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Microwave Theory and Techniques, IEEE Transactions on

Issue 6 • Date June 1988

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Displaying Results 1 - 25 of 28
  • On the scalar approximation in fiber optics

    Page(s): 1100 - 1103
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    It is widely accepted that the scalar approximation is valid when the gradient of the permittivity distribution del epsilon / epsilon is small. Such a condition is demanding since it precludes a rapidly varying permittivity distribution, which is usually the case in a practical optical fiber due to some kind of fluctuation in a fabrication process. Here, the scalar approximation is derived from the electric field integral equation. From the result it is seen that the applicability of the scalar approximation does not depend on the roughness in the permittivity distribution as long as the permittivity in the core is close to that in the cladding. View full abstract»

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  • Comments on "GaAs dual-gate FET for operation up to K-band

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    For the original article see ibid., vol.MTT-32, no.3, p.256-61 (1984). The commenter has rederived expressions from the work by B. Kim et al. and found errors of algebraically inconsistent expressions even with the appropriate approximations taken into account. Equations 10, 11a, 14, 15, 16 and entries in table 1 are corrected.<> View full abstract»

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  • Accurate characterization and modeling of transmission lines for GaAs MMICs

    Page(s): 961 - 967
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    The authors discuss computer-aided design (CAD) tools together with high-accuracy microwave measurements to realize improved design data for GaAs monolithic microwave integrated circuits (MMICs). In particular, a combined theoretical and experimental approach to the generation of an accurate design database for transmission lines on GaAs MMICs is presented. The theoretical approach is based on an improved transmission-line theory which is part of the spectral-domain hybrid-mode computer program MCLINE. The benefit of this approach in the design of multidielectric-media transmission lines is described. The program was designed to include loss mechanisms in all dielectric layers and to include conductor and surface roughness loss contributions. As an example, using GaAs ring resonator techniques covering 2 to 24 GHz, accuracies in effective dielectric constant and loss of 1% and 15% respectively, are presented. By combining theoretical and experimental techniques, a generalized MMIC microstrip design database is outlined View full abstract»

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  • Multiway uniform combline directional couplers for microwave frequencies

    Page(s): 985 - 993
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    An improved optimization technique for multiway uniform forward-directional couplers is presented using a previously published matrix theory of coupled transmission lines. With the help of this computer optimization method, microwave mode-interference combline directional couplers having an arbitrary number of lines can be designed for arbitrary power distribution. Theoretical designs ranging from two-way to nine-way couplers have been tested with success. The observed behavior of some of these couplers is briefly discussed. Typically these couplers exhibited octave bandwidth. A five-way design example of an equal power splitting combline coupler was fabricated using an open microstrip configuration for operation within 1.6-3.2 GHz. The measured characteristics show good agreement with the computed values View full abstract»

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  • The propagation characteristics of signal lines embedded in a multilayered structure in the presence of a periodically perforated ground plane

    Page(s): 968 - 975
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    The propagation characteristics of waves along a periodic array of parallel signal lines in a multilayered structure in the presence of a periodically perforated ground plane are studied. To analyze this structure, the spectral-domain immittance approach is used to derive the Green's function. The surface current density on the conductors is expressed in terms of a set of rooftop subdomain basis functions. The boundary condition is then enforced in conjunction with the Galerkin procedure, leading to an eigenvalue problem for the propagation constant which is solved by the Newton-Raphson algorithm. The dispersion characteristics of these signal lines are studied for both balanced and unbalanced excitations with the relative permittivities of the various layers as parameters. Numerical results are presented and compared with available data. Extension of the present method to treat conductors with finite sheet resistances is also discussed View full abstract»

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  • A directional coupler of a vertically installed planar circuit structure

    Page(s): 1057 - 1063
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    A 3-dB directional coupler is described which is fabricated by installing a vertical second printed circuit board on a main printed circuit board. The added vertical substrate significantly increases the freedom of design parameters. Coupling parameters are easily controlled by changing either the dielectric constants or the thicknesses of the substrates. This makes almost any coupling constant available along with good isolation and a suitable input impedance. The three-dimensional structure also makes a good use of space, resulting in a compact circuit structure. Experimental results agree well with a numerical calculation based on the boundary-element method and show the relaxed tolerances possible in fabrication. Effective permittivities and characteristic impedances for both even and odd modes were obtained and were substituted into the scattering matrix to obtain the parameters for a symmetrical directional coupler. A simplified design chart is also provided showing the dependence of characteristic impedances for odd and even modes on substrate thicknesses used View full abstract»

