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Microwave Theory and Techniques, IEEE Transactions on

Issue 7 • Date July 1991

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Displaying Results 1 - 25 of 28
  • Comments, with reply, on "Formulas useful for the synthesis and optimization of general, uniform contradirectional couplers" by F. Sellberg

    Page(s): 1252 - 1254
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    The commenter addresses the case of the ideal, asymmetric, inhomogeneous coupled-line coupler, which is perfectly matched and isolated at all frequencies (if dispersion can be neglected) and which was not treated in the above-titled paper (ibid., vol.38, pp.1000-1010, Aug. 1990). He refutes the authors' statement that perfect isolation for all frequencies can be achieved on in the case of homogeneous coupler. The author agrees that the statement was incorrect and amends it to say that the coupler is better described as compensated in a distributed and therefore frequency-insensitive manner. He also shows how the treatment in his paper could have stressed the general applicability of his results more.<> View full abstract»

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  • On the modeling of conductor and substrate losses in multiconductor, multidielectric transmission line systems

    Page(s): 1090 - 1097
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    Most models used for the analysis of lossy, multiconductor, multidielectric transmission line systems (MCMDTLSs) are noncausal and fail to accurately predict the signal distortion on practical printed circuits. The authors review the method of analysis and assumptions made in these models and present more accurate models. The authors solve for the time-domain response of a single, lossy, perfectly matched conductor above a ground plane and immersed in a perfect dielectric, assuming transverse electromagnetic (TEM) propagation. The authors also solve for the same line, except that the line is assumed to be perfect while the dielectric is lossy. The TEM mode propagates in such lines and no errors result from this assumption. A brief generalization to MCMDTLSs is described to illustrate the theory, and numerical examples are presented.<> View full abstract»

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  • Indium gallium arsenide microwave power transistors

    Page(s): 1069 - 1075
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    Depletion-mode InGaAs microwave power MISFETs with 1-μm gate lengths and up to 1-mm gate widths have been fabricated using an ion-implanted process. The devices employed a plasma-deposited silicon/silicon dioxide gate insulator. The DC current-voltage (I -V) characteristics and RF power performance at 9.7 GHz are presented. The output power, power-added efficiency, and power gain as a function of input power are reported. An output power of 1.07 W at 9.7 GHz with a corresponding power gain and power-added efficiency of 4.3 dB and 38%, respectively, was obtained. The large-gate-width devices provided over twice the previously reported output power for InGaAs MISFETs at X-band. In addition, the first report of RF output stability of InGaAs MISFETs over 24 h period is also presented. An output power stability within 1.2% over 24 h of continuous operation was achieved. In addition, a drain current drift of 4% over 104 s was obtained View full abstract»

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  • Measurements of all complex permeability tensor components and the effective line widths of microwave ferrites using dielectric ring resonators

    Page(s): 1148 - 1157
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    A method of measuring all the complex permeability tensor components of microwave ferrites using a single cylindrical ferrite sample is described. Two dielectric ring resonators having the same height and internal diameter but different external diameters, operating on HE111± and H011 modes respectively, are applied for these measurements. Permeability tensor components are computed from the measured resonant frequencies and Q factors of these resonators with and without the ferrite sample. Computations are based on the exact eigenvalue equations for these modes. Measurements of all permeability tensor components versus static magnetic field intensity, performed for different ferrite materials, generally confirm results obtained by earlier researchers, but they also contain certain aspects concerning relations between particular permeability tensor components below saturation View full abstract»

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  • A uniform asymptotic expansion for the Green's functions used in microstrip calculations

    Page(s): 1223 - 1226
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    A uniform asymptotic approximation is developed in the limit of small substrate thickness for the Green's functions used in microstrip-type problems. The author develops an approximation which is uniformly valid for all distances from the source in the limit where the substrate region is thin, which is typically the case of interest for microstrip problems. The approximation is valid for a single-layer substrate. The expansions agree with previously published near and far-field results. The approximation is compared with numerical evaluations of the exact integral solution available for the problem. View full abstract»

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  • Low-loss optical branching waveguides consisting of anisotropic materials

    Page(s): 1140 - 1147
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    Low-loss branching waveguides of the mode-conversion type consisting of anisotropic materials are proposed, and their basic wave-guiding characteristics are studied by means of coupled-mode theory. Two mode-conversion sections are introduced on both input and output sides of a conventional symmetric branching waveguide. Each arm of the branching waveguides is assumed to be a single-mode slab waveguide except for the tapered section. A coupled-mode system of equations describing mode-conversion phenomena with respect to the transverse magnetic (TM) mode in the branching waveguides is derived from the field expansion in terms of local normal modes. A Runge-Kutta-Gill method is used to numerically solve the coupled-mode equations. It is found that the proposed branching waveguides suffer mode-conversion losses to a much lesser extent than conventional branching waveguides View full abstract»

