Showing papers on "Antenna array published in 1988"

Comparison of three methods for the measurement of printed antenna efficiency

Abstract: Three methods for the measurement of antenna efficiency are evaluated: (1) the Wheeler cap method, (2) the radiometric method, and (3) the directivity/gain method. Each of these methods was used to measure the efficiency of four different printed antennas (three microstrip patches with various feeds, and an eight-element series-fed microstrip array). These methods and the experimental results which were obtained are discussed. >

Simplification of MUSIC and ESPRIT by exploitation of cyclostationarity

Abstract: It is shown that for the problem of multiple-source location using antenna arrays, the algorithms MUSIC and ESPRIT can be simplified by use of the property called cyclostationarity, which is exhibited by modulated signals. The advantages of the modified algorithms are reduction in the required number of array elements and associated reduction in the SVD (singular-value-decomposition) computations. The disadvantages are the requirement of either knowing or measuring frequency parameters, such as carrier frequency or baud rate, and the requirement of longer integration time for correlation measurement, as well as the requirement of measuring a different correlation matrix for each signal of interest. >

Microstrip phase scan antenna array

Abstract: A microstrip phase scan antenna array is provided having a columnar array microstrip radiating patches mounted on a dielectric substrate. Each column of the array is fed by a separate variable, reciprocal ferrite rod phase shifter which is mounted on the substrate and is coupled to the column which it controls and to a source of millimeter wave energy by microstrip to dielectric waveguide transitions. Each of the phase shifters is controlled by a helical biasing coil surrounding the ferrite rod. All of the biasing coils are serially interconnected by a single scanning control drive wire and the numbers of turns of the coils are related to each other by an arithmetic progression in which the number of turns of a particular biasing coil differs from the number of turns of the adjacent biasing coil in the sequence of biasing coils controlling the array by a constant amount.

Design of log-periodic dipole antennas

Abstract: The goal of the paper is to improve the log-periodic dipole antenna (LPDA) design procedure introduced by Carrel (1961). A computer-aided design technique is introduced, providing an easy-to-use design method of LPDAs. Corrections to Carrel's design contours, and new constant input resistance and truncation coefficients diagrams are presented. The influence of the feeder characteristic impedance, and dipole length-to-diameter ratio on LPDA parameters is studied. Design diagrams for LPDA's typical of HF communications are included.< >

The bandwidth performance of a two-element adaptive array with tapped delay-line processing

Abstract: The bandwidth performance of a two-element adaptive array with a tapped delay line behind each element is examined. It is shown how the number of taps and the delay between taps affect the bandwidth performance of the array. An array with two weights and one delay behind each element is found to yield optimal performance (equal to that obtained with continuous-wave interference) for any value of intertap delay between zero and T/sub 90//B, where T/sub 90/ is a quarter-wavelength delay time and B is the fractional signal bandwidth. Delays less that T/sub 90/ yield optimal performance but result in large array weights. Delays larger than T/sub 90//B yield suboptimal signal-to-interference-plus-noise ratio when each element has only two weights. For delays between T/sub 90//B and 4T/sub 90//B, the performance is suboptimal with only two taps but approaches the optimal if more taps are added to each element. Delays larger than T/sub 90//B result in suboptimal performance regardless of the number of taps used. >

A novel principle for optimization of the instantaneous Fourier plane coverage of correction arrays

Abstract: A novel principle for the design of correlation arrays is introduced, based upon the maximization of the distance between samples. Simulated annealing is applied to the problem of finding solutions for moderate numbers of elements (up to 12). The resulting arrays have symmetric crystalline structures. >

Canonical sources and duality in chiral media (antenna arrays)

