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Showing papers in "IEEE Transactions on Antennas and Propagation in 2000"


Journal ArticleDOI
Abstract: Analytic properties of the reflection coefficient of a multilayer metal-backed slab are considered. The result is a new form of the dispersion relationship, which characterizes the integral of the reflectance over wavelength in terms of the total thickness and averaged static permeability of the slab. The relation may be transformed to an inequality, which produces the least thickness to bandwidth ratio achievable for a physically realizable radar absorber. The particular cases of broad-band and narrow-band absorbers are discussed. The least thickness of a 10-dB broad-band dielectric radar absorber is shown to be 1/17 of the largest operating wavelength. The discussion also involves the results of a numerical study.

608 citations


Journal ArticleDOI
TL;DR: In this article, the behavior of the small fractal Koch monopole is numerically and experimentally analyzed, and it is shown that as the number of iterations on the small Koch monopoles are increased, the Q of the antenna approaches the fundamental limit for small antennas.
Abstract: Fractal objects have some unique geometrical properties. One of them is the possibility to enclose in a finite area an infinitely long curve. The resulting curve is highly convoluted being nowhere differentiable. One such curve is the Koch curve. In this paper, the behavior the Koch monopole is numerically and experimentally analyzed. The results show that as the number of iterations on the small fractal Koch monopole are increased, the Q of the antenna approaches the fundamental limit for small antennas.

457 citations


Journal ArticleDOI
TL;DR: A permutation of the loop-tree or loop-star currents by a connection matrix is proposed, to arrive at a current basis that yields a MoM matrix that can be solved efficiently by iterative solvers.
Abstract: We develop a new method to precondition the matrix equation resulting from applying the method of moments (MoM) to the electric field integral equation (EFIE). This preconditioning method is based on first applying the loop-tree or loop-star decomposition of the currents to arrive at a Helmholtz decomposition of the unknown currents. However, the MoM matrix thus obtained still cannot be solved efficiently by iterative solvers due to the large number of iterations required. We propose a permutation of the loop-tree or loop-star currents by a connection matrix, to arrive at a current basis that yields a MoM matrix that can be solved efficiently by iterative solvers. Consequently, dramatic reduction in iteration count has been observed. The various steps can be regarded as a rearrangement of the basis functions to arrive at the MoM matrix. Therefore, they are related to the original MoM matrix by matrix transformation, where the transformation requires the inverse of the connection matrix. We have also developed a fast method to invert the connection matrix so that the complexity of the preconditioning procedure is of O(N) and, hence, can be used in fast solvers such as the low-frequency multilevel fast multipole algorithm (LP-MLFMA). This procedure also makes viable the use of fast solvers such as MLFMA to seek the iterative solutions of Maxwell's equations from zero frequency to microwave frequencies.

453 citations


Journal ArticleDOI
TL;DR: This paper presents a near-field 3-D synthetic aperture radar (SAR) imaging algorithm, an extension of the 2-D range migration algorithm (RMA) that is justified by using the method of the stationary phase (MSP).
Abstract: An imaging system with three-dimensional (3-D) capability can be implemented by using a stepped frequency radar which synthesizes a two-dimensional (2-D) planar aperture. A 3-D image can be formed by coherently integrating the backscatter data over the measured frequency band and the two spatial coordinates of the 2-D synthetic aperture. This paper presents a near-field 3-D synthetic aperture radar (SAR) imaging algorithm. This algorithm is an extension of the 2-D range migration algorithm (RMA). The presented formulation is justified by using the method of the stationary phase (MSP). Implementation aspects including the sampling criteria, resolutions, and computational complexity are assessed. The high computational efficiency and accurate image reconstruction of the algorithm are demonstrated both with numerical simulations and measurements using an outdoor linear SAR system.

