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Microwave Theory and Techniques, IEEE Transactions on

Issue 8 • Date Aug. 1998

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Displaying Results 1 - 25 of 25
  • Generation of nonminimum phase from amplitude-only data

    Page(s): 1079 - 1084
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    A method is presented for the generation of nonminimum phase from amplitude-only data. The nonminimum phase is generated utilizing the principles of causality and the Hilbert transform. The application of the theory has been applied to some antenna radiation-power patterns and to measured transfer functions of microwave filters to illustrate the applicability of this approach. View full abstract»

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  • Static analysis of arbitrarily shaped conducting and dielectric structures

    Page(s): 1171 - 1173
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    In this paper, a simple and efficient numerical procedure is presented to compute the charge distribution and capacitance of conducting bodies in the presence of dielectric structures of arbitrary shape and finite size. The method presented is robust and provides accurate results for both low as well as high dielectric-constant materials as supported by numerical examples. View full abstract»

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  • An investigation of the high-frequency limit of a miniaturized commercial voltage-controlled oscillator used in 900-MHz-band mobile-communication handset

    Page(s): 1165 - 1168
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    The 900-MHz-band voltage-controlled oscillator (VCO) currently used in a commercial mobile-communication handset has the features of light weight, small size, low phase noise, and low DC current consumption. This paper investigates the problems that may occur when these types of VCO's are employed in next-generation high-frequency mobile-communication handsets. The results show that oscillation may not commence above frequency fT/2 √(Req /Tbb), which is significantly below the fmax of the device itself, due to the effects of the circuit elements. In addition, a new formula is proposed which provides a practical guideline for selection of the active devices. The procedure for extraction of the small-signal model required by the proposed formula is also described in detail. The results obtained with the formula are in good agreement with those obtained from the measured S-parameters View full abstract»

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  • A new approach to nonlinear analysis of noise behavior of synchronized oscillators and analog-frequency dividers

    Page(s): 1168 - 1171
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    An original theory of phase noise in synchronized oscillators is outlined through the phase-locked loop (PLL) approach. The phase-noise spectrum obtained first by the analytical PLL theory and then by a simulator have been compared with very good accuracy. This new approach permits the best understanding of noise conversion in synchronized devices View full abstract»

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  • Development of an improved two-dimensional finite-element code for cylindrically symmetric eigenmodes

    Page(s): 1180 - 1182
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    A new two-dimensional finite-element (FE) eigenmode solver has been developed, which is suitable for calculating cylindrically symmetric modes. The quantity Hθ/r is used in the code to describe the electromagnetic fields instead of Hθ or rHθ, which is preferentially used in the existing codes, and the new formulation with Hθ/r is found to show higher accuracy and smoother convergence with respect to the number of mesh points. Comparison is also made between linear and quadratic elements, resulting in remarkably higher accuracy by the latter View full abstract»

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  • Excitation of leaky modes on multilayer stripline structures

    Page(s): 1062 - 1071
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    A quasi-analytical method for calculating the excitation of leaky modes on multilayer stripline structures by a finite source is presented in this paper. Simple sources such as an infinitesimal dipole near the conducting strip or a delta-gap feed on the conducting strip of the transmission line are considered. The method uses a numerically constructed Green's function for the source in the presence of the conducting strip, which is calculated from Fourier transform theory in terms of a one-dimensional Green's function for a line source in the presence of the conducting strip. The numerical Green's function involves a one-dimensional integration in the longitudinal wavenumber plane. The residue contributions from the poles of the Green's function define the excitation amplitudes of the leaky and bound modes that exist on the structure. The numerical Green's function is also used to numerically calculate the complete current on the strip excited by the source. The correlation between the leaky-mode current and the complete current is used to define the extent of the physical meaning of the leaky mode. The generalized pencil of functions (GPOF) method is used to study this correlation by resolving the complete current on the strip into exponential waves, which are then compared with the current of the leaky mode. The physical meaning of the leaky modes is also analytically examined by consideration of the branch cuts in the longitudinal wavenumber plane for the numerical Green's function integration. A “path consistency condition” is established as a necessary condition for the physical meaning of the leaky mode View full abstract»

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  • A total-variation-diminishing finite-difference scheme for the transient response of a lossless transmission line

    Page(s): 1193 - 1196
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    Total-variation-diminishing (TVD) finite-difference schemes have been used in computational fluid dynamics for accurate solutions of fluid problems involving shock phenomena. This paper investigates the possibility of their application in transient electromagnetic-wave problems. A lossless transmission line with a resistive load is considered to illustrate the application. A TVD Lax-Wendroff finite-difference scheme is presented for the numerical solution of transmission-line equations in time domain. Numerical results show that the TVD scheme can approximate the discontinuous waveforms with remarkable accuracy View full abstract»

