A new implementation of the DFT based on delta modulation (DM) is proposed. It is different from the conventional implementation based on PCM. The hardware structure of the method is constructed without A/D converter and multiplier, so it is simpler and of lower cost. Its SNR can approach that of the conventional one, such as FFT. Computer simulations demonstrate that for deterministic signals, results obtained agree well with theoretical analyses, for band-limited Gaussian signals; if step size is suitably selected, results similar to the conventional DFT can still be obtained. Because of the limitation of the working speed of the device, this method will be suitable for processing speech and seismic signals. Finally, the hardware structure which simply consists of a ROM, an adder and some other auxiliary circuits is given.

The equation of electric field radiated by the current f electron beam in a waveguide with arbitrary cross-section is derived. In this equation, the ordinany dyadic Green s function is replaced by the modified one in which the eigenfield is normalized by the power flow. By this equation, the energy conservation in the radiation process can be proved. This equation can be used to compute the interaction of the actual electron devices.

The analysis and computation of the field distribution of the saddle deflection coil with a ferromagnetic shield by the boundary element method are described, and the limitations of the model proposed by D. M. Fye (1979) is pointed out. The Green s function is expanded by the Maclaurin series, and the analytical forms of the field parameters B₀, B₂ and B₄ are given. The results obtained agree well with the experimentally measured values.

In electron focusing and deflection systems the method of dynamic correction (i.e. the application of field curvature correction lenses and stigmators) can significantly reduce the overall aberration and greatly improve the optical properties of systems. In this paper the following numerical computation problems of dynamic correction are described: (1) the principle of correction lenses and stigmators; (2) the computation of field distributions in electrostatic and magnetic correction lenses and stigmators;(3) the calculation of the signal strengths applied in correction lenses and stigmators which completely cancel field curvature and stigmatism; (4) the effect of correction lenses and stigmators on distortion. From the examples of computation of dynamic correction given in this paper it can be seen that the dynamic correction plays enormous role in improving the electron optical properties.

During the activation and aging, the evaporation components and rates from 4.56:1.44:2 impregnated dispenser cathode have been determined by the vapor-collect method based on AES. (1) the evaporation rate of a cathode after aging differs from that of a just activated cathode by a factor of 5 to 10. The evaporation energy of the former is 4.58 eV, and that of the latter is 4.34 eV. (2) at operating temperatures, the metallic Ba in the evaporated material is about 90%, and the barium oxide is about 9.3%. (3) below 1000℃ the evaporation of Ca is not significant, over 1150℃ the Ca starts evaporating rapidly, particularly in the activation process, it may approach 3.5% at 1250℃.

In this paper, a small horizontal size (0.5 λ) backfire antenna using circular dipole is proposed. The antenna structure, radiation characteristic and experimental results are given. The experimental results demonstrate that the antenna has better electrical performances.

In this paper, a new and general formula of capacitance of a capacitor with anisotropic dielectric shown by generalized orthogonal coordinate and inverse matrix of dielectric constant is derived by use of the displacement current, It provides a new and simpler method for computing capacitance of a capacitor. The formula has been checked by several practical examples.

A low-noise 1.2-1.8 GHz cooled GaAs FET amplifier with mixer bias circuit is reported. The amplifier noise temperature obtained at 20 K ambient in the frequency range of 1.2-1.7 GHz is 10 K. The lowest noise temperature is 4 K. The gain is about 30 dB. An automatic measuring instrument for noise temperature was designed. The noise effect of the input cable and the error analysis of total measuring were made. The total measurement error is 2 K.

The contents, classifications, features and tasks of the power electronics are expounded, and some our own ideas based on foreign research results and our institute work in recent years are proposed. These ideas presented here are for discussion in order to push the discipline forward. Finally, the trends of research and development in the power electronics are summalized.

The kinetic theory based on the expansion of local field in the guiding center coordinate system, presented by Liu Shenggang (1979, 1981), has successfully developed into a theoretical system. A brief discussion about the mathematical background and physical explanation of setting up the guiding center coordinate system is given. By using the methods of the guiding center and waveguide coordinate systems respectively, the same dispersion equations for interaction between an electron beam and TE_mn field in the circular waveguide are rigorously derived.

In this paper, the physical basis of kinetic theory based on the guiding center coordinate system is discussed. And what phenomena happened in gyrotron will be obtained by this theory is also discussed. According to above mentioned discussion, the advantages of this theory have been proved.