Analysis of lossy planar transmission lines by using a vectorfinite element method

The vector finite element method with hybrid edge/nodal triangular elements is extended for the analysis of lossy planar transmission lines. In order to handle lossy conductor transmission lines, the present approach includes the effect of finite conductivity of a lossy area, and the dissipations in metallic conductors and dielectrics are calculated directly by considering a complex permittivity for the lossy region of interest. A propagation constant formulation is used in the FEM, which avoids spurious solutions absolutely and can handle sharp metal edges in inhomogeneous electromagnetic waveguides. Numerical examples are computed for microstrip lines, finlines, and triplate strip lines. The results obtained agree well with the earlier theoretical and experimental results, and thus show the validity of the method. Also, the current distributions on the lossy microstrip lines with finite strip thickness and isotropic substrates are presented     

Hybrid-mode analysis of homogeneously and inhomogeneously dopedlow-loss slow-wave coplanar transmission lines

A hybrid-mode analysis is presented to characterize the propagation properties of uniplanar slow-wave MIS (metal-insulator-semiconductor) coplanar transmission lines. The effect of homogeneous versus gradually inhomogeneous doping profile is investigated as well as the influence of the metal conductor losses and finite metallization thickness on the slow-wave factor and the overall losses. Numerical results indicate that thick-film MIS CPWs can support a slow-wave mode with moderate loss up to 40 GHz when the line dimensions are kept in the micrometer range. Furthermore, it is found that an inhomogeneous doping profile can reduce the overall losses and that the effect of metal conductor losses in heavily doped MIS structures is only marginal. On the other hand, in weakly doped or insulating GaAs material a lossy metal conductor leads to a higher propagation constant, exhibiting a negative slope with increasing frequency     

Propagation Characteristics of a Microstrip Line Printed on a General Anisotropic Substrate

An analysis is presented for determining the propagation modes in a microstrip line printed on a substrate having both electric- and magnetic-type general anisotropies. An integral equation is derived for the unknown current distribution on the microstrip line. The kernel of this equation is a complicated 2x2 matrix function of the substrate anisotropy and of the substrate thickness. In order to determine the dispersion relations for the propagating waves, this integral equation is reduced into a finite system of linear equations by employing Galerkin's technique. Numerical results are given for several cases, and the effect of rotating the anisotropy axis in anisotropic substrates is investigated. The proposed method can be employed to compute the propagation characteristics of microstrip lines printed on anisotropic substrates.     

Complex modes in shielded suspended coupled microstrip lines

The existence of complex modes in electrically shielded suspended coupled microstrip lines has been studied extensively, and the results are presented. A rigorous full-wave spectral-domain approach (SDA) with a newly proposed and tested set of basis functions can efficiently and accurately determine the propagation characteristics of the dominant, higher-order, and complex modes for planar or quasi-planar transmission lines. These basis functions are validated by comparing the convergence study of field solutions with those obtained by various sets of preconditioned bases and by the unconditioned subdomain ones. Excellent agreement is obtained for the propagation constants and the normalized complex longitudinal and transverse current distributions on conducting strips for the strongly coupled microstrip lines. For all the particular case studies discussed, it is shown that the complex modes may exist in all the shielded suspended coupled microstrip lines, even when the substrate dielectric constant is low. Theoretical results for the fundamental, higher-order, evanescent, and complex modes are presented for suspended coupled microstrip lines     

Hybrid-mode computation of propagation and attenuationcharacteristics of parallel coupled microstrips with finitemetallization thickness

The hybrid-mode mixed spectral domain approach (MSDA) is formulated to investigate the dispersion nature of multiple coupled microstrip lines with arbitrary metallization thickness. Incorporated into the solution procedure, a new set of basis functions with δ ^-1/3 field singularity near conductor edges is found to be effective in calculating both the phase and attenuation constants. The computation of conductor loss is based on the perturbation procedure. Over a broad band of frequency spectrum, excellent agreement is obtained between the calculated results and existing experiment data for the metallic losses of a single microstrip and effective dielectric constants of coupled lines. The influence of finite metallization thickness on the frequency dependent modal propagation and attenuation characteristics is presented for both a three-line and four-line structure     

Identification of propagation regimes on integrated microstriptransmission lines

There has been a resurgence of interest in the propagation characteristics of open integrated microstrip transmission lines. This is due in part to the discovery of diverse propagation regimes for higher-order modes on open lines. In contrast to the dominant EH₀ mode, three distinct propagation regimes exist for higher-order modes on microstrip transmission lines. In this paper, a rigorous spectral-domain integral equation formulation is used to analyze propagation in all three regimes. This formulation provides a clear physical picture of the different propagation regimes based on the mathematical location of poles and branch points in the complex spectral-variable plane. As an illustration, the formulation is applied to the case of an isolated uniform microstrip transmission line. The integral equation is discretized via the method of moments, and entire-domain basis functions incorporating suitable edge behavior are utilized to provide convergence with relatively few terms. The results obtained are compared to the results of other workers, and good agreement is observed     

