Compact planar substrate‐integrated waveguide diplexers with wide‐stopband characteristics

Abstract

Compact planar substrate-integrated waveguide (SIW) diplexers with wide-stopband characteristics are presented for the first time based on collaborative multispurious mode suppression techniques including the harmonic staggered technique, centered coupling windows, and offset-centered output ports. The coupling scheme using common dual-mode resonator coupled with multiple single-mode resonators is adopted here to eliminate the T-junctions for size and loss reduction, and the dual-mode coupling controlling technique we previously proposed is also employed to allocate the fractional bandwidths (FBWs) of the two channels flexibly based on the FBW design graph. Additionally, by combining the harmonic staggered technique, centered coupling windows, and offset-centered output ports, good out-of-band rejections can be achieved and excellent wide-stopband characteristics have been implemented intrinsically. Two prototypes including second-order and third-order SIW diplexers are synthesized, designed, fabricated, and tested as demonstrations, extending the stopbands to 1.78f1 and 2.04f1 with the rejection levels better than 17.5 and 20 dB, respectively.