A W-Band Bandpass Waveguide-to-Microstrip Transition With Sharp Out-of-Band Rejection

This letter proposes an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula>-plane waveguide-to-microstrip (W2M) transition with bandpass filtering characteristics. The transition integrates two waveguide resonant cavities, an extended short-circuited waveguide, a transition probe, and two open-loop resonators. The waveguide resonant cavities and short-circuited waveguide introduce three transmission poles within the passband, and obtain preliminary bandpass filtering characteristics. By employing the extended short-circuited waveguide and introducing open-loop resonators, two pairs of transmission zeros are generated on both sides of the passband, improving the out-of-band rejection effectively. The proposed structure demonstrates much improved out-of-band spurious rejection performance. Measured results indicate that the transition achieves a return loss better than 13 dB and an insertion loss lower than0.8dB within the passband. It provides a rejection of more than 50 dB at 80 GHz and 16 dB across 104–110 GHz frequency range.