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Antennas and Propagation, IEEE Transactions on

Issue 3 • Date March 2002

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Displaying Results 1 - 25 of 27
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  • Solution of large dense complex matrix equations using a fast Fourier transform (FFT)-based wavelet-like methodology

    Page(s): 277 - 283
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    Wavelet-like transformations have been used in the past to compress dense large matrices into a sparse system. However, they generally are implemented through a finite impulse response filter realized through the formulation of Daubechies (1992). A method is proposed to use a very high order filter (namely an ideal one) and use the computationally efficient fast Fourier transform (FFT) to carry out the multiresolution analysis. The goal here is to reduce the redundancy in the system and also guarantee that the wavelet coefficients drop off much faster. Hence, the efficiency of the new procedure becomes clear for very high order filters. The advantage of the FFT-based procedure utilizing ideal filters is that it can be computationally efficient and for very large matrices may yield a sparse matrix. However, this is achieved, as well known in the literature, at the expense of robustness, which may lead to a larger reconstruction error due to the presence of the Gibb's phenomenon. Numerical examples are presented to illustrate the efficiency of this procedure as conjectured in the literature View full abstract»

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  • Millimeter-wave Fermi tapered slot antennas on micromachined silicon substrates

    Page(s): 379 - 383
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    This paper presents 90 GHz Fermi-type tapered slot antennas (TSA) on a micromachined 100 μm thick silicon substrate (εr=11.7) and for comparison purposes, 90 GHz Fermi-type TSA on 150 μm thick quartz substrate (εr=3.78). A 100 μm thick wafer is chosen because it is compatible with 90-100 GHz low-noise amplifier circuits on GaAs-InP substrates. The effective thickness of the substrate was reduced by selectively micromachining holes in the silicon wafer using deep reactive ion etching (deep RIE). The radiation patterns of the micromachined antennas were significantly better than the nonmicromachined version and had similar radiation patterns to the quartz design. The etched hole diameter was changed from 300 to 750 μm with minor effect on the radiation patterns. This shows that the predominant reason for the improved patterns lies in the reduced effective dielectric constant and not in substrate-mode suppression effects. This type of antenna is well suited for millimeter-wave imaging arrays View full abstract»

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  • Broadband probe-fed patch antenna with a U-shaped ground plane for cross-polarization reduction

    Page(s): 352 - 355
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    A broadband probe-fed patch antenna with a novel three-dimensional (3D) U-shaped ground plane is proposed and experimentally studied. The proposed antenna has a thick air substrate, and by placing the two flanges of the U-shaped ground plane in parallel to and at a suitable distance from the radiating edges of the antenna's radiating patch, a wide impedance bandwidth (>25%) with much reduced cross-polarization radiation can be obtained, compared to the case with a conventional planar ground plane. In addition, enhanced antenna gain for the proposed antenna is also observed. Details of the proposed antenna and experimental results are presented and discussed View full abstract»

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  • A tunable impedance surface performing as a reconfigurable beam steering reflector

    Page(s): 384 - 390
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    We describe a reconfigurable microwave surface that performs as a new kind of beam steering reflector. The surface is textured with an array of tiny resonators, which provide a frequency-dependent surface impedance. By tuning the individual resonators, the surface impedance, and thus the reflection coefficient phase, can be varied as a function of position across the reflector. Using a reflection phase gradient, the surface can steer a reflected beam. As an example, we have built a simple mechanically tuned surface in which physical motion of only 1/100 wavelength generates a sufficient phase gradient to steer a reflected beam by ±16 degrees. To steer to greater angles, the surface can be configured as an artificial microwave grating, capable of ±38 degrees of beam steering. The concept of the tunable impedance surface demonstrated here can be extended to electrically controlled structures, which would permit more elaborate reflection phase patterns, and provide more capabilities, such as the ability to focus or steer multiple beams View full abstract»

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  • Application of a microgenetic algorithm (MGA) to the design of broadband microwave absorbers using multiple frequency selective surface screens buried in dielectrics

