and controlling the couplings between the adjacent SIW-based cavities to satisfy a predesigned coupling matrix, a bandpass-type filtering functionality with out-of-band RF-input-reflectionless capabilities can be obtained. To this aim, a pair of frequency-complementary channels is employed, namely a bandpass channel for transmission and its complementary resistively loaded bandstop counterpart for stopband RF-power absorption. Based on this design approach, a third-order input-reflectionless SIW bandpass filter and a second-order input-absorptive SIW diplexer are realized. Subsequently, the last cavity resonator of the bandpass channel is replaced by a SIW-based radiator to form a filtenna with the same input-reflection frequency response. In this manner, based on the aforementioned input-reflectionless filter and diplexer, single- and dual-band SIW-based filtennas with reflectionless characteristics are conceived. Measured results of manufactured proof-of-concept prototypes are provided to experimentally validate the proposed design methodology of input-reflectionless SIW-based filter/filtenna. For these built devices of filter, diplexer, and single- and dual-band filtennas, wide-band reflectionless frequency ranges being $47.5\times $ , $18.06\times $ , $27.7\times $ , and $11.6\times $ larger than their associated operational frequency bands are, respectively, demonstrated.