Printed-circuit Transmission Lines Research Articles

Significant contribution of nonphysical leaky mode to the field excited by a source

We were the first to report on printed-circuit transmission lines that nonphysical improper real solutions may have a significant effect on the physical total field excited by a source. We have recently studied such interesting and unexpected effects in more detail, and we have discovered here that a nonphysical leaky solution may also cause a significant effect on the physical near field excited by a source, contrary to earlier belief. This effect has been investigated from the viewpoint of the evolution of eigenvalue solutions, which are extracted from both the finite-difference time-domain numerical data and the measurement data through the generalized pencil of functions technique

Leakage effect of printed circuit transmission lines with multilayered dielectric substrate

We have proposed here a new structure of printed circuit transmission lines in which the dominant mode leaks power through additional dielectric multilayer without affecting neighboring circuits. Such a structure of a microstrip line has a slot on the ground plane and also has a dielectric multilayer under it. Then the appropriate combination of dielectric constant between dielectric layers produces the leakage into the multilayer. This means that the leaky field does not leak into the substrate of the microstrip line, and then we can get the lossy uniform microstrip line above the critical frequency. We present first the dependence of the structural parameters of the proposed microstrip lines on the leakage properties. We also apply such a structure to slot lines as one of coplanar printed circuit transmission lines and confirm that the leakage effect can be successfully controlled by an additional dielectric multilayer. Finally, we present the experimental results for the microstrip line with the dielectric multilayer to verify the validity of the numerical results.

Investigation of integration paths in the spectral-domain analysis of leaky modes on printed circuit lines

The different integration paths that may arise in the spectral-domain analysis of leaky modes on open printed-circuit transmission lines such as microstrip are investigated. There are an infinite number of paths in the complex plane that may be used to construct leaky-mode solutions. Not all of the paths are mathematically. Among the mathematically ones, a certain subset correspond to paths that yield valid solutions. When tracking leaky-wave solutions as frequency changes, it is found that the propagation constants of the leaky modes may go through nonphysical regions where the attenuation constant is negative. These nonphysical regions may appear between physically frequency regions, implying that the leaky modes should be tracked in all frequency regions, including the nonphysical growing ones, in order to obtain the complete frequency dispersion behavior of the leaky mode. The migration of the leaky modes into these nonphysical growing regions gives rise to unconventional integration paths never seen before. Such paths must be used if the dispersion behavior of the leaky modes is to be plotted for all frequencies.

Surface-wave propagation on a grounded dielectric slab covered by a high-permittivity material

A grounded dielectric slab covered by a higher permittivity material would not normally be expected to support surface waves. This conclusion must be modified when the covering material is sufficiently lossy. Assuming a thin slab, approximate analysis shows that the fundamental TM/sub 0/ surface wave is able to propagate if the cover loss is high enough. A numerical analysis has verified these conclusions. Propagation of higher order TM and TE modes is found to be possible above cutoff frequencies, which reduce as cover loss is increased. These results are of significance when printed circuit transmission lines such as microstrip or slotline are used as contact sensors, e,g., for moist materials.

Significant contribution of improper-real solution to the fields excited by a practical source in printed-circuit transmission lines

For conductor-backed coplanar strips, we first reported that nonphysical improper solution has a significant effect on the physical total field excited by a practical source. Here, we quantitatively and experimentally investigate this unexpected effect for slot lines in more detail, and we conclude that it occurs on most, if not all, printed-circuit lines; thus, the effect is rather general.

Analysis of mode coupling on guided-wave structures using Morse critical points

New insight on mode coupling in waveguiding structures is obtained from the theory of Morse critical points (MCP's). It is shown that the traditional coupled-mode formalism has a clear analytical connection with functional properties of the characteristic determinant in the vicinity of the Morse critical point, which determines the minimum of coupling. The relationship between perturbed and independent modes in the mode-coupling region is obtained using the Taylor polynomial of order two about the Morse critical point, and it is found that the coupling factor is proportionally related to the value of a characteristic function at this point. The qualitative modal behaviour in the mode-interaction region is predicted by a simple normal form, which can be geometrically interpreted as a result of the intersection of a saddle surface and a plane corresponding to the minimum of the coupling factor. Numerical results for a variety of guided-wave structures, including printed-circuit transmission lines, planar-slab waveguides, and shielded microstrip-like lines demonstrate the efficiency of the proposed approach for the rapid identification of mode-coupling regions, and for reconstruction of dispersion behaviour in those regions via simple analytic (normal) forms.

