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Microwave Theory and Techniques, IEEE Transactions on

Issue 4 • Date April 1993

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Displaying Results 1 - 25 of 33
  • Comments on "Finite elements for microwave device simulation: application to microwave dielectric resonator filter" [with reply]

    Page(s): 737 - 738
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    The commenter raises some questions regarding the results in the above titled paper by J.P. Cousty et al. (ibid., vol.40, no.5, p.925-32, May 1992). He points out a discrepancy that indicates that either the dimensions given in Fig. 4 or the accuracy of the finite element method are in doubt. He also questions the results of applying the 3-D finite element method to the computation of resonant frequencies of hybrid modes. Two of the authors (S. Verdeyme and P. Guillon) defend the results.<> View full abstract»

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  • Single barrier varactors for submillimeter wave power generation

    Page(s): 572 - 580
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    Theoretical work on single barrier varactor (SBV) diodes indicates that the efficiency of a tripler with a SBV diode has a maximum for a considerably smaller capacitance variation than previously thought. SBV diodes based on GaAs, InGaAs and InAs have been fabricated and their DC properties have been tested. Detailed modeling of the carrier transport properties of the SBV device is carried out in two steps. First, the semiconductor transport equations are solved simultaneously, using a finite difference scheme in one dimension. Second, the calculated I -V and C-V characteristics are used by a multiplier simulator to calculate the optimum impedances and output powers at the frequencies of interest. The authors have developed an analysis technique which complements the harmonic balance technique. Simulations for a case study of a 750-GHz multiplier show that InAs diodes perform favorably compared to GaAs diodes View full abstract»

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  • Asymptotic analysis of mode transition in general class of circular hollow waveguides at the infrared frequency

    Page(s): 733 - 736
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The correspondence between hybrid modes in small- and large-core, circular, hollow waveguides is discussed, using an asymptotic theory for the infrared. Mode changes or mode transitions in several hollow waveguides which depend on the cladding material and the mode order are discussed. For dielectric-coated metallic waveguides, mode changes also depend on the thickness of the coating. For singly cladded hollow waveguides, the region where the mode changes is shown to be in the plane of the complex refractive index (n-jk) of the cladding material, where the HE1-mode in large-core waveguides approaches the TE or TM mode View full abstract»

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  • New approach to the design and the fabrication of THz Schottky barrier diodes

    Page(s): 549 - 557
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    GaAs Schottky barrier diodes with near-ideal electrical and noise characteristics for mixing applications in the terahertz frequency range are described. The conventional formulas describing these characteristics are valid only in a limited forward bias range, corresponding to currents much smaller than the operating currents under submillimeter mixing conditions. Therefore, generalized analytical expressions for the I-V and C-V characteristics of the metal-semiconductor junction in the full bias range are given. A new numerical diode model is presented which takes into account not only the phenomena occurring at the junction, such as current dependent recombination and drift/diffusion velocities, but also the variations of electron mobility and electron temperature in the undepleted epi-layer. A diode fabrication process based on the electrolytic pulse etching of GaAs in combination with an in situ platinum plating for the formation of the Schottky contacts is described. Schottky barrier diodes with a diameter of 1 μm fabricated by this process have already shown excellent results in a 650-GHz waveguide mixer at room temperature View full abstract»

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  • An 86-106 GHz quasi-integrated low noise Schottky receiver

    Page(s): 558 - 564
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    An integrated planar receiver has been developed and tested over the 82-112 GHz bandwidth. The quasi-integrated antenna used in the receiver has a high gain, a high Gaussian coupling efficiency and a wide bandwidth. The mixer design consists of a planar GaAs Schottky diode placed at the feed of a dipole probe suspended inside an integrated horn antenna. The diode uses an etched surface channel and a planar air bridge for reduced parasitic capacitance. At 92 GHz, the room temperature antenna-mixer exhibits a double sideband (DBS) conversion loss and noise temperature of 5.5±0.5 Db and 770 K±50 K, respectively. The measured DSB conversion loss, and noise temperature over a 20-GHz bandwidth (86-106 GHz) remain less than 6.2±0.5 dB and 1000 K±50 K, respectively. The low cost of fabrication and simplicity of the design makes it ideal for millimeter- and submillimeter-wave receivers View full abstract»

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  • A quasioptical resonant-tunneling-diode oscillator operating above 200 GHz

