US2929058A - Sequential lobing system with ferrite phase shifters - Google Patents

Description

March 15, 1960 A. BLASBERG ETAL- 2,929,058

SEQUENTIAL LOBING SYSTEM WITH FERRITE PHASE SHIF'TERS Filed April 4, 1955 SEQUENTIAL LoBtNG' SYSTEM wrrH y PHASE snrnrnns Ltuvrtmcel A. Blasting, vwilma is. Hughes'Qahd Leon s. Lader,` Los Angeles, .Calif.,` assignors to Hughes Aircraft Company, CulverA City, Calif., a corporation of g 'Delaware y g .f application April 4, 195s, seriaiNo. 499,185

` 6 claims." (ci. 343-16) This invention relates to a microwaverantenna lobing system vand more particularly to such asystem which achieves vsequential lobingelectronically utilizing ferrite phaseshifters i Conventional sequential lobing systems rdiatef'and reeverenergy sequentially from each of four waveguide i apertures at thefrocalpoint of a parabolic focusing objectivefg TRitubessequentially 4short circuitfthree of the apertures in `order todirect all ofthe energy. into the fourth. 'This method hashigh insertion loss andis very narrow band in itspoperation-' Other conventional sequential lobing systems are '.those `which lobe mechanically; and there are two undesirable limitations imposed on systems which lobe" mechanically. First there is the inherent periodicity of mechanical systems, v. and secondV the practical restriction to low lobing rates-because of the inertia and friction of the moving parts. The first limitation lends the radar system readily susceptibleto synchronizedjamming and consequent erroneous angle indications. The second limits the rapidity with which data may be obtained, while both limitations invite errors from spurious signal modulation.V

The second limitation stems from the manner in which fire control radar systems function. Ordinarily the antenna in such a system is automatically pointed in that direction in which echoV signals returning from the target are not modulated but are all of equal amplitude since the target is on the axis of the lobing antenna. Thus it is seen that any modulation of the echo signal will introl duce error into the system and cause the antenna to not point accurately at the target. With low frequency lobing and periodic keying of lthe transmitter, false angle indications frequentlyarise from low frequency beats developing between the lobing frequency and any low frequency modulationV component in the returning echo. This modulation mayoriginate-`from such causes as enemy countermeasures, fading, orpropeller modulation.

An existing sequential lobingtracking system is described in Naval Research LaboratoryV Report No.

` 3`6R05-01, June 1947', An Electronically Lobed Track- .of each plane. A difference in signal' amplitudes causes a D.C. error voltage to be developed in the angle circuits which is then used to control the antenna servo` mechanism for automatic tracking. A typical sequence .of events is as` follows: A waveguide in the center of the t `primary array transmitsv an antenna pattern characterized by'a single lobe directlyV along the antenna axis. Then a pulse from the timing generator which controls the transmitter tires TR tubes in three'of the four' Vwaveguide 2,929,058 Patented Mar. .15,

t 2 apertures which symmetrically surroundfthe` transmitting aperture;.thus the fourth waveguide, .which is not effectively short circuited as are the other three and the transmitting aperturereceives on an off-axis lobe.. That event isrepeated three more times, sequentially with the other three receiving apertures sequentially receiving olf-axis lobes. The transmitted on-axis lobe is the same for each pulse. Y

Conventional angle error detection circuits in the above system perform the function of comparing lobed, gated t video pulses andk converting these into D.C. angle error voltages which control Vthe elevation and azimuth antenna servosystems.

. In prior art systemssuch as the above, one must carei fully control vthe impedance at the three junctions in order to channel the energy to one waveguide at a time.

The impedancegs at these junctionsv are controlled by placing the TR tubes an integral number of half wavelengthsaway from Vthe conducting waveguide. The tiring of the TR tubes then insures a short circuit at" these junctions and so directs the energy in the desired channel Vat the desired time.

Since the TR tubes are anintegral number of half wavelengths away at one frequency, the system will only operate satisfactorilyat thatfrequency. Further, TR tubes contribute one db of insertion loss and one db of arcing loss to the system. Also, TR

tubes inherently limit the lobing rate to a low frequency because of the long switching time which is needed for the Vspark` gap TR tubes.

yItis therefore an object of the present invention to provide an electronic sequential antenna lobing system which is not subject to the above disadvantages of the prior art systems.

It is another object of this inventionto provide a system which utilizes ferrite phase Shifters in the antenna feed waveguides which may be shifted at a frequency of the order of thousands of cycles per second.

