US2187015A - Directional aerial system - Google Patents

Description

Jan. 16, 1940- E. c. CORK ET AL 4 2,187,015

DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 1 .epwmo CECIL CORK AND /1 BY 05 PH mos PAWSEY ATTORNEY.

Jan. 16, 1940. g, am ET AL 2,187,015

, DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 2 INVENTORS BY 05' PH L/JDE PAWSEY' A TTORNEY.

.Jan. 16, 1940. E. c. CORK ET AL DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 3 I NV EN TO RS EDWARD CfC/L CORK/MID Jan. 16, 1940.

E. c. CORK ET AL 2,187,015

DIRECTIONAL AERIAL SYSTEM Filed June 18, 1938 4 Sheets-Sheet 4 X Y B 3 2 EL; X 1 1 INVENTORS ATTORNEY. V

Patented Jan. 16, 1940 PATENT OFFICE DIRECTIONAL AERIAL- SYSTEM Edward Cecil Cork, Ealing, London, and Joseph Lade P'awsey, Hillingdon, England, assignors to Electric & Musical Industries Limited, a

British company Application June 18, 1938, Serial No. 214,436 In Great Britain June 26, 1937 3 Claims.

This; invention relates to directional transmittingor receiving aerial. systems, thedirectional propertiesbeing used in the case of transmitters to radiate signals in a predetermined direction and in the case of receivers, for the purpose of improving the signal to noise ratio; by increasing the pick-up signalandlreducing the unwanted interference. "In at'elevision receiving system for example, it may happen that intense interferencemay be set up'b'y apparatus suchas that employed for diathermy purposes. Providing that the angle between the wanted and unwanted signals isgreater than afew degrees, it is. possible to suppress the interference while retaining the wanted signal.

@In. such cases it is highly desirable. that it should be..-possible; to arrange that the region of minimum. pickup; in the directional diagram of an aerial array is insuch; a direction that there is a minimum. of receptiomand preferably a total suppressionyof the unwanted 'signaland a maximum of reception of the wantedsignal.

- One object"v of the present invention is to provide electrical means which may be arranged so that. the region of minimum pick-up in the directional'diagram of a directional receiving-aerial system is directed to'thesource of interference. In another set of circumstances it may be found that-on the re-erection of an aerial array at another site, the situation of the region of minimum pick-up in the directional diagram which has been found satisfactory under ideal conditions for the suppression of interference is poor and displaced-due to the'presence of local objects causing a distortion of the field;

A further object of the invention, therefore, is to provide for selecting andimproving the minimumpick-up region by electrical means to correct for local irregularities. Itis a desirable feature that in: combination with means of observation such as for example, a television receiver,' the adjustment of the minimum referred to should be capable of variation in proximity to the receiver, so the reduction of interference may be observed and the interference eliminated as it arises.

. Another object of the invention is to provide a directional transmitting system in which the region of maximum radiation in the directional diagram is in the direction in which it'is desired to transmit signals.

Accordingto the present invention a directional aerial system includes. two aerials the energy in which is passed through an amplitude control. arrangement to or from a common channel, phase adjustment being effected in one of the aerial leads in order to control the phase of signals passedto or from that aerial relatively to those passed to or from the other aerial to the common channel. The phase adjustment may, for example, be effected by inserting selectedlengths of conductorin the lead from the aerial to the amplitude controlling arrangement associated with that aerial, and provision may be made for continuously effecting ,fine adjustment of the phase displacement. Amplitude control may be effected by means ofa variable resistance or by variable coupling transformer arrangements connected between the two aerials'and the common I Figures-l and 2 are explanatory diagrams and t Figure 3 shows diagrammatically one for'm of aerial system embodying the invention,

Figure 4 shows a modified arrangement of Figure 3. Figures 5, 6 and 9 show further modifications of the present invention, while. Figure 7 shows a type of goniometer which may .be used with the. present invention andv whichisparticularly adaptable to .ultra short waves, and Figure 8 shows the electrical equipment of the goniometer shown. in Figure '7. Y

Referring to Figure 1 of the drawings, two receiving aerials A1 and A2- are shown spaced apart at adistance d, and it is. assumed that asignal is arriving at an angle 0 tothe line between the aerials. There is aphase difference between the signals induced in the aerials due to the .path difference A1C equal to radians. If it is assumed that there is a further phase difference due to the aerial feeders and the phase adjusting arrangements at one or the other of the aerials, the phase difference being indicated by (p and the amplitudes are adjusted to equality, it can be shown that the picked'up signal has an amplitude of which has a maximum value at Hence A cos 6,,,-,,. cos 0 a It will therefore be seen that if the spacing between the aerials is great (a small) the angle between the maximum and minimum of a loop is small, which indicates a large number of narrow loops.

If, therefore, the interference and signal differ in angle by a small amount, it is desirable to space the aerials apart by a considerable distance. It is preferred to make use of a suitable condition such that the interference falls on a region of zero pick-up in the directional diagram of the aerial, while the signal falls within the adjacent region of maximum pick-up.

