Ultra-wideband (from DC to 110 GHz) CPW to CPS transition

A new ultra-wideband, low-loss and small-size coplanar waveguide (CPW) to coplanar strip (CPS) transition which can be used from DC to 110 GHz is presented. The proposed transition connects CPW with CPS by the reformed air-bridge. Two ground planes of CPW are tied at their ends by a line and the centre of the line is connected to the ground strip of CPS by another line. Owing to the symmetry of the proposed structure, the currents of two ground planes of CPW are combined with the same phase and transferred to the ground strip of CPS. With height of 3 μm, the signal line of CPW passes over two connecting lines and is connected to the signal strip of CPS. For the back-to-back transition structure, insertion loss <1 dB and return loss >15 dB are obtained from 0.5 to 110 GHz     

Square-wave propagation along coupled coplanar transmission line

Results of modelling square-wave propagation along coupled coplanar transmission line with grounded centre strip conductor are presented. Improved agreement between numerical and experimental data for the near- and far-end crosstalk voltages has confirmed practical significance of inclusion of multimode propagation in non-ideally grounded coplanar lines.     

Strip Line with Rectangular Outer Conductor and Three Dielectric Layers

A general method is proposed for analyzing the transmission line characteristics of strip lines with rectangular outer conductor and multidielectric layers within a TEM wave approximation. This method uses Green's function for formulating the problem and a variational principle for obtaining practical solutions. The case of the microstrip line is first discussed, and numerical results are found to be consistent with other theories and experiments. The case of strip lines with a rectangular outer conductor and three dielectric layers is examined for various combinations of dielectric materials. Other applications of Green's function and the theoretical limitation of this method are also described.     

Propagation characteristics of superconducting microstrip lines

The modified spectral-domain approach is applied to study the propagation characteristics of high temperature superconducting microstrip lines whose signal strip and ground plane are of arbitrary thickness. In this study, numerical results for effective dielectric constant, attenuation constant, and strip current distribution are presented to discuss the effects due to frequency, temperature, strip thickness, and substrate loss tangent. In particular, the conductor and dielectric attenuation constants of superconducting microstrip line are depicted separately to discuss the mechanism of the line losses. A comparison with published theoretical and experimental results is also included to check the accuracy of the new approach's results     

Characterization of shielded coplanar stripline discontinuities by the space domain integral equation technique

This paper presents a general fullwave analysis for the problem of shielded coplanar stripline (CPS) discontinuities. The analysis is based on the electric field space domain integral equation (SDIE) approach. The Green's functions pertinent to the problem are formulated to take into consideration any number of planar stratified dielectric layers. The method of moments is applied to numerically solve the SDIE for the unknown current distribution over the CPS conductor surface. Numerical results for CPS open-end, series-gap, CPS resonator, and straight CPS series stubs are presented. Most of the included SDIE results are compared with quasi-transverse electromagnetic results, finite difference time domain results, or complex image technique results     

Analysis of a new configuration of coplanar stripline

A new configuration of coplanar stripline is presented and analyzed. This configuration is derived by augmenting coplanar stripline (CPS) with electrically wide lateral ground planes on either side of the balanced pair of signal lines. The ground planes should replace line-to-line coupling in complex circuits and eliminate the TE₀ parasitic dielectric slab waveguide mode. Also, the spacing from signal lines to ground planes can be adjusted to change the characteristic impedance. Spectral domain analysis is used to calculate the dispersion characteristics of this transmission line. Analytical expressions for quasi-static values of the line are presented. This configuration of CPS should be useful for balanced high-impedance lines in monolithic microwave integrated circuit (MMIC) and high speed digital circuits     

Computation of the Characteristics of Coplanar-Type Strip Lines by the Relaxation Method (Short Papers)

The characteristics of new strip lines (i.e., a single strip conductor and a two symmetrical strip-conductor coplanar-type strip line, which consist of single- or two-center strip conductors and ground plates on a dielectric substrate and outer ground conductor) are calculated by the relaxation method. The effect of the outer ground conductor on these lines is analyzed, and the characteristic impedance and velocity ratio are determined. The characteristic impedance is determined experimentally, and the maximum values of the discrepancies compared with the calculated values of each of the lines are 2.0-3.0 percent.     

