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Microwave Theory and Techniques, IEEE Transactions on

Issue 3 • Date March 1996

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Displaying Results 1 - 24 of 24
  • Transmission-line theory approach to solution of state equations for linear-lumped circuits

    Page(s): 479 - 482
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    Linear-lumped circuits containing capacitors and/or inductors are described by differential equations. In computer-aided circuit analysis, these equations are discretized in time, thus being reduced to approximate formulas involving samples of voltages and currents. It is shown that these relations can be interpreted as exact equations for networks containing transmission lines. Hence, some features of the approximate formulas gain a clear physical interpretation. In particular, convergence and energy balance properties of the formulas become obvious, confirming advantages of the trapezoidal rule over all other formulas. View full abstract»

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  • Development of semi-empirical design equations for symmetrical three-line microstrip couplers

    Page(s): 469 - 472
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    Semi-empirical design equations for symmetrical three-line microstrip couplers (TMCs) have been developed. The approach is based on dividing the total capacitance of the system into various basic capacitances, which are then calculated empirically and semi-numerically. The numerical results based on these design equations have been found in good agreement with the previously obtained results View full abstract»

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  • On the network characterization of planar passive circuits using the method of moments

    Page(s): 438 - 445
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    The issue of characterizing multiport planar circuits using the method of moments is addressed. For this purpose two commonly encountered excitation models, the delta-gap voltage, and the impressed-current ones are considered. The two excitation models are thoroughly examined and the conditions are determined under which they become equivalent. Based on this equivalence, it is shown how to correctly use the models for extracting the required network representation of general multiport planar circuits, possibly having transversely multisegmented ports, in an unambiguous way. Supportive numerical and experimental results for the characterization of shielded planar circuits are also provided View full abstract»

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  • The noise-tee - a lightwave device for microwave noise measurements

    Page(s): 490 - 492
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    An innovative lightwave method is proposed to insert noise in electronic circuits in favor of microwave noise measurements. The proposed noise-tee has attractive additional features compared to the use of 50 Ω noise sources: 1) the inserted noise level and noise bandwidth is continuously variable over a wide dynamic range; 2) the wideband scaling accuracy of this level, relative to a pre-calibrated level, equals the accuracy of simple DC-current measurements; 3) level-induced impedance variations are negligible, compared to the 20% impedance variation of a commonly used microwave noise source; and 4) noise-tees enable the realization of 100% reflective noise sources, in favor of two-port noise-parameter measurements View full abstract»

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  • Resonance characteristics of whispering-gallery modes in an elliptic dielectric disk resonator

    Page(s): 473 - 475
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    This paper presents a novel calculation method for resonance characteristics of an elliptic dielectric disk resonator. In the elliptic resonator, electromagnetic energy propagates as a whispering gallery (WG) mode along the edge region of the dielectric disk. In the novel analysis, a local propagation constant of the WG mode at each point of the elliptic disk edge is represented by a propagation constant of a WG mode in a circular disk whose radius of curvature, material constants, and thickness are equal to those of the elliptic disk. Therefore, we can easily calculate the resonance characteristics of the elliptic dielectric disk resonator by applying a conventional technique for the circular dielectric disk. The calculated results of the resonant frequencies and field distribution are well confirmed by experiments View full abstract»

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  • Error bound for the approximate Fourier transformation relationship for nonuniform transmission lines

    Page(s): 482 - 484
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    In this paper, an error bound is presented for Bolinder's well-known approximate formula relating the input reflection coefficient and the local reflectivity parameter of a lossless nonuniform transmission line (NTL) via the Fourier transformation. Despite modern computers allowing an accurate analysis, Bolinder's formula is still of interest. First, it makes possible an approximate synthesis of NTLs which can be used in a subsequent optimization. Second, it supports an intuitive grasp for the electrical properties of NTL's View full abstract»

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  • Generation and transmission of FM and π/4 DQPSK signals at microwave frequencies using harmonic generation and optoelectronic mixing in Mach-Zehnder modulators

    Page(s): 446 - 453
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    A novel method of using the harmonic generation and optoelectronic mixing properties of Mach-Zehnder modulators to generate modulated subcarrier signals at high-order harmonics of the input signals is presented. The method permits the simultaneous transmission over optical fiber of a modulated and an unmodulated signal, both at high-order harmonic frequencies of the input signals, for the purpose of transmitting both a local oscillator tone and the modulated signal required at a base station for microcellular applications. We present the theory of operation and demonstrate the validity of the concept with a narrow band single-tone FM experiment as well as a 20-Mb/s π/4 DQPSK experiment View full abstract»

