Propagation characteristics of MIS transmission lines withinhomogeneous doping profile

The authors present a hybrid-mode analysis of slow-wave MIS (metal-insulator-semiconductor) transmission lines with a gradually inhomogeneous doping profile. In general it was found that, in comparison with homogeneously doped semiconductor layers, a Gaussian-type doping distribution results in lower losses for the slow-wave mode in both thin- and thick-film MIS CPWs. While the effect of the doping profile is more pronounced in thin-film structures which support a slow-wave mode only up to 3 GHz, it is less significant in thick-film structures. On the other hand, numerical analysis indicates that thick-film structures can support a slow-wave mode at moderate loss up to 40 GHz. The behavior of MIS microstrip lines is similar to that of MIS CPWs, except that for thick-film transmission lines an increase in losses can be observed when the doping profile becomes inhomogeneous. The numerical investigation was carried out using the method of lines. Several transmission lines have been investigated, and results are presented for microstrip, coupled microstrips, and coplanar lines     

Quasi-TEM Analysis of "Slow-Wave" Mode Propagation on Coplanar Microstructure MIS Transmission Lines

We present a simple quasi-TEM analysis of "slow-wave" mode propagation on micron-size coplanar MIS transmission lines on heavily doped semiconductors and compare theoretical results with measurements on four such structures at frequencies from 1.0 to 12.4 GHz. Excellent agreement is found, which shows that the "slow-wave" mode propagating on these transmission lines is, in fact, a quasi-TEM mode. Relatively low-loss propagation along with significant wavelength reduction is observed. Conduction losses of the metal, which have been tacitly ignored in previously published "full-wave" treatments of "slow-wave" mode propagation, are included in the theory and are shown to dominate the attenuation at frequencies below 25 GHz and to still be significant at frequencies up to at least 100 GHz.     

A vertically periodic defected ground structure and its application in reducing the size of microwave circuits

The microstrip and coplanar waveguide transmission lines combined by a vertically periodic defected ground structure (VPDGS) are proposed. The slow-wave effect, equivalent circuit, and the performances are shown. As an application example, VPDGS is adopted in the matching networks of an amplifier for size-reduction. Two series microstrip lines in input and output matching networks of the amplifier are reduced to 38.5% and 44.4% of the original lengths, respectively, due to the increased slow-wave effects, while the amplifier performances are preserved.     

New prospective coplanar metal-insulator-semiconductor (MIS)monolithic structure

Research work on various MIS transmission lines is well documented. Useful slow-wave propagation with low loss is always exhibited in recently proposed lower frequency ranges (several GHz). The author is concerned with the essential properties of the micrometre-size coplanar MIS lines. A new loss-reducing monolithic MIS is proposed with reference to physical considerations to ensure a low-cost mechanism     

A spiral-shaped defected ground structure for coplanar waveguide

The authors present a spiral-shaped defected ground structure for coplanar waveguides (DGSCPW), which can be used as a kind of periodic structure for a planar transmission line. The proposed spiral-DGSCPW adopts spiral-shaped defects on both ground planes of CPW. Due to the spiral-shaped defects, the equivalent shunt inductance and slow-wave effects increase more rapidly than the standard CPW or CPW lines combined with the conventional PBG. The modeling and analysis to extract the equivalent circuit, increased slow-wave factor, and simulated and measured performances 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     

High temperature superconducting slow-wave coplanar transmissionlines with normal-metal crossbars

A novel superconducting slow-wave transmission line has been prepared by overlaying a superconducting coplanar waveguide with normal metal crossbars. The crossbars increase the energy storage along the transmission line, reducing the line's group velocity allowing for shorter delay lines. Additionally, the cross-sectional dimensions of the line are smaller than typical transmission line structures, allowing for a further reduction of delay line size. Measurements show a group velocity of about 0.12 the speed of light with low dispersion, a 25 Ω characteristic impedance, and moderate transmission loss. Because the group velocity is largely independent of any properties of the superconductor, these transmission lines exhibit excellent temperature stability and delay reproducibility     

Systematic determination of the propagation characteristics ofcoplanar lines on semiconductor substrate

A method allowing the systematic determination of the propagation characteristics of micron-size waveguides and overcoming the influence of feeding access discontinuities is presented. The complex propagation constant and characteristic impedance of a slow-wave Schottky contact coplanar line are determined in the 1 to 26 GHz frequency range under different DC bias conditions. This method is successfully used to characterize the Schottky contact coplanar line of micron size under drastic conditions, that is, high value of slow-wave factor, significant attenuation, dispersive transmission line, and strong mismatches between feeding line and device under test. Comparisons with transmission line model theoretical results show very good agreement, despite the large slow-wave factor, attenuation, and dispersion of the waveguide. The electric schemes of the feeding access discontinuities are also presented     

High-Q Slow-Wave Coplanar Transmission Lines on 0.35 $mu$m CMOS Process

In this letter, experimental results and trends for shielded coplanar waveguide transmission lines (S-CPW) implemented in a 0.35 $mu$m CMOS technology are provided. Because of the introduction of floating strips below the CPW transmission line, high effective dielectric permittivity and quality factor are obtained. Three different geometries of S-CPW transmission lines are characterized. For the best geometry, the measured effective dielectric permittivity reaches 48, leading to a very high slow-wave factor and high miniaturization. In addition, measurements demonstrate a quality factor ranging from 20 to 40 between 10 and 40 GHz, demonstrating state-of-the-art results for transmission lines realized in a low-cost CMOS standard technology.      