It is a further object to provide a system which achieves sequential lobing by using ferrite phase shifters in the waveguides which have a negligible insertion loss.

It is a further advantage to provide a system which transmits and receives on the same waveguide apertures instead of transmitting through one aperture and receiving through other apertures.

It is yet another object to provide a system which can transmit as well as receive off-axis.

It is another object of the present inventionto provide a system which electronically provides a two-bar searchmg antenna scan. t Y

Briefly, these objects are achieved in the present invention in the following manner: ln each of four waveguide feeds to an antenna there is placed a ferrite phase shifter, and each phase shifter may be operated independently of the others. When none of the phase shifters are energized, the antenna lobe is directed along the antenna axis. However, when one of the phase shifters is energized the resulting lobe is caused to be olf-axis.

tion in the primary array and the phase shifter in the Y up feed is energized, the radar receiver output is in synchronism switched to an up channel and when the down feed is phase shifted, the receiver output is switched to a down channel; similarly with the left and right feeds and left and right channels. The outputs of the up and down channel are amplitudewise compared in an elevation error detecting circuit, and similarly with an azimuth error detecting circuit which is coupled to the left and the right channels. When, for example, a target is at zero degree azimuth with respect to antenna axis but is above the axis of the antenna, the up" channel output will be greater than the down channel output; and the elevation error detecting circuit will have a D.C. output, the magnitude of which is proportional to the difference in signal levels between that received by the up feed and that received by the down feed 'and whose polarity is in a predetermined manner opposite to that when the signal in the down channel is greater. This resulting angle error voltage is then fed to the antenna positioning motor to cause the antenna to be pointed upwards so that its axis will go toward the target. Similarly with the left and rightvchannels, when the target is to the left of the antenna axis, the output oftheazimuth error circuit has a magnitude proportional to the angular distance off-axis to the left and whose polarity is opposite to that when the target is off-axis to the right.

By utilizing ferrite phase Shifters in the waveguide feeds the lobing frequency rnay be increased to the order of thousands o f cycles per second, .and as a consequence low frequency beats which ordinarily develop between the lobing frequency and any low frequency modulation component in the returning echo may be averted. Further nullifying effects may begained by coding the transmitter and receiver to avoid the production and reception o f regular beat frequencies or enemy countermeasures. Y

The .nevel features which are believed t be eherateristic ofthe invention, both as to its organization and' method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection wtih the accompanying drawing in which an embodiment of the invention is illustrated by Way of example. It is to be expressly understood, however, that the drawing is `for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

In the drawing, the gure is a block diagram of the sequential lobing system in accordance with this invention.

Antenna supports four waveguide apertures designated U, D, 1 R (representing respectively up, down, left, and right). Aperture U terminates waveguide 12; aperture D terminates waveguide 14; aperture L terminates waveguide 16 and aperture R terminates waveguide 1 8. At the ends opposite the antenna apertures these waveguides all terminate at waveguide junction 20, which in a conventional manner, equally couples each o f the above four waveguides through waveguide 22 to duplexer 24. Interposed in each of waveguide sections 1 2, 14, 16 and 1S are the ferrite phase Shifters 13, 15, 17 and 19. Ferrite phase shifters of the character which may be here utilized are described and claimed in a copending application of W. A. Hughes entitled Ferromagnetic Microwave Phase Shifter, Serial No. 459,- Q94, filed September 2 9, 1954, and assigned to the same assignee as is the present application. Briefly, as described in that application, a ferrite phase shifter comprises a section of waveguide which contains a small 'segment of ferrite masnefie material- An ,external eleetromagnetic `control Circuit adjacent to the ferrite element receives a D.C. signal of a predetermined polarity to cause signals propagated by the waveguide to be shifted in phase due to the properties of the vferrite material.

