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Antennas and Propagation, IEEE Transactions on

Issue 3 • Date Mar 2001

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Displaying Results 1 - 24 of 24
  • A rigorous derivation of the relation between the effective area and the directive gain and its extension to lossy antennas

    Publication Year: 2001 , Page(s): 413 - 418
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    It is well known that the effective area of a receiving antenna is linearly related to the directive gain of the same antenna in the transmitting mode. Conventionally, this relation is derived by constructing a two-port network involving the transfer impedance between a pair of antennas. Next, by use of the Thevenin theorem, the received power is related with the open-circuit voltage, which in turn is proportional to the transfer impedance. Alternatively, from field analysis, the received power is related to the effective area and the directive gain. Then, the reciprocity theorem is used to equate the transfer impedances between a pair of antennas. Based on these, the area-directivity relation is derived. However, it is indicated that the circuit model with the open-circuit voltage is not rigorous. In this investigation, the reciprocity theorem is used in a different way to directly derive the power absorbed at the load in terms of the radiated electric field in the transmitting mode. Thereby, the area-directivity relation is derived in a straightforward and rigorous manner. In the derivation of the relation, it is seen that the current in the terminal gap should be uniform. Thus, one limitation of this well-known relation is found. The effect of ohmic loss due to finite conductivity of the antenna material can be taken into consideration in the derivation. Thus, the area-directivity relation is extended such that it is applicable to lossy antennas View full abstract»

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  • A simple 2-D/3-D method for fast analysis of patch resonators with high accuracy

    Publication Year: 2001 , Page(s): 470 - 474
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (76 KB)  

    For a patch resonator, a two-dimensional (2-D) planar circuit analysis (modal or contour integral) has advantages of being simple and fast. However, this method does not account for perturbation of the fringe fields at the edge. A three-dimensional (3-D) analysis such as integral equation moment method has the advantage of accounting for the fringe fields at the edge, however, the disadvantage of having to long computation time and high truncation error. A better way is to make use of advantages of both and discard the disadvantages. The result is the combined 2-D/3-D method described in this paper. This method requires a few seconds of computer time, but gives errors of resonance frequency only around 0.5%. The errors in general are within the tolerances of presently available analysis and experiments. Field theory reasons accounting for such fast convergent and low error results, are explained and numerical examples are given View full abstract»

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  • Dual-band circularly-polarized square microstrip antenna

    Publication Year: 2001 , Page(s): 377 - 382
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    New designs of obtaining dual-band circular polarization (CP) radiation of a single-feed square microstrip antenna are proposed and experimentally studied. The proposed single-feed dual-band CP designs are achieved by inserting four T-shaped slits at the patch edges or four Y-shaped slits at the patch corners of a square microstrip antenna. From experiments conducted, a patch size reduction as large as 36% for the proposed design, compared to a conventional CP design without the inserted slits, has been obtained. Details of the design considerations of the proposed antennas are described, and experimental results of the obtained dual-band CP performances are presented and discussed View full abstract»

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  • Analysis of a multiple-beam waveguide for free-space transmission of microwaves

    Publication Year: 2001 , Page(s): 483 - 493
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    The transmission of several quasi-optical beams via one system of oversized focusing mirrors is discussed. The analysis of this multiple-beam waveguide shows that such a system can substantially reduce the total mirror surface compared to the corresponding number of individual lines. With the help of analytic coupling coefficients for Gaussian beam modes deduced from the coupling integrals, configurations of four mirrors are found, which give low losses due to the reconversion of spurious modes generated at the different mirrors. Optimization of the mirror surfaces as a function of system parameters is performed and expressions for the loss as a function of the number of transmission channels are deduced. The results are confirmed by diffraction calculations and laboratory scale experiments. The application to a high-power system promises a very efficient transmission with high mode purity View full abstract»

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  • Enhanced compact range reflector concept using an R-card fence: two-dimensional case

