For the LMDS application, the MMIC based up-conversion mixer was designed using 0.25$\mum$ gate length AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors in the Ka band. The mixer specifications was satisfied within RF frequency range of 24 ~ 28 GHz to cover a similar service of other country. Since the IF frequency has a broadband range of 400 ~ 700 MHz, the IF matching was achieved from LC network on the alumina substrate according to each narrow service band. So this mixer will be ultimately implemented with hybrid circuit. The component having a gain contributes largely to the total system performance improvement. For that reason, we designed active mixer, which is different to reported one from papers and commercial products.
From the simulation, we could know that the designed hybrid mixer has conversion gain of 3 dB, P1dB of 0 dBm, port VSWR of less than 2 and LO isolation of less than 12 dB. Also gain flatness is less than 2 dB in RF frequency range.