Improvement of unloaded Q of image dielectric resonator due to shift of electromagnetic field distribution

Unloaded Q of an image-type dielectric resonator is discussed based on the electromagnetic field distribution. It is shown that a spacer between the dielectric resonator and the shield case reduces the dielectric loss and the conductor loss. The electric field and the magnetic field distributions move in the reverse directions due to the spacer, so that the two losses are reduced. A half-cut image resonator with a dielectric spacer is measured. The unloaded Q is improved by about two times from that without a spacer.