A compact and broadband MMIC power amplifier operating from 18 GHz to 35 GHz is developed for K- through Ka-band applications implementing a rigorous electromagnetic (EM) simulation of closely spaced matching networks. The EM simulation results in a compact chip size as small as 2.16 mm x 2.0 mm and isolations of less than -25 dB up to 40 GHz between neighboring distributed structures. The two-stage balanced power amplifier fabricated using a 0.25 mum AlGaAs/InGaAs/GaAs PHEMT technology has an average gain of 11 dB, return losses less than -10 dB, and P 1 dB above 20.5 dBm from 18 GHz to 35 GHz. This compact and broadband MMIC power amplifier is suited for power amplifiers for most K through Ka-band communication systems such as the FSS, LMDS, and ITS.