Conformal mapping-based models are given for interdigital capacitors on substrates with a thin superstrate and/or covering dielectric film. The models are useful for a wide range of dielectric constants and layer thicknesses. Capacitors with finger numbers n/spl ges/2 are discussed. The finger widths and spacing between them may be different. The results are compared with the available data and some examples are given to demonstrate the potential of the models.

CAD models for multilayered substrate interdigital capacitors

Conformal mapping technique is used to obtain CAD oriented closed form analytical expressions for characteristic impedance per unit length capacitance and relative effective dielectric permittivity of top and bottom shielded multilayered coplanar waveguides. Analytical expressions are deduced for a wide verity of CPW structures. >

CAD models for shielded multilayered CPW

New analytical approximations are derived for the conductor losses of asymmetric coplanar waveguides (ACPW) and coplanar striplines (ACPS) on a finite-thickness dielectric substrate. The expressions hold for lines whose metallizations have thickness much smaller than the slot and strip widths, but suitably larger than the skin penetration depth at the operating frequency. The derivation is based on an extension of the conformal mapping approach formerly proposed by Owyang and Wu (1958) for symmetric lines in air. Comparisons with published data from quasistatic or full-wave numerical analyses are presented to validate the expressions derived for both the symmetric and the asymmetric case. The analytical characterization presented in the paper is well suited for inclusion into CAD codes for MMIC design. >

A CAD-oriented analytical model for the losses of general asymmetric coplanar lines in hybrid and monolithic MICs

In this paper, expressions for the characteristics of some asymmetrical coupled transmission lines are derived. These include expressions for the capacitances, impedances, and phase velocities of asymmetrical coplanar strips, asymmetric coupled striplines, and asymmetric coupled microstriplines. Accuracy of these expressions is compared against available numerical results obtained rising varous numerical methods.

Characteristics of Some Asymmetrical Coupled Transmission Lines (Short Paper)

The electrostatic problem of an arbitrary set of parallel strip electrodes on a dielectric substrate is examined, and a general analytic solution obtained. The general solution requires numerical computation to determine some parameten, but a particular class of problems has been solved completely. The solution for the important practical case of an infinite periodic array of electrodes is determined in the limit of the particular solution as the number of electrodes tends to infinity. W

A General Approach to the Electrostatic Problem of the SAW Interdigital Transducer

An exact method for the computation of the characteristic impedance matrix of coplanar coupled multiconductor stripIines with arbitrary widths is presented. The system of conductors is enclosed in a rectangular shielding box with a homogeneous dielectric medium. Use is made of conformal mapping by hyperelliptic integrals. The reverse problem of determining the geometrical dimensions for a given characteristic impedance matrix is solved by employing an optimization procedure in conjunction with carefully determined initial approximations. This yields low computer running time compared to current methods for the treatment of multiconductor transmission lines.

A Method for the Computation of the Characteristic Immittance Matrix of Multiconductor Striplines with Arbitrary Widths

Design tables for broadband terminations are presented. The termination circuits consist of one or two ?/4 transmission lines in cascade loaded with a resistance in series with an open circuit stub. Since no holes in the substrate or metallic connections with the groundplanes are needed the design is suitable for printed circuits. Measurements have been made on a termination which had a total length of ?/2. The bandwidth was designed to be 85 percent. The experimental result is close to the theoretical predictions. Broadband terminations of this kind may be used in a number of ways. An example of a broadband modified Pi-attenuator without a ground connection is included.

Design of MIC Broadband Loads and Attenuators

The proposed method makes use of conformal mapping technique for a transformation in two steps of multiconductor transmission 1 ines with homogeneous filling. The first mapping is done from a quite arbitrarily shaped conductor set to the upper half-plane with the conductors along the boundary line. The second step is a transformation to a rectangular region with two opposite conductors and magnetic sidewalls to achieve a homogeneous field configuration. The rest of the conductors are transformed into double-sided parallel slits in the magnetic walls. Therefore they do not disturb the homogeneous field if they are given the proper potential. This configuration is used for the computation of the wave impedance matrix. Analysis and synthesis as well is possible by this method.

Characteristric Impedance Analysis of Multi-Conductor Transmission Line of Arbitrary Shape

This paper deals with a method that combines a planar network and a waveguide cavity for use as a power divider. Experimental results for one such power divider with a centre frequency of 12.1 GHz and 15 output ports are presented.

Multi-Terminal Power Dividers Combining Cavity and Stripline Technique

The theory of broadband, non-grounded loads is used for the design of non-grounded attenuators of T and ?x type. Such devices are needed in planar (monolithic) microwave integrated circuits where holes and wrap-arounds are non-desirable. Large bandwidth is achieved for stringent specifications on attenuation and return loss. The proposed methods is based on synthesis in the ?-plane. Mismatch is intendedly used in the design in two ways with differing sign of S11. This fact extends realizability as well.

L. J. Peter Linner

Papers

A Method for the Computation of the Characteristic Immittance Matrix of Multiconductor Striplines with Arbitrary Widths

Design of MIC Broadband Loads and Attenuators

Characteristric Impedance Analysis of Multi-Conductor Transmission Line of Arbitrary Shape

Multi-Terminal Power Dividers Combining Cavity and Stripline Technique

Near-Optimum Design of Bradband, Nn-Grunded Attenuatrs