425 citations


Journal ArticleDOI
TL;DR: In this paper, the L-shaped probe is shown to be an attractive feed for the thick microstrip antenna (thickness around 10% of the operating wavelength), and a parametric study on the rectangular patch antenna is presented.
Abstract: The L-shaped probe is shown to be an attractive feed for the thick microstrip antenna (thickness around 10% of the operating wavelength). A parametric study on the rectangular patch antenna is presented. It is found that the antenna attains 36% impedance bandwidth (SWR/spl les/2) as well as gain bandwidth and about 7-dBi average gain. A two-element array fed by L-probes is also proposed. Experiments show that the array design can substantially suppress the cross polarization of the proposed antenna. Both the antennas have stable radiation patterns across the passband. Moreover, the measured resonant frequencies of the proposed antenna agree well with an existing formula and the L-probe does not have much effect on the resonant frequency.

382 citations


Journal ArticleDOI
TL;DR: In this article, a Sierpinski dipole FSS has been analyzed and measured and the results show an interesting dual-band behavior, and a near field measurement technique is applied to characterize the FSS response to different angles of incidence.
Abstract: The multiband properties of self-similar fractals can be advantageously exploited to design multiband frequency selective surfaces (FSS). A Sierpinski dipole FSS has been analyzed and measured and the results show an interesting dual-band behavior. Furthermore a near-field measurement technique is applied to characterize the FSS response to different angles of incidence. Finally, it is shown that it is possible to tune the FSS response by properly perturbating the geometry of the Sierpinski dipole.

303 citations


Journal ArticleDOI
TL;DR: In this article, a broadband U-slot rectangular patch antenna printed on a microwave substrate is investigated, and the characteristics of the antenna are analyzed by the finite-difference time-domain (FDTD) method.
Abstract: A broad-band U-slot rectangular patch antenna printed on a microwave substrate is investigated. The dielectric constant of the substrate is 2.33. The antenna is fed by a coaxial probe. The characteristics of the U-slot patch antenna are analyzed by the finite-difference time-domain (FDTD) method. Experimental results for the input impedance and radiation patterns are obtained and compared with numerical results. The maximum impedance bandwidth achieved is 27%, centered around 3.1 GHz, with good pattern characteristics.

286 citations


Journal ArticleDOI
TL;DR: Simulation results are performed to investigate the performance of the neural multiple-source tracking algorithm for various angular separations, with sources of random relative signal-to-noise ratio and when the system suffers from Doppler spread.
Abstract: This paper considers the problem of multiple-source tracking with neural network-based smart antennas for wireless terrestrial and satellite mobile communications. The neural multiple-source tracking (N-MUST) algorithm is based on an architecture of a family of radial basis function neural networks (RBFNN) to perform both detection and direction of arrival (DOA) estimation. The field of view of the antenna array is divided into spatial angular sectors, which are in turn assigned to a different pair of RBFNNs. When a network detects one or more sources in the first stage, the corresponding second stage network(s) are activated to perform the DOA estimation. Simulation results are performed to investigate the performance of the algorithm for various angular separations, with sources of random relative signal-to-noise ratio and when the system suffers from Doppler spread.

228 citations


Journal ArticleDOI
TL;DR: The method of moments (MoM) is used to evaluate the mutual coupling between the elements of a given array and the MoM admittance matrix is then used to eliminate the effects of mutual coupling.
Abstract: This paper investigates the effects of mutual coupling between the elements of an array on direct data domain algorithms. Mutual coupling severely undermines the interference suppression capabilities of direct data domain algorithms. The method of moments (MoM) is used to evaluate the mutual coupling between the elements of a given array. The MoM admittance matrix is then used to eliminate the effects of mutual coupling.

