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Microwave Theory and Techniques, IEEE Transactions on

Issue 11 • Date Nov. 1999

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Displaying Results 1 - 18 of 18
  • Guest Editorial

    Page(s): 2057 - 2058
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    Freely Available from IEEE
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  • A three-dimensional quasi-optical self-oscillating mixer

    Page(s): 2144 - 2147
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    A quasi-optical self-oscillating mixer (SOM) consisting of a pair of transistor-loaded grids mounted on opposite sides of a two-dimensional photonic crystal (PC) is presented. The PC facilitates mutual injection locking between the grids and extends the operating range of the SOM by minimizing injection locking to an external source. By combining this with electronic tuning of the free-running oscillation frequency, total elimination of the injection-locking range can be achieved. Radiation patterns at C-band also indicate the ability to detect RF signals in three dimensions View full abstract»

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  • Electromagnetic scattering from a PBG material excited by an electric line source

    Page(s): 2105 - 2114
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    A general procedure Is presented to determine the fields scattered by a periodic structure due to a complex excitation in terms of the structure's plane-wave response. Specifically, the scattered field from an electric line source over a semiinfinite metallo-dielectric photonic bandgap (PBG) material is described. An effective description for the artificial crystal's plane-wave response is used, consisting of angularly parameterized response functions. A methodology for analyzing the electromagnetic response of such a material to a nonplane-wave excitation is provided, whereby a general complex excitation is spectrally decomposed into an integral over a continuous spectrum of homogeneous and inhomogeneous plane waves. An analytic solution for the scattering of each plane wave by the PBG material half-space is then utilized. The complete scattered field is given in a closed integral form, which is computed both numerically and in the asymptotic limit. The effect of the PBG crystal half-space on the scattered field due to an electric line source is presented for frequencies that correspond, for a normally incident plane wave, to a transmission bandgap, a transmission band edge, and an antireflecting plateau. The focusing effects and electric- and magnetic-wall behavior of the PBG crystal are demonstrated. The presented approach promotes both the physical understanding of PBG material systems and the efficiency of the numerical modeling of these systems at frequencies beyond the quasi-static limit of the traditional effective medium theories View full abstract»

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  • Two-dimensional photonic crystal Fabry-Perot resonators with lossy dielectrics

    Page(s): 2085 - 2091
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    Square and triangular lattice two-dimensional (2D) photonic crystals (PCs) composed of lossy dielectric rods in air were constructed with a microwave bandgap between 4-8 GHz. Fabry-Perot resonators of varying length were constructed from two of these PCs of adjustable thickness and reflectivity. The quality factor of cavity modes supported in the resonators was found to increase with increasing PC mirror thickness, but only to a point dictated by the lossiness of the dielectric rods. A 2-D periodic Green's function simulation was found to model the data accurately and quickly using physical parameters obtained in separate measurements. Simple rules are developed for designing optimal resonators in the presence of dielectric loss View full abstract»

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  • Directive photonic-bandgap antennas

    Page(s): 2115 - 2122
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    This paper introduces two new photonic bandgap (PBG) material applications for antennas, in which a photonic parabolic reflector is studied. It is composed of dielectric parabolic layers associated to obtain a PBG material. The frequency gap is used to reflect and focus the electromagnetic waves. This device has been designed using a finite-difference time-domain (FDTD) code. FDTD computations have provided the theoretical reflector's directivity. These results are in good agreement with measurements, and it appears that the PBG reflector presents the same directivity as a metallic parabola. A second application uses a defect PBG material mode associated with a metallic plate to increase the directivity of a patch antenna. We explain the design of such a device and propose experimental results to validate the theoretical analysis View full abstract»

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  • Mutual coupling between millimeter-wave dielectric-resonator antennas

