Miniaturised GaAs PHEMT power amplifiers at Ka- and Q-band using capacitively loaded coplanar transmission lines

By using a coplanar layout, incorporating transmission lines loaded with lumped shunt MIM-capacitors, the size of millimeter-wave power amplifiers can be considerably reduced. This is demonstrated by the design of two compact GaAs PHEMT power amplifiers. While only occupying a chip size of 2.2 mm2 and being operated at a low supply voltage of 3.3 V, these fully-matched two-stage amplifiers deliver a saturated output power of more than 500 m W with 13 and 11 dB linear gain at 35 and 42 GHz respectively. A further size reduction can be obtained by using dual-gate HEMTs, allowing both a higher gain and output power density. For a 1. 1 mm2 size one-stage dual-gate amplifier a gain of 1 0 dB and 0. 5 W output power is obtained at 26 GHz. The output power densities per chip area of these coplanar amplifiers are a factor 2 higher than those of state-of-the-art power amplifiers realised in a microstrip technology.