432,978

PATENT SPECIFICATION

Application Date: Feb. 7, 1934. No. 4093/34.

Complete Specification Left: March 7, 1935.

Complete Specification Accepted: Aug. 7, 1935.

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PROVISIONAL SPECIFICATION

Improvements in and relating to Directional Wireless Aerial Systems

We, ALAN DOWER BLUMLEIN, a British Subject, of 7, Courtfield Gardens, Ealing, London, W.13, and JOSEPH LADE PAWSEY, a British Subject, of 3, Dale Avenue, Hounslow West, Middlesex, do hereby declare the nature of this invention to be as follows:-

The present invention relates to directional wireless aerial systems such as can be used either for transmission or for receipt of electro-magnetic waves. When used for transmission, they are required to radiate the maximum portion of the radiated energy in the direction of the receiving station. When used for reception, they are required to receive as great a portion of the radiation from the transmitter as possible, and to exclude unwanted radiations such as interference arriving in other directions. The arrays can be of similar type for both transmitting and receiving. The gain in efficiency compared with a non-directional radiator or receiver, whether it be expressed as the ratio of wanted to unwanted power radiated, or as signal to noise ratio, is the same for a given type of array. The only difference between transmitting and receiving arrays is that in a receiving array, where the signal strength is sufficient to eliminate any trouble due to noise in the receiving amplifiers, the power efficiency of the array is not of importance, provided that the correct directional diagram is obtained in order to reduce interference pick-up as much as possible. In a transmitting array it is important to keep the power efficiency good in order that a large radiation may be obtained. Arrays may be designed either to give a good horizontal distribution (e.g. to transmit maximum power westward towards a westerly receiving station), or they may be designed to give a good vertical distribution (e.g. radiate maximum power horizontally instead of up and down), or to give a combination of both these desirable properties.

For convenience in description reference will be made more particularly in this specification to transmitting systems and it is to be understood that the systems discussed are also applicable to reception.

In order to obtain such directional arrays it is usual to use radiating elements (which may generally be a quarter to half a wavelength long), spaced at intervals of a quarter to a half wavelength apart and suitably phased so that radiation adds up for the wanted direction but subtracts for unwanted directions. The elements of the array may be separated vertically, along the direction of transmission, or across the direction of transmission.

The elements of an array are usually arranged vertically, although other arrangements may be used for some purposes, and they may be spaced apart vertically (for example arranged one above the other) or horizontally. In some cases the line of elements is along the direction of transmission and in other cases it is across it. The resulting radiation diagrams obtained from various arrangements have been very fully plotted in publications. It is however usually considered that a separation between elements of about a quarter wavelength is necessary in order to develop directional diagrams, since without this separation it is impossible to obtain addition of the effects of two elements in one direction and subtraction in another. Consequently, these directional arrays occupy considerable space, and cannot satisfactorily be employed on any but very short wavelengths.

It is the object of this invention to provide directive arrays where the separations between successive elements are shorter than a quarter wavelength, thus allowing a great saving in space to be effected.

According to the present invention a plurality of aerial elements are specially arranged and have their electrical centres separated by consecutive distances shorter than a quarter of the operating wavelength, at least two successive elements being electrically phased almost in opposition and so that their radiations or receptions substantially neutralise in one direction (the unwanted direction) and fail to neutralise in another direction (the wanted direction).

According to a feature of this invention, an array consists of a number of radiating or receiving elements whose electrical centres are separated by distances not greater than one eighth of a wavelength and at least two adjacent elements of which are electrically phased at least 135° out to phase and so that their radiation or reception substantially neutralises in the unwanted direction and fails to neutralise in the wanted direction.

According to a further feature of the invention an aerial array is constructed of elements arranged in pairs, members of a pair being separated by not more than one eighth of a wave length and being phased at least 135° out of phase and so that their radiation or reception neutralises for an unwanted direction, but fails to neutralise for a wanted direction.

The electrical phasing described above refers not necessarily to the phase of the currents supplied to an element of a transmitting array since the interaction of the elements may modify the phase of the currents within the elements. The phase relationships described refer in a transmitting array to the phase of the actual currents in and voltages along the transmitting elements. Similarly the phasing in a receiving array (which involves the same electrical connections) refers to the phase relationships introduced between the E.M.F.s induced in the elements and the voltages applied to the receiver input. The connections are more simply considered by treating an array as being a transmitting array and adjusting the phasing connections so as to obtain correct currents in and voltages on the elements: the array so designed may then be used as a receiving array by replacing the generator by a suitable receiver.

According to a further feature of the invention, in an aerial array comprising a plurality of elements having their electrical centers separated by distances less than a quarter of the wavelength to be transmitted or received, the phasing means employed for the various elements are so arranged that if the receiving or transmitting frequency is altered over a range adjacent to the optimum frequency of the aerial array, the phasing is so modified by such a change of frequency as to maintain the directional diagram substantially the same.