Duplexer 24 is coupled to transmitter 2 6 through waveguide 28. Duplexer 24 is also coupled to mixer 30 through waveguide 3 2; and local oscillator 34 is also coupled to mixer 30 by means of waveguide 36. Local oscillator 34 provides a signal of such frequency that when mixed with the RF signals received from the duplexen an IF frequency representative of received radar signals is fed to I F channel 38. The outputterminal of IF channel 38 is coupled to a switch 40, which, in a conventional manner, selectively, sequentially channels the output Q .f the .1F Channel. t0 up channel 4.2,

down channel 44, left channed 46 and right channel 48. Up channel 42 and down channel 44 are coupled to elevation error detecting circuit 50 while left` channel 46 and right channel 48 are coupled to azimuth error detecting circuit 52. Error detecting circuits 50 and 52, in a conventional manner, are adapted 'to compare the relative amplitudes of the signal outputs of the respective channels coupled to them.V The comparison means utilized in the detecting circuits may, for example, be a simple capacitor integrator. The err-rcr circuits are then each coupled to the antenna servos 34 which aremechanically coupled asdesignated by dotted line 56 to antenna 10. .Pulsing and switching network 3S is coupled through connector 60 to ferrite phase shifter 13; by connector 62 to phase shifter 15; by connector 64 to phase shifter 17 and by connector 66 to phase shifter 19. Connector 68 couples network 58 to switch 40. f l

System synchronizer 70 is coupled to transmitter 26 and range circuits 72. Range circuits 72 are further coupled to network S8.

- ln a typical mode of operation, synchronizer 76 triggers transmitter 26, which then transmits through duplexer 24, waveguide junction 20, and equally through waveguide sections 12, 14, 16, and 18, through aperturesU, D, L, and R and thence into a transmitted lobe along the axis of antenna 10. For such a transmitted pulse none of the ferritesphase Shifters are lenergized in this mode; however, ,in preparation for receiving echos, phase shifter 13 is caused to be energized to reverse the phase of signals entering aperture U, thus effectively shifting the antenna lobe. Received signals from all four waveguides are fed through waveguide junction 20,

vduplexer 24, mixer 30, IF channel 38, switch 40 and thence to up channel 42 the output signal of which is fed to elevation error detecting circuit 50, which in a conventional manner remembers the amplitude of the video pulse representative of target return when the lobe is shifted by the energization of phase shifter 13.

Then a similar pulse is transmitted anew from transmitter 20 with phase shifter 13 de-energized along with phase Shifters A15, 17 and 19; so that again the transmitted lobe is along the antenna axis. However, when echo signals vare received by the antenna from this second transmitted pulse, phase shifter 15 is energized, and the receiver output is fed to down channel 4d, which in turn couples the video to elevation error detecting circuit 50. Circuit 56 compares this latter video signal with remembered earlier one and then provides a D.C. output, the vpolarity of which is determined by whether the target was above o r below the antenna axis and the magnitude of which is a measure of the angular distance of the target above o r below the antenna axis.

In a similar mannerwa third pulse is transmitted and when echos thereof are received, phase shifter 17 is `energized and the receiver output is switched to left" channel 46 and thence to azimuth error detecting circuit v5.2, which remembers the amplitude of the video pulse received when the antenna lobe was switched to the left.

Finally, a fourth pulse is transmitted and its echos will be received in va lobe, shifted to the right. The receiver output will be switched to right channel 4S and thence to azimuth error detecting circuit 52, which then compares the amplitudes of the signals received when the antenna lobe was `switched to the left versus when it was 4switched to the right. Circuit 52 then provides a D .C. signal, the polarityl of which is determined by whether the target was to the left or the right of the axis and the magnitude of which is a measure of the angular distance to the left or right. Antenna servos 54 are adapted to aim .the antenna in a manner to keep signals returned from the target of the same amplitude regardless of which phase shifter is energized,vwhichis the condition that -the target lie on the antenna axis.

.The pulses of the Switeh netwerk 58 in ,the abpve 'ft-the time subtended by the target echo pulse.

'made possible by the rapid switching ratesV achievable deseii'bewd,inode ofA operation are adapted to seqirentially pulse the'ferrite phase Shifters and switch-40 'responsive to successive synchronizer pulses.` j

A monopulse mode of operation may also be realized 1n this invention. The term monopul'se is .used to describe Y anyl null tracking system` in' whichV complete target'L bearing information isfobtaincd l'by' the Vreception toan electrical pulse, microwave energy passing: through n 'its respective waveguide in a manner to thus shift the of one received pulse., In sucha *mode of operation a Vcomplete cycle of sequential switching'occursduring This Vis with ferrite phase Shifters."-

direction of Vthe lobe of said array of apertures; switching means for sequentially coupling said common junc-V tionto `one. of said receiver channels in synchronism with the action of applying pulses to -said phraseshifters;al pulsing and switching network coupled'to each of said "phase Shifters and to said switching means for sequentially pulsing said'phase shifters'and synchronously coupling In this mode'of operation sequentialfphase shiftingzis- Y caused tooccur only duringrtherange gate. Thus-"in thisy mode,- pulsing" and switching network58 is adapted to sequentially pulse the phase Shifters andswitch 40 lat one end of each of said waveguide sections; an array in' response to "the'leaclingedge of the `range `gate and- I complete at least one cycle, of sequential lobing before the trailing edge of the range `gate. K