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  • Equivalent-circuit parameter extraction for cold GaAs MESFET's

    Page(s): 1243 - 1247
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    The physical basis of the cold-FET method for extracting parasitic resistances and inductances is examined. A method to obtain the source resistance from the gate-current dependence of the FET Z parameters is used to analyze FETs with different gate lengths. Inductance results for FETs with different gate widths suggest that inductance extrinsic to the gate fingers is dominant, and models of the gate inductance support this. The effects that possible dependences of the parasitic-FET equivalent-circuit parameters (ECPs) on the gate and drain bias can have on the extracted intrinsic-FET parameters are discussed. View full abstract»

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  • Measurement of the microwave conductivity of a polymeric material with potential applications in absorbers and shielding

    Page(s): 1158 - 1164
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    The microwave conductivity of a new material, the polymer poly-p-phenylene-benzobis-thiazole (PBT) made conductive by ion-implantation doping with iodine, is measured at 9.89 GHz as a function of temperature using the cavity perturbation technique applicable to thin films of arbitrary shape. The DC and microwave conductivities of PBT are seen to approach asymptotically the low-temperature limit predicted by Mott's energy-dependent hopping model. The potential utilization of conductive polymers in microwave absorbers and electromagnetic interference (EMI) shielding is examined using layered media EM theory View full abstract»

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  • Efficient computation of the free-space periodic Green's function

    Page(s): 1226 - 1229
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    The application of Shanks's transform is shown to improve the convergence of the series representing the doubly infinite free-space periodic Green's function. Higher order Shanks transforms are computed via Wynn's epsilon algorithm. Numerical results confirm that a dramatic improvement in the convergence rate is obtained for the on-plane case, in which the series converges extremely slowly. In certain instances, the computation time can be reduced by as much as a factor of a few thousands. A relative error measure versus the number of terms taken in the series is plotted for various values of a convergence factor as the observation point is varied within a unit cell. Computation times are also provided. View full abstract»

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  • Closed-form expressions for the current distributions on open microstrip lines

    Page(s): 1115 - 1119
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    The authors systematically clarify the characteristics of current distributions for various cases of substrate relative permittivity, shape ratio, and normalized frequency. These characteristics are clarified, and closed-form expressions are proposed. An open microstrip line with isotropic dielectric substrate is numerically analyzed by the spectral-domain method to clarify current distributions on a strip conductor. The current distributions obtained are illustrated in figures for typical cases. A full view of current distributions on a strip conductor in any microstrip line is provided by showing those close-form expressions. These expressions for the current distribution have been compared with the theoretical results, and good agreement has been obtained View full abstract»

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  • GaAs nonlinear transmission lines for picosecond pulse generation and millimeter-wave sampling

    Page(s): 1194 - 1204
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    The GaAs nonlinear transmission line (NLTL) is a monolithic millimeter-wave integrated circuit consisting of a high-impedance transmission line loaded by reverse-biased Schottky contacts. The engineering of functional monolithic NLTLs is considered. Through generation of shock waves on the NLTL, the authors have generated electrical step functions with approximately 5 V magnitude and less than 1.4 ps fall time. Diode sampling bridges strobed by NLTL shock-wave generators have attained bandwidths approaching 300 GHz and have applications in instruments for millimeter-wave waveform and network measurements. The authors discuss the circuit design and diode design requirements for picosecond NLTL shock-wave generators and NLTL-driven sampling circuits. View full abstract»

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  • Multiangle method for temperature measurement of biological tissues by microwave radiometry

    Page(s): 1235 - 1239
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    A new approach for deriving the temperature distribution in biological tissues of microwave radiometry is proposed. It consists in the measurement of the thermal radiation of the body, at a given frequency, as a function of the observation angle, for two mutually orthogonal polarizations. Theoretically, this method yields results comparable to those obtained with the multispectral method. In order to derive the relations between the body temperature and the emitted thermal signal, the biological body is modeled by a set of parallel planar layers, each characterized by constant permittivity and temperature. It is demonstrated that for all practical purposes the radiation pattern of the antenna may be approximated by that of an unbounded plane wave. View full abstract»

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  • Analytically unified DC/small-signal/large-signal circuit design