    Publication Year: 2001 , Page(s): 419 - 428
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    Compact range reflector edge diffraction can be reduced by using an R-card fence. Well-designed R-cards (resistive sheets) placed in front of reflector edges reduce the field variations in the test zone. The keys to successful R-card design are proper choices of both the geometry and resistance profile. In this paper, a two-dimensional (2-D) version of the problem is attacked to show the basic concepts and essential considerations in designing R-cards. The complexity of a design is simplified by separating the different mechanisms associated with R-cards. Undesired mechanisms can be visualized by ray tracing and then eliminated by choosing the correct R-card geometry. The useful impact of this treatment is illustrated as it controls the transmitted energy level through the R-card; thus, the resistance of the R-card is defined based on an optimum aperture taper. Excellent performance in both the cross-range and down-range directions is presented, and the validity of the design is verified over a wide band of frequencies. The simplicity, flexibility, and low cost of this R-card fence concept provides a viable alternative to other edge treatments View full abstract»

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  • On the solution of a class of large body problems with partial circular symmetry (multiple asymmetries) by using a hybrid-dimensional finite-difference time-domain (FDTD) method

    Publication Year: 2001 , Page(s): 354 - 360
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    This paper presents an efficient method to solve a large body scattering problem, viz. a paraboloid reflector antenna system, with only partial circular symmetry. The asymmetry in the system is introduced by two factors, viz. the microstrip feed and an inhomogeneous radome. The paper presents a novel approach, based on the equivalence and reciprocity principles and the “equivalent” aperture theory, to overcome the asymmetry problem. The technique thereby enables substantial computational efficiencies by analyzing the majority of the three-dimensional (3-D) computational domain in an effective two-dimensional (2-D) simulation, with the remainder being analyzed using a 3-D algorithm View full abstract»

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  • On a simple method of obtaining sidelobe reduction over a wide angular range in one and two dimensions

    Publication Year: 2001 , Page(s): 475 - 482
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    A patented technique for suppressing the sidelobes of an array antenna is considered. This technique involves the addition of two elements, one at each end of the array, which together produce an interferometer pattern used for the cancellation of sidelobes. It is shown here that the technique is most effective for uniform illumination and that there then exists an optimum fixed position for the added elements. The amplitude of the excitation of the auxiliary elements determines the angular location of the region of sidelobe reduction while the phase of the excitation tracks the beamsteering phase of the array. Thus, this technique is seen to be easily implemented in an array controlled by coupled oscillators. The technique generalizes in a straightforward manner to two-dimensional (2-D) arrays in which case a set of auxiliary elements on the perimeter of the array is required. A 2-D oscillator controlled array of this type is described here with which one can produce a main beam and a sidelobe suppression region that can be independently positioned anywhere in a hemisphere provided they do not coincide View full abstract»

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  • ARMA-based time-signature estimator for analyzing resonant structures by the FDTD method

    Publication Year: 2001 , Page(s): 327 - 339
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    We propose an algorithm for estimation of the optimal “system” parameters of time sequences (TSs) computed by the finite-difference time-domain (FDTD) method, with the goal of accurate representation of the time-signature using low-order models. The FDTD method requires computation of very long time sequences to accurately characterize the slowly decaying transient behavior of resonant structures. Therefore, it becomes critical to investigate methods of reducing the computational time for such objects. Several researchers have argued that the FDTD-TS can be modeled as the impulse response (IR) of an autoregressive moving average (ARMA) transfer function. However, it is known that determination of ARMA parameters by IR matching is a complex nonlinear optimization problem. Hence, many existing methods in EM literature tend to use Prony-based, linear predictor-type spectrum estimation algorithms, which minimize a linearized “equation error” criterion that approximates the true nonlinear model-fitting error criterion. As a result, significantly high model orders are needed by these methods to achieve good corroboration in the frequency domain, especially when a magnitude spectrum has deep nulls or notches. We propose to use a deterministic ARMA approach, which minimizes the true nonlinear criterion iteratively, and attains significantly improved IR fit over Prony's (1795) method using fewer ARMA model parameters. For a given time-sequence of an analyzed circuit, the issues of model order selection and choice of decimation factor are also addressed systematically. The improved performance of the proposed algorithm is demonstrated with transient simulation and signal analysis of microstrip structures which manifest deep nulls in the frequency domain View full abstract»

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  • Volume integral equation solution of extinction cross section by raindrops in the range 0.6-100 GHz

    Publication Year: 2001 , Page(s): 494 - 499
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    The validity of the volume integral equation formulation (VIEF) is validated for the purpose of estimating the extinction cross section (ECS) of raindrops. The validations are performed against two well-established models. The validated volume integral equation model is employed to calculate the extinction cross sections of raindrops specified by a modified Pruppacher and Pitter (MPP) model. Data are given for drops with mean radii between 0.25 to 3.5 mm in the frequency range 0.6 to 100 GHz. Our study has showed that results of the extinction cross section for vertical and horizontal polarizations can be used to predict rain attenuation in wireless communications View full abstract»

