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With the use of a generalized transfer matrix method based on the mode-matching approach for waveguide step discontinuities, reflection properties of metallic waveguide gratings with rectangular grooves are investigated. A proper design procedure for a compact and wide-band reflector grating which can well support single-mode operation is also discussed. Symmetrical waveguide configuration is shown to be of great significance for single-mode support. From the provided design process, it is found possible to obtain metallic waveguide gratings which satisfy all the specified requirements by properly adjusting only basic grating parameters.

The full-wave analysis based on the singular integral equation method is developed to correctly investigate dispersion properties and field distributions inside a rectangular waveguide grating used in low-voltage traveling wave amplifiers. Simplified treatments of periodic structures with rectangular grating are widely used in the analysis of microwave electron beam devices, providing an actually good accuracy for the calculation of dispersion curves of natural modes in a wide range of grating parameters. However, they do not guarantee the correct field distributions in a close proximity to the grating just where an electron beam is usually passed to get more effective beam-wave coupling. The amplitude of the minus-first spatial harmonic, which is mostly responsible for the resonant beam-wave interaction, can be substantially larger than that predicted by the simplified analysis. In addition, the contribution of the higher spatial harmonics to the total field is shown to be significantly larger than that evaluated from the simplified treatment. Consequences of the enhanced influence of higher harmonics on beam-wave interaction are discussed.

A proper duty cycle of the grating period which provides the maximum reflection for a metallic waveguide grating with rectangular grooves is found by the mode-matching approach. For narrowband reflection characteristics, a grating with sufficient numbers of periods and adequately small corrugation is needed, with cutoff conditions taken into account. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 414–418, 2002.

On the basis of the fluid model of the electron beam, amplification characteristics of a two-dimensional plasma-filled Cherenkov laser at 100 GHz bands are analyzed. By injecting a dense plasma into the background of a Cherenkov laser, the coupling between a relativistic electron beam and an electromagnetic wave at millimeter wavelengths has been improved, and the weak beam-wave interaction problem has become less serious. In particular, we show that due to electron-ion collisions in the background plasma, proper choices of parameters are essential for good operation in this regime. The numerical results indicate that a Cherenkov laser with background plasma can generate higher output power with a greatly enhanced growth rate at a more reasonable interaction length. The plasma injection, in addition, enables the device to gain more output power with a higher beam current.

On the basis of the fluid model of the electron beam, amplification characteristics of a two-dimensional (2D) plasma-filled Cherenkov laser are discussed. The numerical results indicate that plasma injection in a Cherenkov laser greatly enhances its characteristics and enables us to make a compact device.

In this paper, reflection characteristics of metallic waveguide gratings with rectangular grooves are investigated with the effect of the Joule loss taken into account. For this purpose, the scattering matrix for each step discontinuity is first found by using the mode matching method with an impedance boundary condition at the surface of the conductor. Then, the scattering matrix method for the overall waveguide grating is obtained by a generalized transfer matrix. Numerical results show that Joule loss occurs mainly at planar waveguide sections. In order to suppress the loss of a reflector grating, it is shown that it should have a deep grating depth with a small number of periods. This configuration coincides with that for a compact and wide-band reflector grating, which can well support single-mode operation as was pointed out in our previous work.

As a powerful tool for analyzing scattering properties of metallic reflector waveguide grating with rectangular grooves, the transfer matrix method based on the mode matching approach for waveguide step discontinuity is used. From numerical results, it is found that lengths of planar waveguide sections composing the grating should be properly chosen to have the maximum reflection for given transverse dimensions of the waveguide grating. In addition, to have proper reflection characteristics within an adequately small bandwidth around a desired center frequency, the grating should contain sufficient numbers of periods, and transverse waveguide dimensions should be chosen so as to be far enough from cutoff.

With the aid of the multilayer approximation method, the growth characteristics of a two-dimensional Cherenkov laser filled with transversely inhomogeneous and collisional background plasma at millimeter wavelengths are investigated. The accuracy of numerical results is confirmed by comparison with the available analytical solution. We show that the injection of a dense plasma into the background of a Cherenkov laser improves the beam-wave coupling and growth characteristics. Degradation due to electron-ion collisions in background plasma can be kept at an acceptable level by appropriate choices of the plasma and beam parameters. From numerical results, we can identify the main parameter of the inhomogeneous background plasma which affects growth characteristics of a plasma-filled Cherenkov laser.

Growth characteristics of a Cherenkov laser filled with background plasma with a transversely inhomogeneous density profile are discussed with the aid of the multilayer approximation method. The accuracy of the numerical results is confirmed by comparison with the available analytical solution. The effect of electron-ion collisions in the background plasma is also considered. In particular, a noticeable degradation in growth characteristics is found. However, by a proper choice of various parameters, spatial growth rates are kept at the level well over those of the corresponding vacuum devices.

On the basis of the fluid model of the electron beam, amplification characteristics of a two-dimensional plasma-filled Cherenkov laser at 100 GHz bands are analyzed. By injecting a dense plasma into the background of a Cherenkov laser, the coupling between a relativistic electron beam and an electromagnetic wave at millimeter wavelengths has been improved, and the weak beam–wave interaction problem has become less serious. In particular, we show that due to electron–ion collisions in the background plasma, proper choices of parameters are essential for good operation in this regime. The numerical results indicate that a Cherenkov laser with background plasma can generate higher output power with a greatly enhanced growth rate at a more reasonable interaction length. The plasma injection, in addition, enables the device to gain more output power with a higher beam current.