    Page(s): 2164 - 2166
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    The mutual coupling between aperture coupled cylindrical dielectric-resonator antennas (DRAs) is analyzed using the finite-difference time domain method. The perfectly matched layer is used as absorbing boundary conditions. The voltage excitation source of microstrip structure is based on the Zhao's model, in which the source plane or the terminal plane can be moved very close to the discontinuity so that the computational domain can be reduced substantially. The numerical results are verified by measurements and reasonable agreement between theory and experiment is obtained. It is shown that this method is highly efficient for the analysis of DRAs View full abstract»

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  • A novel TEM waveguide using uniplanar compact photonic-bandgap (UC-PBG) structure

    Page(s): 2092 - 2098
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    A novel waveguide using a photonic bandgap (PBG) structure is presented. The PBG structure is a two-dimensional square lattice with each cell consisting of metal pads and four connecting lines, which are etched on a conductor-backed Duroid substrate. This uniplanar compact PBG structure realizes a magnetic surface in the stopband and is used in the waveguide walls to provide magnetic boundary conditions. A relatively uniform field distribution along the cross section has been measured at frequencies from 9.4 to 10.4 GHz. Phase velocities close to the speed of light have also been observed in the stopband, indicating that TEM mode has been established. A recently developed quasi-Yagi antenna has been employed as a broad-band and efficient waveguide transition. Meanwhile, full-wave simulations using the finite-difference time-domain method provide accurate predictions for the characteristics of both the perfect magnetic conductor impedance surface and the waveguide structure. This novel waveguide structure should find a wide range of applications in different areas, including quasi-optical power combining and the electromagnetic compatibility testing View full abstract»

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  • Roles of wave impedance and refractive index in photonic crystals with magnetic and dielectric properties

    Page(s): 2148 - 2150
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    We investigated the roles of wave impedance and refractive index in photonic crystals by means of analytical expressions for edges frequencies of a photonic bandgap (PBG) in a one-dimensional photonic crystal with magnetic and dielectric properties. The analytical expressions were derived when the optical thicknesses of layers are the same. The wave impedance governs the formation of PBG's and the intensity of defect modes. Meanwhile, the position of PBG's and the creation of defect modes are related to the refractive index View full abstract»

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  • A generalized scattering matrix method using the method of moments for electromagnetic analysis of multilayered structures in waveguide

    Page(s): 2151 - 2157
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    The method of moments (MoM) in conjunction with the generalized scattering matrix (GSM) approach is proposed to analyze transverse multilayered structures in a metal waveguide. The formulation incorporates ports as an integral part of the GSM formulation, thus, the resulting model can be integrated with circuit analysis. The proposed technique permits the modeling of interactive discontinuities due to the consideration of a large number of modes in the cascade. The GSM-MoM method can be successfully applied to the investigation of a variety of shielded multilayered structures, iris coupled filters, determining the input impedance of probe excited waveguides, and of waveguide-based spatial power combiners View full abstract»

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  • Magnetism from conductors and enhanced nonlinear phenomena

    Page(s): 2075 - 2084
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    We show that microstructures built from nonmagnetic conducting sheets exhibit an effective magnetic permeability μeff, which can be tuned to values not accessible in naturally occurring materials, including large imaginary components of μeff. The microstructure is on a scale much less than the wavelength of radiation, is not resolved by incident microwaves, and uses a very low density of metal so that structures can be extremely lightweight. Most of the structures are resonant due to internal capacitance and inductance, and resonant enhancement combined with compression of electrical energy into a very small volume greatly enhances the energy density at critical locations in the structure, easily by factors of a million and possibly by much more. Weakly nonlinear materials placed at these critical locations will show greatly enhanced effects raising the possibility of manufacturing active structures whose properties can be switched at will between many states View full abstract»

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  • Vector finite Hankel transform analysis of shielded single and coupled microstrip ring structures

    Page(s): 2161 - 2164
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    The vector finite Hankel transform or the vector Bessel series expansion method is used to calculate the resonant frequencies of shielded single and coupled microstrip annular rings in a stratified dielectric structure. Vector global basis functions are employed to model the unknown currents on the ring conductors, and the calculations of their transforms are described. Calculated resonant frequencies for microstrip rings are presented and found to have good agreement with measurements View full abstract»

