In this paper, a novel suspended stripline IF block is proposed for the design of millimeter-wave finline balanced mixer which covers the full U-band. In high IF frequency applications, IF block of a finline mixer is needed to act as open terminal for IF signal, and is required to have minimum attenuation for LO signal. For the purpose of reducing the insertion loss of the IF block in the LO path, a novel compact low loss IF block is developed for the first time. Then the IF block, two Schottky diodes, a LPF, a finline to waveguide transition and a suspended stripline to waveguide transition are integrated together to compose the mixer. The RF port matching is designed by using impedance substitution method to achieve better RF return loss. The measured results show that a conversion loss of 4.1 to 9.6 dB over a 20 GHz instantaneous IF bandwidth has been achieved when sweeping RF from 40 to 60 GHz under fixed LO condition. The P-1dB at RF port is higher than 5 dBm, and the return loss of RF port is between -18 to -4 dB.
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