    Page(s): 284 - 296
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    Over the years, frequency selective surfaces (FSSs) have found frequent use as radomes and spatial filters in both commercial and military applications. In the literature, the problem of synthesizing broadband microwave absorbers using multilayered dielectrics through the application of genetic algorithms (GAs) have been dealt with successfully. Spatial filters employing multiple, freestanding, FSS screens have been successfully designed by utilizing a domain-decomposed GA. We present a procedure for synthesizing broadband microwave absorbers by using multiple FSS screens buried in a dielectric composite. A binary coded microgenetic algorithm (MGA) is applied to optimize various parameters, viz., the thickness and relative permittivity of each dielectric layer; the FSS screen designs and materials; their x- and y-periodicities; and their placement within the dielectric composite. The result is a multilayer composite that provides maximum absorption of both transverse electric (TE) and transverse magnetic (TM) waves simultaneously for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite. While a single FSS screen is analyzed using the electric field integral equation (EFIE), multiple FSS screens are analyzed using the scattering matrix technique View full abstract»

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  • Wideband linear and circularly polarized patch antenna using a printed stepped T-feed

    Page(s): 356 - 361
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    The inherent disadvantage of the narrow bandwidth of microstrip antennas is overcome by a wideband feed mechanism. A square patch excited by a stepped T-feed probe achieved an octave bandwidth (0.98 to 2.1 GHz) with a voltage standing wave ratio of <2. A similar return loss over an octave bandwidth (1.05 to 2.4 GHz) was measured when two orthogonal stepped T-feed probes fed by a log-periodic balun were used to generate circular polarization (CP). For CP, pattern symmetry is shown to occur over 50% of the band, and the CP 3 dB axial-ratio bandwidth is of the order of 30% View full abstract»

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  • Cavity-backed slot-coupled dielectric resonator antenna excited by a narrow strip

    Page(s): 404 - 405
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    The input impedance of the cavity-backed slot-coupled dielectric resonator antenna excited by a slender strip is investigated theoretically and experimentally. The effect of the cavity size and strip length on the input impedance are studied and discussed View full abstract»

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  • Numerical reflection from FDTD-PMLs: a comparison of the split PML with the unsplit and CFS PMLs

    Page(s): 258 - 265
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    Although perfectly matched layer (PML) absorbing boundary conditions are perfect in theory, an amount of spurious reflection is present in actual computations with the finite-difference time-domain (FDTD) method. This paper compares the reflections produced by three different PMLs, namely the split PML, the unsplit PML, and the recently introduced complex frequency shifted (CFS) PML. It is shown that the reflections from the split and unsplit PMLs are identical, while the CFS PML allows the reflection of evanescent waves to be significantly reduced View full abstract»

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  • Measurement validation of ray-tracing propagation model on double-diffracted paths

    Page(s): 411 - 413
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    This paper presents a ray-tracing propagation model that includes double-diffraction paths from orthogonal edges. Good agreement between the predicted and measured power delay profiles in a typical cellular scene shows the validity and applicability of our model View full abstract»

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  • Broad-band dual-polarized single microstrip patch antenna with high isolation and low cross polarization

    Page(s): 399 - 401
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    This paper presents a new design of a broad-band dual-polarized single microstrip patch antenna with highly decoupled input ports and low cross-polarization (XP) radiation. A prototype of the proposed antenna with center frequency at 1800 MHz is presented. Both the dual linear polarizations have 10-dB return-loss impedance bandwidths greater than 14% and high decoupling between the two input ports (S21 less than -40 dB across the entire bandwidths) is obtained. Moreover, the XP radiation in the principal planes of the dual linear polarizations is seen to be less than -20 dB View full abstract»

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  • Angle-of-arrival statistics for low resolution antennas

    Page(s): 391 - 395
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    In a scattering environment, the propagation paths to a receiving antenna arrive from a certain angular spread of directions. For a low-resolution antenna, an apparent direction of arrival may be defined as the azimuth direction of maximum power. A small array is used as the antenna and the spatial derivative of the phase along the array axis is taken as a measure of the sine of the apparent angle of arrival. The sine of the angle is shown to be Student's t-distributed and from this result the PDF and power spectrum of the angle-of-arrival is determined. The distributions are compared with experimental results for indoor as well as for outdoor measurements View full abstract»

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  • Far-field performance of linear antennas determined from near-field data

    Page(s): 408 - 410
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    The main plane far-field radiation pattern of an antenna under test from the corresponding main plane near-field data, using a circular-line acquisition, is presented. The method is based on the reconstruction of equivalent magnetic currents (EMCs) using decoupled integral equations and one-dimensional source components. The resultant fast procedure is applicable to linear and quasilinear array antennas. Experimental data results and comparison with complete spherical acquisition and center-line acquisition are presented View full abstract»

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  • Broadband dual-polarized patch antennas fed by capacitively coupled feed and slot-coupled feed