Miniaturized CBCPW bandpass filter basedon thin film polyimide on lossy silicon

This letter reports a miniaturized conductor-backed coplanar waveguide (CBCPW) bandpass filter (BPF) based on a thin film polyimide layer coated on a lossy silicon. With a 20-/spl mu/m-thick polyimide interface layer and back metallization, the interaction of electromagnetic fields with the lossy silicon substrate has been isolated, and as a result low-loss and low-dispersive CBCPW line has been obtained. The measured attenuation at 20GHz is below 1.2dB/cm, which is comparable with the CPW fabricated on GaAs. In addition, by using the proposed CBCPW geometry, a miniaturized Ku-band BPF was designed and its measured frequency response demonstrated excellent correlation with the predicted value which validated the performance of the proposed CBCPW geometry used for radio frequency integrated circuit interconnects and filter applications.     

Accurate Analysis of Microstrip Lines on Lossy Biaxial Anisotropic Substrates

We have studied the behavior of the microstrip lines on lossy biaxial anisotropic dielectric substrates. A spectral-domain moment method is used with the Galerkin testing procedure to determine the dispersion characteristics of single and coupled lines. Modes of both even and odd symmetries are included. It is found that the anisotropy of the substrate has a significant influence on the propagation characteristics. The theory is verified by comparison with previously published data.     

Analysis of shielded microstrip lines with arbitrary metallizationcross section using a vector finite element method

The finite element method (FEM) with the high-order mixed-interpolation-type triangular element is used to solve the problem of practical microstrip lines with arbitrary metallization cross section. Analyses are carried out to produce the frequency characteristics of propagation constant, characteristic impedance, and attenuation constant of shielded microstrip lines with rectangular, trapezoidal, and semi-trapezoidal strip cross sections. A comparison of the numerical results with those of the existing results shows good agreement and thus verifies the versatility of the FEM. Also, the numerical results show the effects of the metallization cross sections on the transmission properties and thus emphasize the importance of considering the practical microstrip configurations in the design of miniaturized MMICs     

High frequency electrical circuits on a planar lightwave circuitplatform

We investigated the propagation losses and the characteristic impedances Z_L of coplanar waveguides (CPWs) and microstrip lines (MSLs) on a planar lightwave circuit (PLC)-platform formed on a silica/silicon substrate. The loss of the CPWs was 2.7 dB/cm at 10 GHz on the PLC-platform with 30 μm thick silica layer. Thus, a cm-order circuit of this CPW is difficult to fabricate in the 10 Gb/s module. This is because the silicon substrate has a large loss tangent (tan δ). On the other hand, the loss of the MSLs, where a ground plane shielded the high loss silicon substrate, could be improved to 0.9 dB/cm at 10 GHz with 30 μm thick polyimide. These lower loss MSLs on a PLC-platform can be applied to module operation at 10 Gb/s. Furthermore they have the advantage that they are suitable for application to array device circuits or circuits in a module where several devices are integrated because unlike CPWs the ground planes are not divided by signal lines or DC bias lines. The structure of CPWs and MSLs on a PLC-platform with a Z_L of 50 Ω was also studied in detail     

Frequency-dependent characteristics of thick microstrip lines in lossy multilayered dielectric media

The Spectral Domain Approach (SDA) is used for a rigorous full-wave analysis of thick microstrip lines embedded in lossy multilayered dielectric media. The effects of the conductor thickness on the propagation constant and characteristic impedance are investigated.     

Effects of the Thin-Film Metal Ground Embedded in On-Chip Microstrip Lines

This letter studies the influence of embedded thin-film metallization layers, normally designed as ground planes, upon the dispersive characteristics of multilayer microstrip lines. The spectral domain approach is used to analyze the effects of the metallization thickness as a design parameter in two structures: the thin-film microstrip line and metal-insulator-metal-insulator line. Numerical results indicate that the thin metallization layer can excite the slow-wave mode and change significantly the dispersive characteristics. Moreover, at low frequencies a local minimal attenuation can be achieved with certain metallization thickness. Thus, it is necessary to take into account this thin-film metal ground to achieve reliable numerical simulation from dc to millimeter-wave frequencies     

Application of a Projection Method to a Mode-Matching Solution for Microstrip Lines with Finite Metallization Thickness (Short Paper)

It will be demonstrated that the convergence behavior of the well-knowm mode-matching technique can be improved significantly by a general projection method. The advantage of this approach becomes obvious in the discussion of the electromagnetic field distribution near metal edges. The implementation is rather simple and will be described below. Numerical results and the validity of this method are discussed for shielded microstrip lines with finite metallization thickness.     

