Inverted interconnect between substrate integrated waveguide and coplanar waveguide

A new interconnect between substrate integrated waveguide (SIW) and coplanar waveguide (CPW) is introduced. Contrary to similar interconnects to CPW or grounded CPW (GCPW), in which the top plate of the SIW is transitioned to the center conductor of the CPW, the new design connects the bottom plate of the SIW to the center conductor of the CPW by means of a row of via holes. It is thus termed `inverted´ interconnect. A parametric analysis of the two design parameters involved determines the interconnect design which is validated by two commercially available field solvers. A back-to-back transition is prototyped and measured. Experimental results agree well with theoretical predictions and achieve a return loss of better than 16 dB over the entire 18-28 GHz range with a maximum insertion loss of 1.2 dB. The comparative values of a non-inverted back-to-back SIW-to-CPW prototype are 15 dB and 1.5 dB, respectively. Moreover, the non-inverted transition requires a larger substrate area.