The phasing of the connections to elements of the array may be modified so as to allow for capacity and mutual induction effects of adjacent or closely mounted elements of the array being greater than such effects between widely spaced elements of the array.

The impedance of the feeder and transmitting or receiving apparatus is matched to the impedance of the array, due allowance being made of the change in radiation resistance of any element produced by the adjacent action of elements which are electrically phased almost in opposition.

According to a further feature of this invention a wireless system adapted to operate on a wavelength less than 15 metres comprises an aerial array directionally sensitive in a horizontal plane, the array being carried by a single mast and comprising at least four elements having their electrical centres spaced apart by distances less than a quarter of the operating wavelength.

In carrying the invention into effect, I may proceed as follows:-

Four aerial elements in the form of straight tubes or rods between a quarter and a half a wavelength long are mounted in a row with their axes vertical. The spacing between adjacent rods is EQUAT. HERE where l is the operating wavelength and n is a constant having some suitable value greater than 4 and preferably 8 or more. Starting from left to right, these rods may be designated A, B, C, D.

Considering elements A and B, these are each connected to a wire of a twin feeder. The currents in them will therefore be p out of phase and we may consider the phase of A as being zero and the phase of B as being p lagging. The radiation of these two elements will therefore neutralise with respect to directions at right angles to the plane of the array, but will fail to neutralise in either direction along the array. Branched from the feeder wires supplying A and B, are two feeder wires running to C and D. These feeder wires are so arranged that the length running from the point of junction to each of the elements C and D is EQUAT. HERE greater than the length running from the junction points to either A or B. The element C is tapped from the feeder wire which runs to B, and the element D is tapped from the feeder wire that runs to A. Elements C and D will be p out of phase and will not radiate at right angles to the plane of the array but only along the array. The average phase however of the elements C and D is EQUAT. HERE out of phase with the average A and B, so that the radiation of C and D will neutralise the radiation of A and B in the direction AD, but will fail to neutralise this radiation in the direction DA. The successive relative phase angles of the elements will be:-

A . . . . . . . Zero

B . . . . . . . p lagging.

C . . . . . . . EQUAT. HERE lagging.

D . . . . . . . EQUAT. HERE lagging = EQUAT. HERE lagging

In the above array it will be seen that the adjacent elements A and B and the adjacent elements C and D are in phase opposition, and that the resultant of A and B and the resultant of C and D are also almost in phase opposition except for an amount EQUAT. HERE which is small where n is large and which is produced by an additional length of feeder for the elements C and D, this additional length being EQUAT. HERE or twice the spacing between adjacent elements. Such an additional length of feeder will give the correct phasing of the elements BD over a wide frequency range, since it is a function of the aerial separation and not of the frequency. The p phase shifts between adjacent elements are produced by choosing opposite wires of a balanced feeder. Had this phase shift been introduced by employing extra half wave lengths of feeder to the reversed elements, the array would have been unduly frequency selective as regards its directional diagram.

With the arrangement described, the directional diagram will hold over a wavelength range comparable with the tuning range of the individual elements.

It will be noticed that the array described is insensitive in either direction at right angles to its plane and also in the direction A to D. It will also be seen that this aerial is insensitive in the vertical axis. Efficient radiation and reception occurs towards the direction DA and neighbouring directions only.

It may be necessary to modify the simple phasing arrangements described in order to allow for the affect of the elements B and C being closer together than elements A and D. The criterion of correct phasing is that for a transmitting array the current sin, and voltages along the elements would have the phase relations indicated. With the elements placed very close together, wires may be extended from A towards D, ending very close to D so as to increase the capacity between A and D and to maintain the propagation constant and impedance along the two elements A and D, considered as a twin transmission line, the same as the propagation constant and impedance along the elements A and B. Alternatively, the feeder connections may be so adjusted experimentally as to give the desired effective phasing.

In the array above described, the elements A and B develop a radiation diagram in the horizontal plane, which plotted on polar co-ordinates would resemble a figure 8. Similarly, the elements C and D give a similar figure 8. The part A and B, operating with the pair C and D, develop a further cardioidal diagram superimposed on the original figures of 8. By altering the relative phasing of the elements, any combination of two simple diagrams such as the figure of 8 or the cardioid may be produced.

In general, if q is the angle of a direction of transmission, diagrams may be produced such that the efficiency in any direction is approximately given by the product of a series of multipliers of the form [K + cos (q + A)] where K is a constant, not numerically greater than unity, and A is another constant. In the array considered above, where the separation between elements is very small compared to l , the relative efficiency in various directions is given by the product of (1 + cos q ) and cos q , where q is the angle from the optimum direction.

