Design of a Novel Finline-to-Microstrip Transition for Millimeter-Wave Power-Combining Applications

In this paper, a novel double antipodal finline-to-microstrip transition structure which also serves as a two-way millimeter-wave power combiner is proposed. Back-to-back transitions are fabricated on 0.254 mm RT5880 substrate. A very low back-to-back insertion loss of 0.9 dB and return loss better than 12.0 dB are obtained from the structure in 29-39 GHz. Based on the passive structure, a power-combining amplifier was designed by using four Ka-band monolithic microwave integrated circuit (MMIC) power amplifier chips. The power module showed 37.8dBm output power including the loss of transition and a combining efficiency of 82% in 32-36 GHz.