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  • A novel top-sleeve monopole in two parallel plates

    Publication Year: 2001 , Page(s): 438 - 443
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    A novel top-sleeve monopole antenna in two parallel plates is presented, which is developed to enhance its impedance bandwidth in a significant manner. By the introduction of a sleeve into a common SMA connector with a thin dielectric jacket, a noticeably broad bandwidth on the order of up to 70% is achieved for the proposed antenna. An eigenmode expansion technique is used to simulate the impedance characteristics of the top-sleeve monopole. The effects of geometric parameters of the structure, such as the sleeve length, monopole length, and the plate spacing on its impedance characteristics, are investigated. On the basis of our theoretical studies, an experimental prototype with bandwidth of 50% is designed and its characteristics are confirmed experimentally View full abstract»

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  • Polarizability analysis of cubical and square-shaped dielectric scatterers

    Publication Year: 2001 , Page(s): 451 - 457
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    The polarizability characteristics of nonspherical scatterers, especially cubes and squares, are studied. A surface integral equation for the electrostatic potential has been numerically solved for a cube and a square-shaped object. Nonuniform gridding of the dielectric object has been used to get a good accuracy in the solution. The results obtained for the polarizability of cubes using the surface integral equation are compared with those obtained from the volume integral equation and show a good agreement. We give simple approximation formulas for the polarizabilities as functions of the permittivity of the inclusions. The results give an improvement compared to earlier literature and also present a way to predict the effective properties of mixtures where cube-shaped inclusions are embedded in dielectric environment, which type of mixtures strongly generalize the effective-medium theories of the present literature View full abstract»

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  • A quality measure for ray-tracing algorithms

    Publication Year: 2001 , Page(s): 500 - 502
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB)  

    The paper focuses on the validation of ray-optical techniques as tools fur predicting wide-band radio propagation, in the case of indoor environments. A novel approach to address the topic is proposed: it is based on a likelihood test between the simulations and the measures appropriately treated with a super-resolution technique View full abstract»

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  • Green's function calculations on circular microstrip patch antennas

    Publication Year: 2001 , Page(s): 393 - 401
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    Green's function calculations have been applied to solve the radiation problem of circular microstrip patch antennas. The patch is fed by either a microstrip line or a coax line to be approximated as delta-function-like sources. The resultant Galerkin elements involve only one-fold Sommerfeld-type integrals. The resonant frequency, impedance, and far-field pattern have thus been calculated, which compared nicely with measurements View full abstract»

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  • Novel compact circularly polarized square microstrip antenna

    Publication Year: 2001 , Page(s): 340 - 342
    Cited by:  Papers (75)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    A novel compact circular-polarization (CP) operation of the square microstrip antenna with four slits and a pair of truncated corners is proposed and investigated. Experimental results show that the proposed compact CP design can have an antenna-size reduction of about 36% as compared to the conventional corner-truncated square microstrip antenna at a given operating frequency. Also, the required size of the truncated corners for CP operation is much greater than that for the conventional CP design using a simple square microstrip patch, providing a relaxed manufacturing tolerance for the proposed compact CP design. Details of the experimental results are presented and discussed View full abstract»

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  • Optimal time-domain detection of a deterministic target buried under a randomly rough interface

    Publication Year: 2001 , Page(s): 313 - 326
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    We consider pulsed plane-wave scattering from targets buried under a rough air-ground interface. The properties of the interface are parametrized as a random process with known statistics, and therefore the fields scattered from a particular surface constitute one realization of an ensemble, characterized by corresponding statistics. Moreover, since the fields incident upon a buried target must first penetrate the rough interface, they and the subsequent scattered fields are random processes as well. Based on this understanding, an optimal detector is formulated, accounting for the clutter and target-signature statistics (the former due to scattering at the rough surface, and the latter due to transmission); the statistics of these two processes are in general different. The detector performance is compared to that of a matched filter, which assumes the target signature is known exactly (i.e., nonrandom). The results presented here, as a function of angle and polarization, demonstrate that there is often a significant gain in detector performance if the target signature is properly treated as a random process View full abstract»

