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Microwave Theory and Techniques, IEEE Transactions on

Issue 10 • Date Oct 1991

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Displaying Results 1 - 20 of 20
  • Phase-locked millimeter-wave two-port second-harmonic Gunn oscillators

    Page(s): 1746 - 1753
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    Two-port harmonic oscillators have been developed which are suitable for voltage-controlled-oscillator (VCO) operation in frequency stabilized systems. Two oscillator designs are presented. The first has a fundamental frequency cavity located above the harmonic output cavity and the fundamental is coupled by means of the Gunn device bias-line filter. The second design is an in-line structure which uses a waveguide taper as the filter element separating the fundamental and harmonic frequency components. The latter design is a translation of the first oscillator concept onto a single plane, so that the prospect of an integrated monolithic version is conceivable. The performance of the oscillators is discussed, and a demonstration of their use in a heterodyne phase-locked loop control system is presented View full abstract»

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  • Design of new hybrid-ring, directional coupler using λ/8 or λ/6 sections

    Page(s): 1779 - 1784
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    The authors propose a design method for 1.25 λ-ring and 7λ/6-ring 3-dB directional couplers using λ/8 and λ/6 sections, respectively. In addition, the frequency characteristics of the couplings together with the isolations, the return losses, and the phase differences between the output ports are calculated. The method was experimentally verified for a microstrip network, proving its validity for a microwave component with the basic λ/8 and λ/6 sections proposed View full abstract»

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  • A full-wave mixed potential mode-matching method for the analysis of planar or quasi-planar transmission lines

    Page(s): 1701 - 1711
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    A full-wave mixed potential mode-matching method is presented for the analysis of planar and/or quasi-planar transmission lines. The transmission lines studied consist of layered (stratified) and nonlayered dielectric substrates and metal strips of finite thickness. The y-directed hybrid transverse electric (TE) and transverse-magnetic (TM) Hertzian potentials, perpendicular to the interfaces between each layered region, are employed in the layered regions. The nonlayered regions consist of dielectric step discontinuities that destroy the layered configuration in the horizontal plane, allowing a systematic and easy to handle full-wave formulation of the transmission line problem. The relative convergence criterion needs to be satisfied to obtain accurate electromagnetic field solutions. Theoretical results are in very good agreement with published data for various transmission line structures. Applications of the formulation to the proximity effects of microstrip and microslab lines are illustrated View full abstract»

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  • Synthesis of wide-band planar circulators using narrow coupling angles and undersized disk resonators

    Page(s): 1681 - 1687
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    Circulators using radial/lumped-element resonators with narrow coupling angles that result in gyrator circuits that are as good as, if not better than, those obtained with the classic approach are presented. The form of the lumped element variable is not unique and can be realized by making use of the fringing capacitance at the interface between a dielectric resonator and a substrate with a higher relative dielectric constant than that of the resonator. The topology requires the adjustment of electromagnetic, electrostatic, and network conditions with common parameters, so that a solution that relies on fringing effects only is not generally ensured. The synthesis of octave-band circulators using two quarter-wave-long impedance transformers is reported. A 1-2-GHz circulator based on one such solution with an insertion loss of no more than 0.35 dB between any two ports and typical return loss of 20 dB is described View full abstract»

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  • A multistrip moment method technique and its application to the post problem in a circular waveguide

    Page(s): 1762 - 1766
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    A moment method technique for solving obstacle problems in a waveguide is presented. Instead of using a multifilament current representation, which leads to a slowly converging series, a multistrip representation of the current is proposed. In the procedure, the matrix elements are determined by a series involving integrals of mode functions over the strips and the convergence is improved. The true currents on obstacle surfaces are replaced by equivalent planar currents in a number of waveguide cross sections inside the obstacle. The technique is applied to a pair of metallic posts in the TE11-mode circular waveguide. Numerical results are compared with experimental data View full abstract»

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  • Computer-aided analysis of free-running microwave oscillators

    Page(s): 1735 - 1745
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    The authors present a newly developed free-running steady-state oscillator analysis algorithm suited to large-signal oscillator analysis. Kurokawa's oscillation condition is coupled with the modified nodal admittance form of the circuit equations to avoid degenerate solutions. The algorithm was implemented by using both harmonic balance and frequency-domain spectral balance techniques. It was used in the simulation of monolithically integrated varactor-tuned MESFET oscillator. Good agreement between simulated power and oscillation frequency results was obtained View full abstract»

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  • A new procedure for interfacing the transmission line matrix (TLM) method with frequency-domain solutions

