A Compact K-/Ka-Band Diplexer with Dual-Mode Folded SIW Cavities

The compact diplexer discussed in this paper is intended to feed a dual-band phased array for K-/Ka-band satellite communications (SatCom). Its filters at 20 and 30 GHz rely on a dual-mode cavity design in folded substrate integrated waveguide (FSIW) technology. An additional transmission zero (TZ) is realized by source-load coupling through a higher order mode to improve the upper stopband performance. In this way, the diplexer achieves an isolation of more than 40 dB in the upper passband. The fractional bandwidth (FBW) reaches 14.5% in the lower and 18.6% in the upper passband. The insertion loss (IL) is 1.2 dB and 1.3 dB, respectively. The diplexer is manufactured with a standard printed circuit board (PCB) process. With its footprint of
$2.5\times 5$
mm
²
it is significantly more compact than devices with comparable performance described in literature.