Improved tuning prediction for the microstrip coupled dielectric resonator using distributed coupling

In this paper, accurate modeling of the varactor-tuned dielectric resonator (DR) using distributed coupling between the DR and microstrip lines is investigated on the basis of three-dimensional electromagnetic study. The magnetic coupling between the DR and microstrip line is appreciable over a length greater than the diameter of the DR. The distribution of this coupling should be considered when calculating the electronic frequency tuning range. A novel circuit model is introduced to represent the coupling as distributed, with an integral method to calculate equivalent-circuit parameters efficiently. The distributed model provides much better accuracy than the conventional lumped model. A comparison is made between the calculated tuning range of 23 MHz achieved by the distributed model, which agrees closely with a measurement of 20.2 MHz, and that of 89 MHz predicted by the conventional lumped model. The circuit model of distributed coupling is, therefore, valuable in the design of DR oscillators.