    Page(s): 1076 - 1082
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    The authors examine the inherent analytical relationship between the DC, small-signal, and harmonic balance circuit equations. This provides the basis for unified DC, small-signal, and large-signal analyses using a single nonlinear circuit description. This approach ensures consistent circuit simulation results and permits simultaneous optimization of DC, small-signal, and large-signal responses with multidimensional specifications. Applying this concept to field effect transistor (FET) parameter extraction leads to nonlinear device models suitable for both small-signal and large-signal analyses. The authors also demonstrate simultaneous small-signal and large-signal minimax optimization of an FET broadband amplifier to extend the dynamic operating range View full abstract»

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  • Wide-bandwidth optical phased array based on remote coding configuration

    Page(s): 1216 - 1219
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    Wide-bandwidth weighted array processing requires that the weighting function, applied to each element in the array, be a function of the frequency. The equivalence between a filter embodiment and a correlator embodiment of the weighting function is used to show that the remote coding configuration can serve as a correlation embodiment of the weighting function, thus avoiding the need for true-time delays (TTDs) in the signal path. View full abstract»

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  • An efficient finite-element formulation without spurious modes for anisotropic waveguides

    Page(s): 1133 - 1139
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    A numerically efficient finite-element formulation is presented for the analysis of lossless, inhomogeneously loaded, anisotropic waveguides of arbitrary shape. The electromagnetic field is described either by the three components of a magnetic vector potential and an electric scalar potential or by the three components of an electric vector potential and a magnetic scalar potential. The uniqueness of the potentials is ensured by the incorporation of the Coulomb gauge and by proper boundary conditions. Owing to the implementation of the solenoidality condition for the vector potential even in the case of zero wavenumber, no spurious modes appear. Variation expressions suited to the finite-element method are formulated in terms of the potentials. Standard finite-element techniques are employed for the numerical solution, leading to a generalized eigenvalue problem with symmetric, sparse matrices. This is solved by means of the bisection method with the sparsity of the matrices fully utilized. Dielectric- and ferrite-loaded waveguides with closed and open boundaries and including both isotropic and anisotropic materials are presented as examples View full abstract»

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  • Measurement and analysis of GaAs MESFET parasitic capacitances

    Page(s): 1247 - 1251
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    From S-parameter measurements and subsequent equivalent-circuit parameter (ECP) extraction for a series of 0.25-μm, ion-implanted GaAs MESFETs with different widths and different gate-source and drain-source spacings, parasitic FET pad capacitances and interelectrode capacitances. The active-FET fringe capacitances extracted at pinch-off are compared with results from two-dimensional Poisson simulations View full abstract»

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  • Propagation of transients in dispersive dielectric media

    Page(s): 1165 - 1172
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    The propagation of transient electromagnetic fields in dispersive dielectric media is studied. The dielectric medium is assumed to be linear, isotropic, and homogeneous, and is described by the Debye model. Incident fields are assumed to be transverse electromagnetic plane wave pulses. The dielectric body can assume the form of infinite half space or an infinite circular cylinder, either of which may be homogeneous or stratified. The electric fields induced in the dielectric are calculated from time-domain Maxwell's equations using the finite-difference time-domain method. View full abstract»

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  • Space-charge wave considerations in MIS waveguide analysis

    Page(s): 1126 - 1132
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    A transport-based small-signal analysis of the fundamental mode of propagation in a metal-insulator-semiconductor (MIS) waveguide is presented. The formulation incorporates the full set of Maxwell's equations and the equations of motion of the carriers based on a drift-diffusion model, providing a quantitative description of the space-charge wave induced of the surface of the semiconductor. Effects of an external DC bias on the propagation characteristics are also accounted for. Numerical solutions to the system of equations for a waveguide with typical material parameters and dimensions are obtained using an iterative algorithm. Results indicate that the transverse component of the electric field in the semiconductor is strongly influenced by the screening effect of the charge carriers, whereas the longitudinal component is governed mainly by energy dissipation arising from the conduction current View full abstract»

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  • Optoelectronic approach to on-chip device and circuit characterization at microwave and millimeter-wave frequencies

    Page(s): 1179 - 1193
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    A practical technique for characterizing high-frequency semiconductor devices and monolithic integrated circuits has been developed, with specific emphasis on eliminating one of the primary concerns affiliated with conventional approaches, namely the often insufficient predictability of conditions at interfaces between measurement system and device under test. Arrays of high-speed photoconductive circuit elements, in conjunction with special compensation networks, are thereby utilized to implement, on chip, all signal generation and sampling functions needed to efficiently perform time-domain reflectometry. The acquired time-domain information is then converted into equivalent device-under-test scattering parameter responses. The practicability of the approach is experimentally demonstrated with the help of five individual test structures that are realized in monolithic-integrated-circuit format on a GaAs substrate and operate over a full, uninterrupted 100-GHz frequency interval. View full abstract»

