H. Shigesawa

New interesting leakage behavior on coplanar waveguides of finite and infinite widths

It was recently shown that coplanar waveguides (CPW) leak power in the form of a surface wave above some critical frequency, and that this leakage can cause undesirable crosstalk and package effects. Further studies reveal several interesting behavioral features, including unexpected sharp minima and dimensional dependences. The authors describe these new features, and systemize them to indicate when the leakage effects are strong and when not, when interesting unexpected sharp and deep minima (cancellation effects) occur and how they depend on the structural parameters, and how the leakage behavior varies significantly when the CPW width changes from finite to infinite. >

A versatile leaky-wave antenna based on stub-loaded rectangular waveguide .I. Theory

A new leaky-wave antenna is presented that possesses many desirable features and is suitable for application to both the millimeter-wave and microwave ranges. These desirable features, some of which are unusual, include a simple configuration, a wide flexibility in the range of available beamwidths, the ability to control the beamwidth and the direction of the beam essentially independently, and negligible cross polarization at all scan angles. The antenna structure consists of a parallel-plate stub guide of small height, less than a half wavelength, located off center on the top of rectangular waveguide. The beamwidth is easily controlled from very wide to very narrow by adjusting the stub width or location. The article presents the principle of operation and the theory, employing a new transverse equivalent network that is accurate, but also simple, so that it permits rapid and inexpensive numerical calculations.

Printed-circuit waveguides with anisotropic substrates: a new leakage effect

A new class of power leakage effects has been found for the dominant mode on uniform printed-circuit waveguides when anisotropic dielectric materials are used as substrates. The authors demonstrate, both from physical reasoning and by accurate quantitative calculations, that above a certain critical frequency the dominant mode on uniform printed-circuit waveguides, such as microstrip line, slot line, or coplanar waveguide (whether of finite or infinite width), on suitable anisotropic substrates leaks power into surface waves on the substrate, and that the maximum leakage rate can be rather large. This power leakage is entirely distinct from the leakage or radiation into surface waves that occurs at junctions or discontinuities on the line.<<ETX>>

Mode Propagation through a Step Discontinuity in Dielectric Planar Waveguide

This paper presents two methods for dealing with wave propagation through a dielectric step discontinuity at normal incidence. One method helps to accelerate the convergence of solutions, especially for the TM-mode problem, and the other treats efficiently the continuous mode spectrum by introducing the Legendre transform in the case of open waveguides. As for the former, the singular fields around the dielectric edges are introduced in terms of direct use of their functional forms to the boundary condition, which is fulfilled in the sense of least squares. As for the latter, the expansion in terms of the Legendre functions is performed for optimally divided ranges of a continuous spectrum. A number of numerical examples prove that the methods presented herein are quite powerful for solving the TM-mode discontinuity problems in dielectric waveguides of both closed and open types.

Coupling between different leaky-mode types in stub-loaded leaky waveguides

Several leaky-wave antennas have been described in recent years that possess excellent properties, and they all have in common a parallel-plate stub guide of finite height as part of the cross section. For taller stubs and for larger leakage rates (wider radiated beams), some interesting new exotic interactions occur due to coupling between the desired leaky mode and another leaky mode, which is a modification of the channel-guide mode. Although we have described such coupling behavior briefly previously, this basic new feature (the coupling between two leaky (complex) modes) is not generally known, and is discussed here in more detail and in a more general context. In addition to a broad qualitative discussion, numerical results are presented for structures based on NRD guide and on stub-loaded rectangular guide. We believe that these effects are universal to all leaky-wave structures that possess a finite stub height in the cross section, so that the discussion here serves as a model for what to expect for other structures. >

A new equivalent network method for analyzing discontinuity properties of open dielectric waveguides

A novel network approach is proposed for analyzing interacting discontinuities on open planar dielectric waveguides by accurately taking account of both surface modes and waves with continuous spectra. In this approach, a continuum of the radiation wave is recomposed into a set of the newly defined spectral composite modes, each of which carries a finite magnitude of radiation power. These new modes, in conjunction with surface modes, construct the complete orthonormal set for expressing an arbitrary local field on a dielectric slab waveguide. This leads to an equivalent network approach effective for solving discontinuity problems, even on an open waveguide using the conventional method for closed-waveguide problems. A number of numerical results are shown to demonstrate the usefulness of the proposed approach. >

New surface-wave-like mode on CPWs of infinite width and its role in explaining the leakage cancellation effect

A surface-wave-like mode on coplanar waveguides (CPWs) of infinite width is described. It is explained how the sharp minima in the leakage constant values can be understood in terms of a cancellation effect, and it is shown that the field structure in the frequency range before the minimum is different from that in the frequency range above that minimum. In fact, before the minimum the field is that of the surface-wave-like mode, and after it the field is that of the dominant CPW mode.<<ETX>>

Guidance and Leakage Properties of Offset Groove Guide

A new leaky-wave structure, the offset groove guide, is analyzed accurately by two completely different methods: a novel tee-junction equivalent network approach and a numerical mode-matching procedure. The new structure is discussed first, and it is then shown that the numerical values for the propagation characteristics obtained by each method agree very well with each other, When the offset metal walls are finite in height, an unexpected additional set of leaky modes is present that can couple to the expected offset-groove-guide leaky mode and produce quite complicated but interesting modal behavior. This behavior is discussed as a function of offset and wall height.

A versatile leaky-wave antenna based on stub-loaded rectangular waveguide .III. Comparisons with measurements

For pt.II ibid., vol.46, no.7, p.1042-46. The article describes the measurements that verify the validity of the theoretical expressions for this new type of antenna. Measurements were made both at millimeter wavelengths (40 to 60 GHz) and in the X-band (8 to 12 GHz) frequency range and of two different quantities: the propagation wavenumbers /spl beta/ and /spl alpha/ and radiation patterns. Comparisons were made with numerical values obtained from the theoretical expressions derived in parts I and II and very good agreement was found in all cases.

On the Complex Resonant Frequency of Open Dielectric Resonators

An analytical method is presented for calculating accurately the complex resonant frequency of dielectric pillbox resonators. In this method, an approximated field of the resonator is expanded into a truncated series of solutions of the Hehnholtz equation in the spherical coordinates, and the boundary condtion on the resonator surface is treated in the least-squares sense. The resonant frequency and the intrinsic Q value due to radiation loss are obtained in the form of approximation converging to the exact values. Numericaf results are compared with previously published calculations, which show that the present method is a relatively simple and effective one.