US 3723955 A
Apparatus for producing a beam of radiated energy comprises an array of transducers, a source of reference pulses for determining the frequency of the energy to be transmitted, a frequency divider connected to each of the transducers, and a source of clock pulses connected to the frequency dividers which determine the phase delay between the signals coupled to the respective transducers as a function of clock pulse frequency. Each of the frequency dividers includes an enabling input and an inhibit input with the output of each divider being coupled to its own inhibit input and the enabling input of the next adjacent divider. The reference pulses are coupled to the enabling input of the frequency divider associated with the first transducer. Where desired to shift the beam between 0 DEG and 180 DEG , the phase of the voltage applied to every other transducer element is shifted an additional 180 DEG beyond that provided by the frequency divider.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Lyons et a1.
[ 1 Mar. 27, 1973  BEAM FORMER  Inventors: James Francis Lyons, Mineola; Tul-' lio DeFilippis, North Woodmere,
 Field of Search ..340/3 R, 5 R, 6 R, 16 R, 3, 340/5, 6, 16; 343/100 SA, 113 R, 100.6, 113
 ABSTRACT Apparatus for producing a beam of radiated energy comprises an array of transducers, a source of reference pulses for determining the frequency of the energy to be transmitted, a frequency divider connected to each of the transducers, and a source of clock pulses connected to the frequency dividers which determine the phase delay between the signals coupled to the respective transducers as a function of clock pulse frequency. Each of the frequency dividers includes an enabling input and an inhibit input with the output of each divider being coupled to its own inhibit input and the enabling input of the next adjacent divider. The reference pulses are coupled to the enabling input of the frequency divider associated with the first transducer. Where desired to shift the TRANSDUCER  Reteremves Cited beam between and 180, the phase of the voltage UNITED STATES PATENTS applied to every other transducer element is shifted an additional 180 beyond that provided by the frequency 3,266,010 8/1966 Brightman et al ..343/100 SA divider, 3,281,843 10/1966 Plummet ....343/100 SA 3,295,098 12/1966 Brightman et a1. ..340/ Claims, 10 Drawing Figures Primary Ex a nti rter Richard A. Farley Attorney-Darby & Darby 24 CLOCK 180 PULSE NH a 20b R INH REFERENCE 12b l2n 12o 14a 14b FF 14o ACOUSTICAL m on Patented March 27, 1973 3,723,955
5 Sheets-Sheet 1 R INH 200 NH 20b R INH REFERENCE 5 E /E [2b I20*\ u l l2n E7 E;- 2X
I J 22b FF FF 7 FF A l4n ACOUSTICAL TRANSDUCER on l 34, I 1 Fit I I F l TRANSMITTER CONTROL SIGNAL 40 III PULSEWIDTH SELECTION CONTROL I VOLTAGE GENERATOR SECTOR SCAN LIMITS TO DELAY CORRECTION- COMPUTER MODULE I (44 YAW CORRECTION SIGNAL ,suMMINC ROLL a PITCH NETWORK CORRECTION SIGNAL 42 VOLTAGE CONTROLLEO OSCILLATOR fc INVENTORS JAMES FRANCIS LYONS BY TULLIO DeFl LIPPIS ATTORNEYS Patented March 27, 1973 3,723,955
5 Sheets-Sheet 2 lon-| X IO, SEcTION OF LINEAR ARRAY l IO T n AT ARE SPACED BY d. I"' 'I" TP "I "I" I VELOCITY OF PROPAGATION TIMING OF SIGNALS FOR BEAM I FORMATION AT -I/= I80" I l A [Ah Tp cOS. I8O=T I-Tp-I I TIMING OF SIGNALS FOR BEAM I FORMATION AT -I'= I2O I B 0.5 T -l In- I l:Af=Tp cos. I20=O.5 Tfl I l l TIMING OF SIGNALS FOR BEAM FORMATION AT+= 90 I c l llwT cos. SO=| I l r05 Tp TIMING OF SIGNALS FOR BEAM FORMATION ATI'=60 l D [Af Tp cos. O=Tp:| I
l F i TIMING OF SIGNALS FOR BEAM I FORMATION AT+=O l E EAf=Tp cos. O= T I TIMING 0F SIGNALS FOR BEAM FORMATION AT vARIOuS ANGLES INVENTORS J'AMES FRANCIS LYONS TU LLIO DeFILIPPIS ATTORNEYS Patented March 27, 1973 3,723,955
5 Sheets-Sheet 4 W A 90 W 0 W 5O 3 (NO DELAY) m I54 M 1 l L l l A 52 .1 1 1 B F l l l I I C I l l F (BEAM ATO) li '2 U l l A L60 1 1 L l L 5 FIG. 6a
(BEAM AT 90) 1 1 L INVENTO JAMES FRANCIS LYO S TULLIO DeFLlPPIS ATTORNEYS BEAM FORMER This invention relates to signal generators of the type wherein energy is radiated with a radiation pattern havin g substantially a single directional beam.