The radiation for a given current in an aerial element will be less with the type of array here discussed than would be obtained with the more normal widely spaced elements. On the other hand, the effect of the proximity and opposite phasing of the elements is to reduce the radiation resistance of the individual elements so that, if the ohmic resistance and dielectric losses are small, the same power in the array will generate much larger currents and so compensate for the reduced radiation obtained per ampere. In the limit, when the ohmic resistance and dielectric losses are entirely negligible and the resistance of the aerial elements is entirely due to radiation, the radiation per watt supplied to the aerial will be the same as for a widely spaced array. The effect of the proximity of the aerial elements in the array here considered, is to modify the radiation resistance of the elements so that the matching conditions for the feeder are quire different for this type of array from what they are with the usual widely spaced arrays. For example, the impedance of a half wave element fed from its centre point might be about 80 ohms for a 10 metre wavelength. If a number of these elements are stacked close together to form an array, the effective radiation resistance of an element will fall and may only be 5 ohms for each element. In the case of such a closely spaced array and, for a given input power to the aerial, four times as much current can be driven through each element as can be forced through similar elements of a widely spaced array. In order to utilise the good power efficiently possible from closely spaced arrays, it is necessary to match the feeder with due allowance to a modified radiation resistance and to ensure that the ohmic and dielectric loses are not unnecessarily large.

Although it is possible to arrange the phasing of the various elements to be almost independent of frequency, nevertheless if tuned radiating elements such as half wave aerials are employed it will be found that the tuning to any one frequency is more critical in a closely spaced array than in an array with wider spacing. The reduction of the radiation resistance of the individual elements is in effect a reduction in the decrement of that element looked upon as a tuned circuit, so that it becomes more critically selective with frequency. Also the lengths required to tune to a particular frequency will be modified by another adjacent element.

It must be understood that although the description above has been chiefly directed towards transmitting aerials, it is equally applicable to receiving aerials: the conditions governing efficient selective radiation also governs efficient selective reception. In the case of the receiving aerial however, especially at short wavelength, it often occurs that there is sufficient signal strengths, using an ordinary aerial, to provide plenty of power for noiseless amplification, but that the signals received are very heavily interfered with by extraneous interference arriving at the aerial: adequate reception could be obtained, even at the expense of a loss of signal power at the receiver provided the extraneous interference was reduced. For such conditions a receiving aerial is required with is directive, but not necessarily very efficient, and a closely spaced array according to the present invention may with advantage be used, the phasing and general connections not being such as to deliver the optimum power to the receiving apparatus, but being designed particularly with a view to reducing the interference pick-up: for example, resistive elements may be used to ensure a correct phasing of the various receiving elements of the array. Such aerials are very suitable for use in connection with reception of short-wave broadcast in private residences. For example an array suitable for use at wavelengths of the order of 15 metres or less may, owing to its small size, be attached to the roof or to a chimney stack or supported by a single mast.

Although an array consisting of four elements has been described, any number of elements from two upwards may be employed, and may be arranged to give a wide variety of directional diagrams both in the horizontal and vertical planes. Small arrays composed of closely spaced elements may be combined together, at wide separations, in the manner in which it is common to combine signal elements to form the common types of "beam arrays".

Dated this 7th day of February, 1934.

REDDIE & GROSE,

Agents for the Applicants,

6, Bream’s Buildings, London, E.C.4.

 

COMPLETE SPECIFICATION

Improvements in and relating to Directional Wireless Aerial Systems

We, ALAN DOWER BLUMLEIN, a British Subject, of 7, Courtfield Gardens, Ealing, London, W.13, and JOSEPH LADE POWSEY, a British Subject, of 3, Dale Avenue, Hounslow West, Middlesex, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:

The present invention relates to directional wireless aerial systems such as can be used either for transmission or for reception of electro-magnetic waves. When used for transmission, they are required to radiate the maximum portion of the radiated energy in the direction of the receiving station. When used for reception, they are required to receive as great a portion of the radiation from the transmitter as possible, and to exclude unwanted radiations such as interference arriving in other directions. The arrays can be of similar type for both transmitting and receiving. The gain in efficiency compared with a non-directional radiator or receiver, whether it be expressed as the ratio of wanted to unwanted power radiated, or as signal to noise ratio, is the same for a given type of array. The only difference between transmitting and receiving arrays is that in a receiving array, where the signal strength is sufficient to eliminate any trouble due to noise in the receiving amplifiers, the power of efficient of the array is not of importance, provided that the correct directional diagram is obtained in order to reduce interference pick-up as much as possible. In a transmitting array it is important to keep the power efficient good in order that a large radiation may be obtained. Arrays may be designed either to give a good horizontal distribution (e.g. to transmit maximum power westward towards a westerly receiving station), or they may be designed to give a good vertical distribution, e.g. radiate maximum power horizontally instead of up and down, or to give a combination of both these desirable properties.

