US3056961A - Steerable directional random antenna array - Google Patents

Description

Oct. 2, 1962 G. MITCHELL STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY 4 Sheets-Sheet l Filed Aug. l2, 1958 A'r'roRNEY5 Oct. 2, 1962 G. MITCHELL 3,056,961

STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY Filed Aug. l2, 1958 4 Sheetsiheet 2 INvemoR GEOFf/Qf Y Ml Ter/fu.

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ATTQRN EYS Oct. 2, 1962 G. MITCHELL STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY Filed Aug. l2, 1958 PHASESMFH-'RS w f m 4 INvEN-roR GEOFFREY M/TCHELL #vz/Z n Awww a# 5 Oct. 2, 1962 G. MITCHELL 3,055,961

STERRABLE DIRECTIONAL RANDOM ANTENNA ARRAY Filed Aug. l2, 1,95? 4 Sheets-Sheet 4 O OOO /5 O oooooooooooooooooooo A/ y/LA* T K/ 4/ 142 l DG/ 2 Jr(, o/

YTHTT WCHA F/ @L12 I Vm 'l V7 6/\| T P l 'Ti-"- l G/Z o o/G2 i M l Ye i: s l INVENTR H/ (raw-Mey r1 CHELL i 2 /A-m *i i 3,056,951 ICC Patented oct. 2, 1962 3,056,961 STEERABLE DIRECTIONAL RANDOM ANTENNA ARRAY Georey Mitchell, Boreham Wood, England, assignor to Her Majestys Postmaster General, London, England Filed Aug. 12, 1958, Ser. No. 754,567 Claims priority, application Great Britain Aug. 15, 1957 3 Claims. (Cl. 343-854) The present invention relates to steerable directional aerial systems using a number of lixed spaced aerials, the directional properties in azimuth and elevation of which may be varied electrically, and has for an object to provide such a system which is substantially universally steerable.

Steerable directional aerial systems are known and one system has been proposed in which an array of spaced vertical -aerials is provided, the aerials being positioned in :rows to form a square pattern and the signals from the aerials being combined, after adjustment `for the time delay differences, by means of variable time delay networks. The outputs of the aerials of each row are fed respectively over equi-length co-axial cables to pri' mary variable time delay networks by means of which the signals from the row of aerials are adjusted and combined and the resultant outputs from the primary networks-equal in number to the number of rows of the aerials-are fed to secondary variable time delay networks to be further adjusted and combined, the resultant output being fed to the receiver. The said prior proposal also envisages the provision of several sets of delay networks to enable several outputs to be steered independently for different directions of reception.

A further prior proposal employs a plurality of aerials arranged to `form a circular pattern and comprising diametrically disposed intersecting rows of spaced aerials having individual means disposed between each aerial and one or more receivers or transmitters common to all the aerials yfor adjusting the time differences between the output from or input to the individual aerials, the adjustments for any given direction of reception or transmission being eifected by a common control. According to the said further prior proposal the several outputs of the aerials of each row are fed to an adjustable delay unit common to the row and the signals from the adjustable delay units, which correspond in number 4tothe number of rows of aerials, are combined.

According to the present invention, a steerable directional aerial system comprises an array of spaced aerials distributed over the area of the array, means for grouping selected aerials `for receiving a signal of given frequency and direction of arrival, 'the `aerials being divided into groups according to the space distribution thereof andV the frequency and direction of arrival of the signal, means for shifting the phases of the outputs of all the aerials in a group by the same amount, and means for combining :the phase-shifted outputs of the grouped aerials lfor feeding to a receiver.

y Preferably the -aerials are distributed irregularly over the site area which itself may be irregular in shape. In this way a maximum of flexibility is obtained in laying out the aerial system. Also, an irregular distribution of4 the aerials leads toa reduction of minor lobes in the polar diagram of the system.

The phases of the outputs of the aerials for a given signal may be represented on a vector diagram in which the vectors, each of which represents the output of an aerial, radiate from a common point. By dividing a circle centred on such common point into sectors and by shifting the phases of all the vectors in each sector by a fixed angle determined by the mean angular displacement of the sector from a reference direction, the

resultant response of the aerials can be made sutliciently close for practical purposes to the ideal system in which the output of each aerial is phase-shifted according to the angular position of the vector representing the output of the aerial, with respect to the said reference direction.