Full-wave analysis of coplanar waveguides by variational conformalmapping technique

A new full-wave analysis of coplanar waveguides is presented. The modified mapping technique of C.P. Wen (1969) is used to map the original infinite domain into a finite image domain and also to account for the singularity of fields near the conductor edges. The finite thickness of the dielectric substrate is considered together with the assumptions of lossless guides and negligible metallization thickness. The current distributions on the center signal strip as well as the tangential electric fields over the slot along the air-dielectric interface are examined. Numerical results for the frequency-dependent effective dielectric constants and characteristic impedances of coplanar waveguides are presented. Particular attention is given to the electric field distributions over the air-dielectric interface of slots and the current distributions of the signal strip     

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

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     

Full wave analysis of conductor-backed and multi-layer high-T c superconducting coplanar waveguide

Dispersions, attenuation and characteristic impedance of shielded conductor-backed coplanar waveguide(CBCPW) and shielded three-layer coplanar waveguide (CPW) with finite conductor thickness as well as their superconducting applications are calculated. The method of lines(MoL) is employed to analyze these coplanar waveguides. The analysis is validated by a comparison of the calculated results with those published previously. Effects of finite width of grounded strip for a CPW are considered. Extensive investigation of the numerical convergence for calculation of the characteristic impedance is also described.     

Coplanar Waveguide: A Surface Strip Transmission Line Suitable for Nonreciprocal Gyromagnetic Device Applications

A coplanar waveguide consists of a strip of thin metallic film on the surface of a dielectric slab with two ground electrodes running adjacent and parallel to the strip. This novel transmission line readily lends itself to nonreciprocal magnetic device applications because of the built-in circularly polarized magnetic vector at the air-dielectric boundary between the conductors. Practical applications of the coplanar waveguide have been experimentally demonstrated by measurements on resonant isolators and differential phase shifters fabricated on low-loss dielectric substrates with high dielectric constants. Calculations have been made for the characteristic impedance, phase velocity, and ripper bound of attenuation of a transmission line whose electrodes are all on one side of a dielectric substrate. These calculations are in good agreement with preliminary experimental results. The coplanar configuration of the transmission system not only permits easy shunt connection of external elements in hybrid integrated circuits, but also adapts well to the fabrication of monolithic integrated systems. Low-loss dielectric substrates with high dielectric constants may be employed to reduce the longitudinal dimension of the integrated circuits because the characteristic impedance of the coplanar waveguide is relatively independent of the substrate thickness; this may be of vital importance for Iow-frequency integrated microwave systems.     

A low-impedance coplanar waveguide using an SrTiO3 thinfilm for GaAs power MMIC's

A novel structure for coplanar-waveguide transmission lines with low impedance and low loss is demonstrated in this paper. The new structure simply has a high dielectric SrTiO₃ thin film underneath the coplanar conductors. Due to the high dielectric constant of SrTiO₃, the coplanar line exhibited characteristic impedance as low as 18 Ω with a slot width of 5 μm and the center conductor width of 50 μm, while a conventional coplanar line on GaAs showed only 30 Ω with the same configuration. The newly developed coplanar structure is easily applicable for present GaAs monolithic-microwave integrated-circuit (MMIC) technology, especially for power MMIC's and low-impedance devices     

Coplanar transmission lines on thin substrates for high-speedlow-loss propagation

We investigate the attenuation and phase velocity characteristics of coplanar strip (CPS) transmission lines designed for high-speed, low-loss propagation at sub-THz frequencies. Photoconductor switches driven by femtosecond optical pulses were used to generate propagating picosecond electrical transients. External electrooptic sampling was used to measure the time-domain impulse-response characteristics with subpicosecond time resolution. The finite-difference transmission-line-matrix (FD-TLM) numerical method was used to model picosecond pulse propagation on identical transmission lines. The experiment and the numeric simulations have clarified nonquasistatic high-frequency effects and were shown to agree over a 500 GHz frequency range. Additionally, analytic quasi-static velocity and characteristic impedance formulas have been verified and their frequency range of validity established for the investigated CPS geometries. Radiation into the substrate is the dominant loss mechanism at frequencies above ~100 GHz for the CPS lines on thick substrates. CPS transmission line fabrication on thin substrates has been proposed as a method for reducing high-frequency loss and increasing the microwave propagation velocity. CPS transmission lines fabricated on 8-μm-thick Si membranes have been studied and demonstrated to possess the desired high-speed, low-loss properties     

Analytical analysis of circular-shaped microshield and conductor-backed coplanar waveguide

In this paper, a new type of circular-shaped microshield and conductor-backed coplanar waveguide is proposed. Analytic closed-form expressions for characteristic impedance and effective dielectric constant for the new line are obtained using conformal mapping method under the assumption of pure-TEM propagation and zero dispersion. The new waveguide proposed by this paper can reduce radiation to much less than the conventional coplanar waveguide and microstrip, and can reduce the current concentration at both the edges of the strip conductor.     

