Z. M. Xie

FDTD Analysis of EW Wave Circulating by a Magnetized Ferrite Body in Free Space

An efficient numerical method has been devised for the study of wave circulating by a magnetised ferrite body of an arbitrary shape. It is a finite-difference time-domain formulation that incorporates Murs absorbing boundary conditions and a perfectly matched layer. Several shapes of interest have been studied, including spheres, circular cylinders. The electromagnetic fields inside ferrite and the power-density distribution on the ferrites surface normal to the bias external magnetic field are obtained. It is observed that an incident plane wave would circulate around the magnetised ferrite body in an open space as if the ferrite were placed inside a waveguide junction circulator.

Analysis and design of a coaxial slot antenna for mobile telecommunications

It is foreseen that low-Earth orbit mobile satellites (LEO-MSAT) will be a promising choice to cover suburban and country sides. In contrast to the DBS antenna, the antenna for LEO-MSAT mobile terminals must have an upward-skewed main-beam for satellite tracking. Moreover, it must be low cost, high gain, high-efficiency, and small-in-size. In this paper, an attempt is made to employ a coaxial antenna with circumferential slots for mobile terminals. Because the antenna radiates through apertures and has a very simple configuration avoiding complicated feeding networks, it is expected to be of high efficiency. For antenna analysis, although an infinitely-long coaxial antenna with one slot has been thoroughly investigated, no rigorous analysis is carried out for a finitely-long coaxial antenna with multi-slots. Because the end effect and slot coupling are intractable for conventional methods using function approximation, such as the moment method and mode-matching method, the finite difference time-domain (FDTD) method is used to analyze the slot antenna. For further antenna design, the widths and positions of the slots should be strategically adjusted so that the radiation pattern of the antenna forms a desired upward-skewed donut for satellite tracking.

A coaxial multi-slot antenna used for LEO-MSAT

It is foreseen that suburban areas and countryside will be covered by low-Earth-orbit mobile satellite communications (LEO-MSAT). In order to make LEO-MSAT commercially viable, its mobile terminal must be designed as a consumer product that is low-cost, light-weight, small-in-size, and robust. This is a tall order to be fulfilled because the mobile terminal for LEO-MSAT is more complex than its counterparts for GEO-MSAT although the former has a lower power rating. Comparing with a DBS antenna, a MSAT antenna must be equipped with a steerable main-beam for tracking the satellite position, preferably it is an automatic tracking system. Moreover, the antenna must be low-cost, high-gain, high-efficiency, small-in-size, and preferable low-profile. To this end, an innovative antenna that satisfies most of the aforementioned requirements has been conceived. The innovative antenna is an array comprising two to three antennas. Each antenna itself comprises a coaxial transmission line protruded from a ground plane. In this paper, an accurate analytical technique is developed for studying and designing the element of the novel LEO-MSAT antenna array, the multi-slot coaxial line antenna. The calculated and experimental radiation patterns show that the technique is successful.

The rigorous analysis of a monopole antenna fed by a circumferential slot in a coaxial line

A thick monopole antenna fed by a circumferential slot cut on the outer conductor of a coaxial cable is studied with rigorous field theory in this paper. In our analysis we consider not only the higher-order modes inside the coaxial cable but also the nonuniform distribution of the electric field in the slot. The coupled integrodifferential equations are formulated for the evaluation of the current distribution on the antenna surface as well as the electric field distribution in the slot. The restriction of the slot width and the radii of the antenna are removed from the analysis, The effect of the slot width on the electric field distribution in the slot, the current distribution on the outer conductive surface of the antenna, and the input admittance viewed in the coaxial cable are presented and discussed. The calculated input admittance is in good agreement with the experimental result.

Three dimension edge FEM analysis of inhomogeneous chiral medium loaded waveguide discontinuity

Dielectric-filled waveguides have important applications in many microwave devices, e.g., isolators and phase shifters. In these devices, there are always discontinuity for the constituent dielectrics in both shape and materials. Among them, the chiral medium is particularly receiving much interest because the chirality admittance provides one additional parameter that could make the practical designs more flexible. Traditionally, most of the investigations are based on the mode or field matching method with a particular class of geometries. It has been recognized that for a method to be useful as a good design tool, it must be capable of efficiently handling three-dimensional discontinuities with general configurations. Among the available techniques, the finite-element method (FEM) has been considered to be simplest in formulation and most flexible in modelling arbitrary shaped, inhomogeneously dielectric-filled discontinuity. In this FEM implementation, the use of tetrahedral edge-based vector finite elements is preferred because they are free from divergence, can model continuous tangential fields across dielectric interfaces or on conducting surface, and have small numerical dispersion. In this article the propagation/scattering properties of a chiral media partially filled waveguide are preliminarily investigated.

Finite-difference analysis of cyclic H-plane waveguide three-port circulators with an arbitrary-shape lossy ferrite post

A finite difference method (FDM) with an analytical truncation boundary condition is developed for the analysis of cyclic H-plane waveguide three-port circulators with an arbitrary shape ferrite post. The method is based on scalar wave equations and the analytical field distribution in the rectangular waveguides. A general boundary field equation for an arbitrarily shaped ferrite or dielectric interface is derived. To verify the validity of the present method, the eigenvalue phases of the cyclic three-port empty junctions and the characteristics of H-plane waveguide Y-junction circulators with lossless, lossy cylindrical, composite and triangular ferrite post are calculated. Good agreements with previously published experimental and theoretical results have been achieved. The performance of a Y-junction circulator with a hexagonal ferrite post and the characteristics of a cyclic three-port circulator with a ferrite rod are also investigated.