According to a further feature of the invention therefore, the vectors representing the outputs of the aerials are grouped into a plurality of equal sectors and the outputs of the aerials represented by the vectors in selected sectors are lall shifted in phase by a iixed angle determined by the mean angular displacement of the respective sector from a reference direction thereby to bring the vectors of said selected sectors within the sector containing the said reference direction.

The invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic representation of an aerial array suitable for carrying the invention into effect;

FIGURE 2 is a vector diagram of the respective outputs o-f the aerials of the array;

FIGURE 3 is a vector diagram illustrating a method of phase displacement based on two-sector phasing;

FIGURE 4 is a vector diagram illustrating a method of phase displacement based on four-sector phasing;

FIGURE 5 is a schematic diagram of one form of 'steerable directional aerial system according to the invention;

FIGURE 6 shows an alternative arrangement of the system of FIGURE 5;

FIGURE 7 shows a portion of a punched tape for coutrolling the operation of the system; and

FIGURE 8 is a circuit diagram of control means operable by the punched tape of FIGURE 7.

Referring rstly to FIGURE l, the aerial array shown therein comprises a plurality of unit aerials 1 which are identical and may be regarded, for the purpose of vector analysis, as omnidirectional point sources, and although in the drawings only a limited number of aerials is shown, in practice there will be many more, for example P aerials. A radio-frequency wave having a plane wave front `and incident on the array of aerials 1 i-s shown at 2.

The phase of the output of any one of the aerials 1 relative to the output of a hypothetical reference aerial, for example a reference aerial positioned at the centre of a circ-le 1a enclosing the array, is a function of the direction in azimuth and elevation from which the wave 2 aproaches, the position of the aerial in the array, and the frequency of the radio-frequency wave. The said output phase for each aerial may be denoted by p, Where -1r q5 +1r, and since the array of aerials comprises a large number of irregularly disposed aerials the corresponding values of the angle la for the various aerials may' be assumed to be randomly distributed as shown in the vector diagram of FIGURE 2., in which the arrows 3 represent the relative phase angle of the outputs of the aerials 1 of FIGURE l.

In FIGURE 3 the outputs of the individual aerials are grouped together according to their phases relative to the reference direction in the following manner:

,Group .Af-Outputs for which fp is in the range 0 to +0. The corresponding aerials are designated the A` aerials and their number will be denoted by a.

Group B Outputs for which o is in the range +0 to (1r-0). The corresponding aerials are designated the B aerials and their number will be denoted by b.

Group C.--Outputs for which qa is in the range (1r-0) to fr or the range -vr to (f1-1r). The corresponding aerials are `designated the C aerials and their number will be denoted by c. j

Group D.-Outputs for which is in the range (t9-1r) 3 to 0. The corresponding aerials are designated the D aerials and their number will be denoted by d.

It will be apparent that the direction of arrival (in azimuth and elevation), the frequency of the incoming signal and the position of the aerial in the array will determine in which group an individual aerial will be included.

IIf now the outputs of all the C aerials are rst changed in phase by angle 1r so that the outputs of the C aerials lie within the range to +0, i.e. within the range of the group A aerials, and the outputs of the C aerials are then combined with the outputs of the A aerials, there results a single output indicated in FIGURE 3 by ER which is angularly displaced from the reference vector E0 which represents the resultant output from an ideal system in which the output of each individual aerial is changed in phase so that the outputs are precisely in phase before they are combined. In the method of combining illustrated in FIGURE 3 the outputs of the B and D group aerials are discarded so that the system may be termed to a two-sector system, since only the outputs of the A and C group aerials are utilised. Thus, in FIGURE 3 EA represents the resultant of the outputs of the A group aerials and EC and E'C respectively represent the resultant of the outputs of the C group aerials before and after the phase change.

It is desired to find the magnitude of the resultant ER of adding the output of all the A and C aerials together (i.e. of adding EA and EC), and then to compare this with the magnitude of the EO. Since P is assumed to be large, a substantially uniform average density of vectors representing aerial outputs exists within the sector 0 to +0 (provided the elemental sectors compared for equality of vector density are not too small); therefore the phase of ER closely approaches that of the reference vector EO and it can be readily shown that ER=e a. `il w (l) where e is the amplitude of the output of each unit areial.

Furthermore, since P is large, an inspection of the diagram shows that Equation 4 above enables the response of a simple twosector system in which 0 has any arbitrary value to be compared with that of an idealised system, i.e. one in which all the aerials are used and no phase errors occur, and by choosing a value of a two-sector system which uses all the aerials is obtained, and for such a system i.e. the theoretical response of a two-sector system in which all the aerials are used would be 3.92 decibels below that of an idealised system.