Abstract: The authors examine the characteristics of antenna arrays embedded in unbounded chiral media using the Green's dyadic for electric sources and the Green's vector for magnetic sources. The purpose is to bring to light the new characteristics of sources, both point and extended, which interact with this medium and to examine general characteristics of sources located in a medium with handedness. Very simple quality relations are presented that are characteristic of chiral media when the results are written in terms of the circular eigenmodes. Appropriate measures of chirality such as the chirality admittance and impedance and a dimensionless chirality factor are introduced as needed. It is shown that, in the far field, both point and extended sources, whether electric or magnetic, radiate two electromagnetic eigenmodes which are of opposing handedness. Sources that access only one of the eigenmodes of the medium are demonstrated. Several applications of the results and array performance in chiral media are noted. >

Phase-only synthesis of minimum peak sidelobe patterns for linear and planar arrays

Abstract: Minimization of the maximum sidelobe level for a given array geometry by phase-only adjustment of the element excitations is considered. Optimum phases are obtained by using a numerical search procedure to minimize the expression for the pattern sidelobe level with respect to the element phases. Results for both linear and planar arrays of equispaced elements are presented. The data suggests that optimum sidelobe level is a logarithmic function of array size, and optimum patterns have relative efficiencies that are typically somewhat greater than for comparable-amplitude tapered arrays. An analytic synthesis algorithm is presented for use on very large arrays for which the numerical search technique for the minimization of the sidelobe level is computationally impractical. This method produces patterns with characteristics similar to arrays synthesized using the numerical search method, i.e. relatively uniform angular distribution of energy in the sidelobe region, and generally decreasing maximum sidelobe level as the array size is increased. >

The relationship between tapped delay-line and FFT processing in adaptive arrays

Abstract: The use of fast Fourier transform (FFT) processing behind the elements in adaptive arrays is often considered as a means of improving the nulling bandwidth of such arrays. However, it is shown that the output signal-to-interference-plus-noise ratio obtained from an adaptive array with FFTs behind the elements is identical to that of an equivalent adaptive array with tapped delay-line processing. The equivalent tapped delay-line array has the same number of taps in each delay line as the number of time samples in the FFTs, and has a delay between taps equal to the delay between samples in the FFTs. Thus, while the bandwidth performance of an adaptive array can be improved by using time-delayed samples of each element signal, no further improvement results from taking FFTs of these sampled signals. The same bandwidth performance is obtained by simply weighting and combining the time-domain samples directly. >

Synthesis of sub-arrayed monopulse linear arrays through matching of independently optimum sum and difference excitations

Abstract: Methods are available for the independent synthesis of array excitations which provide either optimum sum or optimum difference pattern performance. In the paper a technique is described to effect the simultaneous synthesis of both sum and difference patterns of a linear antenna array which utilises sub-arraying to increase the number of degrees of freedom above that available with the usual two-section feed network. The particular approach (referred to here as excitation matching) attempts to obtain an optimum sum (difference) and a ‘best compromise’ difference (sum) pattern, by dealing directly with the independently optimum excitations and appropriately adjusting the sub-array weights.

Broad-band array design using the asymptotic theory of unequally spaced arrays

Abstract: The problem of designing broadband linear arrays of omnidirectional sensors is addressed. Attention is restricted to the case of shaded delay-and-sum beamforming. Broadbanding is here defined to mean that the beam-pattern function has little or no frequency dependence of peak response, main-lobe width, plateau sidelobe level, and sinespace separation between the main lobe and the plateau sidelobe. The asymptotic theory of unequally spaced arrays is used to derive relationships between beam-pattern properties and array properties. These relationships are used to translate beam-pattern requirements into functional requirements on sensor spacings and amplitude shadings. The functional requirements are then used to derive a broadband array design. In addition to the design equations, the asymptotic theory is used to derive equations for main-lobe level, sidelobe level, beamwidth, and signal-to-noise ratio (SNR) gain in isotropic noise. A specific example is presented to clarify the concepts and verify that the design procedure actually works. >

Electronically steerable antenna

Abstract: A lightweight antenna array which can quickly scan or switch radiation patterns is characterized by an array (10) of slot-type radiators (14) wherein the impedance of each radiating element can be varied, preferably by a computer controlled circuit containing particular groups of the radiators, wherein each grouping is defined by a unique set of impedance values for the radiators The groups of radiators in the array can be selectively generated to scan and/or switch pattern footprints and/or change near-field radiation characteristics and/or alter antenna aperture size, density, distribution, spacing or frequency of operation An adaptive technique, using an algorithm, can be employed to generate the radiator grouping