    Page(s): 1788 - 1792
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    The authors present a new procedure that interfaces the transmission-line matrix (TLM) method with frequency-domain solutions of electromagnetic fields. Frequency-domain solutions are transformed into appropriate time-domain sequences using the discrete Fourier transform (DFT). Hence, the corresponding boundary Johns matrix can be determined with minimum computational effort. The subsequent treatment consists in convolving the streams of TLM impulses incident on the boundary with a Johns matrix generated with the new approach. The method is used to obtain the time-domain reflection sequence of wideband absorbing terminations in a rectangular waveguide in the dominant mode operation. In addition, the time-domain analysis of pulse penetration through a sheet with high, but finite, conductivity is presented. Good results demonstrate the efficiency of the proposed procedure View full abstract»

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  • A method of moments solution of a cylindrical cavity placed between two coaxial transmission lines

    Page(s): 1712 - 1717
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    The author presents a method for analyzing a dielectric-filled cylindrical cavity separating two coaxial transmission lines. The analysis is based on the method of moments and the equivalence principle taking into account higher order modes excited at the junctions between the cavity and the two transmission lines. Expressions relating the cavity's scattering parameters to the structure dimensions and the dielectric parameters are derived and implemented numerically. Numerical simulation results as well as experimental results are presented. The method was also applied to the measurement of the dielectric parameters of certain dielectric materials View full abstract»

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  • Numerical analysis of waveguide discontinuity problems using the network model decomposition method

    Page(s): 1766 - 1770
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    The use of the network model decomposition method for analyzing arbitrarily shaped H- and E-plane waveguide junctions is discussed. By using the polygon discretization technique previously introduced by the author (1990), the waveguide discontinuity region, which is surrounded by a metallic wall and the reference planes chosen, is first discretized; the topological model and the corresponding network model for the waveguide discontinuity are then established. In the formulation, equivalent current sources connected to the nodes on the boundary of the region are introduced to replace the effect of the field external to the region. The field internal to the region is approximated by the nodal voltage distribution of the network model, which can then be used to determine the scattering parameters of the waveguide junction. A diakoptic algorithm for the solution of the network model is also developed. Numerical results for various H- and E-plane junctions are given, and it is shown that the method compares favorably compares with other theories View full abstract»

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  • Characterization of the shielding effects on the frequency-dependent effective dielectric constant of a waveguide-shielded microstrip using the finite-difference time-domain method

    Page(s): 1688 - 1693
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    The dispersion behavior of a waveguide-shielded microstrip line is investigated using the finite-difference time-domain method. The result is a frequency-dependent effective dielectric constant. Structures having a centred strip are examined to determine the effects of a top cover alone and the effects of two symmetrically placed sidewalls. Structures with an off-centred strip are used to investigate the effects of a single sidewall alone and the combined effects of a single sidewall plus the top wall. The differences between the effects of a single sidewall alone and those of the two symmetrically placed sidewalls are identified. In addition, new results on the combined effects of the top wall plus one sidewall, which are important when considering the placement of the outermost elements of a packaged circuit, are also discussed View full abstract»

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  • Generalized scattering matrix of generalized two-port discontinuities: application to four-port and nonsymmetric six-port couplers

    Page(s): 1725 - 1734
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    A field theory analysis of multiport, multidiscontinuity structures based on the generalized scattering matrix (GSM) of a generalized two-port discontinuity concept is presented. The analysis can be used in any structure equipped with any number of input and output ports, and results in substantial simplifications over previous analyses. The GSMs of generalized two-port discontinuities can also be cascaded with the same procedure as the two-port discontinuities and can be used to determine the electromagnetic field and the Poynting vector at every point of the structure. The GSM of the generalized two-port technique is used to analyze four-port and nonsymmetric six-port branch-waveguide directional couplers, and good agreement between the theoretical results and experimental data is obtained View full abstract»

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  • Theoretical and experimental study of the evolution of fields in an overdimensioned waveguide with a corrugated surface

    Page(s): 1773 - 1779
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    To obtain answers to problems arising in many microwave applications, some labs use overdimensioned corrugated waveguides. The authors propose a theoretical approach with eigenmodes that enables one to determine the values of the limiting frequencies (frequencies of π modes in the periodic structure) of an overdimensioned parallelepiped cavity loaded with a thin corrugation as a function of the height of the aperture. In this approach, the electric field is represented by different analytical functions. The authors compare the theoretical results with the experimental values obtained for different apertures and periodicities, according to the value of the wavelength in comparison with the aperture and the period. Each function is in good agreement in a certain frequency range View full abstract»

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  • Stability ranges of regenerative frequency dividers employing double balanced mixers in large-signal operation

    Page(s): 1759 - 1762
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    The authors present a simple theory which makes it possible to calculate the frequency ranges of stable operation for a regenerative divider employing a double balanced mixer in large-signal operation. The validity of the derived formulas is tested by various network simulations. It is found that, in spite of the relatively simple assumptions for the description of the large-signal behaviour, the boundaries of the stable ranges are described with sufficient accuracy by the derived analytical relations View full abstract»

