Plane Array Research Articles

Beam pattern control by the use of real (vice complex) shading coefficients

The usual method of beam control using complex shading coefficients or complex shading functions involves the algorithm of “phasing or time delaying to a plane,” and then performing a weighted sum. This paper considers the performance of beams formed using real shading coefficients (i.e., no time delay or phase shift being implemented). The algorithm used is a combination of “replica correlations” and the normal “aperture function” for sidelobe control. The array considered in the majority of the work consists of equally spaced finite‐sized acoustic elements or staves arranged on the surface of a right circular cylinder. It has been found, however, that the method works for several geometries including volumetric, line, and plane arrays. The functional dependence of beamwidth, bandwidth, sidelobe level, and sensitivity upon array size in wavelengths is presented. Advantages and disadvantages of the use of the method will be enumerated. Experimental proof of the mathematical model used in this study is contained in a companion paper.

Classification of Axisymmetrica Apertures

A large class of well-known axisymmertic scanning devices such as paraboloidal reflectors, uniform circular pistons, spherical Luneberg lenses, etc., may be compared because they all have Fraunhoffer patterns equivalent to those produced by shaded, circular, plane arrays, i.e., the devices all collimate over a plane circular aperture. The scanning pattern is a normalized Bessel function Δν(z) with ν the order and z = CIRCUMFERENCE/WAVELENGTH × SINE OF THE ANGLE FROM THE APERTURE AXIS. All orders (integral and nonintegral) from ν = 0 to ν → ∞ have been explored and such relevant parameters as sidelobe, beamwidth, and directive-gain versus order have been computed and are shown. The calculation of directive index leads to the algebraic proof that the uniform piston has the best directive gain. For very large apertures, a phased spherical volume array (ν =) and phased spherical surface array (ν = 12) may be included in the general classification.

The acoustic self-radiation impedance of a rigid oscillating disc near a similar stationary disc

The self-radiation impedance of a rigid oscillating disc (ka≯1) in the presence of another such disc, stationary and in the same plane, is derived by a simple approximate method. Resistance values are given in the case of identical discs, with 0·2<ka<1·0 and separation distances up to 7a. These results are intended as a basis for the evaluation of self-radiation impedances of acoustic projectors in plane arrays.

A multiple counter for a beta spectrometer

A single structure consisting of fourteen parallel proportional counters in a plane array has been constructed and installed in the University of Colorado beta-ray spectrometer. All counters are independent of one another and each counter records electrons of a different momentum value. Twelve counters record spectral data over a range of intensities, while two record background. All twelve data counters have demonstrated resolutions of the order of 0.1% at a spectrometer transmission of 0.4% of 4π.

Mobile bend zones in magnesium oxide

Abstract Bend zones are regions in a crystal across which the lattice is bent; the bend occurs across the whole width of the zone. The lattice bending may be due to flexural glide or an array of discrete bend planes or a single bend plane or combinations of these; the composition of a bend zone may vary along its length. Several examples are given of the conditions under which bend zones form in magnesium oxide. They are able to move through existing dislocation bands as a perturbation of the dislocation arrangement in these bands. They arise in an attempt to accommodate strain due to various phenomena, e.g. grip restraint, dislocation configurations and cracks. Comment is made on their role in crack nucleation and growth.

Mutual Coupling with Dipoles in Arrays

Mutual coupling between transducers in a plane array may be eliminated completely if thin oscillating disks are used as radiators. The radiation resistance of such dipoles is very low unless the diameter is about a half-wavelength in the fluid medium or the disk is bordered with a finite rigid baffle. Alternatively, a pseudodipole type of transducer may lead to low mutual coupling without impairing seriously the radiative self-impedance.

Use of the Analog Computer in the Design of Directional Arrays

The usefulness of the analog computer in the design of radiation patterns produced by various arrays of radiating elements is discussed. The analog computer provides an easy and rapid method of continuously plotting the entire pattern from known parameters, such as relative strengths of the elements, element spacing, frequency, and relative phases among the elements. Modifications of any or all of these parameters are easily made and the effects quickly determined. It may be used for a wide variety of arrays, among which are linear and plane arrays with uniform or nonuniform spacing, tapered arrays, and steered arrays in which phase lags readily may be introduced into any number of elements. Although several of the so-called optimum design techniques provide the optimum pattern in only one or two planes, the analog computer quickly provides the patterns for other planes. Also, the sum and difference patterns of two halves of an array may be drawn simultaneously. One such curve presents the locus of the vector amplitude and phase of the signal from one-half of the array.

An Experimental Study of Parasitic Wire Reflectors on 2.5 Meters

This paper presents the results of an experimental investigation of the energy distribution in a horizontal plane due to the juxtaposition of a vertical antenna and parallel parasitic rod-shaped conductors. The reduction of spurious radiation to a minimum, through a special arrangement of the apparatus, results in symmetry of the polar radiation patterns and makes it possible to appraise accurately the dependency of the forward radiation, directivity, and backward radiation on the dimensions of the reflector system. Typical polar distributions of single, double, trigonal, trapezoidal, plane, and parabolic arrays are shown. The distance between antenna and reflector for optimum forward effect, for plane and other multiple-wire arrays, was found to depend, in general, on the number, length, and spacing of the reflector elements. The parabolic reflector is considered in greater detail and, while most of the results are seen to be in qualitative agreement with experiments reported abroad, it is evident that the aperture of a grid reflector is not always a consistent "figure of merit" of its performance. The results of the parabolic arrays are used, finally, to discuss a theoretical formula derived by Ollendorff.