Tunnel diode microwave oscillators employing a novel power combining circuit topology

Negative differential resistance (NDR) devices such as Esaki tunnel diodes (TD), Gunn diodes or resonant tunnelling diodes (RTD) are excellent for the realization of high frequency oscillators. However, for tunnel diodes and RTDs which have large negative differential conductance the output power tends to be low due to the DC instability, parasitic oscillations or the small area devices employed. In this paper, a new power combining circuit topology, incorporating a new design methodology for the DC bias decoupling circuit, has been developed. The oscillator topology uses parallel resonance but with each tunnel diode individually biased and DC decoupled making it possible to employ several tunnel diodes for higher output power. Parasitic bias oscillations are eliminated. Simulation and experimental oscillator results are in good agreement, with a two-tunnel diodes 450 MHz oscillator exhibiting approximately double the output power (-6.5 dBm) as compared to that of a single 600 MHz tunnel diode oscillator (-9.42 dBm), i.e. 3 dB higher.