Wideband reflection type MMIC attenuator with constantphase

Abstract
A method for reducing the unwanted insertion phase variation in an MMIC reflection type attenuator with wide bandwidth (≫ 20 GHz) is described. The analogue reflection type amplitude control circuit uses cold-FETs as variable resistance reflection terminations. At high frequencies, very high phase variation is unavoidable due to the parasitic voltage-dependent reactance. Instead of tuning-out the parasitic reactance of the cold-FET, a novel symmetrical control method is presented for a two-stage attenuator. The phase shift variations from each stage cancel each other by the use of ‘complementary’ control signals.

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