Coupled mode analysis of a finline

A theoretical analysis of a unilateral finline loaded with arbitrary inhomogeneous lossy dielectric material is presented. The rigorous coupled-mode approach is used. The electromagnetic field in the line is expressed in terms of the modes of a ridged waveguide, and the problem is transformed to a matrix eigenvalue equation. Approximate expressions are derived for investigating the properties of the fundamental mode in finlines loaded with dielectric slabs. Dispersion characteristics, the characteristic impedance, and the attenuation due to dielectric losses and the finite conductivity of the metal coating are computed for various line configurations. The numerical results are compared to data obtained by means of the spectral-domain method, proving the validity and usefulness of the proposed approach     

The effect of dielectric loss in FDTD simulations of microstripstructures

The importance of dielectric losses in planar microstrip structures is evaluated with the finite-difference time-domain (FDTD) method. This analysis was previously not possible in many FDTD simulators due to a lack of absorbing boundary conditions (ABCs), which appropriately terminate air/dielectric interfaces for which the dielectric is lossy. The newly proposed lossy two-time derivative Lorentzian material (L2TDLM) model ABC allows for these terminations and is presented and implemented here for three-dimensional FDTD simulations. The effect of dielectric losses on several well-known planar microstrip structures is evaluated. It is shown that the inclusion of these losses in FDTD simulations, which is facilitated by the L2TDLM ABC, is, in fact, important to predict the performance of resonant structure on lossy dielectric substrates     

Electromagnetic coupling of coplanar waveguides and microstriplines to highly lossy dielectric media

The spectral-domain technique is utilized to analyze the coupling characteristics of coplanar waveguides and microstrip lines coupled with multilayer lossy dielectric media. Numerical results illustrating the dispersion characteristics of coplanar and microstrip lines, as well as the various electric field components coupled to highly lossy dielectric media, are presented. It is shown that the presence of a superstrate of lossless dielectric between the coplanar waveguide and the lossy medium plays a key role in setting up an axial electric field component that facilitates leaky-wave-type coupling to the lossy medium. The thickness of the superstrate relative to the gap width in the coplanar waveguide is important in controlling the magnitude of this axial electric field component. The coupling characteristics of the microstrip and coplanar lines are compared, and results generally show improved coupling if coplanar waveguides are utilized. Values of the attenuation constant α are higher for coplanar waveguide than for microstrip line, and for both structures α decreases with frequency     

Rectangular resonators in inverted microstrip and suspended microstrip

Resonant frequency characteristics of rectangular resonators in a generalized shielded suspended substrate line are analysed using a rigorous spectral domain technique. The computed dominant mode resonant frequency of rectangular resonators in a suspended microstrip with centred dielectric, inverted microstrip and suspended microstrip are presented as a function of various structural parameters. These characteristics are distinct from those obtained for a conventional microstrip rectangular resonator. Experiments are carried out in the frequency range 4-18 GHz to verify the computed resonant frequencies for a suspended microstrip with a centred dielectric using first-order basis functions. The results should find applications in the design of inverted microstrip and suspended microstrip passive microwave and millimetre wave integrated circuits.     

Space domain analysis of micro-IDG structures

The microstrip loaded inset dielectric waveguide has been proposed as a transmission medium alternative to microstrip, and as a useful antenna medium at X-band and millimetric frequencies. In the present analysis we consider the case where a multi-layer, multi-conductor microstrip circuit may be housed within inset dielectric waveguide. A generalised transverse resonance diffraction method is developed in the space domain for analyzing such structures. Experimental and theoretical results for the propagation characteristics of the fundamental and first higher order mode of a few different configurations are presented showing good agreement     

Slot excitation of the dielectric disk radiator

Dielectric disk radiators which are excited by a narrow slot in the ground plane of a microstrip line are investigated. The resonance frequencies of the dielectric disk for the HEM₁₁ mode are computed numerically in the complex frequency plane. From the later results, the actual resonance frequency and the Q-factor are obtained. The dielectric disk is made of a high dielectric constant ceramic material with ϵ_r=22. The radiation patterns and reflection coefficients are measured and presented for several slot lengths and dielectric disk dimensions. The radiation patterns are also computed assuming a magnetic current element, which models the slot and excites the HEM₁₁ mode. Good agreement is obtained between the computed and measured results. The results presented here also demonstrate the viability of this type of antenna, which has high dielectric constants an efficient radiator provided the proper mode is excited     

New high-frequency circuit model for coupled lossless and lossywaveguide structures

A coupled transmission line model describing the two fundamental modes of any two-conductor (above a ground plane or shielded) dispersive or nondispersive lossless waveguide system is given. The model is based on a power-current formulation of the impedances but does not need an a priori supposition about the power distribution over each transmission line. The analysis is extended to lossy structures and to the multiconductor situation. Impedance calculations for a typical coupled microstrip configuration are used to illustrate the approach     

