A three-stage power amplifier has been developed, capable of operating without tuning, over a wide frequency band ranging well above 100 GHz. The original intended application of this circuit is as a driver amplifier for a passive frequency multiplier that would generate a local-oscillator signal in a submillimeter-wavelength heterodyne receiver. There is also a growing need for amplifier circuits like this one in other applications, including radar, imaging, scientific instrumentation, and communications.

Figure 1. This Three-Stage Transistor Amplifier with coplanar waveguide interconnections exhibits at least 9 dB of gain over 80 GHz of bandwidth and spans three waveguide bands. Experimental (upper graph) and theoretical (lower graph) amplifier gains are shown as a function of frequency. The experimental data were obtained by measuring the amplifier gain in three different waveguide bands: 65 to 115 GHz (DATA3), 85 to 140 GHz (DATA1), and 140 to 220 GHz (DATA2).

This amplifier features four InP high-electron-mobility transistors in a grounded coplanar waveguide circuit with lumped-element interstage and shunt capacitors. The circuit also features a unique coplanar waveguide power-combining structure in the output stage.

The amplifier operates with a dc power of 400 mW and a 2-V drain bias on each transistor. As illustrated by the graph in Figure 1, the amplifier exhibits 9 to 13 dB of gain over the frequency range from 65 to 146 GHz, and spans three waveguide bands. The output RF (radio-frequency) power was measured to be 25 to 40 mW from 106 to 140 GHz. The chip photograph is shown in Figure 2.

Figure 2. The InP Wide-Band Amplifier is shown in this chip photograph.

This work was done by Lorene Samoska and Sander Weinreb of Caltech, Yoke Choy Leong of UMass, and Mehran Matloubian of HRL for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Electronicss & Computers category.