Generalised approach to modelling shielded printed-circuit transmission lines

A new generalised approach for the full-wave analysis of shielded printed-circuit transmission lines with finite metallisation thickness is presented. A rigorous formulation for the electric field vector is employed, representing the hybrid electromagnetic field in layers of multidielectric media. The dyadic Green's function of the electric kind is derived as a kernel of the vector integral representations for the electric field. Based on the method of overlapping regions, the approach can be applied to the characterisation of a large class of planar waveguiding structures to yield a set of linear algebraic equations of the second kind with a compact matrix operator. Numerical examples are shown for single and coupled shielded planar transmission lines illustrating application of the method. The technique described allows obtaining accurate and mathematically correct solutions of planar waveguide eigenvalue problems.

Comments on the "Criterion of leakage from printed circuit transmission lines"

For original articles see ibid., vol. MTT-38, p. 1719-30 (1990) and vol. MTT-39, p. 54-63 (1991). Leakage of power in printed transmission lines can be due to the excitation of both volume and surface waves. Depending on the frequency of operation several surface waves can be excited in the background waveguide, contributing to the transversal leakage of power. A crucial point in the analysis is to determine how many of these surface modes contribute to the leakage. In this letter, we try to discuss the possibility of excitation of surface-wave modes exponentially growing transversally, but with a wave number less than the phase constant of the transmission line.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Simultaneous propagation of bound and leaky dominant modes on printed-circuit lines: a new general effect

We were the first to report that both the bound and leaky dominant modes can propagate simultaneously on conductor-backed coplanar strips over a frequency range. We have recently studied this interesting and initially unexpected effect in more detail, and we have made two important discoveries: First, the simultaneous-propagation effect can actually occur on most, if not all, printed-circuit transmission lines (its presence depending on the relative line dimensions), so that, contrary to earlier belief, the effect is rather general. Second, we have discovered the surprising presence of a new improper (or nonspectral) real solution, which is nonphysical but whose evolution as a function of dimensional change serves to explain how the simultaneous-propagation effect can occur. The new solution, and its behavior in a completely nonphysical region, thus governs otherwise-mysterious large changes in the physical, measurable solutions.

Numerical techniques for planar and quasi-planar millimeter-wave passive components

The necessity for accurate characterizations of microwave circuits and components is well recognized. This is because of the use of higher frequencies and more complicated circuit configurations. This paper reviews two important numerical approaches to the analysis and design of printed circuit transmission lines, the planar circuit approach and the transverse resonance technique. The former is applicable basically to microstrip quasi-TEM circuits, and constitutes a considerable improvement compared to the conventional transmission line approach. It is, however, an approximate technique that cannot be expected to give extremely accurate results in all practical cases, particularly in the higher frequency spectrum. On the contrary, the transverse resonance technique, in a formulation generalized with respect to the conventional transverse resonance method, is a rigorous full wave technique that can be applied to the characterization of both planar and quasi-planar transmission lines. The extension of this method to the modeling of discontinuities is also illustrated.

Printed Circuit Transmission-Line Characteristic Impedance by Transverse Modal Analysis

Dispersion characteristics of printed circuit transmission lines such as finlines, shielded microstrips, slotlines, suspended striplines, coupled slotlines, and coupled striplines computed by the transverse modal analysis were reported in a previous paper. Application of the transverse modal analysis to compute the characteristic impedances of these printed circuit transmission lines is illustrated in this paper. Favorable comparison with various published data demonstrates the outstanding accuracy achieved by this technique. Combining the characteristic impedance computation with the dispersion results, the transverse modal analysis can be employed for solving various problems in printed circuit transmission lines.

Transverse Modal Analysis of Printed Circuit Transmission Lines

Dispersion characteristics of finned rectangular waveguides, finlines, shielded slotlines, shielded microstrip and striplines, and shielded two-coupled slotlines and striplines are formulated by the transverse modal analysis method. A rectangular cavity is formed by placing two electric walls transverse to a uniform transmission-line system. Considering that the wave propagation is in the direction transverse to the transmission line and to the dielectric discontinuities, the rectangular cavity can be viewed as multiple rectangular waveguide sections joined by the discontinuities. The rectangular waveguide modal analysis technique is readily applicable to obtain the dispersion characteristics by matching the boundary conditions at the discontinuities interface. Numerical solutions are obtained using Galerkin's method, and the results are compared with several numerical techniques for various transmission-line systems.