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  • Optically induced measurement anomalies with voltage-tunable analog-control MMIC's

    Page(s): 1105 - 1114
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    Monolithic microwave integrated circuits (MMIC's) may be measured under relatively high-intensity lighting conditions. Later, when they are packaged, any anomalies found in subsequent measurements could be attributed to unwanted parasitics or box modes associated with the packaging. However, optical effects may not always be considered by radiofrequency (RF) and microwave engineers. For the first time, a qualitative assessment is given for the effects of photonic absorption on three broad-band voltage-tunable analog-control circuits. Each circuit has a different function, with each field-effect transistor (FET) operating in a different mode: a hot FET in a variable-gain amplifier, a cold FET in an analog attenuator, and an FET varactor in an analog phase shifter. All three circuit functions have been implemented using two different FET-based technologies. The first with ion-implanted 0.5-μm GaAs metal-semiconductor FET's (MESFET's) in circuits operating at either 3 or 10 GHz. The second employs epitaxially grown 0.25-μm AlGaAs-InGaAs pseudomorphic high electron-mobility transistors (HEMT's) in circuits operating at 38 GHz. All the MMIC's were fabricated using commercial foundry processes and illuminated under conventional optical microscope lighting conditions. Prominent error peaks have been found at bias points unique to the three different circuit topologies. Large error peaks are found with the MESFET-based circuits, while much smaller error peaks are achieved with the corresponding pseudomorphic HEMT (pHEMT) based circuits View full abstract»

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  • Subspace iteration search method for generalized eigenvalue problems with sparse complex unsymmetric matrices in finite-element analysis of waveguides

    Page(s): 1115 - 1123
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    In this paper, a numerical method for the robust computation of the number of eigenvalues within a closed contour of a generalized complex eigenvalue problem is presented. As a result of this computation, it is possible to perform a systematic search for the eigenvalues, ensuring that no eigenvalues are forgotten, and to optimize their calculation. Application is made to the finite-element modal analysis of inhomogeneous waveguides View full abstract»

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  • Thick eccentric circular iris in circular waveguide

    Page(s): 1177 - 1180
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    Other researchers have observed that eccentric irises possess certain advantageous features that may lead designers to prefer them over the conventional concentric irises. The least-squares boundary residual method (LSBRM) is utilized in this paper to analyze the behavior of such an eccentric-iris structure (of nonzero thickness). Tests have confirmed that the computer model thus obtained is capable of yielding numerical results that are accurate to within ⊥1% View full abstract»

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  • A new technique for the stable incorporation of static field solutions in the FDTD method for the analysis of thin wires and narrow strips

    Page(s): 1091 - 1096
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    The behavior of the fields around many common objects (e.g., wires, slots, and strips) converges to known static solutions. Incorporation of this a priori knowledge of the fields into the finite-difference time-domain (FDTD) algorithm provides one method for obtaining a more efficient characterization of these structures. Various methods of achieving this have been attempted; however, most have resulted in unstable algorithms. Recent investigations into the stability of FDTD have yielded criteria for stability, and this contribution for the first time links these criteria to a general finite-element formulation of the method. It is shown that the finite-element formulation provides a means by which FDTD may be generalized to include whatever a priori knowledge of the field is available, without compromising stability. Example results are presented for extremely narrow microstrip lines and wires View full abstract»

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  • On the computation of the complete spectral Green's dyadic for layered bianisotropic structures

    Page(s): 1158 - 1164
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    This paper shows how to obtain a systematic algorithm for computing the complete spectral Green's dyadic (CSGD) of multilayered bianisotropic planar structures. The top and bottom boundary conditions of the structures can be either electric/magnetic walls or any kind of boundary condition suitable for implementation by means of impedance/admittance dyadics. The method presented here makes use of the fact that the sheets of normally directed surface electric-/magnetic-current density can be transformed into equivalent sheets of transverse electric-/magnetic-current density. Once the problem has been reduced to deal only with transverse current densities, the equivalent boundary method (EBM) is extended to obtain the CSGD. This method has been applied to compute the radiation characteristics of arbitrarily oriented dipoles embedded in different layered structures View full abstract»

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  • Analysis of dielectric E-plane waveguides and design of filters

    Page(s): 1085 - 1090
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    A small-size waveguide made of high-permittivity ceramic is analyzed. The propagation constants are calculated approximately by an approach where the electromagnetic fields outside the waveguide are fully taken into consideration. The analysis values agree well with the experimental values. The constants of equivalent circuit for the metallic strip section are obtained by using a separate model for the analysis of the structure. Based on these results, bandpass filters (BPF's) are designed and fabricated. The fabricated BPF's have better transmission and reflection characteristics than those designed on the basis of a trough-guide model View full abstract»

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  • Efficient time-domain and frequency-domain finite-element solution of Maxwell's equations using spectral Lanczos decomposition method