The two-sector system with just described, divides the vectors representing all the aerial outputs into two groups corresponding to two sectors of angular width 1r, and those in one group are changed in phase by 1r before all aerial outputs are added. This is a particular form of the generalised sector system in which the output vectors are divided into T equal groups such that all the vectors in any one group lie within a sector of angular width 21r/ T; the outputs in each group except one are then changed in phase by the appropriate multiple of 21r/ T to bring all the outputs into said one group and all outputs added. It can be shown that, provided T is fairly small (thus ensuring a uniform average density of vectors throughout each sector) Efo w; S111 where Er is the resultant obtained by bringing into phase the resultants of the vectors in each sector.

The following table shows the value of ET/EO for various values of T.

The table shows that with a system using only four sectors as shown in FIGURE 4 it is theoretically possible to achieve an output which is less than one decibel below that of an idealised system.

Referring now to FIGURE 5, there is shown one form of practical embodiment of a four-sector system according to the invention in which the output of each aerial 1 to P is fed through an amplier 4 and a -distribution network 5 to a plurality of four-way switches 6 corresponding in number -to the number of receivers 1 to Q (not shown). From each lfour-way switch there are four connections to four wideband phase- shift networks 7, 8, 9 and 10 for introducing relative phase-shifts of 0, 1r/2, 1r, and 31r/2 respectively, the outputs from the yfour phaseshift networks being fed to a combining network 11 and thence to the receiver. It will =be apparent that by means ofthe four-way switches 6 the outputs of the aerials may be connected in four groups each group characterised by a relative phase-shift of 0, 11F/2, 1r, and 3w/ 2 respectively, the four-way -switches being yoperated lby a direction control 12 which-depcnding on the frequency and direction of `arrival (in azimuth and elevation) of a signaloperates the switches to group the aerials for connection to the phase-shift networks to give the required phase adjustment before combining the aerial outputs. It will be appreciated that since it is not known to make la wideband phase-.shift network having a constant phase-shift at all frequencies it is necessary to provide in each group a network having a phase-shift which differs -from those in other groups by constant amounts. One of these groups can be looked upon as .the datum with a relative phase-shift of 0 while the others have phase-shifts of 11'/ 2, 1r and 31r/ 2 relative to that in the datum group.

In the :alternative arrangement of FIGURE 6, the elements are arranged similarly to that of FIGURE 5 with the exception that the wideband phase-shift networks 7a, 8a, 9a and 10a are introduced into each aerial circuit before connection to the four-way switches. Thus, the four-way switches 6a of FIGURE 6 have four connections to each aerial circuit and one connection to the corresponding receiver, whereas the vfour-way switches 6 of FIGURE 5 have one connection to the 4aerial circuit and four connections to the receiver.

In the four-sector switching system described above with reference to FIGURES S and 6, only one of the four phase-shift networks is connected at a time `but it will be apparent that by simultaneously connecting two networks corresponding to adjacent 'sectors there would result a phase-shift midway between the two and enable the control system to be operated on an eight-sector basis. Thus, if the four outlets of the four-way switches in FIGURE 5 or the four inlets of the switches in FIGURE 6 are designated A, B, C and D respectively, and if the outlets or inlets Iare connected to networks giving relative phase-shifts of 0, 1r/2, 1r, and 31r/ 2 respectively then the eight different phase-shifts can be obtained by utilising A, A and B together, B, B and C together, and so on.

In yet another arrangement a steered-null response may be obtained instead of a steered maximum response. For example, in a four-sector system a steerednull response may be obtained by arranging for one half of the aerial outputs to be shifted in phase by 1r from the phases which would be required to give a maximum response. A steered-null response is useful in direction finding and in the reduction of interference from unwanted signal-s.

One form of aerial suitable for use in .an array according to the invention and having the desired radiation and impedance characteristics comprises an inverted cone yformed by 16 wires equally spaced around the top of the cone and connected together and to the inner conductor of an aerial feed cable at the base of the cone, the cone being 24 Ifeet 6 inches high and 23 feet across the top of the cone. The aerials are arranged irregularly within the array :but a sufliciently uni-form density of aerials is provided to ensure representative sampling of an incoming signal over the array aperture. Thus there may be between 50 and 100 aerials for an array having an aperture of -from 300 to 400 metres in diameter.

