Broadside Array Research Articles

Effectiveness of optimum beamforming by amplitude shading of transducer arrays

Since array amplitude shading can be implemented with relative ease in sonar receiving systems, the effectiveness of optimum beamforming by amplitude shading [H. S. C. Wang, J. Acoust. Soc. Am. 56, S18(A) (1974)] is investigated in more detail. It is demonstrated that in the case of broadside arrays in an isotropic noise field, the optimized amplitude shading previously reported by the author is identical to the conventional optimum solution allowing both amplitude and phase shading [see, for example, D. K. Cheng, Proc. IEEE 59, 1664 (1971)]. When the ambient noise and interference field is anisotropic, the two solutions are distinct from each other, with the latter yielding slightly lower noise and interference power for a given constrained received signal power. The difference between the noise and interference power at the output of the two optimum beamformers is, however, too small to cause any significant difference in the performance of practical receiving systems. A quantitative comparison of array performance with conventional amplitude shading, optimized amplitude shading, and optimized amplitude and phase shading under various field conditions is exhibited. This further supports our earlier belief that adaptive beamforming based on amplitude shading can provide maximum performance with minimal amount of circuit hardware and/or data processing.

On the use of delays for wide-band superdirective beam forming in endfire and broadside arrays

In algebra, the values of a polynomial over a wide span of time can be inferred from its value and that of its derivatives, measured over a very short span of time. Somewhat analogously, closely-spaced measurements, defining the fine structure of the phase and amplitude distribution over a narrow antenna aperture, can provide the information conventionally obtained from a similar number of elements spaced at half-wavelength intervals over a wider aperture.Superdirective beam patterns, exploiting this principle, are conveniently synthesized by defining the directions in which zero (or minimum) response is required. The correlation between closely-spaced measurements will then cause some reduction of gain, even at the wanted peak of the directional response pattern, but the directivity, i.e. the gain in the wanted direction relative to that in other directions, can be significantly enhanced.Each direction of arrival produces a corresponding pattern of relative propagation delays to the different elements of an array. By suitably equalizing these with non-dispersive delay circuits and then subtracting for null-forming (in place of the usual phase changers), such superdirective arrays can be designed for bandwidths of up to several octaves. Thus superdirectivity can be of considerable value, in certain circumstances, for h.f. radio, sonar or radar.

On the optimum directivity of general nonuniformly spaced broadside arrays of dipoles

In this letter the maximum directivity of general nonuniformly spaced broadside arrays of dipoles is examined. This is done with the help of formulas found by the method of orthonormalization of the base, which includes the array factor.

INLINE AND BROADSIDE EM DIPOLE DIPOLE PROFILING OVER A THIN VERTICAL INFINITELY CONDUCTING VEIN *

AbstractMaster diagrams for electromagnetic responses of nine dipole dipole systems are presented for various depths of a vertical infinitely conducting vein. The YY system gives the minimum anomaly for both the inline and broadside arrays. Among other inline systems, it is difficult to decide the clearcut superiority of one system over the other, whereas the XX system in broadside array gives maximum anomaly.

Laser-excited broadside array

The expansions and contractions of an absorbing medium resulting from the passage of an intensity-modulated laser are utilized to form a thermoacoustic array producing a highly directional acoustic wave propagating perpendicular to the axis of the laser beam.

Octave Bandwidth Constant Beamwidth Underwater Receiving Array

By a method described at the 79th meeting of the Society, a seven-element linear broadside array was designed to give a constant beamwidth of 26° from 10 to 20 kHz. Five elements spaced 12λ at 10 kHz comprised one array. Using three of these and two more, a half-size array with spacing of 12λ at 20 kHz was obtained. Each was filtered then combined to give the array output. The filter functions as specified by the directivity function were approximated since they were not realizable by real elements. The predicted and measured characteristics of the array are presented.

Production of minimum radiation over a given range of angles for a directional aerial array†

In some applications it may be desirable to construct an aerial array to radiate minimum energy in a certain angular sector whilst providing high gain in the required direction. In this paper the far field expression for the radiation pattern of a broadside array is reduced to a function of several variables of the inter-element spacing. The element positions are then optimized to correspond to minimum radiation over ft specified sector. Experimental results have been obtained in accordance with the theoretical predictions, but difficulty was experienced in achieving small signal measurement near the theoretical minima in the laboratory.