Systematic evaluation and analysis for 60-GHz dielectric resonatorscoupled to a microstrip line on a GaAs substrate

This paper presents the first systematic evaluation and analysis of 60-GHz-band TE_01δ-mode cylindrical dielectric resonators coupled to a microstrip line on a GaAs substrate. The loss components of the unloaded Q are analyzed using simple numerical techniques. The distance between the resonator center and the microstrip line which gives the maximum coupling coefficient is found to be approximately 3/5 of the resonator radius, whose ratio is almost constant for all practical cases. The temperature characteristics are also demonstrated and the origins of temperature dependences of the unloaded Q and the coupling coefficient are discussed. An equivalent circuit model for the dielectric resonator coupled to the microstrip line is presented, whose element parameters can express the dependences of the resonant frequency, the unloaded Q, and the coupling coefficient on the structural parameters and the temperature     

An equivalent transmission-line model containing dispersion forhigh-speed digital lines-with an FDTD implementation

The increase in processor speeds in the last few years has created a growing need for the accurate characterization of waveform propagation on lossy printed-circuit-board (PCB) transmission lines. Due to the dispersive nature of pulse propagation on lossy transmission lines, approximations of the classic transmission-line model can fail in this application (i.e., lossless or DC losses approximations). This paper shows how an equivalent transmission-line model can be used to analyze dispersive transmission lines for high-speed digital applications. The equivalent-circuit elements of this transmission-line model incorporate the frequency dependence of the per unit length impedance and admittance caused by the finite conductivity of the conductors as well as the dielectric losses. We show that these equivalent circuit elements can be readily implemented into finite-difference time-domain (FDTD) transmission-line codes, and we present such a FDTD implementation. S-parameters and pulsed waveforms for a circular wire, coplanar waveguides (CPW) and microstrip lines are shown. Finally, we present approximate expressions for analytically obtaining the resistance and inductance per length of a microstrip line     

Analysis of Microstrip Circuits Coupled to Dielectric Resonators

A lumped element circuit model is introduced to represent coupling between a cylindrical dielectric resonator and a microstrip line. The external Q of the structure is computed and compared to experimental data obtained with three different resonators.     

On the circular polarization operation of annular-ring microstripantennas

Circular polarization (CP) operation of an annular-ring microstrip antenna with a pair of inserted slits at its fundamental TM₁₁ mode is proposed and experimentally investigated. Two examples of the proposed antenna fed using a microstrip line at the inner and outer patch boundaries are studied. Results show that the proposed antenna can have good CP performance and, moreover, the required antenna size at a fixed CP operation can be much less than that of a conventional circularly polarized circular microstrip antenna operated at the TM₁₁ mode. Details of the proposed antenna for CP operation are described and experimental results of the CP performance are presented and discussed     

Modelling of dielectric losses in microstrip patch antennas: application of FDTD method

A frequency dependent complex permittivity is used to describe the dielectric losses of a microstrip patch antenna. The theoretical and experimental results for the usual parameters (input impedance, reflection coefficient and radiation pattern) of a rectangular microstrip patch are compared for a lossy and a nonlossy dielectric. Good agreement is obtained between the experimental measurements and theoretical results when the dielectric losses are considered.<>     

A microstrip phase-trim device using a dielectric overlay

A design procedure is given for a microstrip phase-trim device using a dielectric overlay on a conventional microstrip line. The physical operation of the device is based on the change in the effective dielectric constant of the microstrip line caused by the presence of the dielectric layer on top of the microstrip line. The amount of phase trim produced by the device can be selected by the appropriate choice of dielectric constant, height, and length of the dielectric overlay. An approximate expression is given for the effective dielectric constant of the microstrip line as a function of the dielectric constant and height of the overlay. Measured results at 10 GHz are compared with predicted performance     

Microstrip Dispersion Model

The assumption that the quasi-TEM mode on microstrip is primarily a single longitudinal-section electric (LSE) mode leads to a transmission line model whose dispersion behavior can be analyzed and related to that of microstrip. Appropriate approximations yield simple, closed-form expressions that allow slide-rule prediction of microstrip dispersion.     

Finite element analysis of MMIC structures and electronic packagesusing absorbing boundary conditions

In this paper, a three-dimensional finite element method (FEM) is employed in conjunction with first and second-order absorbing boundary conditions (ABC's) to analyze waveguide discontinuities and to derive their scattering parameters. While the application of FEM for the analysis of MMIC structures is not new, to the best of the knowledge of the authors the technique for mesh truncation for microstrip lines using the first and higher-order ABC's, described in this paper, has not been reported elsewhere. The scattering parameters of a microstrip discontinuity are computed in two steps. As a first step, the field distribution of the fundamental mode in a uniform microstrip is obtained by exciting the uniform line with the quasi-static transverse electric field, letting it propagate, and then extracting the dominant mode pattern after the higher order modes have decayed. In step two, the discontinuity problem is solved by exciting the structure by using the fundamental mode obtained in step one. The scattering parameters based on the voltage definition are calculated by using the line integral of electric fields underneath the strip. Numerical solutions for several waveguide discontinuities and electronic packages are obtained and compared with the published data     