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  • Saturation of the SIS mixer by out-of-band signals

    Page(s): 1103 - 1105
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    The tendency of superconductor-insulator-superconductor (SIS) mixers to saturate at low input signal levels is shown to depend on the total signal voltage across the junction, including frequency components outside the band of interest. If large dynamic range is to be achieved, mixers should be designed with embedding networks that present low impedances to the junction at out-of-band frequencies View full abstract»

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  • A low-distortion K-band GaAs power FET

    Page(s): 1023 - 1032
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    A K-band low-distortion GaAs power MESFET was developed by incorporating a pulse-type channel doping profile using molecular-beam-epitaxial technology and a novel 0.3-μm T-shaped gate. The low-distortion FETs offer about 10 to 15 dBc improvement in second-harmonic distortion compared to devices fabricated on a uniformity doped active layer. Significantly larger power load-pull contours are obtained with the low-distortion devices, indicating the improved linearity of these devices. In an 8-20-GHz single-stage broad-band amplifier, up to 10 dBc improvement in harmonic performance was achieved using the low-distortion device. This low-distortion device exhibits very linear transconductance as a function of the gate bias. A typical 750-μm-gate-width device is capable of 26 dBm of output power with 6 dB of gain, and power-added efficiency in excess of 35% when measured at 18 GHz. At 25 GHz, the device is capable of 24 dBm of output power with 5 dB associated gain View full abstract»

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  • An analytical solution for the coupled stripline-like microstrip line problem

    Page(s): 1002 - 1007
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    An analytical method is presented for determining the Maxwell's capacitance matrix of multiconductor shielded microstrips with coupled conductors of arbitrary widths, spacings, and inhomogeneous media, in terms of elliptic integrals. The method is based on conformal mapping and the theory of singular integral equations. Two kinds of problems are presented as examples: the first consists of simple structures with one or two coupled striplines; the other type concerns the general case of multiconductor coupled structures for which simple analytical expressions are not available View full abstract»

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  • Network analyzer calibration using offset shorts

    Page(s): 1097 - 1100
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    Microwave network analyzer accuracy enhancement by offset shorts is investigated. Usable calibration bandwidth and accuracy limitations are determined by applying a previously published model by L.A. Glasser (1978) to the case of a reference short and two offset shorts. Data necessary to emulate the HP 8510 scalar network analyzer are derived and used in the model to provide realistic projections. Convenient techniques for optimizing experimental accuracy and for obtaining an estimate of the uncertainty in actual short circuit and offset short calibration standards are also presented View full abstract»

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  • Quasi-static analysis of a microstrip via through a hole in a ground plane

    Page(s): 1008 - 1013
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    The equivalent circuit of a via connecting two semi-infinitely long transmission lines through a circular hole in a ground plane is found. The π-type equivalent circuit consists of two excess capacitances and an excess inductance. These are quasistatic quantities and thus are computed statically by the method of moments from integral equations. The integral equations are established by introducing a sheet of magnetic current in the electrostatic case and a layer of magnetic charge in the magnetostatic case. Parametric plots of the excess capacitances, the excess inductance, and the characteristic admittance of the via are given View full abstract»

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  • Variational bound analysis of a discontinuity in nonradiative dielectric waveguide

    Page(s): 1105 - 1107
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    The application of the variational bound method to nonradiative dielectric waveguide is described for the analysis of scattering by a dielectric obstacle, in this case a rectangular, air-filled discontinuity (hole) in the dielectric center strip. A variational bound is obtained on the phase shift, which measures the amount by which the asymptotic solution for the fields in the guide in the presence of the discontinuity is displaced relative to the guide without a discontinuity. A major advantage of the procedure is that a closed-form expression for the equivalent network is obtained that can be used directly in the design of networks using reactive components, such as filters. Measured data agree well with the theoretical calculations View full abstract»

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  • Coplanar waveguide and slot line on magnetic substrates: analysis and experiment

    Page(s): 1071 - 1079
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    A full-wave analysis is presented for coplanar waveguide (CPW) and slotline phase shifters on magnetic substrates. The analysis is based on a multilayer Green's function which is formulated using a transmission matrix approach. This approach is modified so that its computational efficiency is increased by deriving the transmission matrices for dielectric and ferrite slabs in a closed form. The Green's function is then applied to the full-wave analysis of a slotline and CPW on infinite-width substrates. Several different multilayered configurations are investigated with respect to their nonreciprocal phase-shift properties. Perfectly conducting sidewalls are then added to the analysis and the resulting configuration is used to study the effect of various CPW parameters on differential phase shift. An experimental structure built on the surface of rectangular ferrite toroid is described and its differential phase analysis compared to measurements. Calculated and measured results are in good agreement View full abstract»