Rigorous analysis of radiation properties of lossy patch resonatorson complex anisotropic media and lossy ground metallization

An extended spectral-domain immittance approach for the rigorous analysis of resonant frequencies and radiation characteristics of microstrip resonators is presented. The dyadic Green's function in the spectral domain is modified to include a complex anisotropic substrate with both permeability and permittivity tensors, lossy ground metallization, and a lossy conducting patch of conventional or superconducting material. Closed-form expressions for the transverse propagation constants and related immittances of TE and TM waves in the spectral domain lead to a CPU-time efficient algorithm that is operational on standard workstations. Numerical results show how the radiation characteristics are affected by losses as well as uniaxial and biaxial anisotropies     

Frequency dependent transmission characteristics of microstrip lines on the finite width substrate or near a substrate edge

An accurate hybrid mode analysis of microstrip lines on the finite width substrate or near a substrate edge including finite metallisation thickness is described. The frequency dependent solutions for the transmission characteristics of the microstrip lines are presented. An approach for avoiding the calculation of higher modes in a rectangular waveguide partially filled with a dielectric is also introduced. The results provide useful information for the design of high packing density millimetre wave MMICs.<>     

A WH/GSMT-based full-wave analysis for planar transmission linesembedded in multilayered dielectric substrates

A new full-wave analysis method, referred to as the WH/GSMT, is developed to solve multilayered planar transmission line problems. First, the scattering of an obliquely incident parallel plate mode (PPM) by a PEC half plane embedded in a multilayered isotropic dielectric substrate within a PEC parallel plate region is analyzed via the Wiener-Hopf (WH) technique. The solution is then incorporated into the generalized scattering matrix technique (GSMT) to find the (complex) propagation constant and characteristic impedance of the planar transmission lines. The lateral power leakage is taken into account rigorously in the WH/GSMT. Numerical results including the microstrip line, conductor-backed slotline, coupled microstrip lines, and antipodal finlines are presented along with a discussion of the advantages/disadvantages of this method     

An efficient two-dimensional graded mesh finite-differencetime-domain algorithm for shielded or open waveguide structures

A finite-difference-time-domain (FDTD) algorithm for the efficient full-wave analysis of a comprehensive class of millimeter-wave and optical waveguide structures is described. The algorithm is based on a two-dimensional graded mesh combined with adequately formulated absorbing boundary conditions. This allows the inclusion of nearly arbitrarily shaped, fully or partially lateral open or shielded guiding structures with or without layers of finite metallization thickness. Moreover, lossy dielectrics and/or lossy conductors are included in the theory. The algorithm leads to a significant reduction in CPU time and storage requirements as compared with the conventional three-dimensional eigenvalue FDTD mesh formulation. Dispersion characteristic examples are calculated for structures suitable for usual integrated circuits, such as insulated image guides, ridge guides, dielectric waveguides, trapped image guides, coplanar-lines and microstrip lines. The theory is verified by comparison with results obtained by other methods     

Finlines in rectangular and circular waveguide housings includingsubstrate mounting and bending effects-finite element analysis

The finite-element method is used to derive the dispersion characteristics and field components of dominant and higher order modes in finlines. The method is accurate and covers the metallization thickness, substrate mounting grooves, bending of the substrate, and arbitrary cross sections. Results for structures already obtained with other methods have been found to agree well with available data. As a new contribution, the effect of substrate bending on the propagation constant is studied. The dispersion characteristics for the dominant and higher order modes for bilateral finlines in circular waveguide housing are calculated. The field plots for all the modes are given     

Accurate Hybrid-Mode Finline Configurations Including Analysis of Various Multilayered Dielectrics, Finite Metallization Thickness, and Substrate Holding Grooves

An accurate analysis of various finline configurations is introduced. The method of field expansion into suitable eigenmodes used considers the effects of finite metallization thickness as well as waveguide wall grooves to fix the substrate. Especially for millimeter-wave range applications, the propagation constant of the fundamental mode is found to be lower than by neglecting the finite thickness of metallization. For increasing groove depth in cases of asymmetrical and "isolated finline," higher order mode excitation reduces the monomode bandwidth significantly. In contrast to hitherto known calculations, this parameter only causes negligible influence on a fundamental mode if the groove depth is lower than hall of the waveguide height.