219 citations


Journal ArticleDOI
Steven A. Cummer1
TL;DR: In this article, a series of mode theory and FDTD simulations of propagation from lightning radiation in the Earth-ionosphere waveguide were performed to investigate the accuracy of these approximations.
Abstract: The ionosphere plays a role in radio propagation that varies strongly with frequency. At extremely low frequency (ELF: 3-3000 Hz) and very low frequency (VLF: 3-30 kHz), the ground and the ionosphere are good electrical conductors and form a spherical Earth-ionosphere waveguide. Many giants of the electromagnetics (EMs) community studied ELF-VLF propagation in the Earth-ionosphere waveguide, a topic which was critically important for long-range communication and navigation systems. James R. Wait was undoubtedly the most prolific publisher in this field, starting in the 1950s and continuing well into the 1990s. Although it is an old problem, there are new scientific and practical applications that rely on accurate modeling of ELF-VLF propagation, including ionospheric remote sensing, lightning remote sensing, global climate monitoring, and even earthquake precursor detection. The theory of ELF-VLP propagation in the Earth-ionosphere waveguide is mature, but there remain many ways of actually performing propagation calculations. Most techniques are based on waveguide mode theory with either numerical or approximate analytical formulations, but direct finite-difference time-domain (FDTD) modeling is now also feasible. Furthermore, in either mode theory or FDTD, the ionospheric upper boundary can be treated with varying degrees of approximation. While these approximations are understood in a qualitative sense, it is difficult to assess in advance their applicability to a given propagation problem. With a series of mode theory and FDTD simulations of propagation from lightning radiation in the Earth-ionosphere waveguide, we investigate the accuracy of these approximations. We also show that fields from post-discharge ionospheric currents and from evanescent modes become important at lower ELF (/spl lsim/500 Hz) over short distances (/spl lsim/500 km). These fields are not easily modeled with mode theory, but are inherent in the FDTD formulation of the problem. In this way, the FDTD solution bridges the gap between analytical solutions for fields close to and far from the source.

213 citations


Journal ArticleDOI
TL;DR: In this paper, a closed-form ESPRIT-based algorithm for multisource direction finding and polarization estimation with arbitrarily spaced electromagnetic vector-sensors whose locations need not be known is presented.
Abstract: This paper introduces a new closed-form ESPRIT-based algorithm for multisource direction finding and polarization estimation with arbitrarily spaced electromagnetic vector-sensors whose three-dimensional (3-D) locations need not be known. The vector-sensor, already commercially available, consists of six colocated but diversely polarized antennas separately measuring all six electromagnetic-field components of an incident wavefield. ESPRIT exploits the nonspatial interrelations among the six unknown electromagnetic-field components of each source and produces from the measured data a set of eigenvalues, from which the source's electromagnetic-field vector may be estimated to within a complex scalar. Application of a vector cross-product operation to this ambiguous electromagnetic-field vector estimate produces an unambiguous estimate of that source's normalized Poynting vector, which contains as its components the source's Cartesian direction cosines. Monte Carlo simulation results verify the efficacy and versatility of this innovative scheme. This novel method maybe considered as a simplification and a refinement over Li's (1993) work.

Journal ArticleDOI
TL;DR: The design of antennas consisting of two strip dipoles the arms of which are printed on opposite sides of an electrically thin dielectric substrate and connected through a parallel stripline is presented, allowing them to be readily manufactured as printed circuits.
Abstract: The design of antennas consisting of two strip dipoles the arms of which are printed on opposite sides of an electrically thin dielectric substrate and connected through a parallel stripline is presented. The antennas are designed to have broad-band or dual-band capability suitable for application in base stations of wireless communication systems. An important advantage of these antennas is their simple structure, allowing them to be readily manufactured as printed circuits. Broad-band antennas with bandwidths greater than 30% for VSWR /spl les/1.5 operating near 2.0 GHz and dual-frequency antennas operating at 0.9 GHz/1.5 GHz and 0.9 GHz/1.8 GHz bands are presented.

Journal ArticleDOI
TL;DR: In this article, the angular power distribution at a mobile station in downtown Paris at 890 MHz was measured using a high-resolution measurement method, with an angular resolution of better than 1/spl deg/ in both azimuth and elevation and a delay resolution of 33 ns.
Abstract: We measured the angular power distribution at the mobile station in downtown Paris at 890 MHz. The transmit antenna was omnidirectional and placed high above rooftops. The receiver antenna, a 21/spl times/41 element rectangular synthetic array, was located on the roof of a van. The refined high-resolution evaluation method, particularly robust against nonstationary signal components, allows an angular resolution of better than 1/spl deg/ in both azimuth and elevation and a delay resolution of 33 ns. Combined angular/temporal domain measurements are crucial for the understanding of the propagation mechanisms. The evaluated sites showed strongly street-dominated propagation. We found a combined circular and rectangular distribution of scatterers around the mobile station in street-dominated environments. Propagation over the roofs was significant; typically 65% of energy was incident with elevation larger than 100. Our results corroborate the hypothesis on the importance of multiple reflections/diffractions in urban macro cells. We explain this behavior by two reasons: narrow streets favoring a canyon effect and strong scatterers without line-of-sight (LOS) to the mobile station.