The following specification and drawings pertain specifically to sonar beam generating apparatus; however, the principles of the invention are not necessarily limited to a particular form of radiation and would have utility in other analogous situations. For example, the beam forming techniques of the invention could be used in radar applications.
When using radiated energy for navigational or searching purposes, it is frequently desirable to scan predetermined sectors of space with a highly directive beam. The more sharply concentrated the beam, the more accurately the target can be located. Initially, such scanning was accomplished by physically moving the beam forming radiator. Subsequently, all-electronic systems were devised which scanned without physical movement of the radiator thereby avoiding the various drawbacks of mechanical scanning systems.
Generally, and by way of example, such prior art electronic scanning systems employ a plurality of radiator elements and circuit means for coupling electrical signals to such radiator elements with a complex frequency or phase relationship such that a highly directive beam is generated in a particular direction. By changing the frequency or phase relationship of the signals fed to the radiator elements, the beam may be caused to scan a preselected sector of space. The present invention is an improvement on such electronic scanning devices.
Referring now to a sonar application, the specific requirements of a typical electronic beam steering system may be considered. As will be apparent to those skilled in the art, the same requirements (or closely analogous ones) will also arise in other applications.
In the first place, the radiation beam should be as narrow as possible and steerable over at least 180. Considering an array of transducers mounted on the bottom of a boat, the beam should be steerable in both azimuth and depression. By way of example, the beam should be capable of scanning 180 in azimuth and adjustable in depression plus or minus 60. Desirably, the system should be operable at any one of several frequencies, for example, in the range of 2.5 to 4.5 k.c. A multifrequency capability provides the ability to successively transmit several pulses, each at a unique depression angle and frequency; operation of several sonar systems in the same general area without mutual interference; and the ability to optimize the operating frequency for local propagation conditions. It is similarly desirable to be able to select a pulse width so that the system operation may be optimized for the particular environment.
It is also desirable to stabilize the beam regardless of the roll and pitch of the ship without having to physically reorient the array of radiator elements which, as a practical'matter, may be impossible. In the following specification and claims, beam stabilization refers to a compensatory operation designed to reduce the effect of physical movement of the array on the beam direction.
In addition to the above properties, it is desirable that 'the beam steering technique provide a simple means for modulating the effective carrier frequency of the array. Because the use of a very large array of radiator elements provides a narrow radiation beam width and consequently discrimination against background reverberation and noise, the ability to modulate the carrier frequency would enable use of the array for conventional communication.
Accordingly, it is the main object of the present invention to provide an all-electrical beam steering system which is improved with particular respect to the above mentioned features, individually and in combination.
A more specific object of the invention is to provide a sonar beam steering device having particular utility with large ocean going vessels.
Briefly, in accordance with the invention, the above and other objects of the invention are accomplished by the use of variable digital delay elements connected between the individual transducers of the array. In the preferred embodiment, such delay elements comprise frequency dividers which introduce a delay dependent upon a clock frequency applied thereto, the translated pulses being independent of theclock frequency. The source of clock pulses may be derived from a voltage controlled oscillator to which inputs representative of the ships attitude are fed. Thus, if the vessels movement tends to displace the beam, the voltage applied to the oscillator can be varied to cause the frequency of the clock pulses to change the delay between the individual array elements such that the beam returns to its normal position.
Referring now to FIG. 1, the principles of the inventions are illustrated in simplified block diagram form. A linear array of radiator elements is shown as consisting of a plurality of acoustical transducers 10a, 10b 10n. As is known, depending upon the phase relationship of the signals fed to the transducers 10a to 10n energy will be radiated with a radiation pattern having substantially a single beam extending in one direction.