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  • Surface waves of printed antennas on planar artificial periodic dielectric structures

    Publication Year: 2001 , Page(s): 444 - 450
    Cited by:  Papers (61)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    The characteristics of surface waves from a Hertzian (elementary) dipole on a multilayer structure with planar periodic material elements are investigated. An integral-equation moment method in conjunction with an analytical array scanning scheme is applied to the boundary-value problem associated with source interaction with infinite periodic structures. A pole-extraction technique and the saddle-point method are applied to find the far-zone periodic surface waves due to a current source. The investigation provides a fundamental study of surface wave properties of printed circuit antennas on planar artificial periodic (photonic bandgap) structures. It is found from the power patterns that surface waves are suppressed in the directions with wave bandgap and greatly enhanced in the directions just outside the bandgap zones. The surface wave pattern may be highly directive and the beam angle varies with frequencies. The finding suggests possible frequency-space selection devices. Experiments are carried out to validate the surface wave bandgap phenomenon and the beam angle frequency-selection property View full abstract»

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  • Ground effects for VHF/HF antennas on helicopter airframes

    Publication Year: 2001 , Page(s): 402 - 412
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    In this paper, the finite element method (FEM) is used to predict the space and surface wave radiation patterns of VHF/HF antennas mounted on a helicopter in the presence of a lossy ground. The equivalent sources of the radiation system are obtained by solving an FEM problem in conjunction with an absorbing boundary condition (ABC) or an impedance boundary condition (IBC). From the equivalent sources, the total radiated field is calculated using the equivalence principle and superposition; the original problem is converted into a set of properly combined Hertzian dipoles referred to as the Sommerfeld problem. Instead of evaluating the Sommerfeld integral rigorously, Norton's approximation is used to improve the overall computational efficiency. The validation of this method is accomplished in two steps: first, the FEM is compared with the finite-difference time-domain method (FDTD) in the absence of a lossy ground; second, the Hertzian dipole problem is solved in the presence of a lossy ground and the results are compared with analytic solutions. Finally, this technique is extended to analyze an antenna on a helicopter above a lossy ground View full abstract»

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  • Far-field time-domain calculation from aperture radiators using the FDTD method

    Publication Year: 2001 , Page(s): 464 - 469
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    It is often desirable to determine the far-field radiation pattern from an aperture in a metal plate. The use of time-domain methods, like the finite-difference time-domain (FDTD) method, is problematic because of the necessity of modeling the entire space of interest. This is often circumvented by using the equivalence principle to determine the far field by equivalent currents generated in the near field. However, these transformations are often mathematically complex. This paper presents an extremely simple formulation for calculating the time-domain fields from some types of aperture radiators. By using wavelet analysis, the pertinent parameters can be compressed and stored to be used later to resynthesize the radiated fields View full abstract»

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  • Measurement and evaluation of multi-antenna handsets in indoor mobile communication

    Publication Year: 2001 , Page(s): 429 - 437
    Cited by:  Papers (32)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    A method for evaluating antenna diversity systems is presented with an example of a handset using up to four antennas in indoor mobile communication. The method includes a “two-at-a-time” measurement test setup that uses maximum likelihood estimation of the covariance matrix and compensation for the imperfect match, which typically occurs during the design and evaluation process for compact antennas. The diversity performance of the antenna system can be presented as an effective order of diversity, which is the equivalent number of equal power, uncorrelated diversity branches for the same diversity gain at a given probability View full abstract»

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  • Finite-difference time-domain analysis of a stacked dual-frequency microstrip planar inverted-F antenna for mobile telephone handsets

    Publication Year: 2001 , Page(s): 367 - 376
    Cited by:  Papers (23)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    We describe a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work in two frequency-bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz, respectively. The proposed microstrip DF-PIFA is fed by a coaxial line, as opposed to two separated feed lines used in the conventional design. The design is carried out in a systematic manner and involves two steps. We begin with an initial configuration of the PIFA that is based on a standard design for a microstrip patch antenna fed by a coaxial line and is derived from an empirical approximation in conjunction with a transmission line model. Next, we employ a computer-aided design (CAD) tool, based on the nonuniform finite-difference time-domain (NU-FDTD) Maxwell solver, to optimize the performance characteristics of the DF-PIFA, including the return loss, the matching of the input impedance, and the far-field radiation patterns View full abstract»