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  • Averaging rules for the scattering by randomly oriented chiral particles

    Page(s): 476 - 478
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    The orientational averages arising when calculating the effective behavior of ensembles of randomly dispersed (chiral) particles are examined. Two methods, i.e., the vector radiative transfer equation (VRTE) and the Lorenz-Lorentz mixing formulas, are briefly discussed. Since integration over products of up to six elements of a rotational matrix are involved, the effort for performing the averaging is high. To minimize the computational burden, rules for evaluating the integrals are given in this communication. Application to average polarizability-tensors are presented View full abstract»

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  • An efficient synthesis technique of tapered transmission line with loss and dispersion

    Page(s): 462 - 465
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    A synthesis technique of lossy and dispersive tapered transmission line is presented that extends lossless cases suggested by Klopfenstein and others. A special optimization process based on the Fourier transform pair and generalized Taylor's procedure is performed to extract the exact null points of lobe-like frequency response in terms of the input reflection coefficient of lossy-tapered line in which the loss may be frequency dependent and distance dependent. The theory is verified by evaluation of a synthesized microstrip taper profile in the lossy case and is expected to be helpful for design of tapered line in the high-frequency microwave integrated circuits (MICs) with loss View full abstract»

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  • FDFD full-wave analysis and modeling of dielectric and metallic losses of CPW short circuits

    Page(s): 485 - 487
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    A finite-difference method in the frequency domain (FDFD) is used to analyze the influence of lossy materials on the scattering behavior of CPW short ends. Not only dielectric losses but also realistic metallic losses are taken into account for the first time in an FDFD method. Both, the numerical results for the three-dimensional structure and the complex propagation constants of the homogeneous waveguide are presented. These are compared with those yielded by an analytical method and shown to be of good agreement. Finally, a simple model is presented, which describes the CPW short end with good accuracy View full abstract»

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  • Temperature-dependent modeling of gallium arsenide MESFETs

    Page(s): 357 - 363
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    A complete temperature-dependent small signal model extraction methodology is used to achieve accurate circuit level simulations of metal semiconductor field-effect transistor (MESFET) amplifier performance over temperature. The procedure applies a previously described field-effect transistor (FET) modeling approach to predict the performance of a small signal amplifier over a -55°C to 100°C temperature range. This work includes a description of the MESFET equivalent circuit element thermal coefficients along with an amplifier simulation. Therefore, for the first time, a clear correspondence between circuit level simulation and measured results over temperature are published together. A new comparison of published temperature-dependent data shows a common agreement for amplifier gain variations of 0.015 dB/°C/Stage for a broad range of designs from 400 K down to cryogenic levels (77 K) View full abstract»

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  • A novel waveguide Y-junction circulator with a ferrite sphere for millimeter waves

    Page(s): 454 - 456
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    A novel waveguide Y-junction circulator with a ferrite sphere is developed for uses at millimeter-wave frequencies. Sphere is preferred because the production cost of a pertinent circulator is lower. Performance of the new circulator is comparable to the conventional one with a cylindrical ferrite. A simple formula is derived for determining the center frequency of a circulator. Good agreement between analytical results and measurements is observed. An extremely fast method is developed to analyze the circulator. Various properties of the circulator can be predicted with reasonable accuracy View full abstract»

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  • A new extraction method for noise sources and correlation coefficient in MESFET

    Page(s): 487 - 490
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    A new extraction method for noise sources and correlation coefficient in the noise equivalent circuit of GaAs metal semiconductor field effect transistor (MESFET) is proposed. It is based on the linear regression, which allows us to extract physically meaningful parameters from the measurement in a systematic and straightforward way. The confidence level of the measured data can also be easily examined from the linearity, y-intercept of the linear regression, and the scattering from the regression line. Furthermore, it is found that the time constant of correlation coefficient whose value is almost the same as that of the transconductance should be considered to model noise parameters accurately. The calculated values of minimum noise figure, optimum impedance, and noise resistance using above approach, show excellent agreement with measurement for a typical MESFET device studied in this paper View full abstract»

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  • Iterative numerical computation of the electromagnetic fields inside weakly nonlinear infinite dielectric cylinders of arbitrary cross sections using the distorted-wave Born approximation