To obtain this relationship, frequency dividers 12a, 12b 12n are coupled to each of the respective transducers through flip-flops 14a, 14b 14n. The frequency dividers are identical and include a resetenable input 16, a divider input .18 and an inhibit input 20. Resetenable input 16 sets the divider for operation; the signals on line 18 are the input signals which are divided by the divider; and a signal on line 20 will inhibit further operation of the divider. Each divider produces an output pulse each time a preselected number of clock pulses appear after an enabling input is applied to line 16a. Frequency dividers of this nature are well known in the digital arts and therefore are not described in further detail.
Each of the frequency dividers is shown as consisting of X stages which means that the divider will count 2 input pulses on line 18 before producing an output pulse on output line 22. The required number of binary stages in each divider is governed by the probable maximum delay error at any divider output due to an accumulation of random reset errors. A limit of 15 microseconds on the maximum error specifies about eight binary stages, i.e., X=8, in which case the incoming pulses on line 18 are divided by 2 or 256.
The reference pulses applied to the reset-enable input 16 of the divider 12a determines the carrier frequency F o to be translated, and as will be more apparent below the reference pulses will occur at twice the frequency F The clock pulses fed to lines 18 of the frequency dividers determine the relative delay between the various transducers and these pulses therefore will occur at a rate dependent upon the direction in which it is desired to aim the beam. If, for example, the desired phase delay is equal to T the clock pulses appearing on line 18 should be at a frequency equal to Z IT The reason for this will be more apparent with reference to the timing diagram of FIG. 2.
As shown schematically in FIG. 1, the clock pulses are generated by a variable clock generator 24 which can change the frequency of the clock pulses, thereby altering the delay provided by the frequency dividers and hence the beam direction.
The operation of the circuit is described with further reference to the timing charts of FIG. 2. Operation is initiated by the appearance of the first reference pulse 30(1) on line 16. The leading edge of this pulse enables the divider 12a whereby counting the incoming clock pulses on line 18a is commenced. After 2* clock pulses have appeared on line 18a, an output signal appears on line 22a which causes flip-flop 14a to change states as shown at 32 in FIG. 2. The time it takes for the 2 clock pulses to produce an output on line 22 is shown at T in FIG. 2.
The output at line 22a is simultaneously used to inhibit the divider 12a via line 20 and to enable frequency divider 12b via its reset-enable input. Consequently at time divider 12b starts to count the clock pulses and a pulse appears on line 22b 2* clock pulses after time t (i.e., time t and flip-flop 14b changes state as shown at 34. Simultaneously, the pulse line 22b is applied to inhibit input 20b to prevent further counting of divider 12b.
When the second reference pulse 30(2) occurs on line 16a, divider 12a is once again enabled so that after 2* more clock pulses have appeared, a signal is produced on line 22a which returns flip-flop 14a to its initial state as shown at 36, and enables counter 12b which had been previously inhibited by the appearance ofa pulse on lines 22b and 20b.
The above process is propagated down the line of dividers, with the wave forms A and B being coupled to the transducers a and 10b. Obvously similar wave forms will be coupled to all of the transducers 10 with the respective phase delays between adjacent transducers being equal to T Thus, at the n" transducer, the total delay with respect to the first transducer will be nT It is known that when the relative phase difference T is equal to the propagation time between adjacent transducers (T,,), the beam will be formed at end-fire. When all voltages are in phase .(T =0) the beam is at broadside. For phase differences between 0 and T,, the beam will be displaced correspondingly.
FIG. 3 is a simplified block diagram of the variable clock pulse generator 24 shown in FIG. 1. As explained below, to assure beam steering from 0 (end-fire) through 90 (broadside) to 180 (end-fire), the period of the clock frequency must vary linerarly from approximately 0 to 2T where T is the propagation time delay between adjacent elements of an array. A control voltage generator 40 produces a voltage versus time function which is used to tune a voltage controlled oscillator 42 to yield the required frequency versus time characteristic. Generator 40 may be a motor driven, tapped (to permit shaping) potentiometer which is conventional, and, as shown, is dependent upon the pulse width selection and sector scan limits desired for the operation. In essence, the output of generator 40 is a voltage which will determine the delay of the individual dividers 12a to 12n and the rate of change of such delay depending upon the illustrated parameters.
Prior to controlling the oscillator 42, the output of generator 40 may be coupled to a summing network 44 which is also responsive to a yaw correction signal, and a roll and pitch correction signal to raise or lower the voltage output of generator 40 such that the output of oscillator 42 will cause the delays produced by the frequency dividers to change the amount required to stabilize the beam. Such correction signals may be generated by computers outside of the invention and which are known in the art.
