Cooled Cascaded Frequency Multipliers at 1 THz

It has been shown by theoretical calculations that the required all-solid-state local oscillator power for a Schottky diode mixer at 1 THz can be obtained by cooling a Schottky varactor frequency multiplier chain. The first reason for the higher output power by cooling is the decreased series resistance of the varactor, which increases the efficiency of the Schottky varactor frequency multiplier by 1-2 dB. The second and more important reason for the higher output power at submillimeter wavelengths is the increased maximum current of the Schottky varactor by cooling, which makes it possible to pump the junction capacitance more effectively. This is especially important for the last stage multiplier at 1 THz, when the optimum peak current needed to pump the capacitance is much higher than the maximum current of the varactor at the temperature of 300 K. The theoretical maximum output power at 1 THz is calculated to increase by about 8 dB from 50 ¿W to 300 ¿W, when the multiplier chain is cooled passively to the temperature of 150 K, for example in a satellite.