A new implementation of the device line measurement technique for accurate microwave oscillator design

In this paper a device line characterization system using a six-port measurement technique is reported for the first time. Device line measurements on a Gunn diode mounted in a coaxial fixture and on a loaded MESFET were performed at C and at L bands, respectively, in order to experimentally optimize the output microwave power and the power efficiency in their respective oscillating modes. Effects of bias conditions on the added power were investigated for both devices. In addition, the effect of the phase of the offset short circuit which terminates the gate-source port of the MESFET was also investigated. Based on these device line measurements, a MESFET oscillator was designed, built, and tested. It was found that the performance of the oscillator was in good agreement with the predicted results obtained from the device line characterization. In addition to its relatively low cost and its ability to perform simultaneous impedance and power flow measurements at an arbitrary power level, the present measurement system has the further advantage of being able to measure the large-signal reflection coefficients of negative resistance devices at the actual power level during oscillation