A novel configuration of subharmonic mixer using an anti-parallel diode pair is presented for operating over the 23-37 GHz band. The monolithic microwave integrated circuit is implemented by GaAs 0.15 μm PHEMT technology with the compact size of 0.85 × 0.85 mm2. This mixer employs a directional coupler, LC low-pass filter, and a short stub for isolating three ports corresponding to radio frequency (RF), local oscillation (LO) input, and intermediate frequency (IF) output ports. The directional coupler also provides impedance transformation between the diode pair, RF, and LO ports. This makes the subharmonic mixer more compact and flexible. The best conversion loss of the subharmonic mixer is 9.4 dB, and the LO-to-RF and LO-to-IF isolations are better than 22 and 31 dB, respectively.
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