The four-Way switches each comprises four parallel radio-frequency paths each of which may include an electronic element, `for example thermionic valve, solidstate diode, or a transistor, which may be operated from one stable condition =to another to make the transmission loss in the path very large or very small respectively. Operation -of the said electronic element is controlled by a conversion and memory circuit which converts instructions received from the direction control system, for example in -the `form of pulses, into a form suitable for operating the electronic element and `to maintain such operation until subsequent instructions are received.

The direction control system is required to translate the operational requirements yfor each receiver as specied in terms of frequency and direction of arrival (in azimuth and elevation) of a signal into -corresponding instructions to .the switches associated with a given receiver.

In computing the instructions .for the switches it is required lirstly to calculate the phase angle :p of the output of each aerial for signals of given wavelengths, azimuthal bearings, and elevational angles and then to determine lthe phase-shift required `for each -aerial when receiving signals of each wavelength, azimuthal bea-ring and eleva-tional angle.

The basic equation used to decide the phase angle 11) of the current in a given aerial relative lto the current in Aan aerial at the centre of the -array is given by qsr=sr cos (or-9,) cos where Sf=distance of the given aerial `from centre. 01r=bearing of the given aerial from centre. ly=waveler1gth of signal.

=azimuthal bearing of signal. =elevational angle of signal.

Lf the result is This procedure must be carried out for each aerial in the array and for each Wavelength and direction of arrival and although the bearing of a station may be known and the angle of elevation found from the characteristics of the ionosphere, variations in the ionosphere give rise to changes in bearing and elevation. Thus, even to receive one station, it is necessary to calculate several sets of sector-switching instructions and in view of the large number of calculations involved to provide switching instructions for receiving a number of differently directed signals the calculations are preferably made by means of an electronic computer and the results recorded for subsequent use in controlling the operation of the switches. Conveniently, the computer is programmed in such a manner that the output is obtained in a form suitable for recording on a tive-unit punched tape which is then employed to control directly the operation of the switches of a four-sector system as described with reference to FIG- URE 4. Other records such as, for example, a magnetic tape, may also be used.

A portion of one such punched tape is shown at 13 in FIGURE 7 in Which the characters indicate sector-phasing instructions for the respective aerials. The first character indicated by the punched hole 14 is a reset character for resetting the electronic switches as will hereinafter be described. A punched hole in the second position as indicated at 15 indicates that the phase of the corresponding aerial leads that of the hypothetical reference aerial by an angle of between 0 and '1r/2 and that therefore no phase-shift is necessary; while a punched hole in the third position 16 indicates a lead in the phase of the corresponding aerial of between 1r/ 2 and 1r and that therefore a lag of 1r/2 must be given by the phase-shift network in order to shift the vector representing the output of the aerial to the required sector of the vector diagram.

The tape of FIGURE 7 is used to control the operation of the Switches and one form of tape-controlled switch is shown diagrammatically in FIGURE 8. In this arrangement the tape is caused to pass under peckers P1, P2, P3, P4, P5, which are arranged to scan the lines of holes in the tape and to make contact with the positive pole of a direct current supply when a hole is encountered. The tape is fed by means of a tape reader feed operated by an electromagnet T which in turn is energised through a motor-driven contact M.

The four peckers P1 P4 are connected respectively to the wipers of four rotary selector switches S1, S2, S3, S4, which are driven at the same speed as the tape reader by means of an electromagnet R also energised from the motor-driven contact M. The tape is arranged so that a reset character as indicated by the punched hole 14 in FIGURE 7 precedes the phase-shifting information for each aerial and this character is scanned by the pecker P5 to operate a release electromagnet Z which restores the selectors S1 S4 to their initial or start position.

As the tape is fed forward one step the selectors S1 S4 are also advanced one step to the position shown in FIGURE 8 and according to whether the corresponding pecker encounters or does not encounter a hole in the tape toggle relays A, B, C and D connected respectively to the four switches S1 S4 are operated or not operated. Thus, and again assuming the tape to be punched as shown in FIGURE 7, the second character 15 will cause relay B to be operated through the pecker P2 and switch S2. Contact B1 of relay B closes a holding circuit for the relay through a contact Y2 of a relay Y connected in parallel with the release magnet Z. Relay B at its contact B2 closes a circuit to open a normally closed diode gate DG2 to permit the output from the aerial 1 to pass through capacitor K2, gate DGZ to the required phase-shift network, 7, 8, 9 or 10 of FIG- URE 5.