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  • High-impedance electromagnetic surfaces with a forbidden frequency band

    Page(s): 2059 - 2074
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    A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas View full abstract»

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  • Enhanced patch-antenna performance by suppressing surface waves using photonic-bandgap substrates

    Page(s): 2131 - 2138
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    The microstrip patch antenna is a low-profile robust planar structure. A wide range of radiation patterns can be achieved with this type of antenna and, due to the ease of manufacture, is inexpensive compared with other types of antennas. However, patch-antenna designs have some limitations such as restricted bandwidth of operation, low gain, and a potential decrease in radiation efficiency due to surface-wave losses. In this paper, a photonic-bandgap (PBG) substrate for patch antennas is proposed, which minimizes the surface-wave effects. In order to verify the performance of this kind of substrate, a configuration with a thick substrate is analyzed. The PBG patch antenna shows significantly reduced levels of surface modes compared to conventional patch antennas, thus improving the gain and far-field radiation pattern View full abstract»

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  • Aperture-coupled patch antenna on UC-PBG substrate

    Page(s): 2123 - 2130
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    The recently developed uniplanar compact photonic bandgap (UC-PBG) substrate is successfully used to reduce surface-wave losses for an aperture-coupled fed patch antenna on a thick high dielectric-constant substrate. The surface-wave dispersion diagram of the UC-PBG substrate has been numerically computed for two different substrate thickness (25 and 50 mil) and found to have a complete stopband in the frequency range of 10.9-13.5 and 11.4-12.8 GHz, respectively. The thicker substrate is then used to enhance broadside gain of a patch antenna working in the stopband at 12 GHz. Computed results and measured data show that, due to effective surface-wave suppression, the antenna mounted on the UC-PBG substrate has over 3-dB higher gain in the broadside direction than the same antenna etched on a grounded dielectric slab with same thickness and dielectric constant. Cross-polarization level remains 13 dB down the co-polar component level for both E- and H-planes View full abstract»

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  • Parallel-plate mode reduction in conductor-backed slots using electromagnetic bandgap substrates

    Page(s): 2099 - 2104
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    By fabricating a resonant slot over a reflecting back plate and filling the resulting parallel-plate with an appropriately designed artificial electromagnetic bandgap (EBG) structure, noticeable enhancements in both radiation pattern and bandwidth are achieved using a significantly lower profile than traditional designs. This design uses a two-dimensional artificial EBG substrate in conjunction with a reflecting plate to completely block radiation from the backside of the slot from propagating to the finite edges of the resulting parallel-plate cavity. Measured and simulated data for conductor-backed slots with homogeneous substrates and with EBG substrates are compared View full abstract»

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  • Radiation from a flanged coaxial line into a dielectric slab

    Page(s): 2158 - 2161
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    The radiation from a flanged coaxial line into a dielectric slab is investigated in this paper. The Hankel transform and mode-matching technique are used to obtain simultaneous equations for the modal coefficients. The residue calculus is utilized to represent the solution in rapidly convergent series. Numerical computations are performed to illustrate the behavior of reflection in terms of the slab permittivity, frequency, and coaxial-line geometry View full abstract»

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  • The application of photonic crystals to quasi-optic amplifiers

    Page(s): 2139 - 2143
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    Quasi-optical spatial power combining provides the high combining efficiency required of solid-state power amplifiers for millimeter-wave frequencies. Photonic crystals (PXTs) are used to implement this type of power combining, as shown by two examples in this paper. The first example describes an all-dielectric structure that provides a carrier for the amplifier array chip satisfying the requirements concerning unilateral transmission and thermal management. The second example describes the use of a high impedance ground plane, based on PXTs, to make the power density incident on the array chip as uniform as possible in order to maximize power and efficiency View full abstract»

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Aims & Scope

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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Meet Our Editors

Editor-in-Chief
Dominique Schreurs
Dominique.Schreurs@ieee.org

Editor-in-Chief
Jenshan Lin
jenshan@ieee.org