Time-domain response of MIS coplanar waveguides for MMICs

An MIS coplanar waveguide propagating a slow-wave mode has been characterised in the time domain. The theoretical analysis proposed to obtain the time-domain response of the line gives results in good agreement with measurements. The circuit analysis used is suitable for the determination of spurious propagation effects, inherent to the use of miniature waveguides encountered in MMICs, such as Schottky contact coplanar lines and coupled microstrip lines laid on MIS substrates.     

Full-wave analysis of integrated transmission lines on layered lossy media

Cohn's method of analysis of the slot line on a dielectric substrate is extended to the case of integrated lines on a lossy inhomogeneous substrate. The slow-wave characteristics of the metal-insulator-semiconductor coplanar waveguide for MMIC applications are calculated and found to be in good agreement with the experiments.     

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     

Analysis of printed transmission lines for monolithic integrated circuits

Planar transmission lines formed with MIS and Schottky barrier contacts are analysed based on the spectral domain technique. Depending on the frequency and the resistivity of the substrates, three different types of fundamental modes are predicted. The calculated slow-wave factors and attenuation constants agree well with experimental results.     

Miniaturized coplanar waveguide bandpass filters using multisection stepped-impedance resonators

We report several types of coplanar waveguide tri-section stepped-impedance resonator (SIR) structures that offer further size reduction compared to the conventional two-section SIRs. In addition, the tri-section SIRs provide flexibility of introducing effective capacitive coupling to the ground lines for realizing slow-wave structures. The slow-wave effect can be used to implement more compact bandpass filters. The principles of achieving size reductions using tri-section SIRs are described and confirmed by simulation results. To demonstrate the effectiveness of the proposed tri-section SIRs in size reduction, the tri-section SIRs with slow-wave effects were implemented in a two-pole directly coupled bandpass filter and a fourth-order quasi-elliptic bandpass filter with reduced size. The measured results matched well with the theoretical prediction.     

Characterization of Co-Planar Silicon Transmission Lines With and Without Slow-Wave Effect

Co-planar lines on silicon substrates with and without slow-wave effect are characterized using time-domain reflectometry (TDR) and vector network analyzer (VNA) measurements, and simulated using a proposed nonphysical resistance-inductance-conductance-capacitance (RLGC) model. The silicon co-planar lines are characterized based on comparison to package transmission lines. Co-planar silicon lines without slow-wave mode are modeled in the same way as package transmission lines, but co-planar lines with slow-wave mode are modeled in a different way from package transmission lines. Hence, a nonphysical RLGC model including slow-wave mode is proposed along with the extraction method from VNA measurements. Simulation results correlate well with time- and frequency-domain measurements for the co-planar silicon lines.     

Characteristics of microstrip transmission lines withhigh-dielectric-constant substrates

An efficient numerical code is developed from a full-wave analysis in the Fourier transform domain to determine the characteristics of a single-strip or multistrip coplanar transmission line. Modes of both even and odd symmetries are included. The impedance of the transmission line is calculated using the power-current equivalent model. Coupling constants between the even and the odd modes are also calculated. Results are provided for a shielded two-strip coupled microstrip transmission line on high-dielectric-constant substrate such as lanthanum aluminate with applications to superconducting transmission lines     

Guided-wave characteristics of periodic coplanar waveguides with inductive loading - unit-length transmission parameters

Periodic coplanar waveguides (CPWs) with inductive loading are thoroughly studied by resorting to unit-length transmission parameters, i.e., propagation constant and characteristic impedance, of an equivalent dispersive and/or lossy transmission line. The admittance-type method of moments (MoM) is at first formulated to full-wave modeling of a finite-cell periodic CPW with the two feeding lines and then the short-open-calibration procedure is carried out to deembed the two-port ABCD matrix of the core periodic CPW section. Thus, the above two parameters can be extracted from the MoM simulation to exhibit their guided-wave characteristics, i.e., slow-wave and bandstop behaviors. It is demonstrated for the first time that, within the bandstop or bandgap, the propagation constant must become complex with a nonzero attenuation constant, while the characteristic impedance appears purely imaginary. Three periodic CPW circuits with six finite cells are then characterized on a basis of the transmission-line theorem and the derived S-parameters are validated by Momentum simulation and RF measurement.     

Compact superconducting coplanar meander line filters

Novel slow-wave coplanar waveguide (CPW) filters using high temperature superconductor (HTS) films are presented. Both half-wavelength and quarter-wavelength resonators are used in the filter topology. The miniaturisation is achieved using meander structure and interdigital grounding lines. A 3-pole Chebyshev bandpass filter has been designed, fabricated and studied. The untuned experimental results are in very good agreement with the simulated responses.     

Analysis of the dispersion characteristics of slow-wave structures with two microwave propagation channels

Models of rectangular and axially symmetric resonator slow-wave structures, which are built using transmission matrix for determining the characteristics of the slow-wave structures in different operation modes, are investigated. Elements of the transmission matrix are determined from the results of 3D simulation with the use of the HFSS software. In the analysis of the dispersion characteristics, slow-wave structures with two microwave propagation channels are studied and simulated using a 4×4 transmission matrix.     

Characteristics of coplanar transmission lines on multilayersubstrates: modeling and experiments

Characteristics of coplanar transmission lines on multilayer substrates expressed in analytic formulas have been obtained using conformal mapping. The accuracy of these formulas has been verified experimentally on a variety of coplanar transmission lines using differential electro-optic (DEOS) sampling. For coplanar waveguides, the theory differs from the experiment by less than 3%; for coplanar striplines, the differences are less than 6%