Whispering-Gallery mode resonator method has been presented for complex permittivity evaluation of low loss dielectric materials in millimeter wave region. As a problem, it has been found that the evaluation error slightly dependens on the frequency for a sample. It comes from approximated analysis which is used in the procedure. In this paper, a mode-matching method is applied to this evaluation technique to have improvement of the measrued results. It is confirmed experimentally that reliability of the presented method is improved for the millimeter wave permittivity measurement.

The millimeter wave bandpass filter using the Whispering-Gallery mode (WG mode) dielectric disk resonators is presented in this paper. A 4 stage maximally flat bandpass filter is constructed with the PTFE disk resonators. For the filter design, the coupling coefficients of this mode in the coupled disk resonators are calculated by an approximated separation of variables method. Furthermore, the external Q values of the disk resonator excited by a dielectric waveguide are investigated experimentally. Designed center frequency is 60 GHz and 3 dB band width is 150 MHz. Furthermore, as an attempt to improve the spurious characteristics, another filter structure which consists of some kinds of dielectric disk is tested. As a result, some spurious responses are reduced considerably.

A new set of self-consistent linear equations is presented for the analysis of the startup characteristics of gyrotron oscillators with an open cavity consisting of weakly irregular waveguides. Numerical results on frequency detuning and oscillation starting current for a whispering-gallery-mode gyrotron are described in which these equations were utilized. Experiments for making a check on the effectiveness of the derived equations showed that they well express the operation of gyrotrons in comparison with the linear theory using an empty cavity field as the wave field.