    Page(s): 400 - 412
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    The electromagnetic scattering by weakly nonlinear infinite dielectric cylinders is the topic dealt with in this paper. The cylinders are assumed to be isotropic, inhomogeneous, and lossless and to have arbitrarily shaped cross sections. A time-periodic illumination of the transverse magnetic type is considered. The nonlinearity is assumed to be expressed by the dependence of the dielectric permittivity on the internal electric field, under the hypothesis that the operator responsible for the nonlinearity does not modify the scalar nature of the dielectric permittivity and produces a time-periodic output. The electromagnetic scattering is then described by an integral equation formulation, and the electromagnetic field distributions inside and outside a scatterer are approximated by an iterative numerical procedure starting with the application of the distorted-wave Born approximation. In a simplified version of the approach, the classic first-order Born approximation is used. The convergence of the approach is discussed in several examples. In the computer simulations concerning cylinders with different cross-section shapes, the effects of the nonlinearity on the field-component fundamental frequency were evaluated for different values of the nonlinear parameters in the case of a Kerr-like nonlinearity and of a uniform incident plane wave. The generation of higher-order harmonics was also considered View full abstract»

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  • Mode orthogonality relations and field structure in chirowaveguides

    Page(s): 465 - 469
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    By analyzing the vector and scalar equations for chirowaveguides, two forms of mode orthogonality relations are obtained: the vector formulated orthogonality and the scalar formulated orthogonality. The first one is applicable to the general case of open chiroplasma or chiroferrite waveguides. It is shown that for two parallel-plate isotropic chirowaveguides, these two forms of orthogonality relations differ. Based on mode orthogonality relations, it is shown that in chirowaveguides the polarization of so-called complex modes differs from that of propagating or evanescent modes. The correlation between field components of two complex modes that transfer active power flow in chirowaveguides is obtained View full abstract»

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  • Variational solution of microwave circuits and structures

    Page(s): 460 - 462
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    A unified variational formulation for microwave planar transmission lines and lumped-element impedances is developed and applied to an isolated stripline power splitter. Scattering parameters are calculated via the transfinite-element method and the numerical results are corroborated by three-port experimental measurements. The microwave impedance of a thin-film isolation resistor is separately measured and included in the model View full abstract»

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  • Accurate small-signal modeling of HFET's for millimeter-wave applications

    Page(s): 432 - 437
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    In this paper we discuss the small-signal modeling of HFET's at millimeter-wave frequencies. A new and iterative method is used to extract the parasitic components. This method allows calculation of a π-network to model the heterojunction field-effect transistor (HFET) pads, thus extending the validity of the model to higher frequencies. Formulas are derived to translate this π-network into a transmission line. A new and general cold field-effect transistor (FET) equivalent circuit, including a Schottky series resistance, is used to extract the parasitic resistances and inductances. Finally, a new and compact set of analytical equations for calculation of the intrinsic parameters is presented. The real part of Y12 is accounted for in these equations and its modeling is discussed. The accounting of Re(Y12 ) improves the S-parameter modeling. Model parameters are extracted for an InAlAs/InGaAs/InP HFET from measured S-parameters up to 50 GHz, and the validity of the model is evaluated by comparison with measured data at 75-110 GHz View full abstract»

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  • Theory and numerical calculations for radially inhomogeneous circular ferrite circulators

    Page(s): 419 - 431
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    This paper presents a new theory for the operation of microstrip and stripline circulators, specially set up to permit radial variation of all the magnetic parameters. A computer code, taking only a few seconds per calculated point on a modest computer, was developed from the theory, and calculated results are given. In the theory we develop a two-dimensional (2-D) recursive Green's function G suitable for determining the electric field Ex anywhere within a microstrip or stripline circulator. The recursive nature of G is a reflection of the inhomogeneous region being broken up into one inner disk containing a singularity and N annuli. G has the correct properties to allow matching to the external ports, thereby enabling s-parameters to be found for a three-port ferrite circulator. Because of the general nature of the problem construction, the ports may be located at arbitrary azimuthal angle φ and possess arbitrary line widths. Inhomogeneities may occur in the applied magnetic field Happ, magnetization 4πMs, and demagnetization factor Nd . All magnetic inhomogeneity effects can be put into the frequency dependent tensor elements of the anisotropic permeability tensor. Numerical results are presented for the simpler but immensely practical case of symmetrically disposed ports of equal widths taking into account these radial inhomogeneities. Studies of breaking up the area into 1, 2, and 5 annuli are undertaken to treat specific inhomogeneous problems. The computer code which evaluates the recursive Green's function is very efficient and has no convergence problems View full abstract»

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  • Dielectric slab-loaded resonant cavity for applications requiring enhanced field uniformity