The selector Wipers together with the tape are then stepped one step by operation of the motor-driven contact M and the second character of the tape is read. In

7 the case of the tape shown in FIGURE 7 this is the character 16. This character will be read by the pecker P4 to cause relay H to be operated to connect the aerial 2 to the required phase-shift network in a similar manner to that described above with reference to the operation of relay B.

The stepping of the tape and of the selectors S1 S4 is continued until all the aerials have been connected to the required phase-shift networks, after which the motor-driven contact M is stopped.

When it is desired to steer the major lobe of the aerial array to a new direction a new section of tape is read and the rst character thereof is scanned by the pecker P5 which causes the selector release magnet Z to operate to restore the selectors to their initial position and also operates relay Y which opens its contacts to release the previously operated and locked-up toggle relays.

It will be understood that although a switching control system employing electromagnetic switches has been described, the invention is not limited to such an arrangement and that electronic switching elements may be employed to carry out the functions of the selector switches S1 S4 and associated relays described with reference to FIGURE 8.

I claim:

l. A steerable directional aerial system comprising an array of spaced aerials distributed over the area of the array, said aerials having outputs of different phase upon reception of a signal of given frequency and direction of arrival, the aerials being divided into groups according to the space distribution thereof and the frequency and direction of arrival of the signal such that the aerials in each group have outputs the phases of which lie within limits corresponding to the particular group, means for shifting the phase of the outputs of all the aerials in each group by a predetermined amount which is the same for the aerials for any group but which differs from group to group depending upon the mean phase displacement of the group with respect to the phase of a reference group, and means for combining the phase-shifted outputs of the groups of aerials for feeding to a receiver, each aerial being connected to a plurality of switching means each adapted to connect the aerial through a selected one of a plurality of phase-shift networks to a separate receiver associated with one switch means of each plurality of switching means there being thus a plurality of receivers corresponding in number to the number of said plurality of switching means, whereby upon operation of a switch means in each plurality of switch means associated with one receiver the output of each aerial is shifted in phase in accordance with the characteristics of the phase-shift network selected by each switch means.

2. A steerable directional aerial system comprising an array of spaced aerials distributed over the area of the array, said aerials having outputs of different phase upon reception of a signal of given frequency and direction of arrival, the aerials being divided into |groups according to the space distribution thereof and the frequency and direction of arrival of the signal such that the aerials in each group have outputs the phases of which lie within limits corresponding to the particular group, means for shifting the phase of the outputs of all the aerials in each group by a predetermined amount which is the same for the aerials for any group but which differs from group to group depending upon the mean phase displacement of the group with respect to the phase of a reference group, and means for combining the phase-shifted outputs of the groups of aerials for feeding to a receiver, the receiver being connected to a plurality of switching means each adapted to connect the receiver through a selected one of a plurality of phase-shifting networks to an aerial associated therewith, the number of switching means thus corresponding in number to the number of aerials, whereby upon selective operation of each switching means in the said plurality of switching means the output of each aerial is shifted in phase in accordance with the characteristic of the phase-shifting network selected by its associated switching means.

3. A steerable directional laerial system comprising an array of irregularly spaced aerials distributed over the area of the array, said aerials having outputs of different phase upon reception of a signal of given frequency and direction of arrival, the outputs being represented by vectors, the aerials being divided into groups in which the output vectors lie within the limits of corresponding sectors, phase shifter means associated with the aerials of each group for shifting the phase of the outputs of the aerials of the respective groups, each phase shifter means having several predetermined selectable values of phase shift corresponding :to the mean phase displacements between the corresponding sector and different reference phases, means for selecting the phase shift values of the respective phase Shifters to shift the mean phase of said sectors to the same reference phase, and means for combining the phase shifted outputs of the groups of aerials.

References Cited in the file of this patent UNITED STATES PATENTS 4', 1,738,522 Campbell Dec. 10, 1929 0 2,245,660 Feldman et al. June 17, 19141 2,432,134 Bagnall Dec. 9, 1947 2,444,425 Busignies July 6, 1948 2,466,354 Bagnall Apr. 5, 1949 2,510,280 Goddard June 6, 1950 FOREIGN PATENTS 168,845 Austria Aug. 25, 1951 496,027 Great Britain Nov. 23, 1938 545,052 Great Britain May 8, 1942

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