A 3.5 db noise-figure, S-band, medium-power, forward-wave injected-beam crossed-field amplifier

Recent noise-figure measurements on crossed-field amplifiers indicate that such devices are not necessarily noisy. With proper design considerations the noise-figure value of a crossed-field amplifier can be reduced appreciably. In this paper the measurements made on a low-noise (3.5 db) S-band, medium power (saturation power about 12 watts) forward-wave crossed-field amplifier are discussed. The amplifier, using a short Kino gun and a velocity-jump-type configuration at the gun exit, was designed after taking into account several considerations necessary for noise-reduction purposes. The various parameters are optimized for low noise and maximum gain; the experimental values deviate very little (less than 5 percent) from the design values of these parameters: Under optimum conditions large space-charge smoothing is noticed. The criticality of these parameters on the tube performance (noise figure and gain) is discussed. Mostly, the deterioration in noise figure (due to a small deviation in one of the parameters) can be closely compensated by adjusting one of the other parameters. The effect of mismatch (along the line and at the input-output terminations) on the deterioration of noise figure is discussed. Reduction in noise figure by several decibels is achieved over a wide band (the gain changes by a comparatively small amount) by adjusting the match at the output section. Noise properties of the short Kino gun are investigated under different modes of operation.