HEMT amplifier for 30 GHz low noise receivers

Results on HEMT (high-electron-mobility transistor) microstrip low-noise amplifiers in the 3- GHz band are presented. The designed circuits were fabricated on 10 mil (0.254 mm) thick polytetrafluorethylene glass-fiber substrate (ε_r=2.17). The basic structure used in all matching networks is a pair of edge-coupled microstrip lines with two opposite ports open-circuited. No lumped DC-blocking capacitor is used. Results are presented on two amplifiers, both having input and output WR-28 interfaces. The first is a one-stage amplifier, and the waveguide-to-microstrip transition used in both ports consists of a ridge waveguide step transformer. The second has three stages and uses a microstrip E-probe transition to waveguide in both ports. The one-stage amplifier exhibits a noise figure lower than 4 dB and an associated gain greater than 5 dB at 30 GHz. The three-stage amplifier has a 5 dB noise figure and 15 dB gain at 27 GHz