    Page(s): 720 - 722
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    A quasioptical resonant-tunneling-diode (RTD) oscillator is demonstrated at frequencies above 200 GHz. The oscillator is stabilized by a semiconfocal open cavity. The maximum output power and the linewidth are approximately 50 μW and 20 kHz, respectively, at a fundamental frequency of 210 GHz. By varying the cavity length, the oscillator frequency can be adjusted over a 0.4-GHz range in a repetitive manner. This behavior is explained by analogy with laser oscillators. The quasioptical RTD oscillator is well suited as a local oscillator for low-power radiometric mixers View full abstract»

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  • Parameter extraction of microwave transistors using a hybrid gradient descent and tree annealing approach

    Page(s): 726 - 729
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Tree annealing is a robust optimization scheme which can be used to find the valleys of an error surface. The problem of entrapment in local minima is not a factor with this type of optimization, but it is much slower than gradient-based techniques. The method presented here attempts to take advantage of the speed of gradient-based methods and of the efficient pseudorandom searching abilities of tree annealing. The result is a technique which behaves as a directed multistart gradient method. All minima encountered during optimization are recorded, thus providing alternatives in case of a nonphysical final solution. The technique is used in the extraction of a modified Materka-Kacprzak model of a GaAs MESFET View full abstract»

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  • CAD of T-septum waveguide evanescent-mode filters

    Page(s): 731 - 733
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    A mode-matching-based design for an evanescent-mode waveguide filters with T-septum shaped metal inserts is presented. Owing to the wideband characteristics of the T-septum waveguide, the proposed design constitutes a significant improvement over common evanescent-mode filters with respect to both size reduction and stopband behavior. The theoretical approach is verified for the example of a three-resonator 8.8-GHz filter prototype of less than 3/4-in length. The second passband is beyond 27 GHz. Since the design procedure takes higher-order mode interactions into account, good agreement between theory and experiment is obtained over the entire measurement range between 8.2 and 40 GHz View full abstract»

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  • A reciprocity formulation for the EM scattering by an obstacle within a large open cavity

    Page(s): 702 - 707
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A formulation based on a generalized reciprocity theorem is developed for analyzing the external high-frequency EM scattering by a complex obstacle inside a relatively arbitrary open-ended waveguide cavity when it is illuminated by an external source. This formulation is also extended to include EM fields whose time dependence may be nonperiodic. A significant advantage of this formulation is that it allows one to break up the analysis into two independent parts, one dealing with the waveguide cavity shape alone and the other with the obstacle alone. The external scattered field produced by the obstacle (in the presence of the waveguide cavity structure) is given in terms of a generalized reciprocity integral over a surface ST corresponding to the interior waveguide cavity cross-section located conveniently but sufficiently close to the obstacle. Furthermore, the fields coupled into the cavity from the source in the exterior region generally need to propagate only one way via the open front end (which is directly illuminated) to the interior surface ST in this approach, and not back, in order to find the external field scattered by the obstacle View full abstract»

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  • Cooled Schottky varactor frequency multipliers at submillimeter wavelengths

    Page(s): 565 - 571
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    The efficiency of a Schottky varactor frequency multiplier at submillimeter wavelengths can be increased by cooling the diode. The increased mobility of the free carriers causes the series resistance to decrease, and the efficiency can increase as much as a few dB at low input power levels. At high output frequencies and at high power levels the efficiency of the multiplication is decreased by the current saturation, because the junction capacitance cannot be pumped effectively. When the diode is cooled, the maximum current of the diode increases and much more output power can be expected. There are also slight changes in the I-V characteristic and in the diode junction capacitance, but they have a negligible effect on the efficiency of the multiplier. The theoretical maximum output power near 1 THz is calculated to increase by about 10 dB from 50μW to 500μW, when the multiplier chain is cooled to 77 K. However, considerable improvement in the efficiency can be achieved by cooling to 150 K, which is easily attained in space by passive cooling View full abstract»

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  • Quasi-static analysis of shielded microstripline by a modified boundary element method

    Page(s): 729 - 731
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A modified boundary element method for analyzing the shielded microstrip-like structure is presented. The boundary integral equations are derived via Green's second identity with the adjoint fields chosen to satisfy the boundary conditions along the outside shielding conductor. Numerically, these result in a considerably reduced matrix size compared to that using free space Green's functions as the adjoint fields. The computation time for off-diagonal element of the matrix can be decreased by taking the Maclaurin series expansion forms of the infinite sums. Results for microstrip line are found to be in good agreement with those in the literature View full abstract»

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  • End-effects in quasi-TEM transmission lines