Scattering by a truncated periodic array

Abstract: The problem of scattering by a frequency-selective surface (FSS) comprising an array of metallic patches is considered for investigating the effect of truncation of the FSS on its scattering characteristics. The induced surface current on each patch of the array, as well as the scattered far-field pattern of the truncated array, are computed using the spectra-Galerkin method. The usefulness of the results for the truncated screen problem in the design of FSS is discussed. >

Analysis of mutual coupling between a finite phased array of dipoles and its feed network

Abstract: The mutual coupling effects between a finite phased array of dipoles and its feed network are analyzed. The feed network is typically a corporate feed consisting of split-tee power dividers cascading to form a certain power distribution over the aperture. A simple iterative approach is used to solve the interaction between elements and feed. The radiation of a finite dipole array are first found for a given voltage excitation. These radiation impedances are then used as loads for the feed network, and the n+1 port network problem is analyzed. Due to the interaction between the feed network and dipoles, the antenna parameters such as mismatch, antenna pattern, and gain are all affected. These effects can be determined from the analysis of the network representation. Numerical results for a typical phased array with a corporate feed show that the resultant VSWR of the feed pattern degradation is due to the mutual coupling effects. >

Antenna patterns of nonsinusoidal waves with the time variation of a Gaussian pulse. III

Abstract: The development of antenna theory for nonsinusoidal electromagnetic waves has been based on the idealized rectangular pulse. In practice, an antenna that is designed to operate in the mode of an electric hertzian dipole would radiate a pulse that best approximates a Gaussian one when the driving current consists of a linear transient. The principle of radiation of nonsinusoidal electromagnetic waves with the time variation of Gaussian pulses is discussed. The properties of the Gaussian pulse are presented, i.e., the autocorrelation function, energy spectral density, and spectrum. Antenna patterns, such as peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern are derived for a Gaussian pulse received (or radiated) by a linear array antenna. Computer plots of the derived antenna patterns are presented that show a considerable improvement in the angular resolution capability over that of the antenna patterns that have been derived for a rectangular pulse. >

Array feed synthesis for correction of reflector distortion and vernier beamsteering

Abstract: An algorithmic procedure is described for the synthesis of a planar-array for paraboloidal reflectors to provide simultaneously electronic correction of systematic reflector surface distortions as well as a vernier electronic beamsteering capability. Several f/D ratios and distortion models were examined that are typical of large paraboloidal reflectors. Numerical results are presented showing that, for the range of distortion models considered, significant on-axis gain restoration can be achieved with a one-ring (seven-element) array. However, with seven elements, the array parameters that maximize system gain, do not provide uniform beam-steering (+or-1 BW) and an additional ring (19 elements) is required. For arrays either 7 or 19 elements, the results indicate that the use of high-aperture-efficiency elements in the array yields higher system gain than can be obtained with elements having lower aperture efficiency. Contour plots of the focal-plane fields are also presented for various distortion and beam-scan-angle cases, showing the dynamic nature of the problem. >

Localization performance of arrays subject to phase errors

Abstract: The passive localisation of radiating sources using an array subject to random perturbations in sensor phases is presented. All source signals as well as additive noises observed at the sensors are assumed to be independent identically distributed zero-mean Gaussian random processes. Cramer-Rao bounds are derived for source bearings and ranges for the phase errors at each sensor. It is shown that accurate phase calibration can be achieved when the number of sources exceeds a certain minimum. The locations of the calibrating sources need not be known a priori and need only satisfy mild regularity conditions. A calibration procedure is proposed which uses maximum-likelihood techniques. >

Mode stability of radiation-coupled interinjection-locked oscillators for integrated phased arrays