Journal ArticleDOI
TL;DR: In this article, a post-wall waveguide-fed parallel-plate slot array is designed and fabricated for various sizes of 76-GHz post wall waveguide and achieved 40-50% efficiency with 35.3 dBi gain with 39.3% efficiency at 77.0 GHz at 104 mm/spl times/100 mm.
Abstract: We design and fabricate various sizes of 76-GHz post-wall waveguide-fed parallel-plate slot arrays. The post-wall waveguide is an array of metalized via-holes with a narrow spacing in a grounded dielectric substrate. The antenna can be easily made at low cost by conventional PCB (printed circuit board) fabrication techniques such as via-holing, metal plating, and etching. We have obtained 40-50% efficiency for various sizes from 26 mm/spl times/24 mm to 104 mm/spl times/100 mm. We have measured 35.3 dBi gain with 39.3% efficiency at 77.0 GHz in an antenna sized 104 mm/spl times/100 mm.

Journal ArticleDOI
TL;DR: In this article, a parameter study of dual-polarized tapered slot antenna (TSA) arrays is presented, where the key features that affect the wideband and widescan performance of these arrays are analyzed.
Abstract: A parameter study of dual-polarized tapered slot antenna (TSA) arrays shows the key features that affect the wide-band and widescan performance of these arrays. The overall performance can be optimized by judiciously choosing a combination of parameters. In particular, it is found that smaller circular slot cavities terminating the bilateral slotline improve the performance near the low end of the operating band, especially when scanning in the H-plane. The opening rate of the tapered slotline mainly determines the mid-band performance and it is possible to choose an opening rate to obtain balanced overall performance in the mid-band. A longer tapered slotline is shown to increase the bandwidth, especially in the lower end of the operating band. Finally, it is shown that the H-plane anomalies are affected by the array element spacing. A design example demonstrates that the results from the parameter study can be used to design a dual-polarized TSA array with about 4.5:1 bandwidth for a scan volume of not less than /spl theta/=45/spl deg/ from broadside in all planes.

Journal ArticleDOI
TL;DR: In this article, a new heuristic UTD diffraction coefficient for non-perfectly conducting wedges is proposed, which is an extension of the heuristic one given by Luebbers (1984) and as simple as that to compute.
Abstract: A new heuristic UTD diffraction coefficient for non-perfectly conducting wedges is proposed. The coefficient is an extension of the heuristic one given by Luebbers (1984) and as simple as that to compute. In the case of forward-scattering and neglecting the surface wave effects, the new coefficient gives a result close to Maliuzhinets's (1958) solution, also deep in the shadow region where the previous one fails. Moreover, it makes the special care used by Luebbers to deal with grazing incidence unnecessary.

Journal ArticleDOI
TL;DR: In this article, a detailed study of the effects of varying the dielectric insert parameters was carried out and useful guidelines were presented for the design of MSDRAs. And the MSDRA greatly facilitates the integration with a printed feed distribution network for use in a large array environment.
Abstract: The multisegment dielectric resonator antenna (SDRA) has previously been developed to significantly enhance the coupling to a microstrip line. The MSDRA greatly facilitates the integration with a printed feed distribution network for use in a large array environment. The thickness and permittivity of the dielectric insert of the MSDRA can be adjusted to match the element impedance to that of the feed line. A detailed study of the effects of varying the dielectric insert parameters was carried out and useful guidelines are presented for the design of MSDRAs.

