Wideband Measurement of Millimeter Circuits for Varactors and Impatts

We propose to measure the impedance of a millimeter IMPATT circuit by using a modulated microwave signal source -or a signal with two frequency components. The diode is biased below its breakdown voltage, and it is used both as a tuning capacitance and as a demodulator for the high frequency current flowing through it. This method enables to measure the circuit impedance and losses without dismounting the diode. It is capable of wideband operation even with frequency selective circuits.