Abstract: An analysis is presented of a two-element, 10-GHz array consisting of two oscillators coupled solely by means of the free-space interaction between their respective antenna elements. The oscillators are modeled as energy-storing L-C tank circuits in parallel with voltage-dependent negative conductances. A simplified far-field slot antenna model is used to derive the mutual admittance of the two antennas. Even-odd mode analysis yields the normal modes of the system, and a theorem from averaged potential theory is used to determine which mode is stable. Two microstrip Gunn diode oscillators were built to verify the essential features of the model. Oscillator frequencies, relative phases, and radiation patterns were measured as functions of the interantenna distance, and the periodic alternation of modes with distance predicted by theory was confirmed quite well. >

Array synthesis with excitation constraints

Abstract: We present an efficient and flexible method for the optimal synthesis of a shaped beam linear array in the paper. This method is capable of dealing with unconstrained as well as constrained synthesis problems. It is based on an iterative process, whose convergence depends on a proper choice of the first approximation. This choice is discussed in detail, and some examples are presented which show the effectiveness of the method in finding the optimal array for a given power pattern.

Omnidirectional cylindrical antenna

Abstract: An antenna array with circular symmetry made up of an array of cylindrica shaped printed circuit elementary antennas. It is made up of small radiating sources which are placed in superposed circles on a cylindrical surface. The sources are distributed at constant angular intervals on the circles. They have little coupling between themselves. On each circle of sources, they are energized in phase and with the same amplitude. An angular phase shift can be provided between the group of sources on a circle and those of another circle. The antenna can be energized by a three-layer printed circuit line. It can be made up by an array of doublets folded into sheets. Inside the cylinder the transmitter is installed to which is applied a signal to be transmitted and which supplies the modulated carrier to the array of radiating sources.

Deterministic thinned aperture phased antenna array

Abstract: A phased array antenna (10) includes a plurality of radiating elements (14) arranged in concentric rings (11, 12) to form a deterministically thinned antenna aperture which facilitates heat removal from the array, while minimizing side lobe signals and thereby increasing directively of the antenna for a preselected antenna gain. The radiating elements (14) in any one of the rings (11, 12) are the same radiating size, and the spacing (L, L') between elements in the same ring and between elements in adjacent rings (S, S') is determined by the number of elements in each ring. The rings may be any of several shapes, including circular or polygonal.

Technique for antenna array pattern synthesis with controlled broad nulls

Abstract: The author presents a new technique for synthesising antenna array pattern with controlled broad nulls. The approach taken in the paper is to integrate the power response of the array over a spatial region of interest and force it to be less than or equal to a small quantity. The optimal weight vector is obtained by minimising the weight vector norm subject to a linear and a quadratic constraint. Numerical techniques based on matrix factorisation are proposed to reduce the computational complexity. Subsequently, a set of linear constraints, also known as eigenvector constraints, are used to approximate the effect of the quadratic constraint in order to maintain a broad null over the spatial region of interest. This set of eigenvectors can be viewed as an efficient representation of array signals of specified angular occupancy. >

The SCORE approach to blind adaptive signal extraction: an application of the theory of spectral correlation

Abstract: A new approach to blind adaption of antenna arrays is presented that has the capability to extract PCM, AM, and FDM-FM communication signals-of-interest (SOIs) from cochannel interference environments using only known spectral correlation properties of those SOIs, i.e. without using knowledge of the antenna array manifold, SOI waveform, or SOI direction-of-arrival to train the array. The class of self-coherence restoral (SCORE) objective functions is introduced, and flexible algorithms for adapting antenna arrays to optimize these objective functions are developed. It is shown that these algorithms will maximize the SOI SINR at the output of any antenna array when a single SOI with self-coherence at a known value of frequency separation and an arbitrary number of interferers without self-coherence at that frequency separation are impinging on the array. >