Transient response of a microstrip line circuit excited by anexternal electromagnetic source

The transient voltages and currents induced by an external electromagnetic field along a microstrip line interconnecting active and/or passive components are studied by using a distributed-source transmission-line model. The influence of the angle of incidence as well as that of the microstrip geometrical and electrical parameters on the line response is analyzed. The instantaneous voltage and power induced on the loads by various types of pulse excitations are computed. Numerical results are obtained both for dispersive and nondispersive lines. A line feeding a transistor microwave amplifier is also considered. The results show the effects of the multiple reflections of the field inside the dielectric substrate and of the signal at the ends of the line. Indications of how to reduce the coupling between the external field and the considered structure are given     

A Parallel-Plate Waveguide Approach to Microminiaturized, Planar Transmission Lines for Integrated Circuits

The parallel-plate waveguide with a two-layer loading medium, a conducting semiconductor substrate, and a relatively thin dielectric layer approximates the interconnections in many integrated systems if the fringing fields are ignored. The fundamental mode of this structure is an E mode which is a surface wave. Its propagation behavior is analyzed in this paper and the equations are evaluated by highly accurate numerical methods. The semiconducting substrate is characterized by its dielectric constant and conductivity. A critical conductivity /spl sigma//sub min/ exists and is related to the cross sectional and material parameters. If the substrate conductivity is given by /spl sigma//sub min/ then the attenuation constant of the line is a minimum. The same value of conductivity yields minimum phase distortion at maximum bandwidth. If the conductivity is larger than /spl sigma//sub min/ the substrate acts as a poor conductor with associated skin effect; if it is smaller, lossy dielectric behavior results. Analysis shows that it is appropriate to subdivide the frequency range into three intervals. The lowest-frequency interval is characterized by propagation which resembles diffusion. This is caused by the loss in the dielectric layer. The next frequency range extends to some upper frequency which is determined by substrate conductivity and the cross-sectional dimensions. In this interval, the phase velocity of the fundamental mode is controlled by the ratio of dielectric to semiconductor thickness, which, if typical interconnections are considered, implies a very low velocity. This property indicates that the structure can serve as a delay line. Further increases in frequency result in higher phase velocities. Skin effect and dielectric loss behavior describe the propagation in this third interval.     

一种基于耦合线和环形微带线的负群时延电路

负群时延电路(NGDC)在微波系统中有着广泛应用,文中提出了一种基于有损耦合线和环形微带线的负群时延电路。该电路由耦合线和微带传输线组成。基于射频领域中偶模-奇模分析方法,分析该电路的偶模和奇模的输入导纳,得到电路的S 参数。利用HFSS 电磁仿真软件对该负群时延电路结构做了优化设计,实物加工并测试。测试结果表明:在中心频率2.36 GHz 时,该电路的负群时延值约为-1.4 ns,插入损耗S21约为-3.9 dB,反射系数S11约为-9.5 dB,实测与仿真结果吻合。这种新颖的负群时延电路结构简单、信号损耗小、易于加工,可用于微波和无线通信等领域。     

A new development of an equivalent circuit model for magnetostaticforward volume wave transducers

A three-port equivalent circuit model of microstrip transducers used for the generation and detection of magnetostatic forward volume waves (MSFVW) is derived from fundamental physical considerations. In this circuit model, each microstrip MSFVW transducer is modeled as a three-port circuit incorporating a frequency-dependent series reactance, a frequency-dependent lossless transformer, and a lossy transmission line. Circuit parameters are determined in closed form by the use of solutions of pertinent boundary-value problems. The effects of parasitics, for example, capacities of bonding pads, are easily taken into account. Some typical transducer configurations are analyzed numerically. The three-port model developed is in excellent agreement with experiments. The model can be applied directly to nonuniform arrays of microstrips weighted by varying the separation between strip centers and the widths of successive strips or reversing the current direction of some groups of strips     

基于介电非线性机制的微带电路无源互调效应研究

微带电路无源互调产生机制尚无定论并且缺乏可靠的理论预测方法,本文基于等效受控源模型,建立了基于介电非线性机制的微带线无源互调的解析计算模型,同时,通过对比测试聚四氟乙烯玻纤布介质微带线和空气介质微带线的三阶互调规律验证了介质非线性是微带电路无源互调的一种主要非线性来源,并提取了非线性参数.实验结果显示聚四氟乙烯玻纤布介质微带线比空气介质微带线的传输互调高了约20dB,反射互调高了约15dB,表明介质非线性是聚四氟乙烯玻纤布介质微带线互调的主要来源.同时,根据本文建立的微带线互调计算解析模型,提取聚四氟乙烯玻纤布介质基板的三阶非线性相对介电常数.本文研究方法可以进一步用于其它微带电路无源互调规律计算研究.