The apparatus illustrated in FIG. 1 is capable of scanning through only ninety degrees, i.e., from 0 (end-fire) to (broadside) or 90 to (end-fire) depending upon the manner in which the transducer elements are connected to the signal generator. The problem is that to scan from 180 to broadside the phase relationship'of the respective transducers must be the mirror image of that required to scan from zero to 90. The meaning of this may be more clearly understood with reference to FIG. 4.
At the top of FIG. 4, five transducer elements are illustrated as 10 l0 10,, 10,, 10,, For convenience each of the transducer elements are shown spaced so that the propagation time of the acoustic energy between respective elements is equal to T, Beneath the illustrated transducer elements five series of wave forms A to E are illustrated. Each series of wave forms corresponds to a given beam direction 111 with each series consisting of five individual waves corresponding to the respective transducer elmments as labeled thereon. For ease in reading, the wave forms themselves are represented only by short verticlal lines corresponding to the positive going cross-over of the respective waves.
In the series of wave forms A, the phase delay between each of the respective transducer elements is shown as being equal to the propagation time T, in which case it may be assumed that the beam will be formed at 180 Wave forms B show the phase relationship reduced to T,,/2 in which case the beam is formed at I20. Wave forms C show the signals at each of the transducer elements to be in phase in which case the beam is formed at broadside.
To sweep from 90 to 0 it is necessary to convert the relative phase lag of wave forms A and B into a phase lead. Thus, as shown in wave forms D, the input to element 10 leads 10 etc., by T /2 whereby the beam is produced at an angle equal to 60 As the phase lead is increased to T as illustrated in wave forms E, the beam scans toward 0. The significance of FIG. 4 is its showing that to scan through 180 it is necessary to change a phase lead to a phase lag (or vice versa).
A novel manner for converting this phase lag to a phase lead is illustrated in FIG. 5. The operation of FIG. 5 is substantially identical to the operation of the circuit illustrated in FIG. 1 and corresponding circuit elements have been numbered in the identical fashion. The significant difference in this case is that each delay channel comprises two separate dividers which are designated by the numeral corresponding to the previously mentioned counter having appended thereto a prime mark Thus, channel A includes counters 12a and 12a. A further distinction is that each of the flipflops 14a, 14b 14n include set and reset outputs Q and 6 which are respective complements of each other, adjacent flip-flops having different outputs coupled to their associated transducer elements.
The reason for the use of two counters in each channel is explained below wherein the operation of FIG. 5 is described with reference to the timing charts of FIG. 6.
In FIG. 5 the reference pulses are fed at the frequency F (2F, in FIG. 1) with the complement of the reference frequency indicated at F appearing on line 16a. The relationship between the reference frequency F, and F, is shown in lines A and B of FIG. 6a.
In FIGS. 6b and 6d four wave forms A, B, C and D are shown in each case. These wave forms represent the voltages which would appear at the inputs to four consecutive transducer elements, say a, 10b, 10c and 10d, respectively. Only four transducer elements are described for purposesof explanation but it should be obvious that the discussion hereinbelow could be expanded to include any number of elements, with the principles being the same.
FIG. 6a represents the wave forms as they would appear if there were no delay inserted between the pulses appearing on lines 16a and 16a and the transducer element 10a (i.e., the clock pulse period is zero). Under these circumstances, the wave forms applied to each of the transducers will be displaced in phase 180 with respect to the adjacent transducers, as shown in FIG. 6a.
To prevent the formation of back-lobes in the transducer radiation pattern, it is desirable that the physical distance between adjacent transducers (e.g., 10a and 10b) be such that the propagation time between them is less than one-half the period of the reference frequency F,,. It is recalled that to scan the beam through 90 it is necessary to introduce a phase delay equal to the propagation time T,. Therefore, the requirement introduced above for preventing the formation of backlobes means that the 180 phase reversal between adjacent elements is more than that required for a 90 scan of the beam. For explanatory purposes, it may therefore be assumed that if the transducers were fed with the wave forms illustrated in FIG. 6a a beam would be produced pointing in the direction shown to the right of the wave forms by arrow 50.