Further. modes of operation may be those `in which the transmitted pulse, aswell as the received pulse, pass through an energized phase shifter. It may be readily seen that for appropriatelr'applications it is Vpossible in t this systeml to transmit a lobe` either on the antenna axis or off the antenna axis andalso to receive a lobe on the antenna axis yor off the antennay axis at `any given time.,l However, itis ,desired-usually to transmita lobe on the antenna axis in order to increase the tracking range and reduce the energy illuminating the ground.

A further mode of operation is particularlyadapted to searching radar; and in sucha mode the pulses are transmitted aswell as received in sequence above and below the antenna axis with the angle errorfdetecting circuits disconnected and only fthe range circuits operating. The lobe switching in this mode will decrease by 4a factor of Vtwo the number of bars in the search scan required to cover a given vertical angle in space.

It may also be'readily seen that instead of ferromagnetic phase Shifters, ferroelectric phase Shifters may be used in which an electric field applied across a ferroelectric material, such as barium titanate in the waveguide, may change the dielectric constant of the ferrite and phase shift the waveguide by the desired 180 degrees.

What is claimed is:

1. A microwave high speed sequential antenna lobing system comprising; a reflective antenna having a focal point; a. plurality of waveguide sections having a.l common junctionfat one end of each of said waveguide sections;

a plurality of feed apertures arranged in close proximity to said focal point and coupled to respective ones of said waveguide sections at their ends opposite said common junction; a plurality of receiver channels; switching means interposed between said common junction and said receiver channels for sequentially coupling said junction to individual ones of said receiver channels; a ferrite phase shifter interposed in each of said waveguide sections for phase shifting, in response to a pulse, micro- Wave energy passing therethrough to thus shift the lobe of, said antenna; a pulsing and switch actuating means coupled to each of said ferrite phase Shifters and to said switching means for sequentially pulsing said phase Shifters and actuating in synchronism therewith said switching means to couple said junction to a predetermined one of said receiver channels in a manner such that each receivers output is a measure of signal strength received in the antenna lobe while shifted in a predetermined direction.

2. A high speed radar sequential antenna lobing system comprising: a plurality of receiver channels; scanning means including an array of a plurality of waveguides terminating in apertures for transmitting radar pulses and receiving echos thereof from a target and having a common junction at their ends opposite said apertures; a ferrite waveguide phase shifter interposed in each of said waveguides for phase Shifting, in response of four antennafeed `apertures arranged in close proximity to said focal pointandl terminating respective ones fof said waveguide `section at their ends opposite said cnr'nmon junction, the four apertures being ,disposed one immediately above the axis ofthe antenna,lone below the axis, one to the leftjof` said axis and one to the right of said axisyfour receiver channels; switching means interposed between said'common junction and said receiver channels for sequentially coupling, in response to an electrical pulse, said junction to respective individual vones of said receiver channels; a ferrite phase shifter in-V terposed in each of said waveguide sections for phase shifting in response to an electrical pulse, microwave energy passing therethrough in a manner to shift the direction. of the lobe of Said antenna; a pulsing and Switch actuating means coupled to each of said ferrite phase Shifters and to said switching means forpulsing sequentially said vphase Shifters and actuating in synchronism therewith said switching means for coupling said junction to oneof said receiver channels in a manner such that each channels output signal is a measure'of signal strength received in the antenna lobe while it is shifted in a predetermined angular direction. Y

4. VA microwave monopulse sequential antenna lobing system comprising: a reffective antenna of the 'character which Aeffects a directional lobe and having a focal point;

