In this work, a coupled-oscillator system with coupling networks containing discrete transmissions lines, made up of inductors and varactors, is presented. Under weak coupling conditions, it is possible to obtain two stable phase-shift intervals, -90° to 90° and 90° to 270°, by using two different values of the varactor bias voltage. For each of these two bias voltages, the inter-stage phase shift is varied with the tuning voltage of the outermost oscillators, so the use of the discrete lines provides a simple mechanism to increase the phase-shifting capabilities. The two bias voltages of the line varactor diodes are selected so as to obtain optimum operation conditions in each phase interval, with minimum frequency deviation, maximum and unambiguous tuning parameter excursion and a flat phase-noise response versus the imposed phase shift. The impact of the novel type of coupling network on the stability properties is investigated with an explicit semi-analytical formulation. Agreement has been obtained with measured results.

This work has been supported by the Spanish Government under contract TEC2014-60283-C3-1-R and the Parliament of Cantabria (12.JP02.64069).