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     

Embedded microstrip interconnection lines for gigahertz digitalcircuits

Transmission line structures are needed for the high-performance interconnection lines of GHz integrated circuits (ICs) and multichip modules (MCMs), to minimize undesired electromagnetic wave phenomena and, therefore, to maximize the transmission bandwidth of the interconnection lines. In addition, correct and simple models of the interconnection lines are required for the efficient design and analysis of the circuits containing the interconnection lines. In this paper, we present electrical comparisons of three transmission line structures: conventional metal-insulator-semiconductor (MIS) and the embedded microstrip structures-embedded microstrip (EM) and inverted embedded microstrip (IEM). In addition, we propose closed-form expressions for the embedded microstrip structures EM and IEM and validate the expressions by comparing with empirical results based on S-parameter measurements and subsequent microwave network analysis. Test devices were fabricated using a 1-poly and 3-metal 0.6 μm Si process. The test devices contained the conventional MIS and the two embedded microstrip structures of different sizes. The embedded microstrip structures were shown to carry GHz digital signals with less loss and less dispersion than the conventional MIS line structures. S-parameter measurements of the test devices showed that the embedded microstrip structures could support the quasi-TEM mode propagation at frequencies above 2 GHz. On the other hand, the conventional MIS structure showed slow-wave mode propagation up to 20 GHz. More than 3-dB/mm difference of signal attenuation was observed between the embedded microstrip structures and the conventional MIS structure at 20 GHz. Finally, analytical RLCG transmission line models were developed and shown to agree well with the empirical models deduced from S-parameter measurements     

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.     

Dissipation Loss Effects in Isolated and Coupled Transmission Lines

This paper describes a computer-aided analysis of dissipation losses in uniform isolated or coupled transmission lines for microwave and millimeter-wave integrated-circuit applications. The analysis employs a quasi-TEM model for isolated transmission lines and for the even- and odd-mode transmission lines associated with coupled-line structures. The conductor and dielectric losses are then related to equivalent charge density distributions, which are evaluated using a method-of-moments solution. The transmission lines treated by this analysis may contain any number of Iossy conductors and inhomogeneous dielectrics, consisting of any number of different homogeneous dielectric regions. A development is provided to explicitly relate the four-port terminal-electrical performance of directional couplers to evaluated even- and odd- mode loss coefficients. Examples of evaluated losses are presented in graphical form for isolated lines of inverted microstrip and trapped inverted microstrip and edge-coupled microstrip with a dielectric overlay. The analysis accuracy has been confirmed using microstrip and coplanar waveguide configurations. A comparison is made of the total loss characteristics for microstrip, coplanar waveguide, inverted microstrip, and trapped inverted microstrip. Calculations are compared with measurements for the coupled-line structure. Accuracy of the solution and suggested refinements are discussed. Five computer programs are documented.     

The influence of finite conductor thickness and conductivity onfundamental and higher-order modes in miniature hybrid MIC's (MHMIC's)and MMIC's

The effect of finite metallization thickness and finite conductivity on the propagation characteristics of conductor-backed CPW on thin substrate is rigorously analyzed. A self-consistent approach is used together with the method of lines (MoL) to determine the propagation constant, losses and field distribution of the fundamental and first two higher-order modes in coplanar waveguides (CPWs) with finite metallization thickness and lossy backmetallization. The method used is general and can be applied to miniature MHMICs and MMICs including lossy semiconductor substrate. It is shown that the onset of higher-order modes limits the usable frequency range of conductor-backed CPWs. The analysis also includes microstrip transmission lines on thin substrate material. It is demonstrated that a resistive strip embedded into the microstrip ground plane may potentially be useful in the design of integrated planar attenuators     

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.     

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     

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     

Perforated microstrip structure for miniaturising microwave devices

The perforated slow-wave microstrip is proposed for high-frequency microwave devices and characterised experimentally and theoretically up to 7 GHz. The perforated structure is realised with a periodic-inductive-section-maintained uniform edge-shape. The slow-wave factor is demonstrated to be 1.2 times larger than that of a conventional microstrip over a wide frequency range. The perforated slow-wave microstrip shows reduction of physical length and superior quality-factor. The proposed structure is easier to fabricate than other slow-wave structures, which require multilayer substrates     

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     

Suppression of mode coupling in conductor-backed asymmetric coplanar strips using slow-wave electrodes

Shorted-ground conductor-backed asymmetric coplanar strips support unwanted noncoplanar modes that adversely affect the performance of such transmission lines at higher frequencies. It is shown that coupling from the desired coplanar mode into the noncoplanar modes can be suppressed using slow-wave electrodes. This suppression scheme is verified by measuring the S-parameters of both conventional and slow-wave transmission lines of this type in the 0.05-50 GHz range.     