    Page(s): 666 - 672
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    Magnetostatic analysis of a finite-length two-wire transmission line yields simple closed-form expressions for inductive end-fringing and interaction between ends. A further argument relates the results to capacitive end effects. Application to microstrip-like lines, twin-strip line and coplanar waveguide is outlined. It is demonstrated by explanation and comparison with the literature that these effects are the dominant discontinuity elements in short lengths of line, vias, resonators, bends, and other basic microwave configurations View full abstract»

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  • Semi-discrete finite element method analysis of arbitrary microstrip elements-static solution

    Page(s): 680 - 686
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The semi-discrete finite-element method (FEM) is applied to solve the Poisson equation for a class of microstrip structures. This numerical technique is a variant of the conventional FEM. Its name stems from the fact that finite-element approximation is implemented only along two of the Cartesian coordinates, while the solution dependence on the third is handled analytically. When applicable, this method is simpler and more economical than the conventional fully-discrete version. Convergence properties of the solution are examined, and its validity tested for a number of geometries through comparison with other solutions and published data View full abstract»

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  • Full-wave analysis of a transversely magnetized ferrite nonradiative dielectric waveguide

    Page(s): 647 - 651
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    A full-wave analysis is applied to a nonradiative dielectric waveguide where the isotropic dielectric slab is replaced by a transversely magnetized ferrite. The characteristic equation is obtained and the corresponding effects are discussed. The above structure exhibits reciprocal propagation characteristics. Nonreciprocal effects are also possible with a proper dielectric loading. Several numerical results are presented in the form of dispersion curve and an operational diagram, as a function of several ferrite and guide parameters. Electronically tuned and nonreciprocal devices can be implemented using this simple structure View full abstract»

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  • Concurrent network diakoptics for electromagnetic field problems

    Page(s): 708 - 716
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    A new modification to circuit-based diakoptics equations which allows the efficient manipulation of equivalent circuit models which represent Maxwell's equations is presented. A formulation of the diakoptics equations is given whereby torn subnetworks used to form the problem domain under consideration can be connected on a nearest neighbor basis. This formulation allows an algorithm which is suitable for implementation on a parallel computer to be written. It has been implemented on a transputer array configured with two different topologies. The computational efficiency of each topology is appraised and considerable computational advantage demonstrated with respect to the classical sequential variant of the technique. The procedure is then applied to sample electromagnetic field problems in order to verify its utility. Finally it is used to compute the performance of a patch microstrip hybrid coupler View full abstract»

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  • A frequency-dependent finite-difference time-domain formulation for general dispersive media

    Page(s): 658 - 665
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    A weakness of the finite-difference-time-domain (FDTD) method is that dispersion of the dielectric properties of the scattering/absorbing body is often ignored and frequency-independent properties are generally taken. While this is not a disadvantage for CW or narrowband irradiation, the results thus obtained may be highly erroneous for short pulses where ultrawide bandwidths are involved. In some recent publications, procedures based on a convolution integral describing D(t) in terms of E(t) are given for media for which the complex permittivity ∈*(ω) may be described by a single-order Debye relaxation equation or a modified version thereof. Procedures are, however, needed for general dispersive media for which ∈*(ω) and μ*(ω) may be expressible in terms of rational functions, or for human tissues for which multiterm Debye relaxation equations must generally be used. The authors describe a new differential equation approach, which can be used for general dispersive media. In this method D(t) in terms of E(t) by means of a differential equation involving E, and their time derivatives. The method is illustrated for several examples View full abstract»

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  • Resonance of a rectangular microstrip patch on a uniaxial substrate

    Page(s): 698 - 701
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    Effects of uniaxial anisotropy in the substrate on the complex resonant frequency of the microstrip patch antenna are investigated in terms of an integral equation formulation. The complex resonant frequency of the microstrip patch antenna is calculated using Galerkin's method to solve the integral equation. The sinusoidal functions that are selected as the basis functions, which show fast numerical convergence. Numerical results indicate that both the resonant frequency and the half-power bandwidth are increased due to positive uniaxial anisotropy and decreased due to negative uniaxial anisotropy View full abstract»

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  • A small dielectric TEM mode resonator with a crossing slot and its application to a cellular radio VCO

    Page(s): 639 - 646
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    A small TEM-mode dielectric resonator which features a crossing slot on the outer ground conductor plane is presented. The slot, functioning as a short-ended stub line serially inserted into the transmission line, can tune the resonant frequency down. The resonant frequency in a stripline resonator structure is rigorously analyzed by a method based on the spectral domain approach and the equivalent circuit is derived. This resonator is used in a cellular radio VCO with a varactor connected across the slot. The performance of the VCO in the 900-MHZ cellular band is described View full abstract»

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  • A versatile moment method solution of the conventional and modified coplanar waveguide T-junctions