For example, if the signal and interference differ in direction of arrival of 10 degrees and the direction of the signal is perpendicular to the line of the aerials (i. e. cos emax o) then the spacing to give this condition would be 10. Elly In order that the nature of the phase and amplitude control arrangements may be more fully understood, reference will now be made to Figure 2 of the accompanying drawings which shows two aerials A1 and A2 and feeder lines I and 2 which are approximately matched to the aerials. The dotted rectangles 3 and 4 contain phase controlling and amplitude controlling arrangements respectively. The phase controlling network includes sections of feeder 5 which may be selectively included in or disconnected from the line by plug-in contacts or by a switching device. The selection of the lengths of feeder included enables phase adjustment to be effected in steps of 60 between 0 and 360 and finer adjustment of phase difference between the signals received may be effected by the provision of a tuned circuit including inductance 6 and capacity l, which introduces a variable phase difference controllable by the condenser E of approximately plus or minus 45.

The amplitude control device consists of a resistance 8 connected at opposite ends to the aerials A1 and A2, and provided with a tapping 9 connected to a receiver not shown in the drawings.

A practical form of directional aerial system is shown in Figure 3 which includes two aerials A1 and A2 and a dial switch Hi. which serves to connect selected lengths of line H, l2 or l3 for coarse variation of the phase shift desired.

A parallel tuned circuit M is arranged at a point A a quarter of a wavelength away from the point B at which the receiver is connected, the tuned circuit serving to effect fine adjustment of the degree of phase shift. It is known that a parallel tuned circuit M connected as shown is equivalent to a series tuned circuit arranged at the point B and has the advantage of allowing one side of the variable condenser forming part of the tuned circuit to be connected to earth.

A variable resistance I5 is connected at a point also a quarter of a wavelength away from the point B for the purpose of controlling the amplitude of the signals fed from one of the aerials to the receiver. In this case also the parallel connected resistance is equivalent to a resistance connected in series at the point B, but again the parallel connection enables one side of the resistance to be connected to earth. A changeover switch l6 enables the resistance IE to be transferred to the aerial which has induced in it the greater undesired signal.

If it is more convenient the phase and amplitude control arrangements may be divided into sections on either side of the point B at which the receiver is connected, but the arrangement illustrated in Figure 3 of the drawings possesses the merit that the relative phase and amplitude controls are independent.

In the modified form of Figure 3 shown in Figure 4 the tuned circuit ll of Figure 3 has been replaced by two identical tuned circuits I1 and I8 and a resistance l9 equal in magnitude to the characteristic impedance of the feeder (Z0) has been added in series with the tuned circluit 18. The variable condensers of the tuned circuits IT and i8 are ganged together for simultaneous adjustment.

In a similar manner the resistance l5 of Figure 3 has been replaced in Figure 4 by two equal variable resistances 20 and 21 connected to points in the feeder a quarter of a wavelength apart. The resistances 20 and 2| are also ganged for simultaneous adjustment. A resistance 22 is connected in series with the variable resistance 2| and has a value equal to the characteristic impedance of the feeder (Z0).

It is a property of the network including the resistances 20, 2! and 22 that when matched at the aerial end, the input impedance at the point of connection of the resistance 22 to the feeder, is equal to the value of the characteristic impedance of the feeder independently of the value of the resistances 20 and 2!.

Variation of the resistances 20 and 2| serves to vary the attenuation of the signals from the aerial to which they are connected without change of phase. tuned circuits l1 and I8 and the resistance I 9 has a constant input impedance at the point at which the resistance [9 is connected to the feeder and variation of the ganged condensers of the tuned circuits from the tuned position varies the phase of the signals received from the aerial to which they are connected substantially without attenuation. Coarse phase adjustment is provided by a rotary switch 23 which serves to select tapping points along a conductor 24 which is one half a, wavelength long.

Referring, now, to Figure 5 of the accompanying drawings, a modification is shown in which coarse phase adjustment is effected by connecting aerial A1 through a switch 25 to a variable tapping point in a length of feeder 26 which may be about one wavelength long. Fine phase adjustment is effected by the tuned circuit 21, amplitude control being effected by the variable resistance 28. The lead 29 is connected to a receiver as in the preceding arrangements. The length of feeder 26 is terminated by a resistance 30 approximately equal in value to the character istic impedance of the length of feeder 26. The resistance 3|! allows a very simple tapping switch Similarly, the network including the l 25 tobe used without variations dueto the varying length of the dead end of the lengthof mitting' aerials, In both the cases-of transmitting and receiving systems, it is of coursedesirable to avoid waste of power as much as possible, and as the amplitude control by means of variable resistance does involve waste of power, the following methods of efiectingamplitude control ofiers alternatives which may be adopted and are of particular advantagein the case of transmitting systems.

Thus referring toFigure 6 of the drawings an is varied by switching in more or less turns of the coil L3 the relative amplitudes in the aerials is affected. It is desirable that L1 and L2 should not have direct coupling with each other and that as the coupling M1 and M2 varies, the load on the transmitter should remain constant.

