A transistor microwave power-source

A single UHF power transistor has been used as a simultaneous amplifier and frequency multiplier to generate substantial microwave power well above the cut-off frequency of the transistor. An RCA 2N3375 silicon N-P-N planar transistor of the "overlay" design has yielded output powers of 3.5 watts at 1.0 Gc (28% efficiency), 1.5 watts at 1.5 Gc (20% efficiency), and 0.3 watts at 2.0 Gc (4% efficiency) with an input power of 1 watt at 500 Mc. This device generates the high-frequency power by driving the non-linear capacitance of the base-collector junction with the amplified power at the fundamental frequency. The harmonic output power is greater than that obtained with a class-C multiplier by virtue of varactor action. The measured equivalent output circuit of the transistor contains a small constant resistance in series with a variable capacitance which is inversely proportional to the square-root of the collector-base voltage. The results of an analysis using the equivalent circuit in conjunction with the multiplication mechanism agree well with measurements. Discussion will be given of the bandwidth and frequency limitations of this device.