基于电磁带隙结构的微带天线小型化设计

提出了一种确定电磁带隙结构慢波波长的分析方法,利用电磁带隙结构支持慢波传播的特性,设计了一种小型化微带天线。以"*"型电磁带隙结构作为接地板,增大了天线的相对电长度。天线工作于2 GHz,相对带宽为2.57%,最大增益为5.45 dB,相比于传统天线,该天线的尺寸减小了40%,带宽有了一定的提高。最后,进行了天线的实物制作和测试,天线的实测结果和仿真结果吻合良好。     

基于谐振器慢波传输线的小型化宽阻带谐波抑制功分器

该文提出一种基于谐振器慢波传输线的小型化宽阻带谐波抑制功分器,该谐振器慢波传输线由矩形谐振器、T型谐振器和蛇形线构成,来取代功分器中的1/4波长传统微带传输线。所设计制作的功分器,其尺寸仅为传统微带功分器的37.4%。实验结果表明,该功分器回波损耗大于10 dB的带宽范围为0.1～1.19 GHz,在2.2～11.05 GHz频率范围内衰减大于20 dB,具有较宽的阻带从而具有抑制谐波效果。仿真和测试结果较为吻合,验证了所提设计方法的有效性。     

Air-Cavity Transmission Lines on Anodized Aluminum for High-Performance RF Modules

In this study, we form air-cavity transmission lines on anodized aluminum substrates. The fabricated transmission lines are microstrip, grounded CPW, and microshield structures. Thick anodized alumina is used as the post of the suspending structures, and it is realized very easily using selective chemical wet-etching. The insertion losses of the fabricated transmission lines on the anodized aluminum are within a range of 0.2-0.26 dB/mm, and they improve greatly after realizing air-cavity structures to 0.043-0.076 dB/mm at 40 GHz.     

Design of Interdigitated Capacitors and Their Application to Gallium Arsenide Monolithic Filters

Theoretical expressions for the interelectrode capacitance and conductor losses for an array of microstrip transmission lines are presented. The effect of finite conductor thickness is included in the analysis by introducing equations for the effective width of the transmission lines. Good agreement between theory and experiment is observed up to 18 GHz. Experimental results obtained from a lumped-element GaAs monolithic bandpass filter are in excellent agreement with theory. The filter has 1.5-dB insertion loss at 11.95 GHz and greater than 22-dB loss in the stopband. The filter measures 0.58x 1.3x0.203 mm.     

Slow-wave directional coupler and its applications

The directional coupler and the traveling-wave directional filter made of coupled slow-wave microstrip lines are proposed and their characteristics discussed. These structures exhibit interesting characteristics not readily available in conventional transmission lines.     

Invited paper Characteristics of travelling waves along the non-linear transmission lines for monolithic integrated circuits: a review

A general analysis of non-linear wave propagation along transmission lines with voltage-dependent capacitance is presented. In particular, slow-wave structures like MIS and Schottky-barrier strip lines are examined. A spatial periodicity is included explicitly. The theoretical treatment is based on suitable equivalent circuits leading to characteristic wave equations. With regard to practical devices, the solutions show a variety of different phenomena as determined by the parameters of the non-linearity, dispersion and dissipation and the boundary conditions. Experimental results performed on a slow-wave model line are included.     

The Traveling Wave IMPATT Mode: Part II -- The Effective Wave Impedance and Equivalent Transmission Line

The coupling between a microstrip and a distributed IMPATT diode was investigated in a field analysis. An effective wave impedance in the traveling wave diode can be defined as the ratio of the space-average transverse electric and magnetic fields. This impedance is related to an effective characteristic impedance by a geometry factor. Thus the coupling question is reduced to the coupling between two transmission lines. In addition the diode is modeled in an equivalent transmission line. The equivalent series impedance and shunt admittance are found. The shunt admittance is approximately equal to the admittance (per unit length) of a discrete diode of identical doping profile. The coupling analysis presented here seems applicable to microstrip interfaces to traveling wave structures other than the IMPATT diode.     

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