Propagation characteristics of coplanar-type transmission lineswith lossy media

Lossy coplanar-type transmission lines are analyzed based on the hybrid-mode formulation by combining the spectral-domain approach with the perturbation method. Introducing a finite thickness of metallization and choosing the proper basis functions for the thick conductor model prevent the integrals used for calculating the conductor losses from becoming singular when evaluated at the conductor edge. An orthogonality relation is used to reduce the double infinite or semi-infinite integral to a single integral, thus reducing the computation effort drastically. Numerical computations by new basis functions for the thick conductor show convergence rates as fast as those for the zero-thickness cases. Numerical results include the effective dielectric constants, characteristic impedances, and total losses (conductor and dielectric losses) for slot lines and symmetrical and asymmetrical coplanar waveguides     

Characterization of MIS structure coplanar transmission lines forinvestigation of signal propagation in integrated circuits

A full-wave analysis of metal-insulator-semiconductor (MIS) structure micron coplanar transmission lines on doped semiconductor substrates is carried out using a finite-difference time-domain approach. Metal conductor loss is taken into account in the analysis. Line parameters and electromagnetic field distributions are calculated over a wide frequency range involving slow-wave and dielectric quasi-transverse-electromagnetic mode limits. Measurements of these line parameters, varying substrate resistivity from 1 to 1000 Ω-cm, in the frequency range up to 40 GHz are also presented, and these agree with the analysis quite well. On the basis of these results, an equivalent circuit line model is induced and some considerations on the relationship between line structure and properties made     

Computation of Coplanar-Type Strip-Line Characteristics by Relaxation Method and its Application to Microwave Circuits

The characteristics of new strip lines [i.e., a single strip-conductor coplanar-type strip line (S-CPS), a two symmetrical strip-conductor coplanar-type strip line (T-CPS), and a coupled strip-conductor coplanar-type strip line (C-CPS), which consists of single two-center strip conductors or coupled strip conductors and ground plates on a dielectric substrate and outer ground conductor] are calculated by the relaxation method. The effect of the outer ground conductor and side wall on these lines is analyzed and the characteristic impedance and phase-velocity ratio are determined. The characteristic impedance is determined experimentally and the maximum values of the discrepancies compared with the calculated value of each of the lines are 2.0-3.0 percent. Application examples of the coplanar-type strip line to microwave transistor amplifier and parallel-coupled filter are shown. A transistor amplifier of small size, light weight, wide bandwidth, and improved reliability is achieved. A parallel-coupled filter small in size (reduction ratio is more than 50 percent), with good frequency symmetry and featuring easy resonance frequency fine tuning is obtained.     

Characteristic Impedances of Multiconductor Strip Transmission Lines

The design of certain log-periodic microwave circuit elements requires a knowledge of the characteristic impedances of a system of four-coupled strip transmission lines. The system of four strip conductors between parallel ground planes is capable of supporting four different TEM modes which have different characteristic impedances. In this paper, the characteristic impedances of the four modes are determined by a variational method. The variational solution is an upper bound to the exact characteristic impedance of the line. In general, the coplanar strip conductors are located at an arbitrary (but identical) displacement from the parallel ground planes. When the separation between the broadside-coupled strips is precisely one-half the spacing between the parallel ground planes, two of the mode impedances may be determined exactly by means of conformal mapping. The variational solutions are compared to the exact solutions for this special case. Because of the "cell image" principle which holds for the problem, the mode solutions presented here also apply to various single- and two-conductor strip transmission lines with arbitrary displacements. As a result, solutions for the following strip line configurations are available from the analysis: a single strip conductor in a trough, or between parallel ground planes; two coplanar strips between ground planes; two broadside-coupled strips in a trough, or between parallel ground planes. An extensive set of curves are presented which show the characteristic impedances of the four modes as a function of the relative dimensions of the strip transmission line.     

A 0–55-GHz Coplanar Waveguide to Coplanar Strip Transition

A broadband coplanar waveguide (CPW) to coplanar strip (CPS) transmission line transition directly integrated with an RF microelectromechanical systems reconfigurable multiband antenna is presented in this paper. This transition design exhibits very good performance up to 55 GHz, and uses a minimum number of dissimilar transmission line sections and wire bonds, achieving a low-loss and low-cost balancing solution to feed planar antenna designs. The transition design methodology that was followed is described and measurement results are presented.     

An Analysis of Gap in Microstrip Transmission Lines

Although microstrip transmission lines have been widely used in microwave integrated circuits, the discontinuity structures in the microstrip transmission lines such as a gap, an abruptly ended strip conductor, and so on, have hardly been analyzed. An analytical method and numerical results for a gap capacitance in the microstrip transmission line are described. The equivalent circuit parameters are formulated with three-dimensional Green's functions, based on a variational principle. The numerical results are in good agreement with the published experimental data. The fringing effect of an abruptly ended strip conductor is also investigated.