Microwave Measurement of Varactor Diode Q-factors without Matching or Standard Impedances†

Abstract It is shown that Q-factors of varactor diodes may be measured at microwave frequencies without the usual procedures of matching into the diodes series resistance or the use of calibrating impedances and that a very simple method is possible with an arbitrary fixed lossless transformation between the measuring line and the diode element. Used in conjunction with an automatic impedance display unit and a modified Smith chart the method leads to a direct display of varactor Q's. It is possible to show also the varactor series resistance and capacitance on the same display but this involves calibration with known impedances.