The requirement is to scan the beam from end-fire to end-fire (i.e., 0 to 180); therefore it is necessary to introduce sufficient delay through the individual dividers to move the beam to an end-fire position as shown at 52 in FIG. 6b. The amount of time delay required for this purpose is shown for purposes of explanation as the time interval 54, and, recalling the operation of the circuit of FIG. 1, this means that the output of divider 1217 will be delayed with respect to divider 120 by time interval 54, and so forth. However, because of the 180 phase shift introduced by the flip-flops 14, the effect of introducing this slight delay will be to produce wave forms wherein the input to element 10b is advanced with respect to element 100, and so forth. In other words, the insertion of a 180 phase shift by the flipflop 14 plus the delay interval 54 from the divider 1211 provides the same results which would be achieved if in some manner the divider 12a advanced the successive wave forms by a time interval 56 with the net result that the beam is formed at end-fire or 0.
As the delay 54 is increased, the apparent phase advance 56 decreases so that the beam 54 continually scans from 0 toward broadside until the phase delay introduced is sufficient to overcome the 180 phase shift of the flip-flops and the transducer outputs are all in phase. This situation is illustrated in wave forms 60 with the required delay interval illustrated at 56 and the direction of the beam at 60. The difference between time intervals 56 and 54 (shown as' 62) will be equal to the propagation time T, since this is the phase delay required to scan through As the time delay 56 continues to increase, the wave forms continue to shift in the direction illustrated by FIG. 6d until, when the delay is equal to the interval 64, the beam is generated at i.e., end-fire. Thus, comparing wave forms 6d and 6b, wave form B appears now to lag wave form A and since the total phase difference between the respective wave forms is equal to twice the propagation time, the respective beams will point in opposite directions as shown by arrows 52 and 66.
Wave forms 6a and 6d have been presented solely for the purpose of explaining the operation of the invention. It is also for this reason that the prolonged plateaus appears in FIG. 6c and 6b, such plateaus being intended to provide an indication of the delay from an initial starting time before a given pulse would appear in the respective channels. Of course, during operation, these plateaus do not exist.
From what has previously been said it is apparent that the total delay which must be introduced by the counters must exceed twice the propagation time T, It is further recalled that the 180 phase shift will always be more than that required to scan the beam through 90. Therefore, because the maximum delay provided by the counters must exceed one-half the period of the reference frequency regardless of that frequency, the circuit of FIG. 1 would not be operative. This may readily be seen with reference to FIG. 2 wherein, if the delay is greater than the distance between pulses 30(1) and 30(2) (which is one-half the reference period), the required reset/enable andinhibit signals cannot appear at the required times.
To avoid this drawback two dividers 12a and l2a'are provided with. the reference frequency being applied on line 16a and its complement on line 16a. After the incomingreference frequency pulse on line 16a has been delayed by counter 12a (depending upon the clock frequency), an output appears upon line 22a which sets flip-flop l4 applying the set output to transducer 10a. Half the reference period later, a pulse appears on line 16a and is propagated through counter 12a with the same delay to appear on output 22a and reset the flipflop 14a. Thus, regardless of how long the delay is, the flip-flop 14a will always be reset one-half the reference period after it has been set and the desired wave form will always be produced. The output of counter 12ais V coupled to the reset/enable input of counter 12b and the output of counter 12a coupled to the reset/enable input of counter 12b and so forth down the entire line through counters 12n and 12n. As explained above, alternate counter outputs are used to set and reset the adjacent flip-flops 14.
FIG. 7 illustrates an alternative embodiment of the 180 scanning system which maybe employed with a circuit identical to that illustrated in FIG. 1. At the top of FIG. 7, lines 14a, 14b 14n-l and 1411 are shown which may be considered the outputs of the flip-flops 14a, 14b 14n. According to this embodiment of the invention, a switching circuit is connected between these flip-flop outputs and the respective transducers 10a, 10b I011 illustrated at the bottom of the drawing. The switching circuit consists of two AND gates 70 and 72 and an OR gate 74 connected to each channel and gates 70 and 72 are enabled by the set or reset outputs of a flip-flop 76 as shown.
The operation of FIG. 7 is simple and can be readily understood with reference to FIG. 4 from which it can be seen that to scan from 90 to 180 it is only necessary to reverse the phase relationship required to sca from to 90.
To scan from 0 to 90 an enabling signal on line 78 sets flip-flop 76 which enables gate 70a, 70b, 72nl and 72n. Consequently, and in an obvious manner, the signals appearing on line 14a, 14b 14n-l and 14h are coupled through the gates 70a, 70b 72n-1, 72n to the respective transducers a, 10b l0n-l and HM. This provides the phase relationship illustrated in wave forms A and B of FIG. 4.
