Broadband $E$ -Band WR12 to Microstrip Line Transition Using a Ridge Structure on High-Permittivity Thin-Film Material

A rectangular WR12 waveguide to microstrip line (MSL) transition using a very thin high-permittivity ceramic substrate (ε
_r
= 9.9 and h = 127 μm) is presented and analyzed. The proposed configuration uses a gradually extending metal ridge over a thin-film MSL to ensure electric field transformation, and an accurate impedance matching, while maintaining a good electrical contact, without any soldering or gluing. The fabricated prototype has been successfully tested in terms of insertion and return losses. The obtained results exhibit a bandwidth of more than 37% at -10 dB with an insertion loss of 1.5-2.7 dB, over the entire 60-90-GHz frequency band. The design simplicity and suitability for high-permittivity thin-film substrates, as well as the very broadband operation capability, enable it to be easily integrated with various planar monolithic microwave integrated circuits/miniaturized hybrid microwave integrated circuits microstrip circuits for different millimeter-wave applications.