    Page(s): 457 - 460
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    This paper introduces and analyzes a rectangular resonant structure that provides an alternative to the multimode resonant cavity in applications requiring enhanced field uniformity. The resonant cavity contains four dielectric loading slabs placed along the cavity walls. Its first resonant mode is related to the uniform field distribution supported in a rectangular TEM waveguide. The electromagnetic fields within the cavity are described using a closed-form approach, with approximations taken to account for the presence of two of the loading slabs. Application of the boundary conditions leads to an eigenvalue formulation, which is used to determine resonant frequencies and electromagnetic field distributions within the cavity. Measurements of both resonant frequencies and electric field magnitudes confirm the analysis. This work provides the basis for future analyses and implementation of slab-loaded cavities in both scientific and industrial settings View full abstract»

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  • New simple procedure for the computation of the multimode admittance or impedance matrix of planar waveguide junctions

    Page(s): 413 - 418
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    Much effort has been devoted in the past to the development of electromagnetic simulation algorithms for waveguide junctions that could at the same time include higher-order mode interactions and lead to computationally efficient codes. Even though this is indeed a classical subject, there is still a strong interest in this area as waveguide systems become increasingly complex, and ever shorter development and manufacturing times are required. In this paper a simple method is described for the evaluation of the multimode network representation of planar waveguide junctions in terms of admittance or impedance parameters. The key feature of the method is that it starts from the wanted final results, the equivalent network representation, in order to obtain an analytic expression for the evaluation of the relevant matrix elements. The procedure is based on general network theory and is equivalent to ideally measuring directly the value of the admittance or impedance elements. In this paper the evaluation procedure is fully described. Measured results of actual hardware are then compared with simulations indicating that the codes developed are indeed very accurate as well as computationally very efficient View full abstract»

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  • Design of impedance transformers by the method of least squares

    Page(s): 389 - 399
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    The method of least squares is applied to the theory of small reflections of transmission lines to develop numerical algorithms for the design of stepline and tapered line impedance transformers to match two impedances over a frequency band. The transformer characteristic impedance function is expanded by polynomials, pulse functions, approximate operators, and piecewise linear functions to construct an error function for the input reflection coefficient which, after minimization, gives the line impedance and length. The computer programs could be used to design a transformer under the specified conditions and then to optimize the design under the constraints of a problem View full abstract»

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  • Improving microwave imaging by enhancing diffraction tomography

    Page(s): 379 - 388
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    In this paper, a technique for enhancing the reconstruction quality of diffraction tomography for microwave imaging is presented. The technique invokes the WKB approximation in conjunction with utilizing measurement data at more than one frequency to overcome some of the limitations of diffraction tomography. The resulting formulation has a mathematical interpretation which leads to some interesting insights into the limitations of diffraction tomography. Numerical implementation of the technique is also described and actual simulation results using this implementation for a variety of two-dimensional (2-D) objects are provided. These show that indeed significant improvements over conventional diffraction tomography are possible with our enhanced technique View full abstract»

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  • Extracting a bias-dependent large signal MESFET model from pulsed I/V measurements

    Page(s): 372 - 378
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    In this paper a new large-signal metal semiconductor field effect transistor (MESFET) model suitable for applications to nonlinear microwave CAD has been developed and the different phenomena involved in the nonlinear behavior of the transistor have been studied. The importance of this work lies in the fact that multibias starting points (hot and cold device) for pulsed measurements are used to derive a single expression for Ids that describes the dc as well as the small and large signal behavior of the transistor, while taking into account the quiescent point dependence. The algorithms of this new model can easily be incorporated into commercially available nonlinear simulators. The operating-point dependent current Ids is modeled by two nonlinear sources: one of them is the dc characteristic nonlinear equation, and the other represents the differences between dc and pulsed characteristics at every bias point. A complete large-signal model is presented for a 10*140 μm GaAs-MESFET chip (F20 process) from the GEC-MARCONI Foundry and a 16*250 μm MESFET chip (DIOM process) from the Siemens Foundry. Comparisons have been made between simulations and measurements of pulsed characteristics at different operating points. There was very good agreement between the Pin /Pout measurements and the MDS simulations using the complete large signal model View full abstract»

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  • A practical technique for designing multiport coupling networks

    Page(s): 364 - 371
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    A new technique is proposed for designing a passive lossless coupling network transforming any prescribed N by N symmetric immittance matrix into a corresponding N by N diagonal immittance matrix. A principal application of the technique is in the design of matching networks between N uncoupled resistive source impedances and planar antenna arrays. The technique is based upon repeated applications of Givens rotations, which can be implemented by a cascade connection of four-port directional couplers. Thus, both in the design technique and in the subsequent hardware implementation, our approach represents a significant departure from past design procedures. Existing synthesis methods involve the use of multiwinding transformers, which are impractical at microwave frequencies 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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