When it is desired to scan from 90 to 180 a reset signal is applied to line 80 causing flip-flop 76 to enable the gates 72a, 72b 70n-1 and 70n. Under these circumstances, the output of flip-flop 14a is coupled through gates 70n and 74n to transducer 10n. Flip-flop 14b is coupled through gates 70n1, 74n-1 to transducer 10n-l. Flip-flop l4n-l is coupled through gates 72b and 74b to transducer 10b; and flip-flop Mn is coupled through gates 72a and 74a to transducer 10a. Those lines and transducers between channels B and N-l will be similarly switched to provide the mirror image when scanning from 90 to 180 so that the required phase relationship indicated in wave forms D and E of FIG. 4 will be obtained.
In the above explained embodiments of the invention the output to the transducers are in the form of square waves although the transmitter energy will generally be in the shape of a sine wave. The required filtering may take place in the transducer itself which may inherently filter out the frequencies of interest or, if preferred, separate filter elements may be interposed between the flip-flops and the transducers.
The invention has been illustrated and described with reference to a linear array of elements, but in fact the invention is specifically designed for use with a planar array of elements wherein each row may correspond to the linear array herein described. Moreover, certain principles of the invention are not necessarily limited to digital apparatus and, particularly with respect to the 180 steering, would have equal utility with other types of variable delay elements which are known in the art. Other modifications of the invention will also be obvious to those skilled in the art, and the invention should not be limited except as defined in the following claims.
What is claimed is:
1. Beam forming apparatus for use with an array of transducer elements, comprising at least one frequency divider connected to each of said transducer elements, means for applying clock pulses to said dividers means for applying reference pulses having a preselected frequency to the first of said dividers, each of said dividers having an enabling input for enabling operation thereof and an inhibit input for preventing the divider from dividing the clock pulses, the output of each divider being coupled to its own inhibit input and the enabling input of the next adjacent divider.
2. Apparatus according to claim 1, including bistable means connected between the output of each divider and its associated transducer element, said bistable means changing state each time a pulse appears at the output of its divider.
3. Apparatus according to claim 2, wherein said reference pulses have a frequency twice the frequency of the energy to be translated.
4. Apparatus according to claim I, wherein the transducers are spaced so that the propagation time between adjacent transducers is less than half the period of the energy to be translated.
5. Apparatus according to claim 4, including means for inserting a phase difference of between adjacent transducer elements.
6. Beam forming apparatus for applying a plurality of progressively phased voltages to a linear array of spaced radiators, comprising a multi-stage digital delay means connected to each transducer for coupling said voltages to said transducer elements, each of said digital delay means being operable in response to the output of the next preceding delay means, means for simultaneously applying clock pulses to all of said delay means, said delay means producing a delayed output upon receipt of a preselected number of clock pulses, and means for applying a signal having a preselected frequency to the input of the first of said digital delay means only, said preselected frequency determining the frequency of the energy transmitted by said array.
7. Beam forming apparatus according to claim 6, wherein each of said digital delay means comprises an n stage frequency divider responsive to said clock pulses and having an enabling input and an inhibit input, said enabling inputs being connected to the output of the preceding divider, said inhibit inputs being connected to the outputs of the associated dividers.
8. Apparatus for producing a beam of radiated energy comprising an array of transducer elements, said transducer elements being spaced so that the propagation time of the energy between adjacent elements is less than half the translated frequency, two digital dividers coupled to each of said transducer elements, means for applying clock pulses to said dividers, means for applying reference pulses having a preselected frequency to one of the dividers associated with the first of said transducers, means for applying the complements of said reference pulses to the other divider associated with said first transducer, each of said dividers having an enabling input for enabling operation thereof and an inhibit input for preventing the divider from dividing the clock pulses, the output of each divider being coupled to its own inhibit input and the enabling input of one of the dividers associated with the next adjacent transducer, and bistable means connected to each pair of dividers and their associated transducers for introducing an additional 180 phase shift in the voltages applied to said transducers.
9. Apparatus for steering a beam of energy comprising an array of linear transducer elements, the propagation time of the energy between adjacent transducer elements being less than one-half the period of the frequency to be transmitted, means including variable delay means for producing a plurality of successively