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With instantaneous and in situ characteristics, mode discriminators based on mode-selective coupling principles attract much attention, but their working bandwidth is restricted by the distribution of the equal distance between adjacent holes and the equal radius of all holes. Meanwhile, the equal-interval and unequal-radius distribution of holes can increase the bandwidth of the mode discriminators remarkably. Therefore, the basic theory, designing method and example of the mode discriminators based on the equal-interval and unequal-intensity (i.e. various radii of holes) coupling are brought forward in this paper. The formulas of coupling intensity in terms of binomial distribution and Chebyshev distribution are also presented. The calculation shows that the working bandwidth of the mode discriminators based upon mode-selective coupling according to binomial distribution or Chebyshev distribution can reach 15% to 19%, which is twice over that of equal-interval and equal-intensity coupling mode discrimin...

In order to enhance the power capability of the helix travelling wave tube, a novel tape helix slow wave structure (SWS), which is supported by helically arrayed radial dielectric-support posts, is developed. Each dielectric post can be easily brazed with the tape helix and the metal envelope by means of a special soldering. This kind of supporting mode can protect the dielectric supporting posts from being broken by the thermal stress in the case of high temperature. A hybrid model is set up in consideration of the influences of both the radial thickness of the tape helix and these discrete dielectric-support posts. The dispersion equation and interaction impedance of the helical SWS are obtained. The calculated results using this hybrid model presented in the paper show good agreements with the HFSS simulation results. All the results presented here can provide a good basis for designing the novel tape helix SWS.

This paper concerns a new circular-arc-shaped helical groove all-metal structure, and emphasizes the propagation characteristics of the slow wave. By using approximate field-matching conditions, the dispersion equation and the coupling impedance of this circuit are obtained. The dispersion curves and coupling impedances of the fundamental wave and some harmonics are calculated and the influences of various circuit dimensions are discussed. The calculation results show that the bandwidth can be improved by increasing the arc angle or decreasing the pitch of the structure; a 50% bandwidth is achieved by deviating the phase velocity within ±5%. As a new slow-wave structure for a travelling wave tube, this circuit has an attractive feature, namely the bandwidth is broad while power capacity is high.

The travelling-wave tube is an important high-power microwave amplifier. The ridge-loaded ring-plane slow-wave structure can provide high output power in a relatively broader bandwidth. Starting from the beam-present wave equation, the dispersion relation for the interaction between the electron beam and the symmetrical mode propagating in this slow-wave circuit is obtained in this paper by means of the variational method. Making use of the Newton downhill method the numerical results of small-signal gain and phase velocity are given. The influences of the radius and current of the electron beam, the acceleration voltage and the geometrical dimension of the slow-wave structure on the smallsignal gain and phase velocity are discussed. The instantaneous operating bandwidth can be estimated from the diagrams of the relation between the gain and the frequency. This paper provides a theoretical basis for designing the ridgeloaded ring-plane travelling-wave tube.

A new method for designing a directional coupler form the TE0, mode in a circular waveguide to the TE10 mode in a rectangular waveguide 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 TE11mode. Some couplers with parameters d/2;100dB, p≳100 dB,p ≳100 dB for the TE11 mode and p > l0 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.