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  • The propagation of signals along a three-layered region: microstrip

    Page(s): 1080 - 1086
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    The tangential components of the electric field on the air-substrate surface of a three-layered region such as microstrip are determined for the case when the source is a unit electric dipole on that surface. This is done by integrating the rigorous Hankel transforms subject to the condition k20<|k 21|≪|k22|, where k0 is the wavenumber of air, k1 of the substrate, and k2 of the conductor. It is found that the field consists of lateral-wave terms and direct-wave terms with different wavenumbers and phase velocities with each term consisting of two components. These terms determine the coupling between vertical currents in connections from the air surface to the conducting plane. It is concluded that distortion of signals as they propagate along the surface of microstrip is not due to dispersion in the ordinary sense that the permittivities of the air or the substrate are frequency-dependent; rather it is due to the fact that each signal separates into two parts, the one traveling in the air, the other in the dielectric with different phase velocities. If the permittivity of the substrate is frequency-dependent, the part of the signal traveling in it will suffer dispersion; the lateral-wave part in the air will not View full abstract»

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  • New equivalent circuits for inhomogeneous coupled lines with synthesis applications

    Page(s): 1087 - 1094
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    Equivalent circuits for inhomogeneous coupled-line sections are presented which enable cascade synthesis procedure to be applied to the design of very-broadband inhomogeneous filters. Here, the term inhomogeneous means that the even and odd modes have different phase velocities and different electrical lengths. The method has been implemented in the design of inhomogeneous high-pass filters constructed in suspended substrate stripline, when the even-mode characteristic impedance is much greater than the odd-mode characteristic impedance. An approximate but highly accurate synthesis of a 3:1 bandwidth-inhomogeneous distributed high-pass filter is described. The procedure is almost purely analytic, and computer-aided design is required only for fine tuning adjustments. The theoretical feasibility of designing such filters for upper-pass bandwidths of greater than 8:1 is demonstrated View full abstract»

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  • Frequency-dependent analysis of a shielded microstrip step discontinuity using an efficient mode-matching technique

    Page(s): 976 - 984
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    The basic concepts of the mode-matching technique are used to formulate the boundary condition problem associated with the microstrip step discontinuity problem. The fields on both sides of a discontinuity are expanded in terms of the normal hybrid modes of the shielded microstrip line. The properties of these hybrid modes are determined by applying a previously developed analytical approach due to R. Mittra and T. Itoh (1971) using singular-integral-equation techniques. In addition to propagating modes, higher-order modes are also taken into account. The higher-order modes are evanescent-type waves. The propagation constants of the evanescent waves in general are found to be complex numbers. A mode-matching procedure is developed to determine the reflection and transmission coefficients of the discontinuity. The use of two types of products to treat the boundary conditions for the continuity of the tangential electric and magnetic fields results in a highly efficient and numerically stable solution. Numerical results are computed for several step discontinuities and the results are compared with previously published data View full abstract»

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  • Low-loss twists in oversized rectangular waveguide

    Page(s): 1033 - 1042
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    The unwanted mode conversion from twists in overmoded waveguides is calculated from numerical integration of the coupled-mode equations, considering simultaneous coupling of the five lowest-order modes coupled in a twist. Twists with tapered or linearly varying rates of twist are shown to be superior in medium- or broad-band applications to those with uniform twist rate. Measurements consistent with these theoretical calculations are discussed for uniform twists in WR90 waveguide at 60 GHz and for an electroformed twist having a linearly tapered rate of twist in WR187 waveguide from 15.7 to 17.7 GHz. The coupling coefficients needed in the calculations are derived and are compared with the results of other work, including a modal expansion of the dominant mode in twisted waveguide. The work also considers the transmission through an oversized waveguide with a mode converter generating a trapped unwanted mode, and the result for the dependence of the resonance depth on the mode conversion and the attenuation of the trapped mode is found View full abstract»

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  • A new development of an equivalent circuit model for magnetostatic forward volume wave transducers

    Page(s): 952 - 960
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    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 View full abstract»

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  • Investigation of the saturation properties of gyroamplifiers

