R. S. Chen

Analysis and development of millimeter-wave waveguide-junction circulator with a ferrite sphere

This paper presents a class of new easy-to-fabricate ferrite-sphere-based waveguide Y-junction circulators for potentially low-cost millimeter-wave applications. A new three-dimensional modeling strategy using a self-inconsistent mixed-coordinates-based modal field-matching procedure is developed to characterize electrical performance of the proposed circulator. It is found that the circulating mechanism of the ferrite-sphere post is different from its full-height ferrite counterpart in that the new structure operates in a turnstile fashion with resonant characteristics, while the conventional device operates on a transmission cavity model. Extensive comparable studies between the new and conventional circulators are made to show that the electrical behaviors of the new structure are also distinct and radial power-density profiles are not stationary, as in the case of the full-height ferrite post circulator for different geometrical parameters. Results obtained by the analysis technique are compared with the available results for a full/partial-height ferrite circulator, showing an excellent agreement. Our calculated and measured results are also presented for W-band circulators with the proposed ferrite-sphere technique, indicating some interesting characteristics such as the frequency offset behavior of the isolation and reflection curves. In addition, radial power-density profiles are plotted inside and outside the ferrite sphere to illustrate its intrinsic circulating mechanism, as well as its difference, as compared to its full-height ferrite structure.

Input impedance of a coaxial-line fed probe in a thick coaxial-line waveguide

The Greens functions for determining the electromagnetic fields inside a semiinfinite coaxial line due to a radially directed, infinitesimally thin, and short-current element have been derived. In addition to the TEM mode, TE and TM modes are also considered. Based on the Greens functions, a closed-form formula for determining the input impedance of a probe in a coaxial line terminated at an arbitrary load has been derived. Good agreement is observed between the theoretical results and experimental measurements over a wide frequency band for several configurations of interest. At low frequencies where the TEM mode is dominating, there is practically no difference between the results obtained by the rigorous analysis and those by a simple formula derived from the transmission-line theory. However, at frequencies where TE and TM modes are no longer insignificant, there is a noticeable discrepancy between the results obtained by the rigorous and not-so-rigorous methods.

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 robust 3-D higher-order finite element analysis of microwave devices

In this paper, we present a robust higher-order finite element method (FEM) for efficient and accurate analysis of microwave devices. The solution algorithm employs higher-order tetrahedral elements, which are particularly suitable for modeling complex devices, in conjunction with the multifrontal solver. This algorithm is combined with the asymptotic waveform evaluation (AWE) and complex frequency hopping (CFH) techniques to perform fast frequency-sweep calculations. Numerical results are presented to demonstrate the performance of the solution algorithm.

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.

FDTD investigation of end effect and multislot effect on the circumferentially slotted coaxial antenna

The finite-difference time-domain method (FDTD) is first applied to investigate the reflection and radiation properties of a finitely long coaxial antenna with circumferential slots on its outer surface. The end effect and multislot effect intractable for the moment method and mode-matching method are analyzed efficiently and demonstrated in detail. According to the accurate analysis, the circumferential slots have a strong influence on the characteristics of the antenna. This effect can be used to effectively adjust the impedance matching and radiation pattern of the antenna. The verification of the method is also presented by reference to the experiment and the literature.xa0©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 35–39, 1999.