A variational method for the analysis of inhomogeneous broadside-coupled striplines is described. The data for even- and odd-mode characteristic impedances, effective dielectric constants, and mode phase velocity ratios are presented. It is found that the phase velocity ratio may be varied over the range 1.14 /spl les/ ( V/sub e/ / V/sub 0/) /spl les/ 3.6 for broadside-coupled suspended microstrip lines (BSML) and 0.36 /spl les/ ( V/sub e/ / V/sub 0/) /spl les/ 0.93 for broadside-coupled inverted microstrip lines (BIML) using materials with dielectric constant less than 16 and S/b /spl ges/ 0.05, W/b /spl les/ 2.0. The effect of nonzero strip thickness is also calculated. It is noticed that the effect of thickness is more pronounced for the odd-mode case than for the even mode. Losses are obtained using the incremental inductance rule of Wheeler. The odd-mode attenuation constant is always higher than the even-mode value.

Characteristics of Inhomogeneous Broadside-Coupled Striplines

The scattering parameters for a coupled symmetrical three-Iine system in an inhomogeneous dielectric medium (e.g., microstrip) are derived directly in terms of a set of three orthogonal modes. The obtained results show that the condition for isolation of nonadjacent ports (e.g., ports 1 and 3 in Fig. 1) does not result from putting the corresponding per unit length immittance parameters equal to zero (i.e., z/sub 13/ =y/sub 13/ = 0). The use of such a three-line system as a six-port reflectometer is analyzed in terms of the derived scattering parameters. The reflectometer discussed in this paper allows an unknown impedance to be measured using a standard impedance.

On the Use of a Microstrip Three-Line System as a Six-Port Reflectometer

Quasi-planar realizations of a combline bandpass filter and diplexer using multiple coupled suspended substrate striplines (MCSSSs) have demonstrated good performance at K-band without any tuning. The N MCSSSs excite N zero-cutoff-frequency quasi-TEM modes. A computer-aided filter design approach employing a rigorous spectral domain approach and 2N-port microwave circuit theory accounts for the effects of the N quasi-TEM modes, the couplings through nonadjacent MCSSSs, and cover height. Two 19.5-20.5 GHz MCSSS combline filters with different cover heights have been built and tested to compare their filter characteristics. The reduction in cover height has been found to decrease the amount of nonadjacent coupling through MCSSSs and to result in better filter stopband performance. An 18.5-19 GHz and 20-20.5 GHz MCSSS diplexer is also presented. All the measured results for the combline filters and diplexers agree well with the theoretic calculations. >

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K-band quasi-planar tapped combline filter and diplexer

Symmetric n-way power dividers (and combiners) are needed to feed multi-element antennas and to combine the output powers of a number of solid-state amplifiers and oscillators over a broad frequency range. We present a unified method of analysis for computing the frequency responses of symmetric, n-way power dividers of the Wilkinson, radial, and fork types, whose transmission lines are allowed to be coupled and nonuniform and may be surrounded by an inhomogeneous dielectric medium. The method is based on the analysis of a simple one- or two-port network for each of the n eigenmodes of the power-divider structure, resulting in a considerable improvement in the speed of computation, as well as a sizable reduction in storage requirements, as compared to a standard method of nodal analysis. Furthermore, the aforementioned one- and two-port networks facilitate the design and optimization of the power dividers over a desired frequency band.

Computation of the frequency response of a class of symmetric N-way power dividers

This paper analyzes the propagation parameters of the general, shielded, broadside, edge-coupled, symmetric strip transmission line using the transverse transmission line method combined with the variational technique in the space domain. A simple approximation to the charge distribution on the conducting strip is assumed. Extensive design data on the characteristic impedances, effective dielectric constants are generated for a) broadside, edge-coupled, homogeneous striplines, b) broadside, edge-coupled, microstrip lines, c) broadside, edge-coupled, microstrip lines with inverted dielectric. The effect of the shielding side walls on the characteristic impedances is investigated. The results presented should find application in the design, fabrication of directional couplers, filters having complex electric responses.

Broadside, Edge-Coupled, Symmetric Strip Transmission Lines

Parallel coupled microstrip lines in an inhomogeneons medium are studied. The quasi-static capacitance is shown to be linear with regard to the dielectric constant epsilon/sub r/ simplifying the formalism used for analyzing microstrip filters. The electromagnetic advantages of the homogeneous medium carry over to the inhomogeneous medium. This result is obtained by equalizing all the velocities of the propagation modes.

E. Rivier

Papers

Parallel Line Microstrip Filters in an Inhomogeneous Medium