Journal ArticleDOI
TL;DR: In this article, a self-initiating multiple signal classification (MUSIC)-based direction-finding and polarization estimation algorithm in spatio-polarizational beamspace is presented for an arbitrarily spaced array of identically oriented electromagnetic vector sensors.
Abstract: A novel self-initiating multiple signal classification (MUSIC)-based direction-finding (DF) and polarization-estimation algorithm in spatio-polarizational beamspace is presented for an arbitrarily spaced array of identically oriented electromagnetic vector sensors. An electromagnetic vector sensor, already commercially available, is composed of six colocated, but diversely polarized, antennas distinctly measuring all six electromagnetic-field components of a multisource incident wave field. This proposed algorithm: (1) exploits the incident sources' polarization diversity; (2) decouples the estimation of the sources' arrival angles from the estimation of the sources' polarization parameters; (3) uses ESPRIT on pairs of vector sensors to self-generate coarse estimates of the arrival angles to start off its MUSIC-based iterative search without any a priori information on the incident sources' parameters; (4) estimate the sources' polarization states; and (5) automatically pairs the x-axis direction-cosine estimates with the y-axis direction-cosine estimates and with the polarization estimates. Monte Carlo simulation results verify the efficacy of the proposed method.

Journal ArticleDOI
TL;DR: In this paper, a pair of right-angle slots and a modified U-shaped slot in a rectangular microstrip patch were used for bandwidth enhancement of a microstrip antenna with good radiating characteristics.
Abstract: With the loading of a pair of right-angle slots and a modified U-shaped slot in a rectangular microstrip patch, novel bandwidth enhancement of microstrip antennas is demonstrated. The required dimensions of the right-angle slots and modified U-shaped slot for bandwidth enhancement with good radiating characteristics have been determined experimentally in this study and the obtained antenna bandwidth can be as large as about 2.4 times that of a corresponding unslotted rectangular microstrip antenna. Details of the antenna design and experimental results are presented and discussed.

Journal ArticleDOI
TL;DR: In this article, a dual-band planar inverted-F antenna (PIFA) is proposed for wireless local area network (LAN) applications, which uses single feed only.
Abstract: The development of small integrated antennas plays a significant role in the progress of rapidly expanding wireless communication applications. This paper describes a novel dual-band planar inverted-F antenna (PIFA) for wireless local area network applications. The proposed PIFA uses single feed only. A novel top-plate geometry, a U-shaped slot, is discussed. An example is given for this novel slot shape for frequency bands of 2.4 and 5.2 GHz. Simulation based upon the method of moments (MoM) is used to model the performance of the antenna. Comparisons with results measured on fabricated antenna structures are provided for simulations validation.

Journal ArticleDOI
TL;DR: In this article, a hybrid technique based on combining ray tracing and finite-difference time-domain (FDTD) methods for site-specific modeling of indoor radio wave propagation is presented.
Abstract: The paper presents a hybrid technique based on combining ray tracing and finite-difference time-domain (FDTD) methods for site-specific modeling of indoor radio wave propagation. Ray tracing is used to analyze the wide area and FDTD is used to study areas close to complex discontinuities where ray-based solutions are not sufficiently accurate. The hybrid technique ensures improved accuracy and practicality in terms of computational resources at the same time since FDTD is only applied to a small portion of the entire modeling environment. Examples of applying the method for studying indoor structures and penetration of wave from outdoor to indoor are given at 2.4 GHz. Numerical results are compared with known exact solutions or results of the full wave analysis or traditional ray model to demonstrate the accuracy, efficiency, and robustness of the novel method. Numerical results are also compared with reported measurement results for waves at 1.29 GHz penetrating an external wall with metal-framed windows. Cumulative distributions of field envelope obtained from the hybrid method show close resemblance to the Rayleigh distribution, which conforms to the reported measurement results.

Journal ArticleDOI
TL;DR: In this article, a time-domain combined field integral equation is derived and shown to offer solutions devoid of any resonant components, which can be used for the analysis of transient scattering from closed structures.
Abstract: In the past, both the time-domain electric and magnetic field integral equations have been applied to the analysis of transient scattering from closed structures. Unfortunately, the solutions to both these equations are often corrupted by the presence of spurious interior cavity modes. In this article, a time-domain combined field integral equation is derived and shown to offer solutions devoid of any resonant components. It is anticipated that stable marching-on-in-time schemes for solving this combined field integral equation supplemented by fast transient evaluation schemes such as the plane wave time-domain algorithm will enable the analysis of scattering from electrically large closed bodies capable of supporting resonant modes.

