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.

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.

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.

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.

As a new type all-metal slow-wave structure of the millimeter wave TWT, The helical groove has a lot of advantages: large power handling capability, large sizes, high precision and moderate bandwidth. Of the helical groove structure, the haft-circular helical groove can achieve wider passband than the rectangular helical groove can do. The approximate and much simple matching method of the fields of the half-circular structure is presented in this paper. The more general expressions of the dispersion characteristic and coupling impcdencc, in which the fast-wave modes and slow-wave modes are considered simultaneously, are obtained. It is indicated from the results of the numerical calculation that choosing suitable dimensions of the structure and suppessing the backward wave osillation, this kind of slow-wave structure can operate over 50% “hot” relative bandwidth.

The hole-gap helical groove waveguide, as a all-metal slow-wave circuit, has advantages of good heat dissipation and great size, and thus is suitable for use of mm TWT. By means of an approximate field theory, the expressions of the dispersion equation and the coupling impedance of the hole-gap helical groove waveguide is obtained in this paper. The influence of various circuit dimensions on the dispersion relation and the eoupling impedance is discussed by the numerical computation.

The design of a 8mm TE13 mode gyrotron is given in this paper. Discussions about the selection of the dimensions of the RF structure and electron gun are presented. Calculated results of the operating parameters of the gyrotron are also given. At 37.SGHz, pulse power 56kW is obtained for the gyrotron manufactured according to our design. Mode pattern obtained by scorching method shows that the mode of the output millimeter wave is TE13.

All-metal slow-wave structures are being paid great attention because of their advantages, such as good heat dissipation, high power capacity, wide passband, good wholeness of structure and large size etc. The emphases in this paper concentrate on the present state of study of four types of structures: helical groove, ring-plane, folded waveguide and periodically loaded waveguide, including theoretical analyses and practical applications. The problems and directions for future studies of these types of slow-wave circuits are also discussed. It is pointed out that all-metal slow-wave structures are suitable for applications in millimeter wave vacuum devices, like TWT, BWO, Gyro-TWT, and relativistic devices.

A novel sectorial groove-gap P, F structure for cusptron (gyromagnetron) is presented and its characteristic equation and stored energy expression are derived. The magnetron-like vane structure is a special case of this structure. The calculated curves of dispersion, energy and efficiency are given and the results show that maximum efficiency n = 16.1% is obtained when the sectorial groove-gap is evolved to vane structure.