Submillimeter-wave BWO´s

It is the goal of this study to explore concepts of making milliwatt output level backward-wave oscillators for frequencies in the range of 600 GHz up to at least 2,000 GHz. Such sources would find many scientific uses, particularly as local oscillators in receivers for submillimeter spectroscopy. We are currently studying designs using ion beam assisted etching to produce small slow-wave circuits on diamond substrates. The interdigital line is a fundamental backward-wave circuit and has a much higher coupled impedance than the traditional vane circuit, but the much smaller size is not a limitation with modern photolithography and ion beam etching technology. Low frequency scaled cold circuit tests showed that the coupled impedance is reasonably high and the tuneable bandwidth can be 40 percent or more. With the higher coupled impedance, lower beam density (and cathode density) can be used, and magnetic fields of only a few kilogauss are required. Hence, it appears that low voltage, wideband, long life, and lightweight submillimeter BWO sources are feasible. An experiment with an 18 µm pitch interdigital line etched on diamond, designed to oscillate at 600 GHz with a 4 kV beam and 3 kG magnetic field, is being constructed.