    Page(s): 1141 - 1149
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    An efficient three-dimensional solver for the solution of the electromagnetic fields in both time and frequency domains is described. The proposed method employs the edge-based finite-element method (FEM) to discretize Maxwell's equations. The resultant matrix equation after applying the mass-lumping procedure is solved by the spectral Lanczos decomposition method (SLDM), which is based on the Krylov subspace (Lanczos) approximation of the solution. This technique is, therefore, an implicit unconditionally stable finite-element time and frequency-domain scheme, which requires the implementation of the Lanczos process only at the largest time or frequency of interest. Consequently, a multiple time- and frequency-domain analysis of the electromagnetic fields is achieved in a negligible amount of extra computing time. The efficiency and effectiveness of this new technique are illustrated by using numerical examples of three-dimensional cavity resonators View full abstract»

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  • New empirical unified dispersion model for shielded-, suspended-, and composite-substrate microstrip line for microwave and mm-wave applications

    Page(s): 1187 - 1192
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    By introducing the concept of “virtual relative permittivity,” this paper reports several closed-form dispersion models for a multilayered shielded/unshielded microstrip line over 1<εr⩽20, 0.1⩽(w/h)⩽10, (h3/h)⩾2 in the frequency range up to 4 GHz.cm. The maximum deviation of the one model against the results of the spectral-domain analysis (SDA) is limited to 3%, while for the other three models, the maximum deviation is <2% and the root-mean-square (rms) deviation is <0.8%. This paper also reports improvement in the closed-form model of March for the determination of εeff(O) of the shielded microstrip line View full abstract»

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  • A novel dimension-reduction technique for the capacitance extraction of 3-D VLSI interconnects

    Page(s): 1037 - 1044
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    In this paper, a new capacitance extraction method called the dimension-reduction technique (DRT) is presented for three-dimensional (3-D) very large-scale integration (VLSI) interconnects. The DRT converts a complex 3-D problem into a series of cascading simple two-dimensional (2-D) problems. Each 2-D problem is solved separately, thus we can choose the most efficient method according to the arrangement of conductors. We have used the DRT to extract the capacitance matrix of multilayered and multiconductor crossovers, bends, vias with signal lines, and open-end. The results are in close agreement with those of Ansoft's SPICELINK and the Massachusetts Institute of Technology's (MIT) FastCap, but the computing time and memory size used by the DRT are several (even ten) times less than those used by SPICELINK and FastCap View full abstract»

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  • Transient analysis of microwave active circuits based on time-domain characteristic models

    Page(s): 1097 - 1104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A modular method is presented to speed up transient simulation of microwave active circuits which consist of linear components and active devices that are often nonlinear. Firstly, the linear components and active devices are individually characterized by time-domain characteristic models (TDCM's) and lumped equivalent circuits, respectively, to reduce the computer memory. Then, based on deconvolution, the TDCM's of linear components are synthesized from the terminal voltages and currents of step voltage excitation, which are simulated by the finite-difference time-domain (FDTD) method. Finally, transient analysis of a one-dimensional (1-D) discrete-time system is applied to obtain the terminal responses of the microwave active circuits, in which a larger sampled step is chosen to reduce the simulation time. This method is employed to two realistic circuits to validate its efficiency and accuracy. The results are in good agreement with the time-consuming direct FDTD simulation of entire circuits View full abstract»

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  • Study of the dispersion characteristics of planar chiral lines

    Page(s): 1150 - 1157
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    This paper analyzes the dispersion characteristics of the fundamental modes of some basic chiral planar transmission lines: microstrip, slot-line, coplanar waveguide (CPW), and a coupled microstrip line, including the possible frequency dependence of the chiral parameters. The dispersion characteristics are computed after finding the zeros of the determinantal equation resulting from the application of the Galerkin method in the spectral domain. Because of the biisotropic nature of the substrate, a 4×4 matrix differential equation has been solved to obtain the spectral dyadic Green's function (SDGF). This function is explicitly obtained in terms of a closed-form 4×4 transition matrix that relates the transverse electromagnetic fields at the upper and lower interface of the chiral substrate. This fact is key to developing fast computer codes since it avoids numerical matrix exponentiations. The numerical results have shown that the chiral nature of the substrate basically adds an additional parameter to control the propagation characteristics of the analyzed lines and, in general, makes the lines more dispersive, showing even resonant-like behavior View full abstract»

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  • A new dispersion model for microstrip line

    Page(s): 1183 - 1187
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    This paper presents the phenomenological dispersion law and a new logistic dispersion model (LDM) for the microstrip line which has a root-mean-square (rms) accuracy of <1% and a maximum deviation of <2% for any W/h ratio, any permittivity, and at any operating frequency. The model is also applicable to the conductor of finite thickness. The eight existing dispersion models have also been compared against the experimental results and against the spectral-domain analysis (SDA) over a wide range of parameters View full abstract»