Journal ArticleDOI
TL;DR: In this article, a low-profile design for dual-band dual-polarized SAR applications was investigated, where stacked-patch configurations were used to meet the bandwidth requirements, especially in the L-band, where a balanced transmission line feed was used to minimize cross polarization.
Abstract: For dual-band dual-polarized synthetic aperture radar (SAR) applications a compact low-profile design is investigated. The operating frequencies are in the L and C-bands, centered about 1.275 and 5.3 GHz, respectively. Since the C-band frequency is larger by a factor of four, its array elements and inter-element separations are smaller by the same ratio. Thus, to allow similar scan ranges for both bands, the L-band elements are selected as perforated patches to enable the placement of C-band elements within them. Stacked-patch configurations were used to meet the bandwidth requirements, especially in the L-band. The C-band element was designed numerically, but the perforated L-band one required final experimental optimization. Also, in the latter case of L-band, a balanced transmission line feed was used to minimize cross polarization. For the C-band elements, slot coupling was used and, to simplify the feed, symmetric parasitic slots were incorporated to minimize cross polarization. No vertical connections were utilized, and electromagnetic couplings resulted in a compact low-profile design, with an electrically and thermally symmetric geometry.

Journal ArticleDOI
TL;DR: In this article, a coupled surface-volume integral equation approach is presented for the calculation of electromagnetic scattering from conducting objects coated with materials, which can be easily accelerated using fast solvers such as the multilevel fast multipole algorithm.
Abstract: A coupled surface-volume integral equation approach is presented fur the calculation of electromagnetic scattering from conducting objects coated with materials. Free-space Green's function is used in the formulation of both integral equations. In the method of moments (MoM) solution to the integral equations, the target is discretized using triangular patches for conducting surfaces and tetrahedral cells for dielectric volume. General roof-top basis functions are used to expand the surface and volume currents, respectively. This approach is applicable to inhomogeneous material coating, and, because of the use of free-space Green's function, it can be easily accelerated using fast solvers such as the multilevel fast multipole algorithm.

Journal ArticleDOI
TL;DR: A new theory of multipath shape factors that greatly simplifies the description of small-scale fading statistics of a wireless receiver is presented and these shape factors are shown to describe the statistics of received signal fluctuations in a fading multipath channel.
Abstract: This paper presents a new theory of multipath shape factors that greatly simplifies the description of small-scale fading statistics of a wireless receiver A method is presented for reducing a multipath channel with arbitrary spatial complexity to three shape factors that have simple intuitive geometrical interpretations Furthermore, these shape factors are shown to describe the statistics of received signal fluctuations in a fading multipath channel Analytical expressions for level-crossing rate, average fade duration, envelope autocovariance, and coherence distance are all derived using the new shape factor theory and then applied to several classical examples for comparison

Journal ArticleDOI
TL;DR: In this paper, the Fourier/split-step approach is extended to a wide-angle form, allowing larger propagation angles with respect to the horizon and a new impedance boundary condition is derived for electromagnetic waves incident on a finitely conducting surface that enables solution of the parabolic wave (PWE) using the previously developed mixed Fourier transform.
Abstract: We address the numerical solution of the parabolic wave equation over terrain using the Fourier/split-step approach. The method, referred to as a shift map, generalizes that of Beilis and Tappert (1979) who introduced a coordinate transformation technique to flatten the boundary. This technique is extended to a wide-angle form, allowing larger propagation angles with respect to the horizon. A new impedance boundary condition is derived for electromagnetic waves incident on a finitely conducting surface that enables solution of the parabolic wave (PWE) using the previously developed mixed Fourier transform. It is also shown by example that in many cases of interest, the boundary may be approximated by discrete piecewise linear segments without affecting the field solution. A more accurate shift map solution of the PWE for a piecewise linear boundary is, therefore, developed for modeling propagation over digitally sampled terrain data. The shift-map solution is applied to various surface types, including ramps, wedges, curved obstacles, and actual terrain. Where possible, comparisons are made between the numerical solution and an exact analytical form. The examples demonstrate that the shift map performs well for surface slopes as large as 10-15/spl deg/ and discontinuous slope changes on the order of 15-20/spl deg/. To accommodate a larger range of slopes, it is suggested that the most viable solution for general terrain modeling is a hybrid of the shift map with the well-known terrain masking (knife-edge diffraction) approximation.

