Broadband interconnects between coplanar waveguide and substrate integrated waveguide for dense packaging and integration

Two new interconnects between coplanar waveguide (CPW) and substrate integrated waveguide (SIW) are introduced and studied. Contrary to previously published interconnects, the new ones are shorter and require less space on the printed-circuit board. Thus they are ideally suited for dense packaging and integration. The first one is a regular interconnect that runs the slots of the CPW directly into the SIW. It is straightforwardly designed and achieves 26 dB return loss over a 10 GHz bandwidth centered at 23 GHz. The second interconnect is of the inverted type. It is 43 percent shorter than the first one over the same frequency range and at the same return loss level. Experimental results conducted at back-to-back transitions agree well with theoretical predictions. The shortest inverted interconnect achieves a measured back-to-back return loss of better than 18.5 dB over the entire frequency range with a maximum insertion loss of 1.28 dB. The comparative values of the regular back-to-back CPW-to-SIW prototype are 23 dB and 1.0 dB, respectively.