For convenience in description reference will be made more particularly in this specification to transmitting systems and it is to be understood that the systems discussed are also applicable to reception.

In order to obtain such directional arrays it is usual to use radiating elements (which may generally be a quarter to a half a wavelength long, spaced at intervals of a quarter to a half a wavelength apart) and suitably phased so that radiation adds up for the wanted direction but subtracts for unwanted directions.

The elements of an array are usually vertical although other arrangements (such for example as horizontal, along or across the direction of transmission) may be used for some purposes, and they may be spaced apart vertically (for example arranged one above the other) or horizontally. In some cases the line of elements is along the direction of transmission and in other cases it is across it. The resulting radiation diagrams obtained from various arrangements have been very fully described in publications. It is, however, usually considered that a separation between elements of about a quarter wavelength is necessary in order to develop directional diagrams, since without this separation it is impossible to obtain simultaneously addition. With zero phase difference, of the effects of two elements in one direction and annulment, with 180° phase difference in another direction. Consequently, these directional arrays occupy considerable space, and cannot satisfactorily be employed on any but very short wavelengths.

It is the principal object of this invention to provide directive arrays where the separations between successive elements are shorter than a quarter wavelength, thus allowing a great saving in space to be effected.

According to the present invention there is provided an aerial array comprising four radiating elements arranged in a pair of pairs, at least two adjacent elements being spaced apart by less than EQUAT. HERE and extreme elements of the four being spaced apart by less than EQUAT. HERE, wherein the elements of one of said pairs are connected to one point in a subsidiary feeder, the elements of the other pair are connected to another point in the same or another subsidiary feeder and a main feeder is connected to a point in the subsidiary feeder or to the join of the two subsidiary feeders, characterised in that the feed to one element of each of said pairs is in such phase relation to the feed to the other element of each pair that, taken separately, each pair has a directional diagram of the form r=A [K = cos q ] [K2 + cos (q + a)] where r is the radius vector of the diagram in a direction making an angle q with a fixed direction, a is a constant angle, A and B are constants, K1 and K2 are further constants not numerically greater than unity and l is the operating wavelength.

The term "point in a feeder" is, in this specification, taken to mean not necessarily an electrically common point but a transverse section of a feeder. Thus when two elements are connected to a point in a feeder one may be connected to one conductor and the other to an adjacent point in the other conductor of a two wire feeder.

According to a modification of the present invention an aerial array having the features mentioned above is arranged as a receiving aerial.

The relative phases of the currents in the elements will not, in general, be the same as those of the currents fed thereto since the interaction of the elements may modify the phase of the currents within the elements.

The impedance of the feeder and transmitting or receiving apparatus is matched to the impedance of the array, due allowance being made for the change in radiation resistance of any element produced by the adjacent action of elements which are electrically phased almost in opposition.

The invention will now be described by way of example with reference to the accompanying drawings, wherein Figs. 1, 2, 3 and 4 show aerial arrays according to the present invention.

Fig. 5 shows a typical polar diagram of an aerial according to the present invention,

Fig. 6 shows a view in elevation of a modification of a part of the aerial of Fig. 1, and

Fig. 7 shows a view in plan of the arrangement of Fig. 6.

Referring to Fig. 1, which illustrates in principle one application of the invention, four aerial elements A, B, C, D in the form of straight tubes or rods half a wavelength long are mounted in a row with their axes vertical. The spacing between adjacent rods is EQUAT. HERE where l is the operating wavelength and n is a constant having some suitable value greater than 4 and preferably 8 or more.

Considering elements A and B, these are each connected by wires 1 and 2 to the inner and outer conductors 3 and 4 respectively, or a concentric feeder 5. The currents in them will therefore be p out of phase and we may consider the phase of A as being zero and the phase of B as being p lagging. The radiation of these two elements will therefore neutralise with respect to directions at right angles to the plane of the array, but will fail to neutralise in either direction along the array. Branched from the feeder 5 supplying A and B, is a feeder 6 running to C and D, the feeder 6 of characteristic impedance equal to the measured impedance at the bottom of the aerial CD is so arranged that the length of the conductors 7, 8 running from the point of junction 9 to the elements C and D is EQUAT. HERE greater than the very short length 51 running from the junction point 9 to either A or B. The element C is tapped from the feeder conductor 4 which is connected to B, and the element D is tapped from the feeder wire 3 that is connected to A. The very short length of feeder 51 between the point of junction 9 and the end thereof which is connected to elements A and B may be regarded as constituting one subsidiary feeder and the feeder 6 may be considered as a second subsidiary feeder connected at one end to the pair of elements C, D, and at its other end to the join of the short feeder 51 with the main feeder 5. Elements C and D will be p out of phase and will not radiate at right angles to the plane of the array but only along the array. The average phase however of the elements C and D is EQUAT. HERE out of phase with the average of A and B, so that the radiation of C and D will neutralise the radiation of A and B in the direction AD, but will fail to neutralise this radiation in the direction DA. The successive relative phase angles of the elements will be:

A . . . . . . Zero

B . . . . . . p lagging

C . . . . . . EQUAT. HERE lagging

D . . . . . . EQUAT. HERE lagging = EQUAT. HERE lagging.