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  • Resonant frequency and quality factors of a silver-coated λ/4 dielectric waveguide resonator

    Page(s): 1124 - 1131
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    In this paper, resonant frequency, radiation loss, conductor loss, and dielectric loss of a silver-coated λ/4 dielectric waveguide resonator are investigated. Leakage of the electromagnetic field from the open-end face of the resonator is the only source of radiation, which also affects the resonant frequency. New theoretical expressions are devised to calculate resonant frequency, conductor quality (Q) factor, dielectric Q factor, and radiation Q factor. Effective conductivity of the silver-coated resonator is estimated from experimental unloaded Q factor. The theoretical analysis is validated by the experimental result and the data obtained using the finite-difference time-domain (FDTD) technique. Finally, we have designed and fabricated a dual-mode bandpass filter using this resonator View full abstract»

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  • Analysis of a slot-coupled T-junction between circular-to-rectangular waveguide

    Page(s): 1173 - 1176
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    This paper presents a rigorous analysis of a slot-coupled T-junction between a primary circular cylindrical waveguide and rectangular waveguide, forming the coupled T-arm. The analysis is based on moment-method formulation using full-wave basis functions and Galerkin's technique for testing. Expression for the coupling and reflection coefficients are found, taking into account the effect of finite wall thickness of the circular waveguide in which the coupling slot is milled. A comparison between the theoretical and experimental results on coupling and return loss are presented View full abstract»

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  • A wide-band multiport planar power-divider design using matched sectorial components in radial arrangement

    Page(s): 1072 - 1078
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    This paper proposes a new multiport planar power-divider design by radially combining the sectorial components and the input and output matching networks. This design can achieve good input match over a wide bandwidth without resorting to transformer sections of high-impedance lines, which are difficult to realize. This approach is applied to the design of 4-and 14-way center-fed power dividers in microstrip structures with good input match (voltage standing-wave ratio (VSWR) <1.5) over a bandwidth of 30% and 15%, respectively. The return loss of output ports and the isolation among them in the 14-way divider are less than -13 dB. A simple analysis method using the radial transmission-line theory to model the microstrip sectorial components is employed to characterize the power dividers. The calculated scattering parameters are found to be in good agreement with the measured data View full abstract»

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  • Analytical evaluation of the asymptotic impedance matrix of asymmetric gap discontinuities

    Page(s): 1132 - 1140
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    New analytical formulas have been developed for evaluating the asymptotic impedance matrix of an asymmetric gap by using the integral transform method. Application of the newly derived formulas shows a dramatic improvement of the computation time for evaluating the overall impedance-matrix elements for the symmetric and asymmetric gaps while retaining the accuracy View full abstract»

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  • Optimization of a 250-GHz Schottky tripler using novel fabrication and design techniques

    Page(s): 1055 - 1061
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    A technique for optimizing a diode waveguide mount for millimeter- and submillimeter-wave applications has been developed. The structure consists of a planar rectangular radiator for which an accurate derivation of impedance is available. The planar radiating probe incorporates the diode contacting tip, is fabricated integrally with the microstrip filter, and is used in a 230-290-GHz frequency tripler. Modification of the tripler using the described technique resulted in an improvement of ≈6 dB in available output power, compared to the authors' previous results for this device. Device output power exceeds 8.5 mW at 245 GHz for an input power of 132 mW. The best flange-to-flange efficiency (in excess of 11%) was achieved at 3.3-mW output power. This technique was then applied to a waveguide mount, incorporating two diodes contacted in parallel, so that greater input power could be handled. This resulted in a tripler with a maximum output power of 15 mW at 270 GHz for an input of 280 mW View full abstract»

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  • Reducing losses in dielectric waveguide discontinuities

    Page(s): 1045 - 1054
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    Rectangular dielectric waveguides are used in millimeter-wave applications. They have low loss and wide bandwidth at high frequencies. Another major advantage to dielectric waveguides is that they are inexpensive to design and manufacture. However, a major disadvantage to the dielectric waveguide is that they experience relatively high losses at bends and T-junctions. This paper looks at a novel approach in reducing the insertion loss in dielectric waveguide bends and T-junctions. A high dielectric material is inserted at the discontinuity, causing the electromagnetic energy to be coupled and launched toward the output. The dielectric constant of the material, position of the material, and shape of the material are instrumental in reducing the insertion loss. A transition discontinuity in the form of a 45° bend has also been found to reduce insertion loss when properly designed. The size, shape, and location of the discontinuity and the high dielectric material are optimized and compared to the results without a high dielectric material. The 90°- and 45°-bend simulations were verified by building test structures and comparing predictions of the insertion loss to measurements 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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