An investigation into the frequency-settling time and post-tuning drift of broadband microwave varactor-tuned oscillators

The Post-Tuning Drift (PTD) of microwave Varactor-Tuned Oscillators (VTOs) has been identified as a factor which can limit the switching speed of broadband microwave Phase Locked Loops (PLLs). This paper describes a technique developed to measure the PTD transients of VTOs to a high degree of accuracy, using an improved pulse generator and a delay-line discriminator. Detailed observations of the transients of bipolar and Gunn oscillators are shown, as plots, and discussed. A typical requirement is: to switch in frequency at 10 GHz by 250 MHz and settle to within 500 Hz of final frequency within 10 microseconds. If the VTO has large PTD, the rate of change of frequency can be too large for the loop to compensate, and long-term frequency and phase transients are seen at the PLL output