The proposition to name the helical waveguide with the inner wall removed helical groove is presented in this paper. As an all-metal slow-wave circuit, the ridge-loaded helical-groove structure is especially suited for use in millimeter TWT’s due to its advantages of large size, high manufacturing precision, and good heat dissipation. However, the analysis of this slow-wave circuit was never before done. For analyzing this structure, the cylindrical coordinates are employed in the center space and the helical ones are used in the gap and groove regions. Making use of the matching conditions of the RF fields and the continuity of the voltage and current at the boundaries, the expressions for the dispersion and the coupling impedance of the ridge-loaded helical groove are obtained. The relationship of the dispersion and impedance to the ridge dimensions are also given. It is indicated from the calculation results that approximately 30% bandwidth for this structure can be achieved.

Mode discriminators based on mode-selective coupling principle have a series of advantages. The designing method of this type of discriminator is presented in this paper. The emphasis is put on the mode-selective coupler with a multihole and multigroup of coupling holes. All of the dimensions of the discriminator are determined by this method. The calibration and power measurement of the discriminator are also investigated. Some design examples of discriminators for 35- and 70-GHz gyrotrons, which can be applied to discriminate the TE11, TE01, and TE02 modes and the TE01, TE02, and TE03 modes, respectively, are given.

The design method of mode selective directional couplers from a transverse electric mode in a circular waveguide to the fundamental mode in a rectangular waveguide is presented in this paper. The design results for a TE01 circular mode coupler intended for use in the output power measurement of a high power gyroklystron are reported; these results indicate that more than 50-80dB directivity and sufficient suppression of unwanted modes can be obtained with a coupler less than 0.7 m in length. The effects of frequency and rectangular waveguide size on coupler parameters are also discussed in this paper.

A method for designing a waveguide-stripline-coaxial line directional coupler is presented. The relationships between coupling coefficient and directivity with the geometric dimensions of the directional coupler are derived theoretically. The parameters of manufactured couplers are also measured and the results show good agreement with the calculated results.

A new method for designing a directional coupler form the TE01 mode in a circular waveguide to the TE10 mode in a rectangular wavegnide is presented. This method is used to design a - 50 dB coupler for use in the sampling measurements of a very high power gyroklystron. By varying the rectangular waveguide size the suppression of the unwanted circular modes except the TE11 mode can be increased and by modifying the distance between the last two coupling holes the coupler directivity can be maximized. By using the coupling function Φ(x) to make a second group of coupling holes we can greatly improve the suppression of the TE11 mode. Some couplers with parameters d≥100dB, p≥100dB for the TE11 mode and p>10 dB for most of the other unwanted modes were designed by this method.