Journal ArticleDOI
TL;DR: In this paper, the authors measured data for mutual coupling coefficients and scan-element patterns and examined element resonances, predicted by numerical infinite-array analysis, and found that the central elements are heavily affected by the finiteness of the arrays due to strong mutual coupling between array elements.
Abstract: Two 9/spl times/8/spl times/2 (144 element) dual-polarized endfire tapered-slot phased arrays have been built. Measured data for mutual coupling coefficients and scan-element patterns are presented. Also, element resonances, predicted by numerical infinite-array analysis are examined. The dimensions of the two arrays are identical. They differ in that plated-through vias have been repositioned to eliminate element resonances. One array was expected to operate from 1.0 to 4.6 GHz and the other from 1.0 to 5.9 GHz. It was found that, at low frequencies, the central elements are heavily affected by the finiteness of the arrays due to strong mutual coupling between array elements. Extrapolation of the observations indicates that a tapered-slot phased array, designed for wide-angle scanning, should be comprised of at least 30-40 rows and columns of elements to obtain low-frequency performance that is comparable to infinite-array predictions. In spite of the smallness of the array, predicted-element resonances could be identified by examination of the phase of the mutual coupling coefficients. Based on these observations, the plated-through vias are adequate to remove element resonances.

Journal ArticleDOI
TL;DR: In this paper, a simple model that explains the behavior of the Sierpinski fractal antenna is presented, and the model is applied to predict the behavior when the flare angle is modified and its validity is assessed by comparing its predictions with measured data.
Abstract: A simple model that explains the behavior of the Sierpinski fractal antenna is presented. This model shows that the multiband behavior of the Sierpinski fractal antenna is a consequence of its fractal nature. The model is applied to predict the behavior of the Sierpinski fractal antenna when the flare angle is modified and its validity is assessed by comparing its predictions with measured data.

Journal ArticleDOI
TL;DR: In this article, the complex Poynting theorem has been used to show that the antenna is essentially equivalent to a one port lossy network, where the Foster reactance theorem holds for antennas.
Abstract: The calculation of antenna Q has been an interesting and a controversial topic for years. We first give a rigorous study of antenna Q by introducing a complete description of the complex power balance relation for an antenna system. Using the complex Poynting theorem, we have shown that the antenna is essentially equivalent to a one port lossy network. The Foster reactance theorem is usually stated for a lossless network. The main purpose of this paper is to determine whether the Foster reactance theorem holds for antennas. By making use of a complex frequency domain version of the Poynting theorem, we have shown that the Foster reactance theorem is valid for an antenna. Finally, the Foster reactance theorem for the antenna has been applied to demonstrate the widely held assumption Q/spl ap/1/B, provided Q/spl Gt/1, where B stands for the fractional bandwidth of an arbitrary antenna.

Journal ArticleDOI
TL;DR: In this article, the authors developed an ultrawide-band (UWB) coherent random noise radar operating over the 1-2 GHz frequency range, which achieved phase coherence by using heterodyne correlation of the received signal with a time-delayed frequency-shifted replica of the transmit waveform.
Abstract: The University of Nebraska has developed an ultrawide-band (UWB) coherent random noise radar operating over the 1-2 GHz frequency range. The system achieves phase coherence by using heterodyne correlation of the received signal with a time-delayed frequency-shifted replica of the transmit waveform. Knowledge of the phase of the received signal and its time dependence due to target motion permits the extraction of the mean Doppler frequency from which the target speed can be inferred. Theoretical analysis, simulation studies, and laboratory measurements using a microwave delay line showed that it was possible to estimate the Doppler frequency from targets with linear as well as rotational motion. Field measurements using a photonic delay line demonstrated the success of this technique at a range of about 200 m at target speeds of up to 9 m/s. Analysis shows that the accuracy with which the Doppler frequency can be estimated depends not only on the phase performance of various components within the system, but also upon the random nature and bandwidth (BW) of the transmit waveform, and the characteristics of unsteady target motion.