    Page(s): 687 - 692
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    The conventional and modified coplanar waveguide (CPW) T-junctions, both symmetric and nonsymmetric, are investigated using the full wave moment method with duality for the electric and magnetic currents. The method is shown to be accurate and computationally more efficient than the finite-difference-time-domain (FDTD) method previously used to solve these T-junctions. The results show that the dispersion in the S-parameters of the different types of CPW T-junctions investigated can be minimized by a proper choice of the dimensions and locations of the air bridges. The versatility of the method is demonstrated by its ability to solve complicated CPW structures with different types of air bridges, such as the modified CPW T-junction View full abstract»

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  • A 200 GHz tripler using a single barrier varactor

    Page(s): 595 - 599
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    The authors present results for a tripler to 200 GHz using a single barrier varactor (SBV). The performance of the tripler, over an output frequency range from 186 to 207 GHz, has been measured in a crossed waveguide mount. The theoretical performance of the device and the tripler mount have been calculated using large signal analysis. An overall efficiency of 2% was achieved with efficiency at the device of above 5%. A comparison of theoretical and measured results and a discussion of various losses in the mount and the varactor are also presented View full abstract»

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  • Scattering parameters measurement of a nonreciprocal coupling structure

    Page(s): 652 - 657
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    A novel ferrite image guide was designed and tested from 26.5 to 40 GHz. The nonreciprocal structure consisted of two dielectric image guides separated by a ferrite slab. M-type hexagonal ferrite was used with its C-axis oriented parallel and perpendicular to the direction of propagation. The S-parameters of the device were measured for a nonuniform external biasing magnetic field applied parallel to the C-axis of the ferrite slab. Nonreciprocal effects were observed for all cases considered above. The results imply applications for ferrite devices operating at millimeter wavelength frequencies, such as isolators, filters, modulators, switches, phase shifters, etc View full abstract»

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  • 2×2 quasi-optical power combiner array at 20 GHz

    Page(s): 717 - 719
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    The design concept and the experimental results for a power combiner made of two strongly coupled FET oscillators use in a quasi-optical array are reported. To demonstrate the approach, a 2×2 planar array has been fabricated using a direct connection through a microstrip line. Taking the input impedance of the slot radiator into account, circuit the passive part of the array is investigated. The length of the microstrip feed lines are regulated to achieve the desired sum radiation pattern. At an operating frequency of 20 GHz, sum radiation patterns have been observed in both the H-plane and the E-plane View full abstract»

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  • Determination of Schottky diode sampling mixer frequency response from diode conductance waveforms

    Page(s): 723 - 726
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    Conversion loss variations at microwave frequencies for Schottky diode harmonic sampling mixers are predicted from a time and frequency domain analysis of diode conductance waveforms. A circuit model for the mixer is used to find a nonlinear integral-differential equation governing the sampling mixer's time domain behavior. An iterative solution is used to determine the diode conductance waveform, the Fourier transform of which is the frequency response of the sampler. Experimental verification is given for three different values of sampling capacitors and two different sampling chamber delays over a 2-40 GHz range View full abstract»

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  • A planar quasi-optical SIS receiver

    Page(s): 609 - 615
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    A planar, quasi-optical SIS (superconductor-insulator-superconductor) receiver operating at 230 GHz is described. The receiver consists of a 2×5 array of half-wave dipole antennas with niobium-aluminum oxide-niobium SIS junctions on a quartz dielectric-filled parabola. The 1.4-GHz intermediate frequency is coupled from the mixer via coplanar strip transmission lines and 4:1 balun transformers. The receiver is operated at 4.2 K in a liquid helium immersion cryostat. Accurate measurements of the performance of single untuned array receiver elements are reported. A mixer noise temperature of 89 K DSB (double sideband), receiver noise temperature of 156 K DSB and conversion loss of 8 dB into a matched load have been obtained. This mixer noise temperature is approximately a factor of two larger than that of current state of the art waveguide mixers using untuned single junctions a the same frequency View full abstract»

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  • The influence of metallization thickness on the characteristics of cascaded junction discontinuities of shielded coplanar type transmission line

    Page(s): 693 - 697
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A full-wave analysis based on the mode-matching technique is applied to analyze cascaded junction discontinuities of coplanar-type transmission lines, coplanar waveguide (CPW) and finline. Results for a CPW-finline transition, a shielded CPW gap and a symmetric notch incorporating the finite metallization thickness effect are presented. The influence of metallization thickness on the coupling effect exhibited by cascaded junction discontinuities is also presented and discussed 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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