In the above array it will be seen that the adjacent elements A and B and the adjacent elements C and D are in phase opposition, and that the resultant of A and B and the resultant of C and D are also almost in phase opposition except for an amount of EQUAT. HERE which is small where p is large and which is produced by an additional length of feeder for the elements C and D, this additional length being EQUAT. HERE or twice the spacing between adjacent elements. Such an additional length of feeder will give the correct phasing of the elements BD over a wide frequency range, since it is a function of the aerial separation and not of the frequency. The p phase shifts between adjacent elements are produced by choosing opposite wires of a balanced feeder. Had this phase shift been introduced by employing extra half wave lengths of feeder to the reversed elements, the array would have been unduly frequency selective as regards its directional diagram.

With the arrangement described, the directional diagram will hold over a wave length range comparable with the tuning range of the individual elements.

It will be noticed that the array described is insensitive in either direction at right angles to its plane and also in the direction A to D. It will also be seen that their aerial is insensitive in the vertical axis. Efficient radiation and reception occurs towards the direction DA and neighbouring directions only.

It may be necessary to modify the simple phasing arrangements described in order to allow for the effect of the elements B and C being closer together than elements A and D. The criterion of correct phasing is that for a transmitting array the currents in, and voltages along the elements should have the phase relations indicated. With the elements placed very close together, wires 47, 48 of Figs. 6 and 7 may be extended as shown from A towards D and from D towards A respectively; wire 47 terminates in a length of conductor 49 located parallel with and close to element D and wire 48 terminates in a length of conductor 50 located close to element A. In this way the capacity between A and D is increased and the propagation constant and impedance along the two elements A and D, considered as a twin transmission line are maintained the same as the propagation constant and impedance along the elements A and B. Alternatively, the feeder connections may be so adjusted experimentally as to give the desired effective phasing. This adjustment may be made by tapping the leads from the ends of feeders 51 and 6 on to elements A and D or elements B and C at point other than the ends of these elements. Thus in the case of element A the lead 1 may be attached to the element at a suitable short distance from the lower end. As an alternative, or in addition to the above method of adjustment, the lengths of the elements themselves may be slightly altered to obtain the desired phasing.

In the array above described, the elements A and B develop a radiation diagram in the horizontal plane, which plotted on polar co-ordinates would resemble a figure of eight. Similarly, the elements C and D gave a similar figure of eight. The pair A and B, operating with the pair C and D, develop a further cardioidal diagram superimposed on the original figures of eight. The resultant diagram is thus the product of a figure of eight and a cardioid a typical example of which is shown in Fig. 5. By altering the relative phasing of the elements, any combination of two simple diagrams such as the figure of eight or the cardioid may be produced.

In general, if q is angle of a direction of transmission, diagrams may be produced such that the efficiency in any direction is approximately given by the product of a series of multipliers of the form [K + cos (q + a)] where K is a constant, not numerically greater than unity, and a is another constant. In the array considered above, where the separation between elements is very small compared to l , the relative efficiency in various directions is given by the product of (1 + cos q ) and cos q , where q is the angle from the optimum direction. This is one particular case of the product of two multipliers [K1 + cos q } and [K2 + cos (q + a)] the constants K1 and a having the value zero and K2 having the value 1. The polar diagram in this particular case (in which the radius vector r for any angle q is given by r = cos q (1 + cos q ) is shown in Fig. 5. In this Figure there is shown the horizontal polar diagram of an aerial consisting of four suitably spaced and phased vertical elements, the elements being arranged near point O and spaced apart along the line Ox.

The radiation for a given current in an aerial element will be less with the type of array here discussed than would be obtained with the more normal widely spaced elements. On the other hand, the effect of the proximity and opposite phasing of the elements is to reduce the radiation resistance of the individual elements so that, if the ohmic resistance and dielectric losses are small, the same power in the array will generate much larger currents and so compensate for the reduced radiation obtained per ampere. In the limit when the ohmic resistances and dielectric losses are entirely negligible and the resistance of the aerial elements is entirely due to radiation, the radiation per watt supplied to the aerial will be the same as for a widely spaced array. The effect of the proximity of the aerial elements in the array here considered, is to modify the radiation resistance of the elements so that the matching conditions for the feeder are quite different for this type of array from what they are with the usual widely spaced arrays. For example, the impedance of a half wave element fed from its centre point might be about 80 ohms for a 10 metre wavelength. If a number of these elements are stacked close together to form an array, the effective radiation resistance of an element will fall and may only be 5 ohms for each element. In the case of such a closely spaced array and, for a given input power to the aerial, four times as much current can be driven through each element as can be forced through similar elements of a widely spaced array. In order to utilise the good power efficiency possible from closely spaced arrays, it is necessary to match the feeder with due allowance to a modified radiation resistance and to ensure that the ohmic and dielectric losses are not unnecessarily large.