This latter condition requires for similar aerials that Both of these conditions are satisfied if the m M =a constant.

coils L1 and L2 are arranged at right angles to each other and the coil L3 is angularly disposed with respect to them in a manner of a radio goniometer. p 1

The coils L1, L2 and L3 may take the form shown in Figure 7, the electrically equivalent arrange ment being shown in Figure 8. The coils L1 and L2 are made from a piece of copper sheet, cruciform in shape, the limbs of the cross being bent up to form a box like structure as shown. The

coil L3 is formed of strip coppernarrower than the strips forming the coils L1 and L2 and is mounted on a hollow shaft 32 so as to be r0.- tatable within the box formed by the strip coils L1 and L2. The leads 33 to the coil L3 pass through the hollowshaft 32. The relation between the physical form of the coils and the e1ectrical circuit as shown in Figure 8 the points X--X1 and YY1 having corresponding positions in the two figures.

The values of L1, L2, M1, M2 may be selected to give a unity transformation ratio so that the same feeder may be used throughout and the feeder to the transmitter or receiver remaining matched for any setting of the coil L3. Alternatively other transformation ratios may be obtained by adjustment of the coil dimensions. Each coil is individually tuned and the appropriate feeder connected in parallel across the tuned circuit formed.

The arrangement described with reference to Figures 7 and 8 is adapted to use balanced feeders but it is probable that in view of the very low impedance circuits obtained with this construcimpairing the effectiveness of the device:

An alternative method of effecting amplitude control is shown in Figure 9, in which the coupling arrangement shown in Figures 7- and 8 is replaced by a tapped half wavelength line. The aerials A1 and A2 are connected 'to points. on. a half wavelength line 33. short circuited at each end and connected at its center to a transmitter .or receiver by alead 34. The tapping points and 35 are maintained. at one quarter of a wave:- lcngth. apart and the variation of amplitude: is obtained by moving the tapping points simultaneously along the line The input impedance at the mid point P of the line is where R is the resistance'of each aerial assumed to be equal and Z0 the characteristic impedance of the half wavelength line.

If the reactance is tuned out as indicated by the condenser 31 the device forms a unity ratio transformer. The relative amplitudes in the aerials A1 and A2 is given by tan 6. For a small range of amplitude control the reactance will not materially change assuming Z0 to be suitably selected so that the system remains substantially tuned. 1

The invention may be applied not only to dipoles and similar aerials, but generally to directional systems. It could, for example, be used in a system combining different types of aerials to produce several controllable regions of minimum pick-up or radiation in a directional diagram. In the case of reception, it will be seen that the arrangement described enables the direction of reception of the array to be changed byvelec'trical means, and complete suppression of any given fixed source of interference may be effected even in the presence of distortion of the field caused by neighboring objects. It will be seen also that the interference suppressing arrangements are located at the receiver so that interference from a given source may be suppressed when it arises.

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. A directional aerial system including two aerials, an aerial lead connected to each aerial,

a common channel coupling said leads to a transducer, means connected to one of said leads for varying the phase of signals therein with respect to signals in the other lead and means in the other of said leads for varying the amplitude of signals therein with respect to the signalsin said first lead, said first means comprising an inductance and a capacity connected in parallel and connected to a point in said aerial lead one quarter of a wavelength from'the point of connection of said leads to said common channel and said second means comprising a variable resistance connected at a point one quarter of a wavelength from said point of connection of said lead to said common channel.

2. A directional aerial system including two aerials, an aerial lead connected to each aerial,

a common channel coupling said leads to a transducer, means connected to one of said leads for varying the phase of signals therein with respect to signals in the other lead and means in the other of said leads for varying the amplitude of signals therein with respect to the signals in said first lead, said first means comprising an tion, concentric feeders may be used without inductance and a capacity connected in parallel and connected between a point in said first aerial lead one quarter of the wavelength from the point of connection from said leads to a common channel and ground, said second means comprising a variable resistance connected between a point one quarter of a wavelength from said point of connection in said other aerial lead and ground.

3. A directional aerial system including two aerial leads connected to each aerial, a common channel coupling said leads to a transducer, means connected to one of said leads for varying the phase of signals therein with respect to signals in the other lead, and means in the other of said leads for varying the amplitude of signals therein with respect to signals in said first lead, said first mentioned means comprising a pair of identical parallel tuned circuits spaced apart by one quarter of the length of the operating wave and connected between ground and said first aerial lead, a resistance equal in magnitude to the characteristic impedance of said lead being connected in series with one of said parallel tuned circuits, said second means comprising a pair of equal resistances spaced apart by one quarter of the length of the operating wave and connected between ground and said other aerial lead, a resistance equal in magnitude to the characteristic impedance of that lead being connected in series with one of said resistances whereby the phase of the signals in one of said leads may be varied without variation of the attenuation, and the attenuation of the signals in the other of said leads may be varied without change of phase in the signals in that lead.

EDWARD CECIL CORK.

JOSEPH LADE PAWSEY.

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