The paper describes a method for producing an angular deflection, or continuous rotation, of any directional pattern formed from a circular (or cylindrical) array, by means of a simple linear progressive phase shift across the input ports of a multiple-port matrix network, whose output ports feed the array elements. If the progresive phase shift has a value of o radians between adjacent ports, the directional pattern is rotated through an angle of o radians. The principal advantage of the technique is that it enables any aperture distribution of a circular array to be electronically rotated by the simple phasing techniques normally associated with a linear array. It is also shown that the matrix network may take the form of a Butler-type matrix, which may be easily realised using only hybrid networks and phase shifters.

A transformation between the phasing techniques required for linear and circular aerial arrays

This paper describes methods for enabling the directional pattern of a cylindrical array to scan continuously and repetitively through 360° by electronic means. This requires that the circular aperture distribution corresponding to the far-field directional pattern should be subjected to rotation relative to the fixed array. Methods are described for independent control of the amplitude and phase of the aperture distribution in order to synthetise suitable forms of directional pattern. Certain theoretical and practical limitations on the proposals are also discussed. The techniques are applicable, in principle, to both transmission and reception; a brief discussion of the relevance of the proposals to radar and sonar is also given.

Cylindrical arrays with electronic beam scanning

This thesis describes a mathematical and experimental study
of circular arrays of directional antennas.
For directional pattern synthesis in circular arrays of
omnidirectional elements, mode-analysis or Fourier
harmonic analysis technique has previously been used. This
thesis describes the effect of using any directional
element on the mode properties - in the horizontal plane,
and on the vertical directional pattern of such arrays.
The effect of random amplitude and phase errors in the
excitation of circular arrays and of mutual coupling with
reference to directional pattern synthesis is also studied.
A procedure is outlined for designing circular arrays of
directional elements and a design of an experimental 16-
element circular array is then presented. This is an
8 foot diameter array of 16 wideband elements each having
a pattern of the form (l+cosφ) for operation at 200-400MHz
frequency band. Various mode patterns are computed for
the array to determine their purity. The theoretical
wideband performance of the array is also examined.
New techniques are described for the synthesis of single
and 2n sharp nulls in otherwise omnidirectional patterns
of circular arrays and the mechanism for independent
steering of these nulls is also described. Patterns are
computed to demonstrate and theoretically study the
techniques.
Finally, experimental results are presented to
complement the theoretical study of circular arrays and
null patterns.

Directional pattern synthesis in circular arrays of directional antennas

The problems of direction-finding at high frequencies may divided for convenience into three groups, (a) those dealing with instrument itself, (b) those dealing with phenomena occurring in course of propagation of the waves, and (c) those concerned with interpretation of the bearings once the readings have been obtained.As to the instrument, the basic type of high-frequency direction-finder during the past decade has been the Adcock, using spaced vertical aerials. During the war years, attempts were made to improve performance of the simple Adcock direction-finder by the use of earth mats or arrangements of radial counterpoise wires. Some reduction of polarization error on sites of low conductivity was thereby achieved. There were advances in bearing display, particularly in regard instantaneous direct-reading types, while improvements in design components such as receivers and goniometers have resulted in all-round improvement in the performance of high-frequency ground station direction-finders.To overcome the difficulties of polarization error inherent in Adcocktype direction-finders, several types of practical spaced-loop directionfinders have been developed in recent years. These are all of the rotating coaxial-aerial type.Future improvements in instrumental design are likely to involve departure from the small-aperture spaced-aerial arrangement, and systems of wide aperture, in which the direction of the wavefront is determined by measurements made at widely separated points are forecast. Reduction of certain types of wave-interference errors, particularly those due to scattering, is likely to be achieved.Recent advances in knowledge of the propagation of waves in the high-frequency band have been concerned chiefly with ionospheric waves. A good deal of information of a statistical nature concerning the deviations suffered by these waves has been accumulated but much still remains to be done, particularly as regards a study of the characteristics and structure of the ionospheric irregularities causing deviations. During the war years various attempts to overcome some the difficulties encountered when dealing with ionospheric waves were made. Of these, the most important were the ray selection technique involving apparatus for the selection of a single ray component of complex signal) and the employment of groups or clusters of directionfinding stations in place of single stations. In the future, the use instruments of large aperture is likely to cause both of these techniques to be outmoded.Once a bearing from a single direction-finding station or a group bearings from a network of direction-finding stations has been obtained, there arises the problem of deciding what information is contained the figures as to the true direction or position of the transmitter. This is the problem of interpretation and it is essentially a statistical one. There are at least two parts to the problem, (a) to determine, a priori, the probable accuracy of the individual bearing or bearings; and (b) with this information to determine the most probable location the transmitter and establish areas within which there is a given probability of finding the transmitter. The first of these two problems is essentially the more difficult, and though there have been attempts at a solution by various schemes for “classifying” the bearings according to probable errors there is still no fully satisfactory solution. Given solution of the first, the second problem is mathematically simple, the solution being found in terms of the principle of least squares. In the future, the development of mechanical, electronic or other devices which will carry out the necessary operations automatically is likely to proceed.