An anticipative adaptive array for frequency-hopping communications

Abstract: To fully utilize the theoretical processing gain achievable when an adaptive array and frequency hopping are combined, frequency compensation is required. Improved versions of an anticipative adaptive array are examined that provide efficient compensation by adapting the complex weights at each antenna element to the appropriate values for a carrier frequency before that frequency is received. The underlying adaptive algorithm used is the maximum algorithm. Computer simulation results are used to compare the different versions of anticipative processing. These results show that an appropriate version ensures the rapid convergence of weights to values that provide wideband nulling of the interference and noise. >

The application of a biquadratic programming method to phase only optimization of antenna arrays

Abstract: Antenna array optimization by a biquadratic programming method is formulated with variable-phase (analog and digital) and constant amplitude excitation. The method can optimize an antenna performance index expressible as a ratio of Hermitian quadratic forms. Power gain optimization and least-squares pattern synthesis with a specified gain are illustrated. Linear, planar, and circular arrays with dipole or circular loop elements are optimized, taking mutual coupling effects between antenna elements into account. The method shows much more rapid convergence characteristics than the Rosenbrock (1960) and Fletcher-Power (1963) methods. >

Circular array of outward sloping monopoles for vehicular diversity antennas

Abstract: A circular array of outward-sloping monopoles is analyzed as a diversity antenna for vehicle rooftop mounting. The monopoles are assumed to approximate minimum scattering antennas, have sinusoidal current distributions, and reside on an infinite, perfectly conducting ground plane. The envelopes of the received signals are considered Rayleigh distributed. The advantage of the array configuration is that the feedpoint spacing can be made almost arbitrarily small, even for a large number of branches. A three-element array with element lengths of 0.6 wavelengths and feedpoint spacing 0.1 wavelengths operating at 463 MHz was field-tested and the results are in good agreement with the analysis. >

Instrumental variable adaptive array processing

Abstract: An instrumental variable (IV) approach is presented for estimating the weights of an adaptive antenna array. Theoretical analysis of the IV method shows that the antenna gain weights are independent of finitely correlated noise, so that unbiased estimation of signal arrival angles is possible. Only matrix inversions are required to compute the weight estimates. In this sense, the IV method provides performance comparable with eigenvector techniques but with lower computational burden. Both minimal and overdetermined IV estimators are derived. The overdetermined estimators give the same theoretical array weights as minimal estimators, but yield more accurate weight estimates in real data situations. Simulation results are presented to compare these IV methods with one another and with conventional matrix inversion weight estimators. In these examples it is seen that IV methods are able to resolve closely spaced interference sources when conventional matrix inversion techniques cannot. It is also shown that overdetermined methods are capable of providing weight estimates with lower variances than those of minimal methods. >

The effect of a finite-distance signal source on a far-field steering Applebaum array-two dimensional array case

Abstract: Approximate expressions are obtained for the output signal-to-noise ratio (SNR) expressed in terms of the finite signal distance and signal direction for a finite-distance signal source's effect on the performance of a far-field steering two-dimensional Applebaum-type adaptive array. The expression is shown to be consistent with the actual simulated value. Using that expression, a simplified rule is obtained to determine the distance between the signal source and the array center at which the output SNR loss is given by a specific value. The SNR value so obtained varied with two-dimensional signal direction. The analysis for the case of an arbitrarily located array is presented, followed by the cases for rectangular, circular and elliptical arrays. It was found that this distance associated with the given SNR value is always less for a rectangular array than that of a linear array when the total number of array elements for both are equal and the performances of an elliptical array are similar to those of a circular array. >

General radiation-pattern synthesis technique for array antennas of arbitrary configuration and element type

Abstract: An interactive iterative-synthesis technique is presented, which is of particular use for far-field patterns defined in terms of power only. The method is applied in general to three-dimensional array configurations composed of different element types, with the required far-field defined over large angular regions. Suggestions for extending the method to near-field, simultaneous multiparameter or constrained synthesis are also given. The description of the method is presented for three different conditions, depending on whether both the array amplitude and the phase or just the amplitude or the phase are variable. Examples of the method, applied to various practical synthesis problems, and comparisons to other techniques are also given.