Improvement of Microwave Dielectric Resonators by Its Segmentation and Resultant Gaps

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If one divides a dielectric resonator perpendicularly to the electric field, the dielectric loss will decrease, because the electric energy concentrates in the gap, resulting in a augmented unloaded Q. But the resonant frequency increases at the same time. We have tried to improve the basic characteristic of microwave band pass filters (BPFs) by use of these properties. Its application to the desired mode decreases the transmission loss of the pass hand, while that to the unwanted modes will improve the spurious characteristics because the desired mode dees not change the resonant frequency appreciably We studied those possibilities in detail by the EM simulation and confirmed it by experiments.Secondly, the image resonator configuration meant for miniaturization and improvement of heat dissipation of a resonator is known to degrade its Q value due to the increased eddy current on the contacting metal shield. Our proposal is to introduce the air gap between the resonator and metal shield, and has succeeded to reduce the eddy current less as well as the dielectric loss. In fact, the degraded Q of 7000 was recovered to be 13000.While we were tying to fabricate a high-quality BPF on the basis of the results above, we found the importance of the control of coupling coefficient of both the wanted/unwanted modes and extended our plan to the study of physics of coupling coefficients. Based on the coupled mode theory, we found a variety of expressions, including the period of energy exchange between resonators, the difference of overlap integral of the electric and magnetic fields respectively, excitation of dipole moment in the dielectric resonator and the difference of electric and magnetic evanescent energies. We will be able to control the coupling coefficient between adjacent resonators in a BPF so as to realize the improved characteristics.