Realizable method of pattern synthesis for array antenna

The problem of realization of an arbitrary current distribution on an broadside array antenna derived from the theory of pattern synthesis is treated and some practical methods are proposed. In these methods, the input voltage of each antenna is transformed by a reactive transformer to take the required value. In one of the methods, experiments to yield Chebyshev patterns were performed and satisfactory results were obtained.

Symmetry properties of linear broadside arrays

Optimality properties are proved for arrays that exhibit symmetry about their geometric centers. Specifically, a symmetric array has smaller sidelobes than a nonsymmetric one; this is true not only for exact realization but, in the worst case, for inexact realization as well.

Antennas with transmission-line interconnections

Arrays of cylindrical dipoles and monopoles are usually driven by means of interconnecting transmission lines, whereas analyses of such arrays are generally made in terms of currents or voltages with assigned relative amplitudes and phases at the individual input terminals. Moreover, it is commonly assumed that the distributions of current along all elements are the same and without phase variation. The properties of broadside and endfire arrays are treated with full consideration of interconnecting transmission lines and the effect of mutual coupling on the distributions of current. Driving-point admittances and field patterns of arrays of half-wave and full-wave elements are given. A novel broadside-endfire array is described.

Wide-Bandwidth Constant-Beamwidth Acoustic Array

A linear broadside array can be made to have constant beamwidth over wide frequency ranges by using logarithmic element spacing and the proper filtering and combination of signals from the elements. Such an array is achieved by choosing the array size and linear element spacing to give the desired beamwidth and side-lobe suppression at the lowest frequency of interest. An identical array at twice the frequency will be half as long with half the spacing. When the signals from these two arrays are properly filtered and combined constant beamwidth over an octave band results. When the arrays are superimposed, redundancy allows a reduction in the number of elements. This process can be continued to cover the desired bandwidth and a log spacing results. Results obtained from a five-element array covering 0.3 to 3 kHz are presented. [Partially supported by LTV-Electrosystems.]

Antenna arrays with partially tapered amplitudes

A new technique is presented for linear array design based on a form of limited amplitude tapering. It is shown that desirable pattern characteristics can be achieved using an amplitude distribution that is uniform over all but a few of the outermost pairs of array elements, resulting in a partially uniform array. This method applies equally well to broadside and endfire arrays, and can be used to place pattern nulls in one or more specified directions or to eliminate virtually all radiation over one or more sectors of space. When compared with Dolph-Chebyshev arrays corresponding to the same sidelobe levels, partially uniform arrays provide a simpler excitation scheme in general and, in some cases, higher directive gain and a lower maximum-to-minimum excitation ratio. Both theoretical and experimental examples are given.

The Z-transform and unequally spaced arrays

It is shown that under certain conditions, Z-transform theory can be applied to simplify analysis and synthesis of unequally spaced antenna arrays. The approach provides significant advantages over other techniques since the method yields closed-form expressions for array factors that are otherwise often cumbersome and difficult to work with analytically. The method is useful for both broadside and endfire arrays and allows many of the results originally derived for equally spaced arrays to be applied.

Near-Field and Far-Field Radiation from an Experimental Electrically Steered Planar Array

Current interest in electrically steered transducers has led to new experimental and theoretical work. Several years ago extensive measurements were made on a large planar broadside array. Experimental results in the near and far fields agreed to excellent accuracy with theory based upon the assumption of an infinite, plane rigid baffle. This paper includes new experimental results for a similar transducer array which was electrically steered to seven different angles from broadside to endfire. These results are compared with theory based upon the infinite baffle assumption. It is demonstrated that both near-field and far-field errors increase as the steering angle approaches the endfire case. It is concluded that the effects of a finite baffle must be considered in any theory that is to be used for arrays steered to large angles from broadside. This observation is also important relative to radiation impedance computations.

Possible Continuum Emission from Jupiter at 18 Mc/sec.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Possible Continuum Emission from Jupiter at 18 Mc/sec. Barrow, C. H. ; Williams, J. Abstract Observations of Jupiter have been made with an interferometer consisting of two identical broadside arrays, each of four whole-wave dipoles, on an east-west baseline of 16 wavelengths. The beam of each array was centered on the zenith and had half-power points at about + 130 in the north- south direction and + 250 in the east-west direction. The receiver was phase switched with variable time constant and bandwidth. Some typical records are presented. In some of these the conventional Jupiter bursts appear superimposed on a fringe envelope while in others the pen returns to the zero-centered baseline between bursts of activity. The over-all time characteristics of the instrument were such that the pen should readily have returned to the center zero between bursts had the incident radiation from Jupiter gone to zero for periods of more than a few seconds. It is suggested that the former type of record indicates the presence of some weak background continuum radiation of intensity less than about 10-21 W m-2 (cps)-1. This effect was not observed on many occasions and presumably indicates either that continuum emission is not a frequent occurrence or that it is usually of too low an intensity to be recorded by the interferometer. The research is supported by the National Aeronautics and Space Adminstration Grant number NSG-224-61 Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110424 Bibcode: 1967AJ.....72Q.785B full text sources ADS |