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  • A new algorithm for the accurate alignment of microwave networks

    Page(s): 1754 - 1758
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    The authors present a new algorithm suitable for the accurate alignment of microwave networks. The algorithm is developed from the sensitivity analysis of the network response with respect to the adjustable elements and does not require knowledge of the network model. The algorithm computes the required adjustment as the solution of a Gauss-Newton system of equations and is implemented by quantifying the adjustment of each individual element setting. This procedure does not demand a previous characterization or calibration of the adjustable elements and has been proved to be efficient for the accurate alignment of different types of microwave filters View full abstract»

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  • A comparison of two approximations for the capacitance of a circle concentric with a cross

    Page(s): 1784 - 1788
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    The maximum and minimum capacitances on circles concentric with an internal cross are determined for a four-lobed and an eight-lobed equipotential distribution. It is found that the relative difference between the maximum and minimum effective capacitances of the eight-lobed curves is about an order of magnitude lower than the same difference in the four-lobed curves, for comparable geometries. It is shown that the average and the geometric means of the maximum and minimum effective capacitances on the multilobed curves are excellent approximations of the exact values. In fact, the error in the average of the maximum and minimum effective capacitances decreases exponentially as their relative difference decreases so that the average value for the eight-lobed case is a better approximation than the average for the four-lobed case by at least an order of magnitude, in the cases of most interest. The increased accuracy obtained from the eight-lobed equipotential distribution is presented in graphical form View full abstract»

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  • A method for the rapidly convergent representation of electromagnetic fields in a rectangular waveguide

    Page(s): 1796 - 1799
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    A modified image method for calculating the fields produced by straight electric and magnetic current segments is proposed and found to be effective for calculating the fields near the source. Computing errors of the field increase as the distance from the source to the observation point increases. Therefore, the modified image method is improved for the accurate calculation at any position by adding a correcting term. In order to check the adequacy and usefulness of the method considering the term, its error is compared with that of the method without it View full abstract»

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  • Analysis of E-H plane tee junction using a variational formulation

    Page(s): 1770 - 1773
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    A three-port equivalent network for an E-H plane tee junction is determined taking into account the effect of waveguide wall thickness and considering the contribution of the dominant mode to the imaginary part of the self-reaction. The parameters of the three-port equivalent network are determined. From a knowledge of the equivalent network parameters, the net impedance loading, reflection coefficient, and coupling are evaluated for an E-H plane tee junction. A comparison between theoretical and experimental results is also presented View full abstract»

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  • Open resonator for precision dielectric measurements in the 100 GHz band

    Page(s): 1792 - 1796
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    Dielectric properties of fused silica, MgO, AlN, and BN were measured using an open resonator at frequencies around 100 GHz. The resonator is of the semifocal type and consists of a concave and a plane mirror, and the frequency variation method is used. To increase the reliability of measurement data, the operating frequency and thickness of the samples were chosen so as to make the parameter Δ=1 for every sample. The radius of curvature of the concave mirror is deduced with sufficient accuracy from the resonant frequencies of the transverse-electric-mode TEM0.0 and TEM1.0 modes, which results in a precise determination of resonator length. The standard deviation of measurements was less than 0.1% in permittivity and about 10% in loss tangent View full abstract»

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  • Broad-band simultaneous measurement of the complex permittivity tensor for uniaxial materials using a coaxial discontinuity

    Page(s): 1718 - 1724
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    A technique is presented for simultaneously measuring the complex values of the permittivity tensor of uniaxial materials. A gap in a coaxial line is filled with the material under test. Complex elements of the permittivity tensor are computed from measurements of the S-parameters (S11 and S21 ) made on the gap taking into account higher order modes excited at the discontinuity. The authors demonstrate that this problem is reduced to two systems, each containing three equations with three unknowns. Computer time is therefore reasonable without affecting accuracy. Measured complex permittivity data from 45 MHz to 18 GHz are presented. Good agreement between calculated and generally accepted values is obtained View full abstract»

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  • Propagation characteristics of coplanar-type transmission lines with lossy media

    Page(s): 1694 - 1700
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    Lossy coplanar-type transmission lines are analyzed based on the hybrid-mode formulation by combining the spectral-domain approach with the perturbation method. Introducing a finite thickness of metallization and choosing the proper basis functions for the thick conductor model prevent the integrals used for calculating the conductor losses from becoming singular when evaluated at the conductor edge. An orthogonality relation is used to reduce the double infinite or semi-infinite integral to a single integral, thus reducing the computation effort drastically. Numerical computations by new basis functions for the thick conductor show convergence rates as fast as those for the zero-thickness cases. Numerical results include the effective dielectric constants, characteristic impedances, and total losses (conductor and dielectric losses) for slot lines and symmetrical and asymmetrical coplanar waveguides 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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