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  • Capacitance of a circular symmetric model of a via hole including finite ground plane thickness

    Page(s): 1229 - 1234
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    The capacitance of a simplified model of a via hole is calculated based on an integral equation approach for the surface charge density. The formulation of the problem is based on an integral equation for the surface charges combined with an analytical solution at the ground plane opening. The finite ground plane thickness is explicitly taken into account. Numerical data are obtained for a large range of realistic geometrical data. The relative importance of the contribution to the total capacitance coming from the ground plane opening is explicitly evaluated. It is found that the via capacitance is proportional to the square root of its height, at least for the range of geometrical data considered. View full abstract»

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  • A multiline method of network analyzer calibration

    Page(s): 1205 - 1215
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    The author presents a method for the calibration of network analyzers. The essential feature is the use of multiple, redundant transmission line standards. The additional information provided by the redundant standards is used to minimize the effects of random errors, such as those caused by imperfect connector repeatability. The resulting method exhibits improvements in both accuracy and bandwidth over conventional methods. The basis of the statistical treatment is a linearized error analysis of the TRL (thru-reflect-line) calibration method. The analysis presented is useful in the assessment of calibration accuracy. It also yields results relevant to the choice of standards. View full abstract»

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  • Full-wave analysis of aperture-coupled microstrip lines

    Page(s): 1108 - 1114
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    Two methods are presented for the analysis of aperture-coupled microstrip lines. Assuming a quasi-transverse electromagnetic traveling wave incident on the feeding line, an expression for the wave on the coupled line is derived. First, the moment method is used and the current on the coupled line is represented by a traveling wave propagating away from the slot. In the second method, the reciprocity theorem is applied to the coupled line. Both the moment method and the reciprocity method make use of the exact Green functions and produce results that are in very close agreement. An equivalent circuit is derived and the S-parameters are computed. Theoretical results are verified with measurements View full abstract»

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  • A cooled 1-2 GHz balanced HEMT amplifier

    Page(s): 1239 - 1243
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    The design details and measurement results for a cooled 1-GHz-bandwidth L-band high electron mobility transistor (HEMT) amplifier are presented. No facilities-were available for measuring low-temperature S parameters, but the HEMT noise parameters were measured at a physical temperature of 12 K. The absence of S-parameter information precluded the design of a feedback amplifier, so a balanced configuration was adopted. This has the advantage of providing a good input match even though the amplifiers in the two arms of the balanced circuit are poorly matched. However, there are disadvantages. The loss of the input hybrid degrades the noise temperature and coupling errors in the hybrids, and differences between the amplifiers reduce the gain and result in a noise contribution from the input load. In the amplifier described, these effects degrade the noise temperature by less than 1 K. The amplifier uses commercially available packaged HEMT devices. At a physical temperature of 12 K the amplifier achieves noise temperatures between 3 and 6 K over the 1 to 2 GHz band. The associated gain is approximately 20 dB. View full abstract»

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  • Complex images for electrostatic field computation in multilayered media

    Page(s): 1120 - 1125
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    A rapidly convergent algorithm to find the spatial simulated images of a point charge in multilayered media is presented. The simulated images turn out to be complex; i.e. they have complex amplitudes and are located at complex positions. Surprisingly, these complex images give the static field in multilayered media very accurately (errors ~0.1%). The examples of two- and three-layered media are examined, together with the available exact image solutions of singly or doubly infinite series View full abstract»

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  • Systematic determination of the propagation characteristics of coplanar lines on semiconductor substrate

    Page(s): 1083 - 1089
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    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 View full abstract»

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The IEEE Transactions on Microwave Theory and Techniques focuses on that part of engineering and theory associated with microwave/millimeter-wave components, devices, circuits, and systems involving the generation, modulation, demodulation, control, transmission, and detection of microwave signals. This includes scientific, technical, and industrial, activities. Microwave theory and techniques relates to electromagnetic waves usually in the frequency region between a few MHz and a THz; other spectral regions and wave types are included within the scope of the Society whenever basic microwave theory and techniques can yield useful results. Generally, this occurs in the theory of wave propagation in structures with dimensions comparable to a wavelength, and in the related techniques for analysis and design..

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