    Page(s): 934 - 938
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    The saturation properties of a TE0n gyroamplifier are investigated using a particle-in-cell numerical code. The effect of beam velocity spread is analyzed. It is found that for velocity spread of up to 5%, the reduction in efficiency can be compensated by extending the interaction length. A numerical optimization of efficiency enhancement using a tapered magnetic field was demonstrated. A change in the saturation mechanism from phase trapping to thermalization using the suggested tapering was observed View full abstract»

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  • Generalized microstrip on a dielectric sheet

    Page(s): 939 - 951
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    A procedure is described for arriving at a close approximation to the capacitance between symmetrically placed conducting strips, possibly of different widths, on opposite sides of a dielectric sheet. The procedure is based on static methods, following K.G. Black and T.J. Higgins (1955) for total capacitance of the structure with vacuum dielectric everywhere, and using H.A. Wheeler's (1964) method for determining the series component of dielectric capacitance. Dielectric polarization is included while refraction at the vacuum/dielectric boundary is ignored in the method; its effect is subsequently shown to be small. The derived equations are valid for all finite impedance, all values of relative dielectric constant, and all conductor widths. The maximum absolute error is estimated to be O(0.001Z'), where Z' is the impedance of a generalized microstrip on a dielectric sheet View full abstract»

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  • Design and performance of a 215 GHz pulsed radar system

    Page(s): 994 - 1001
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    A high-power 215-GHz pulsed radar system developed for remote-sensing applications is described that is capable of making backscatter measurements from terrain targets at ranges of several kilometers under normal atmospheric conditions. By using separate transmit and receive antennas, the amplitudes of the polarization matrix elements may be measured conveniently. A dedicated data acquisition system was developed allowing up to 15 range gates to be sampled at 100-ns intervals. Instrument stability of ±1.0 dB yields accurate scattering measurements of a variety of terrestrial targets. System performance and calibration, together with measurements of snow backscatter coefficients made during early 1987, are discussed View full abstract»

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  • Magnetically tunable rectangular waveguide E-plane integrated circuit filters

    Page(s): 1014 - 1022
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    A rigorous field theory method is described for the computer-aided design (CAD) of magnetically tunable E-plane metal-insert filters, where the waveguide sections are symmetrically loaded with ferrite slabs, and for large-gap finlines filters on a ferrite substrate. The design method is based on field expansion in suitably normalized eigenmodes which yields directly the modal scattering matrix of all discontinuities. The theory includes both higher-order mode interaction and the finite thickness of the metal inserts. Optimized data are given for magnetically tunable Ku-band metal insert and finline filter examples. The metal-insert type achieves a tuning range of its operating midband from about 14.1 to 15.7 GHz. The theory is verified by measurements View full abstract»

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  • Frequency normalization of constant power contours for MESFETs

    Page(s): 1107 - 1110
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    The constant power contours have been measured on MESFETs with different doping profiles over the frequency range 8-16 GHz for a fixed input power level at different bias points. At each frequency, the contours are normalized with respect to the load for maximum power output; within experimental accuracy, the normalization holds fairly well, independent of frequency under certain limits. The concept is an extension of small-signal mismatch circles. In case of large-signal applications, the mismatch contours are no longer circles, because of the way the saturation current and breakdown voltage limits are attained. The contours present some reflection coefficient loci with respect to a given load View full abstract»

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  • A rigorous method for computation of ferrite toroidal phase shifters

    Page(s): 929 - 933
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    Coupled-wave theory is used to calculate the performance of twin-toroidal phase shifters. Computation results show that this method is effective, rather simple, and easy to handle. In comparison with the single-toroid phase shifter, the twin-toroidal model's phase shift is considerably larger and its production is simpler. The wires carrying magnetizing currents are located in the weak microwave electric field area. Hence, their influence on the performance of the phase shifter is negligible; this also facilitates production. The loss factors of these two kinds of toroid phase shifters are about the same. Experimental results are in good agreement with theoretical analysis. On this basis, it is concluded that coupled-wave theory is a powerful method for treating electromagnetic problems of waveguides loaded with magnetized ferrites View full abstract»

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  • Analysis of microstrip circuits using three-dimensional full-wave electromagnetic field analysis in the time domain

    Page(s): 1064 - 1070
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    In this method, the circuit is excited by a raised cosine pulse source that includes broadened frequency components. The frequency characteristics are then computed from the Fourier transform of the output transient responses. To evaluate the validity and capability of the method, a side-coupled microstrip filter is analyzed and the frequency characteristics are calculated. A quasistatic analysis of this filter is also presented and the results compared with measurements. The frequency characteristics calculated with the full-wave analysis in the time domain show excellent agreement with the measured values, thus demonstrating the validity and the power of the analytical method 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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