fcur waveguide sections having a common junction at'one end of each of said waveguide sections; an array of four antenna feed apertures arranged in close proximity tosaid focal point and terminating respective ones of said waveguide sections at their ends opposite said common` junction, the four apertures being disposed one immediately aboev the axis of the antenna, one below the axis, one to the left of said axis and one to the right Yofsaid axis; an up receiver channel, a down receiver channel, a left receiver channel and a right receiver channel; switching means interposed between said common junction and said receiver channels for sequentially coupling, in response to an electrical pulse, said junction to respective individual ones of said receiver channels; a ferrite phase shifter interposed in each of said waveguide sections for phase shifting, in response to an electrical pulse, microwave energy passing therethrough in a Amanner to shift the direction of the lobe of said antenna; a pulsing and switch actuating means coupled to each of said ferrite phase Shifters and to said switching means for pulsing sequentially said phase Shifters and actuating in synchronism therewith said switching means for coupling said junction to respective receiver channels in a manner such that each receivers output signal is a measure of signal strength received in the antenna lobe while it is shifted in a predetermined angular direction, said pulsing and switching network sequentially pulsing all of said ferrite phase Shifters in response to and during the time of a conventional range gate signal impressed upon said network from conventional range circuits of the system; an elevation error detecting cir cuit and an azimuth error detecting circuit, said elevation error detecting circuit being coupled to said up and v iowa ,Channels and Said azimuth effet dsteitlg eiwit being coupled to said left and right channels, said error detecting circuits being coupled to conventional antenna servos, said` elevation error detecting circuit comparing the levels o f signal strength returned from atarget while the antenna lobe is shifted in the respectivevertical direction and to-provide a D.C. signal to theantenna servos, the polarity of which is predetermined by. whether and electromechanical directional positioning means, a-

the target is above or below the antennaaxis and the tude of which is a measure ofthe angular distan?? OifV axisto electronically scan a region in which Va target is situated and to provide error signals representative 0f the angular position of the target off the antenna axis for controlling the angular positioning of the antenna in a mannerft'o null the error signals, the system :comprising: anantenn'a having a directive axis, a .focus point, and electromechanical directional positioning means,'a plurality Of four feed apertures supported on said antenna and symmetrically disposed in closep roximity to saidV focus point in a manner such that with respect to the antenna axis when pointing herizontally a first of said apertures is furthest upward, a second aperture is furthest downward, a third apertureis further leftward, and a fourth aperture is furthest rightward; a waveguide junction; four waveguide sections one each interposed between said apertures and saidjunction; a ferrite phase shifter interposed in each of said waveguide sections for phase shifting, responsive to an electrical pulse, microwaveV energy passing through the respective waveguide section in a manner to thus selectively electronically shift the direction of the antenna lobe; a pulsing and switching network individually coupled to each of said phase Shifters `for providing electrical pulses for sequentially actuating said phase Shifters and for providing a switching signal in synchronism with each of said electrical pulses.

6. A sequential antenna lobing system of the character for electronically scanning a region in which a target is situated and for providing error signals representative of the angular position of the target off the antenna axis for controlling the angular positioning of the antenna in a manner to null the error signals, the system comprising: an antenna having a directive axis, a focus point,

l 5. A sequential antenna lobing system of the character i piuraiity of four'feed apertures supported on said antenna and symmetrically disposed in close proximity to said focus, peint in `a manner such that with respect to the antenna axis when rpointing horizontally Va first of said apertures is furthest upward, a second aperture is vfurthest downward, a third aperture is furthest leftward, and a fourth aperture is furthestA rightward; a waveguide junction; four waveguide sections, one each interposed between respective ones of said apertures and said june:

tion; aifeirite phase shifter interposed in each of said waveguide sections for phase shifting, responsive to an electrical pulse, microwave energy passing through the respective waveguide section in a manner to thus selectively electronically shift the direction of the antenna lobe; a puising and switching network individually cou- Y pled to each of saidV phase Shifters for providing electrical pulses for sequentially actuating said phase Shifters and for previding aswitching signal in syn-` chronisrn with each offsaid electrical pulses; iirSt, secnd, third,l and fourth receiving channels; switching means responsive to said switching signal for sequentiall-y coupling said common junction to respective individual ones of said channels; an elevation error detecting circ uit coupled to said first and second channels and an azimuth detecting circuit coupled to said third and fourth channels, said elevation error detecting circuit comparing the relative amplitudes of signals received from the target when the antenna lobe is shifted upward Versus when said 'lobe is shifted downward and providing an antenna positioning control signal the polarity and magnitude of which are respectively determined by whether the target is angularly displaced above or below said antenna axis and by the angular magnitude of said displacement, said azimuth error detecting circuit similarly providing a control signal the polarity of which is determined by whether the target is angularly displaced off-axis to the left or to the right andthe magnitude of which is a measure of the amplitude of said angular displacement,

References Cited in the file of this patent UNITED STATES PATENTS www

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