Although it is possible to arrange the phasing of the various elements to be almost independent of frequency, nevertheless since half wave aerials which are tuned radiating elements are employed it will be found that the tuning to any one frequency is more critical in a closely spaced array than in an array with wider spacing. The reduction of the radiation resistance of the individual elements is in effect a reduction in the decrement of that element looked upon as a tuned circuit, so that it becomes more critically selective with frequency. Also the lengths required to tune to particular frequency will be modified by other adjacent elements.

In Fig. 2 four aerial elements E, F, G, H are arranged vertically in a vertical plane. The spacing between G and H and the spacing between E and H is not greater than three quarters of the operating wavelength. The elements E and F have wires 10 connected to their lower ends the two wires 10 being arranged to extend towards each other. A pair of wires 11 extends upwardly from the free ends of wires 10 and a further pair of wires 12 is arranged parallel to wires 11. Wires 12 have their lower ends connected together through a resistance 13. Adjustable bridges 14 are provided between wires 11 and 12 by means of which the length of conductor between the lower ends of aerial elements E and F and resistance 13 may be varied. Close to the wires 12 is arranged a loop circuit comprising two vertical wires 15 connected at their upper ends to a condenser 16 and at their lower ends to the end 17 of a concentric subsidiary feeder 18. In a similar way the conductors G, H are connected through conductors 101, 111, 121 and bridges 141 to a resistance 131 and a loop circuit comprising conductors 151 and condensers 161 is connected to the end 171 of feeder 18. The end 17 of feeder 18 is connected to one end of a main feeder 19 through an impedance matching transformer comprising a shunt condenser 20 and exposed lengths of conductors 21. The other end of feeder 19 is connected to a transmitter or receiver (not shown).

The loop circuits 15, 16 and 151, 161 are tuned to the operating frequency of the array and each acts as one winding of a transformer, these transformers being denoted by 22 and 221, whereby the aerial elements E, F, G, H are coupled to the feeder 18. Transformers 22 and 221 serve to match the aerial impedance to the characteristic impedance of the feeder 18, the matching being adjusted by varying the degree of coupling between the two windings. In order that the currents in a pair of elements E, F or G, H may be equal it is necessary to reduce capacity between the windings of the transformers 22, 221 to a minimum. For this purpose the tuned loops are arranged to couple with maximum current low potential points in the aerial circuits. Further, feeder 18 is of low characteristic impedance and loose coupling in trans-transformers 22, 221 is thereby made possible. The inter-winding capacity of transformers 22, 221 may be still further reduced by constructing them of thin wires. The wires 15, 151 may be 3 inches apart, wires 12, 121 being spaced therefrom by 1/8th inch.

It may be arranged that the leads 10 from the aerial elements E, F together with bridges 14, conductors 12 of transformer 22 and resistance 13 operate as approximately one half wavelength. In this case if elements E and F have lengths equal to one half wavelength then the system comprising elements E, F and the associated transformer 22 and leads thereto operates as approximately three half wavelengths. Elements E and F may have lengths less than one half wavelength, the lengths of wires 11 and 12 being then increased so that the total length remains effectively three half wavelengths. Elements G, H and transformer 221 are arranged in a similar way.

The pairs of elements E, F and G, H have their elements phased in opposition by being connected, as described, to opposite ends of symmetrical transformers 22, 221. The desired phase difference is introduced between the two pairs by means of the length of feeder 18 which is included in the lead to G, H but is not in the lead to E, F.

In closely spaced aerials of this type the frequency selectivity may be inconveniently high and may lead to sideband cutting particularly when a carrier, modulated with the high frequencies necessary for high definition television, is being transmitted or received. Resistances 13, 131, of suitable value, are therefore included in order to increase the damping of the array, and thereby reduce its frequency selectivity.

In Fig. 3 a pair of vertical aerial elements K, L each of which may have a length equal to one half the operating wavelength are connected at their centres, in phase opposition to one another, to the ends of a concentric feeder 23. Thus the upper half of K and the lower half of L are connected to the ends of the electro-conductor 24 of feeder 23 and the other halves of K and L are connected to the sheath 25. Branches from the centre *** of feeder 23 is a subsidiary feeder *** leading to a phase adjustment of device 28. The electrical lengths of feeders 23 and 27 between their point of connection 26, and aerial elements K and L and phase adjustment device 28 are arranged to be equal to one quarter of the operating wavelength. Their actual lengths will therefore be less than one quarter of the wavelength in air, and therefore the spacing between elements K and L will be less than half the wavelength.