    Page(s): 346 - 351
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    Designs of broadband dual-polarized patch antennas fed by promising feed structures of a capacitively coupled feed and a slot-coupled feed (antenna A), two capacitively coupled feeds of a 180° phase shift and a slot-coupled feed (antenna B), and two capacitively coupled feeds of a 180° phase shift and two slot-coupled feeds (antenna C) are proposed and experimentally studied. The first two feed designs are for the excitation of a single-element broadband patch antenna, while the last design is for a two-element broadband patch antenna. These proposed patch antennas have a thick air substrate, and the 10 dB return-loss impedance bandwidths obtained for the two polarizations are all greater than 13%. High isolation (<-30 dB for antenna A, <-32 dB for antenna B, <-35 dB for antenna C) between the two feeding ports for the entire impedance bandwidth of the proposed antennas can be obtained. Also, improved cross-polarization levels (>20 dB) in both E and H plane patterns for the two polarizations of antennas B and C are achieved View full abstract»

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  • Electrically small self-resonant wire antennas optimized using a genetic algorithm

    Page(s): 297 - 300
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    One of the major limitations of electrically small antennas is that as the size of the antenna is decreased its radiation resistance approaches zero and its reactance approaches plus or minus infinity. Most small antennas are inefficient, nonresonant and, thus, require matching networks. In this investigation, we use a genetic algorithm (GA) in conjunction with the numerical electromagnetics code to search for resonant wire shapes that best utilize the volume within which the antenna is confined. Antenna configurations, over a ground plane, having from two to ten wire segments, were optimized near 400 MHz and then built and tested. As the cube size deceased from a side length of 0.096λ to 0.026λ, the computed Qs increased from 15.8 to 590. The measured Qs increased from 16.0 to 134 for cubes of 0.093 to 0.037λ on edge. This process for designing small antennas using a GA produced new self-resonant antenna configurations View full abstract»

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  • Numerical analysis of two-arm spiral antennas printed on a finite-size dielectric substrate

    Page(s): 362 - 370
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    A two-arm spiral antenna (SA) printed on a dielectric substrate backed by a conducting plane is analyzed under the condition that the dielectric substrate has a finite side length of L. The analysis is performed using the finite-difference time-domain (FDTD) method. The computation space for the FDTD method is reduced to one-half of the full computation space by virtue of the antenna arm symmetry with respect to the feed point. The numerical evaluations for the radiation characteristics are briefly described, and the SA (the spiral antenna with a conducting plane of infinite extent) is analyzed. It is found that the input impedance remains constant with side length L⩾0.8 wavelength in this analysis model. It is also found that as L increases, the axial ratio improves with the gain remaining relatively constant (the gain variation is within 1 dB). The SAfinite (the spiral with a conducting plane having the same finite size as the dielectric substrate) is also analyzed. It is revealed that the effects of L on the axial ratio and gain are relatively large compared with those on the former SA View full abstract»

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  • Accurate analysis of wire structures from very-low frequency to microwave frequency

    Page(s): 301 - 307
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    Based on the accurate model developed in our previous paper, a general method is proposed to analyze wire structures in the free space or above multilayered media, which is valid from very-low to microwave frequencies. In this method, loop-tree basis functions have been applied to overcome the low-frequency breakdown problem, which can represent the nature of the Helmholtz decomposition of the current. The proposed method can be used to study wire antennas, or it can be incorporated with other methods to analyze circuit problems containing wire structures View full abstract»

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  • A small CP-printed antenna using 120° sequential rotation

    Page(s): 398 - 399
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    We present a small printed antenna with broadband impedance and axial ratio (AR) characteristics. The antenna consists of three sequentially rotated shorted equilateral patches, with excitation phasings of 0°, 120°, and 240°, respectively. The measured 10-dB return loss and 3-dB AR, bandwidths of the compact antenna are 31% and 27.5%, respectively View full abstract»

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  • Finite difference analysis of electrically large parabolic reflector antennas

