A Broadband Low-Loss SICL to Ridge Waveguide Transition for Millimeter-Wave Applications

In this brief, a millimeter-wave (mmWave) broadband low-loss substrate integrated coaxial line (SICL) to ridge waveguide (RIWG) transition is proposed. The transition realizes the conversion from the TEM mode in SICL to the $TE_{10}$ mode in RIWG through a T-shaped patch. To achieve broadband and low loss characteristics, a multi-section impedance transformer is employed to enhance the matching performance at low frequencies, and metalized via array matching structures are used to improve the matching performance at high frequencies. For verification, a back-to-back transition prototype was designed and fabricated, and the measured results agree well with the simulated ones. The measured results indicate that the transition structure has a wide operating bandwidth of 71%, covering 23 GHz to 48.35 GHz, and the insertion loss is lower than 0.35 dB within the entire operating band. The merits of the proposed transition, e.g., compact size and stable performance, make it promising for advanced millimeter-wave circuits and systems.