A similar pair of elements M, N is arranged in the same plane as and parallel to K and L, element M being located between elements K and L. Elements M and N are connected at their centres to a feeder 231 (which is not fully shown in the drawing). The feeder 231 is similar to 23 and may be arranged in the same horizontal plane as, but slightly displaced horizontally with respect to, feeder 23. A secondary subsidiary feeder branches from the centre of feeder 231 and is similar to subsidiary feeder 27. This second subsidiary feeder also terminates at phase adjustment device 28, a portion of this subsidiary feeder being shown at 271. The centre conductors 29, 291 of feeders 27, 271 are connected to shield 34 of the phase adjustment device 28, the shield 34 being also connected to the sheath 35 of feeder 32. Thus elements K and L are both connected to point 26 in feeder 23 and elements M and N are connected to a similar point in feeder 231. These two points are connected by means of subsidiary feeders 27, 271 to phase adjustment device 28 where they are connected to main feeder 32.

In order to suppress currents which tend to flow along the outside of feeders 23, 231, *** circuits are provided. In the case of feeder 23 these comprise two auxiliary conductors 36, preferably of substantially the same external dimensions as the sheath *** each connected at one end to the sheath and having the other end located adjacent and insulated from the corresponding end of the sheath 25, but connected to the internal conductor 24 as shown. In order to tune the circuits complete the end portions of the sheath 25 *** auxiliary conductors 36 and the ends of the sheath 25. By this means the output of the sheath 25 is caused to present a high impedance to currents at the *** frequency. Similar rejecter *** (not shown) are provided on feeder 231.

The arrangement is therefore such that equal currents flow in phase opposition to one another in elements K and L and also in elements M and N. A desired phase difference between the pairs of elements K, L and M, N is obtained by providing suitable impedances in the phase adjustment device 28. In the case shown these impedances are in the form of condensers 30, 301 which must have suitable different capacities and therefore different effective electrical lengths.

In the arrangement of Fig. 4, four elements P, Q, R, S, each of which may have a length equal to half the wavelength at which the system is to operate, are arranged in a vertical plane. Each of the elements P, Q, R, S is broken at its centre, the two ends so formed being connected to the conductors of a two wire feeder. A main feeder 38 is connected at one end to the mid point of a subsidiary feeder 39. The other end of main feeder 38 may be connected to a receiver or transmitter. Subsidiary feeder 39 is of rectangular U-shape and is of such size and is so arranged that its ends 40, 401 lie midway between the centres of elements P and Q and elements R and S respectively. Feeders 38 and 39 are both of the concentric type. To the end 40 of feeder 39 there are connected two further sections 41, 42 of concentric feeder. Section 41 leads directly to the centre of element P, has its sheath 43 connected to the lower half of element P and has its inner conductor 44 connected to the upper half of element P. Section 42 has a length which excess the length of section 41 by some suitable amount less than one quarter of the operating wavelength and is folded so that its end remote from the end 40 of feeder 39 is located adjacent the centre of element Q. Element Q is connected to section 42, the upper half of element being connected to the sheath 45 and the lower half of element Q being connected to the inner conductor 46.

In a similar way the end 401 of feeder 39 is provided with further sections of feeder 411, 421 similar to sections 41, 42 respectively. Section 411 has a sheath 431 which is connected to the upper half of element R and an inner conductor 441 which is connected to the upper half of element R and an inner conductor 441 which is connected to the lower half of element R. Section 421 has a sheath 451 and an inner conductor 461 connected respectively to the lower and upper halves of element S.

It will be seen that elements P and Q are connected in opposite senses to the end 40 of feeder 39 but since the lengths of sections 41 and 42 are unequal and differ by less than one quarter of the operating wavelength there will be a phase difference greater than 135° between elements P and Q. For example the length of section 42 may exceed that of section 41 by one eighth or less of the operating wavelength in which case the phase difference will be 157˝° or more. Sections 411, 421 are so constructed and arranged that a phase difference exists between elements R and S equal to that between P and Q.

By suitable adjustment of the spacing between the elements P, Q, R, S and the phasing of the pairs P, Q and R, S the array can be arranged to have the desired polar diagram.

In this example and also in the previous ones the four elements are not necessarily in one plane but may be arranged in different planes. For example, elements P and Q may be in one plane and elements R and S in another plane, and these planes may or may not be parallel to one another.