A broadside log-periodic antenna

This invention teaches an antenna array of the broadside type in which dipoles of differing electrical lengths are stacked vertically above and below an imaginary plane with electrical lengths increasing with increasing distance in moving above and below the imaginary plane. The antenna has symmetry in that for each dipole of the array below the imaginary plane, for example, there is a dipole of substantially equal electrical length and spacing approximately the same distance above the imaginary plane. Transposed feeder harness means are employed for joining adjacent dipoles and common output (input) terminals are provided in a position substantially at the location of the imaginary plane. Directional characteristics are obtained by means of Veeing the dipole arms and/or providing a vertically aligned ground screen positioned behind the antenna stack array. In another embodiment a similar array may be positioned immediately behind the first array in place of the ground screen. Directional characteristics may be obtained through coupling an output (input) utilization means to one and then the other of the arrays which are coupled at their feed terminals by means of a transposed feeder section. The array may also be joined with a conventional endfire array, for example, to form a broadside VHF endfire array and an endfire UHF array or conversely, a broadside UHF array and an endfire VHF array. Omnidirectional characteristics may be introduced if such an application is either desired or required by bending or otherwise forming the dipole arms so as to provide a substantially U-shaped configuration for each dipole. As another embodiment the ground screen may be replaced by parasitic elements arranged in a vertically stacked array with the parasitic element being provided for each dipole in the broadside array and being positioned in substantially behind its associated dipole.

Effect of Thevenin Equivalent Internal Impedance on Velocity Control and Acoustic Power of Planar Broadside Arrays

A Thevenin equivalent circuit for array elements, which has an input force in series with a radiation impedance and an internal impedance ZI, is discussed. The arrays considered are 80-element, close-packed, unshaded arrays, with many different ka and ZI. Four limitations to input voltage are discussed: velocity, transducer voltage, available power, and cavitation. Velocity-limited acoustic power is maximum for infinite |ZI| (equal velocities) and worst for RI=0 and XI between −XSELF and −2XSELF. Cavitation-limited acoustic power is maximum for ZI=0, when about 3 dB more power is obtained than with equal velocities and, with steered arrays, more than 3 dB. A velocity control factor UCF=|Z12|/|ZI+ZSELF| is presented, where Z12 is the mutual impedance between nearest-neighboring pistons. Velocity-limited acoustic power decreased as UCF increased.

The optimum directivity of uniformly spaced broadside arrays of dipoles

The optimum directivity of various types of uniformly spaced broadside arrays of dipoles is investigated theoretically in this paper. The formulation is processed with the aid of an array matrix. The expression for the optimum directivity and the corresponding excitation are expressed directly in terms of the elements of the array matrix. The computed values are assembled in several sets of curves, and the results are compared with the directivity of uniformly excited arrays.

The theory of broadside arrays

The general King-Sandler array theory has been examined in detail for the case of broadside arrays. Since it is not necessary to assume identical current distributions on every element in the array, a distinction is made between specified base currents and voltages. The driving-point impedances for specified base currents and voltages are presented for arrays of up to 25 elements. The effect of interaction between the element currents in the base impedances and radiation patterns is clearly shown for the broadside array. The results indicate that the major effect of unequal current distributions in the broadside array is to cause important variations in the driving-point impedances and little effect in the radiation patterns.

Antennafier arrays

The integrated transistorized dipole antennafier (antenna-amplifier) is ideally suited for use in array systems. The advantages include ease of amplitude-distribution control, low noise, high gain, high reliability and simplicity. The integration is achieved by using the antenna as a circuit element of the transistorized amplifier, thus eliminating the tuned input circuits and transmission lines commonly used. A four-element broadside array of antennafiers is described in which the gain of each element is varied by controlling the base bias. Binomial, uniform, edge and Dolph-Chebyshev distributions were chosen to show the wide variation of beam control possible; the resulting measured and calculated patterns, half-power beamwidths, gain over a half-wavelength dipole, and noise temperatures are presented. A method of experimentally evaluating the noise performance, based on a theoretical development, is also described.