Fundamental problems in radio direction-finding at high frequencies (3ߝ30 Mc/s)

The application of multiloop arrays to high-frequency direction finding in the complex reradiation environments of shipboard sites is analyzed in detail. Theoretical results show that the bearing error and blurring are reduced and multivalued calibration curves are eliminated as the number of loops in the array is increased. The coaxial spaced loop is shown to produce a 2 to 1 reduction in bearing error with respect to the simple loop and eliminates multivalued calibration curves for thin reradiators. The use of combination arrays such as n and (n- 1) or n and (n- 3) loops are shown to produce unambiguous direction finding patterns. The DF performance characteristics of a coaxial spaced loop plus simple loop array are demonstrated for a shipboard site. Comparison of simple loop and three loop array calibration curves verify the performance characteristics predicted by the theory.

Multiloop antenna arrays for high-frequency shipboard direction finding

An account is given of the progress in naval radio direction-finding both on land and in H.M. Ships during the last ten years.On land, the Admiralty has been specially concerned in highfrequency (3–30 Mc/s) direction-finding. Some parts of the very-high-frequency range (30–300 Mc/s) are also of interest, notably in the band used for communication with fighter aircraft, 100 to 156 Mc/s. In the field of h.f. direction-finding, the factors limiting the accuracy at present obtainable with the standard Adcock-type apparatus are critically reviewed. Brief descriptions are given of several new systems in h.f. direction-finding on land, in which it is suggested further research would be profitable.The paper describes further developments in ship-board m.f. direction-finding, and the research and development work carried out in the h.f., v.h.f., u.h.f. (300–3000 Mc/s) and s.h.f. (3000–30000 Mc/s) bands.It is shown that accurate direction-finding on high frequencies in ships offers considerably greater difficulties as compared with those encountered on m.f. This is due to the greater disturbances caused by the secondary fields radiated by various parts of the ship's structure and rigging. It is also shown how the essential conditions have been derived for siting the direction-finder aerial in a position where the effects of secondary radiation will not excessively degrade the performance. The paper considers the principles of design employed in the ship-board h.f. direction-finder and explains how the various requirements of accuracy, sensitivity, coverage of the whole h.f. band with a minimum of design and operating complexity, reliability, sensefinding and quickness in operation, involve a compromise in which the highest performance in any one particular is unattainable. The essential performance data are given for the apparatus widely fitted during the recent war.The various aspects of research and development in v.h.f. directionfinders for ships are considered and it is shown that the ship conditions are less adverse in the v.h.f. case than they are in h.f. direction-finding.In keeping the paper to a reasonable length, only a brief introduction is given to the work done in the wide field of u.h.f. and s.h.f. directionfinding. Many of the techniques in these frequency bands merge with those of radar, with the important difference that direction-finding must always attempt to cover the widest possible frequency range with the simplest possible apparatus.The applications of radio direction-finding to naval purposes are briefly stated.

C. Crampton

Papers

Naval radio direction-finding