It must be understood that although the description above has been chiefly directed towards transmitting aerials, it is equally applicable to receiving aerials: the conditions governing efficient selective radiation also govern efficient selective reception. In the case of the receiving aerial however, especially at short wavelengths, it often occurs that there is sufficient signal strength, using an ordinary aerial, to provide plenty of power for noiseless amplification, but that the signals received are very heavily interfered with by extraneous interference arriving at the aerial: adequate reception could be obtained, even at the expense of a loss of signal power at the receiver, provided the extraneous interference was reduced. For such conditions a receiving aerial is required which is directive, but not necessarily very efficient, and a closely spaced array according to the present invention may with advantage be used, the phasing and general connections not being such as to deliver the optimum power to the receiving apparatus, but being designed particularly with a view to reducing the interference pick-up; for example resistive elements may be used to ensure a correct phasing of the various receiving elements of the array. Such aerials are very suitable for use in connection with reception of short-wave broadcast in private residences. For example an array suitable for use at wavelengths of the order of 15 metres or less may, owing to its small size, be attached to the roof or to a chimney stack or supported by a single mast, the elements of the array being arranged as a unitary structure.

Although an array consisting of four elements has been described, any number of pairs of elements from two upwards may be employed, and may be arranged to give a wide variety of directional diagrams both in the horizontal and vertical planes. Small array composed of closely spaced elements may be combined together, at wide separations, in the manner in which it is common to combine single elements to form the common types of "beam arrays".

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:-

  1. An aerial array comprising four radiating elements arranged in a pair of pairs, at least two adjacent elements being spaced apart by less than EQUAT. HERE and extreme elements of the four being spaced apart by less than EQUAT. HERE , wherein the elements of one of said pairs are connected to one point in a subsidiary feeder, the elements of the other pair are connected to another point in the same or another subsidiary feeder, and a main feeder is connected to a point in the subsidiary feeder or to the join of the two subsidiary feeders, characterised in that the feed to one element of each of said pairs is in such phase relation to the feed to the other element of each pair that, taken separately, each pair has a directional diagram of the form r = A [K + cos q ], and in that the feed from the main feeder to one pair in relation to that to the other pair is so phased that the overall directional diagram of the array has the form r = B[K1 + cos q ] x [K2 + cos (q + a)] where r is the radius vector of the diagram in a direction making an angle q with a fixed direction, a is a constant angle, A and B are constants, k1 and k2 are further constants not numerically greater than unity and l is the operating wavelength.
  2. An aerial array having the features claimed in claim 1, and arranged as a receiving aerial.
  3. An aerial array according to claim 1 or 2, wherein all the adjacent aerial elements of the four are spaced apart by less than EQUAT. HERE.
  4. An aerial array according to any of the preceding claims, in which the aerial elements have such lengths that they are inherently tuned.
  5. An aerial array according to any of the preceding claims, wherein the spacing between the elements of said pairs is not greater than one eighth of said wavelength.
  6. An aerial array according to any of the preceding claims, wherein each of said elements is connected at a current antinode to a feeder.
  7. An aerial array according to any of claims 1 to 5, wherein energy is fed to or derived from one end of each element or a pair of aerial elements by means of an electro-magnetic coupling device, located equidistant from the elements of said pair.
  8. An aerial array according to claim 7, wherein conductors connecting said coupling device to the aerial elements are of such electrical length that said coupling device is located at a voltage anode with respect to said aerial elements.
  9. An aerial array according to claim 7 or 8, wherein said coupling device comprises a transformer one circuit of which is associated with a feeder and comprises a first loop, a part of said first loop being located close to a second loop which is connected to one end of each of said pairs of aerial elements.
  10. An aerial array according to claim 9, wherein said first and second loops comprise single thin wires.
  11. An aerial array according to claim 9 or 10, wherein said first loop is approximately tuned to the operating wavelength.
  12. An aerial array according to claim 9, 10 or 11, wherein said second loop and the leads which connect it to the aerial elements are approximately tuned to the operating wavelength.
  13. An aerial array according to any of the preceding claims, wherein elements of different pairs are suitably phased apart by connecting them to a transmitter or receiver through suitable different impedance’s having different effective electrical lengths.
  14. An aerial array according to any of the preceding claims, wherein one element of one pair is located between the elements of the other pair.
  15. An aerial array according to claim 12, wherein a pair of elements are connected at their centres in phase opposition to the ends of a first feeder, to the centre of which is connected one end of said subsidiary feeder or one end of one of said subsidiary feeders.
  16. An aerial array according to claim 15, wherein said first feeder has an electrical length substantially equal to half the operating wavelength.
  17. An aerial array according to any of claims 1 to 13, wherein an element is disposed closer to the other element of the same pair than to either element of the other pair.
  18. An aerial array according to any of the preceding claims wherein one or more damping resistances are inserted in the aerial elements or in the leads thereto, whereby the frequency selectivity of the aerial system is reduced.
  19. An aerial array according to any of the preceding claims having said elements constructed and arranged as a unitary structure.
  20. An aerial array substantially as described or as shown in the accompanying drawings.

Dated this 7th day of March, 1935.

REDDIE & GROSE,

Agents for the Applicants,

6, Bream’s Buildings, London, E.C.4.

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. - 1935.