    Page(s): 266 - 276
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    A reflector antenna is analyzed using the finite-difference method (FD). The induced current densities on an axially symmetric parabolic reflector are rigorously calculated. The measured equation of invariance (MEI) is used to terminate the FD mesh very close to the reflector surface. To take advantage of the axial symmetry, the theory of coupled-azimuthal potentials (CAPs) is employed. Illustrative results are obtained for reflector antennas with different aperture dimensions. Results by physical optics (PO) approximation are also included for comparison. The purpose of this paper is not to replace ray optics (RO) and PO in the design of reflector antennas, but to demonstrate the advancement in the FD method, which hitherto was limited to low-frequency and closed-boundary regime. The calculated surface current densities of a reflector antenna do show that the normal component of the current densities at the edges exhibits high standing waves which are missing in PO, and which we know should be there. The standing wave of current densities may not affect the main beam, but certainly will have an effect on side lobes and have a major impact in estimating the loss of the antenna View full abstract»

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  • Discrete multiloop, modified multiloop, and plate-loop antennas-multifrequency and wideband VSWR characteristics

    Page(s): 371 - 378
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    Three types of loop antennas are presented: discrete multiloop (ML), modified ML and plate-loop (PL) antennas. The discrete ML and modified ML antennas are composed of N square loops. The N square loops of the modified ML antenna are connected by wires at the loop corners. The PL antenna is regarded as a modified ML antenna with infinite loops (N=∞). The analysis of the discrete ML antenna shows that one of the N loops resonates when its circumference is approximately one wavelength. It follows that the discrete ML antenna has N minima in the frequency response curve of the VSWR. In contrast to the discrete ML antenna, the modified ML has a VSWR with a wide-band frequency response: approximately 16% with N=7, which is more than 2.5 times as wide as that for a single-loop antenna (N=1). Further analysis reveals that the PL antenna has a VSWR bandwidth similar to that of the modified ML antenna. The maximum gain of the PL antenna is approximately 9 dB, which is very close to those of the discrete and modified ML antennas View full abstract»

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  • A dual-L antenna with a novel tuning technique for dual frequency applications

    Page(s): 402 - 403
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    A planar dual-L antenna with a novel tuning technique is presented for an integrated GPS/PCS dual-band application. The tuning structure is made of a metal stub attached to one of the shorting plates of the dual-L, antenna, and thus facilitates the independent tuning for lower frequency bands. Simulation and measurements were performed and dual bands of 1565.19 MHz-1585.65 MHz and 1850 MHz-1990 MHz with a return loss better than -10 dB were achieved View full abstract»

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  • Shorted spiral-like printed antennas

    Page(s): 396 - 397
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    We present two electrically small printed antennas suitable for mobile communication handset terminals. The conductor shapes of the proposed shorted patch antennas maximize the length of the current path for a given area thereby significantly reducing the resonant frequency of the antenna. Reductions in operating frequencies of the order of seven to ten have been achieved View full abstract»

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  • Electromagnetic scattering by inhomogeneous dielectric bodies of revolution embedded within stratified media

    Page(s): 405 - 407
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    A method of moments (MoM) solution for scattering by heterogeneous bodies of revolution (BOR) embedded within a multilayered environment is given. A modal volume integral equation (VIE) is formulated in the mixed potential form and solved with the use of the specialized basis functions View full abstract»

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  • Wavelet analysis of transients in fractal superlattices

    Page(s): 338 - 345
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    Fractal superlattices are designed by alternating dielectric layers according to an iterative fractal process. The discrete self-similarity of such stratified structures can be remotely detected from interrogation by an incident pulse. In this paper, the impulse response of one-dimensional Cantor superlattices is computed and the wavelet transform is applied to the reflected signal in order to explore its temporal distribution of singularities. For a sufficiently narrow pulse, the skeleton of the wavelet-transform modulus-maxima exhibits a hierarchical structure that makes apparent the iterative process governing the construction rule of the interrogated fractal superlattice and its geometry. In the reflected signal, such hierarchy reveals the existence of singularities that are distributed on the governing Cantor set. Finally, the similarity dimension is extracted from reflection data and a strategy for estimating the stage of growth is developed View full abstract»

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  • Efficient radar target recognition using the MUSIC algorithm and invariant features

    Page(s): 325 - 337
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    An efficient technique is developed to recognize target type using one-dimensional range profiles. The proposed technique utilizes the Multiple Signal Classification algorithm to generate superresolved range profiles. Their central moments are calculated to provide translation-invariant and level-invariant feature vectors. Next, the computed central moments are mapped into values between zero and unity, followed by a principal component analysis to eliminate the redundancy of feature vectors. The obtained features are classified based on the Bayes classifier, which is one of the statistical classifiers. Recognition results using five different aircraft models measured at compact range are presented to assess the effectiveness of the proposed technique, and they are compared with those of the conventional range profiles obtained by inverse fast Fourier transform 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