Two Differential Wideband SIW-to-RWG Transitions for Thin Single Layer Substrates with Additional Tapering for D-Band Applications

Rectangular waveguides (RWGs) are the standard interface above 110 GHz, starting with the D-Band. Thus, transitions to connect integrated circuits and components, offering a low insertion loss across the complete waveguide band are required. This paper presents the design of such transitions from an RWG to a differential microstrip transmission line. Apart from a multi-section stepped impedance transformer it proposes the use of an additional substrate taper at the first step. This design is verified via a realization in two different single layer substrates with thick metal cladding. Those are the Rogers RT/duroid 5880 and RO3003, respectively. Measurement results show return losses above 15 dB and 12 dB, respectively. The best achieved insertion loss equals 0.6 dB, while the corresponding 3dB bandwidths cover more than the entire D-band.