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  • On the application of numerical methods to Hallen's equation

    Publication Year: 2001 , Page(s): 383 - 392
    Cited by:  Papers (38)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The so-called Hallen integral equation for the current on a finite linear antenna center-driven by a delta-function generator takes two forms depending on the choice of kernel. The two kernels are usually referred to as the exact and the approximate or reduced kernel. With the approximate kernel, the integral equation has no solution. Nevertheless, the same numerical method is often applied to both forms of the integral equation. In this paper, the behavior of the numerical solutions thus obtained is investigated, and the similarities and differences between the two numerical solutions are discussed. The numerical method is Galerkin's method with pulse functions. We first apply this method to the two corresponding forms of the integral equation for the current on a linear antenna of infinite length. In this case, the method yields an infinite Toeplitz system of algebraic equations in which the width of the pulse basis functions enters as a parameter. The infinite system is solved exactly for nonzero pulse width; the exact solution is then developed asymptotically for the case where the pulse width is small. When the asymptotic expressions for the case of the infinite antenna are used as a guide for the behavior of the solutions of the finite antenna, the latter problem is greatly facilitated. For the approximate kernel, the main results of this paper carry over to a certain numerical method applied to the corresponding equation of the Pocklington type View full abstract»

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  • Analysis of circular reflector antenna covered by concentric dielectric radome

    Publication Year: 2001 , Page(s): 458 - 463
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    The radiation from a two-dimensional cylindrical reflector antenna with a concentric dielectric radome is analyzed in an accurate manner for both H and E polarization cases. The problem is first formulated in terms of the dual series equations, and then it is regularized by using Riemann-Hilbert problem technique. The resulting matrix equation is solved numerically, with a guaranteed accuracy, and sufficiently little CPU time is needed. The feed directivity is included in the analysis by the complex source point method. Various characteristic patterns are obtained for the front-fed reflector antenna geometries in this study View full abstract»

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  • Nonreciprocal microwave bianisotropic materials: reciprocity theorem and network reciprocity

    Publication Year: 2001 , Page(s): 361 - 366
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (100 KB)  

    There are many attempts to generalize the reciprocity theorem for bianisotropic media. With formal introduction of notion of reaction for bianisotropic media, we can formulate reciprocity conditions for the medium parameters. We can also extend the procedure used for a gyrotropic medium and consider the complementary, or the Lorentz-adjoint, bianisotropic medium, which satisfies the reciprocity theorem. Definition of the notion of reaction in bianisotropic media is, however, not so trivial. We consider some important aspects of the physical admissibility to use the notion of the reaction as a “physical observable” in bianisotropic media. The questions also arise: for what kinds of the known bianisotropic media is the reciprocity theorem physically applicable? Based on what kind of bianisotropic media, can nonreciprocal microwave devices be realized? We show that a novel class of microwave bianisotropic materials-magnetostatically controlled bianisotropic materials (the MCBMs)-are “physically justified” materials. The Onsager-Casimir principle and the notion of reciprocity are applicable in this case. New nonreciprocal microwave devices based on the MCBMs can be realized View full abstract»

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  • Characterization of electromagnetic band-gaps composed of multiple periodic tripods with interconnecting vias: concept, analysis, and design

    Publication Year: 2001 , Page(s): 343 - 353
    Cited by:  Papers (52)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    This paper examines the performance of an electromagnetic band-gap structure (also known as photonic band-gap). The structure is purely metallic and infinitely periodic in two dimensions with a finite periodicity in the third dimension. An effective band-gap exists when within a certain frequency range, the reflection is 100% for all angles of incidence and all polarizations. The performance of the structure is explained from a physical point of view by isolating the effects of each parameter of the structure. Cascading two periodic arrays with a very small separation distance gives a capacitance effect for the overlap region. The capacitance is shown to control the lower edge of the band-gap. Cascading more closely coupled periodic arrays gives a rejection band, with the separation controlling the upper edge of the band. An effective band-gap is shown to exist when different layers are connected with vias. The structure examined in this paper has an effective band-gap from 30 GHz to 100 GHz. The calculations are performed using the method of moments (MoM) to solve an integral equation with the periodic Green's function as its kernel. The computations are extensive because they involve double infinite summations. A customized Z-matrix interpolation scheme is, therefore, used to speed the total calculation time, without sacrificing accuracy View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung