US3740752A - Mode interferometer squinting radar antenna - Google Patents

Mode interferometer squinting radar antenna Download PDF

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Publication number
US3740752A
US3740752A US00219731A US3740752DA US3740752A US 3740752 A US3740752 A US 3740752A US 00219731 A US00219731 A US 00219731A US 3740752D A US3740752D A US 3740752DA US 3740752 A US3740752 A US 3740752A
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Prior art keywords
waveguides
coupling
waveguide
phase shift
section
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Expired - Lifetime
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US00219731A
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English (en)
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I Goldmacher
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RTX Corp
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United Aircraft Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/30—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array
    • H01Q3/34—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture varying the relative phase between the radiating elements of an array by electrical means
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
    • H01Q13/02—Waveguide horns
    • H01Q13/025—Multimode horn antennas; Horns using higher mode of propagation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/2664—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture electrically moving the phase centre of a radiating element in the focal plane of a focussing device

Definitions

  • Lateral displacement of the phase center of the electromatic wave feeding a reflector from a feed horn is 343/781 3 3 322 achieved by interference between a plurality of modes Fie'ld 778q781 created by combining suitably adjusted and mixed i waves from each of two waveguides into a single waveguide which is twice the width of either.
  • the displaced I v phase center provides a squint angle, off of boresight, ['56] NifE g g z z sE s giiE -N rs to the wave reflected from the reflector.
  • An initial method of scanning a radar beam includes orienting the antenna, including the feed horn and reflector, in the desired primary beam direction.
  • the phased array radar which, without a reflector, steers a beam in a desired direction by means of a single wave created by the interference of a plurality of individual waves of mutually different phases.
  • such antennas are known tob e quite costly because of the large number of relatively expensive phase shifters required toimp lement the antenna.
  • radar antennas have been provided with a squint? function which is the ability'to orient the beam in a direction slightly off the boresight of the reflector. This has been achieved mechanically, either by adjusting the lateral position of the feedhorn with respect to the reflector, or by adjusting the lateral position of the reflecthereover render the mechanical squinting antenna unsuitable in many applications.
  • the primary object of the present invention is to provide non-mechanical squinting to a beam of electromagnetic energy emanating from a reflector.
  • a complex waveguide assembly includes two channels with means disposed in at least one of them to provide a relative phase shift between the waves in'each of them, means for coupling a portion of the relatively phase adjusted wave in each channel into the other channel with an additional phase adjustment, the last named means feeding a combining waveguide section having a primary dimension substantially twice that of either" of the wave- 2 guide sections of the two channels, thereby to produce at least two modes of the original wave which interfere in a manner to provide a singlecombined wave, the effective phase center of which can be located laterally across the last section by adjusting the original mutual phase difference between the waves.
  • phase adjusted coupling means may comprise a short slot cross coupler providing coupling of substantially 50 percent of each wave into the other channel'and a 90 phase shift.
  • the mixing sec tion includes means to provide. electrical tuning thereof, thereby to support a less dominant mode therein.
  • the invention provides a relatively simple and low cost means of achieving beam squinting. It may be electronically adjusted at high speeds, and can be extremely accurately controlled.
  • FIGS. 1-4 are illustrations of transverse electromagnetic waves relevant to the present invention
  • FIGS. 5-7 are schematicized illustrations of the effects of lateral displacement ofan approximate phase ce'nterof a wave illuminating a reflector
  • FIG. 8 is a simplified, partially broken away perspective view of one embodiment of the present invention.
  • an' end view of a waveguide 10 has super posed thereon amplitude vectors 12 illustrating an electromagnetic wavein a TE mode.
  • the end view of the waveguide 10 has superposed thereon amplitude vectors l4 illustrative of an electromagnetic wave in the TE mode.
  • the amplitudes of the waves add vectorially so as to produce a single combined wave as illustrated by the dashed line 16.
  • the TE mode is shown as being so related to the TE mode that the left half of the TE mode is in phase with the TE mode.
  • the configuration of the total wave shape can be shifted so as to achieve a total wave having a different mode configuration as illustrated by the dashed line 18 in FIG. 4.
  • the position of the maxima of the waves 16 and 18 represent the maximum displacements to the right and the left (as in FIGS. 3 and 4).
  • Adjustments in phase between and 180 Of the T mode would provide total waves having amplitude maxima inbetween those of the two waves 16, 18.
  • adjusting the phase of the TE mode relative to the TB mode can adjust the lateral position of the maxima of the total wave.
  • This maxima can be considered, in terms of a'feedhorn feeding a reflector in a radar antenna, as a phase center of the wave emanating from the feedhorn toward the reflector, in an approximate sense. That is to say, one can consider the phase-center to be the point of maximum amplitude of a transverse wave emanating from a feedhorn toward a reflector. 7
  • phase center of the energy illuminating a parabolic'reflector produces a phase change of the energy in the aperture plane of the antenna, which changes the direction of the secondary pattern (the reflected energy) as it leaves the reflector.
  • the present invention is predicated onutilizin'g the shifting of the approximate phase center in the illumination of a reflector so as to alter the direction of the primary wavefront from the reflector, thereby to provide mode interferometer control over the direction of the wavefront.
  • FIG. 6 illustrates that with the phase center of thewave 28 emanating from the feedhorn shifted laterally (in a manner similar to that illustrated in FIG. 3), then the approximate phase center of the wavefront is similarly shifted (upward in FIG. 6).
  • FIG 7 illustrates that shifting of the maximum amplitude of the wavefront emanating from the feedhorn 20 (as illustrated by the dashed line 32) downwardly as seen in FIG. 7, causes'an opposite affect to'that illustrated inFIG. 6 so that the reflected wave is reflected at an angle whichis upward (as seen in FIG. 7) from. the boresight of the reflector 22, as illustrated by the arrows 34.
  • the configuration of the wavefront emanating from a waveguide or a feedhorn may be altered in a number of ways.
  • One preferred embodiment of apparatus suitable for producing the desired mode interference in accordance with the present invention is illustrated in FIG. 8.
  • the feedhorn 20 is seen to comprise the final section (designated E in FIG. 8) of a complex waveguide assembly 21.
  • radiation enters the complex waveguide assembly 21 through openings 33, 34 at a proximal end 35 thereof, which comprises two separate waveguides along section A of the complex waveguide assembly.
  • both of the waves are of the type illustrated in FIG. 1 (TE,,, mode) and in phase with each other.
  • These waves may be derived from a single waveguide in a given radar system by using a short slot coupler (of the type well known in the art) with a suitable phase shift, or by using a Y split-v ter; or by use of any other known meansto achieve two separate waves from one.
  • a phase shifter 44 is disposed.
  • This may suitably comprise a ferrite section 46 having an electrical winding 48 therethrough and a pair of matching sections 50, 52 disposed on opposite ends of the ferrite 46.
  • Such a structure is disclosed in a copending application of the same assignee entitled A TEMPERATURE STABI- LIZED LATCI-IING PHASE SHIFTER, Ser. No. 185,974, filed on Oct. 4, 1971 by Peter W. Smith.
  • phase shifter 46 of a reciprocal type, (or of a nonreciprocal type with a suitable switching provision made therefor) may be utilized as desired to suit any implementation of the present invention. Control over the amount of phase shift within the phase shifter 46 is dependent upon the magnitude of average current through the device, which can be controlled with a DC current intensity or with pulsewidth modulation, in any known fashion that is found suitable.
  • the current winding 48 may be suitably controlled by a squint control circuit 54, which may comprise a simple, manually ad justed current control (such as a potentiometer) or it may comprise a more complex control mechanism such as a well known beam steering computer suitably adv justed to control current.
  • a squint control circuit 54 may comprise a simple, manually ad justed current control (such as a potentiometer) or it may comprise a more complex control mechanism such as a well known beam steering computer suitably adv justed to control current.
  • a short-slot coupler is provided due to the fact that a pair of metallic walls 56, 58am separated, or spaced apart, so that radiation in each waveguide spills into the other, on a substantially fifty fifty basis, with a phase lag in the transmitted portion of the wave. That is, a wave entering through the opening 33 will provide 50 percent of its power into a channel 59 of the waveguide; and that portion of the wave transmitted into the waveguide channel will have a 90 phase lag with respect to the original wave that passes through the phase shifter 46, and with respect to the other half of the wave in a channel 60 of the waveguide.
  • the wave entering through opening 34 is similarly split.
  • the next section, D again has the waves separated into two waveguide sections, one of which includes a second phase shifter 61 in which the electrical winding 62 is controlled in a constant fashion by a voltage source 64 so as to provide a constant phase shift through the phase shifter 60 of substantially 90.
  • the last section, E is a single waveguide, having twice the dimension of the individual waveguide sections (33,
  • the two waves that enter the final section, E are TE mode waves each having an amplitude and a phase which is dependent upon the variable phase shift provided-by the phase shifter 46 and the fixed phase shift provided by the phase shifter 60, the losses in these phase shifters, the fact that 50 percent of the power of one is coupled into the other in section C, and so forth.
  • These waves are of varying amplitude and phase (both absolutely and with respect to each other) as a function of the control provided by the squint control 54 to the phase shifter 46.
  • relative phase shifts between the two channels of O to 180 are desired; this can be achieved by adjusting the phase shifter 46 commensurately between 0 and 180.
  • the two TE modes enter section E from the respective waveguide channels, they interfere with each other so as to produce a single TE mode across the entire dimension of section E and a TE mode across the entire section which is equivalent to two TE modes as they enter at 180 phase shift to each other, as illustrated in' FIGS. 3 and 4 and described hereinbefore.
  • These waves add together and result in a total wave (which is of the type described and illustrated by dashed lines in FIGS. 3-7 hereinbefore) emanating through the open, distal end63 of the waveguide.
  • the invention may be more simply derived, if desired, by using separate waveguides for sections A, B, D and E with a known short slot coupler inserted inbetween the separate waveguides as a substitute for the section C.
  • the TE mode has no trouble existing in section E of the complex waveguide assembly
  • the TE 7 mode in section E can be sufficiently perturbed by the wall 58 so as to attenuate it significantly unless tuning is provided.
  • a tuning screw 68 may be adjustably inserted through the bottom (or top) of the waveguide. As is known in the art, a variable amount of insertion will tune section E to promote the existence of the TE mode.
  • the screw 68 may be located along the central axis somewhere midway between the end of the wall 58 and the opening 62.
  • the phase shifter 46 is preferably located very near to the right end of the separating wall 56.
  • the phase shifter 60 should be located some distance from the right-hand end of the separation wall 58 so that the high dielectric constant of the phase shifter 60, making the waveguide appear to be wider than it really is, will not allow penetration of high order modes into that section of the waveguide.
  • a free length of waveguide to the right (as seen in FIG. 8) of the phase shifter 60, with air dielectric therein, provides an electrical width which is too short to support other than the TB", mode of'the individual waveguide.
  • phase shifters 46, 61 may be found to be advantageous, because of the heavy loading that the losses in the phase shifters 46, 61 provide to one channel to provide similar losses in the other channel.
  • dielectric may be inserted in the unshifted channel (34, 59) simply to provide a loss match between the two channels, or, the significant thing is only the relative phase shifts and amplitudes between the two waves is significant (and not their absolute values), phase shifters with a fixed phase shift and dielectric loss may be put into the channel (34, 59) for operation differentially with the phase shifters 46, 60.
  • phase shifter 46 may be left in the position shown, and the phase shifter 61 may be put in the channel 59, instead of as shown. The only difference then would be a different phase required within the phase shifter 46 which is accommodated by the particular current provided by the squint control 54.
  • the cross coupler (section C) preferably provides a substantially 50 percent split of the energy in each channel (causing a coupling of half of the energy of each into the other). Otherwise, there is a tendency for the amplitude of the TE mode in section E to not be equal to the amplitude of the TE section mode in section E.
  • the phase shifter 61 being set for a phase shift of 90 on the other hand, if other than substantially a 50 percent coupling is provided in section C, this can be accommodated by adjusting, on a dynamic and continuous basis the phase provided in the phase shifter 61. Since this is a complex function to perform and may be very costly, it is preferable to repercent inter-channel coupling in section C.
  • the length of the void between the walls 56, 58 is on the order of half a waveguide wavelength (as is known, for a given frequency, the wavelength is longer in the waveguide than it is in free space, and as used herein wavelength refers to the waveguide wavelength).
  • phase shifter 61 Since the nature of the phase shifter 61 is dependent upon the precise apparatus used to provide cross coupling between the two channels, it may be considered together with cross coupling means as a means for providing cross coupling at a given phase shift; in that context, the areas and 71 on opposite sides of the wall 58 which extend beyond any phase shifter 61 may be considered to be a pair of waveguides fed by the cross coupling and phase adjusting means.
  • Apparatus for coupling electromagnetic waves between waveguides and a reflector comprising:
  • a first section comprising a first pair of waveguides and means for providing a variable relative phase .shift between waves in'said waveguides, said waveguides each being of substantially the same primary dimension;
  • a second section comprising a second pair of waveguides having the same primary dimensions as said first pair of waveguides and means for providing a relative phase shift to wave energy in said second pair of waveguides;
  • a fifth waveguide having a primary dimension substantially twice that of said first and second waveguides, said fifth waveguide connected to said second pair of waveguides.
  • tuning means in said fifth waveguide adapted for adjustment to electrically tune said fifth waveguide to support a desired wave therein.
  • Apparatus for coupling electromagnetic waves be tween waveguides and a reflector according to claim 1 wherein said short slot coupler provides coupling of substantiallySO percent of the wave energy in each one of said first pair of waveguides with each one of said second pair of waveguides.
  • phase shift means of said second section comprises means for providing a substantially 90 phase shift.
  • variable relative phase shift means is adjustable to provide relative phase shifts of approximately to approximately 180.
  • Apparatus for coupling electromagnetic waves between waveguides and a reflector comprising:
  • a first section comprising first and second waveguides and means for providing a variable relative'phase shift between waves in said waveguides, said waveguides beingof a primary dimension to support a TB mode of a wavetherein;
  • a second section comprising third and fourth waveguides having substantially the same primary dimension as said first and second waveguides;
  • coupling means for coupling and phase shifting wave energy between said first section and said second section, said coupling means coupling a substantial portion of wave energy in said sections between said first and fourth waveguides with a substantial phase shift, coupling a substantial portion of wave energy in said sections between said second and third waveguides with a substantial phase shift, coupling a substantial portion of wave energy in said sections between said first and third waveguides .with a minor phase shift and coupling a substantill portion of wave energy between said second and fourth waveguides with a minor phase shift, said coupling means providingan additional relative phase shift between wave energy in said third waveguide and wave energy in said fourth wave guide; and
  • tuning means in said fifth waveguide adapted for adjustment to electrically tune said fifth waveguide to support a desired wave therein.
  • Apparatus for coupling electromagnetic waves between waveguides and a reflector according to claim 8 wherein said additional relative phase shiftmeans comprises means for providing a substantially phase shift.
  • variablerelative phase-shift means is adjustable to provide relative phase shifts of approximately 0 to approximately fifth waveguide having a primary dimension sub-

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US00219731A 1972-01-21 1972-01-21 Mode interferometer squinting radar antenna Expired - Lifetime US3740752A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2626926A1 (de) * 1976-06-16 1977-12-29 Licentia Gmbh Verfahren zur steuerbaren strahlschwenkung bei reflektorantennen
FR2594260A1 (fr) * 1981-05-22 1987-08-14 Thomson Csf Source primaire hyperfrequence pour antenne a balayage conique et antenne l'incorporant.

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2981946A (en) * 1947-09-30 1961-04-25 Rca Corp Antenna feed system
US2994869A (en) * 1950-05-23 1961-08-01 Orville C Woodyard Microwave antenna system
US3423756A (en) * 1964-09-10 1969-01-21 Rca Corp Scanning antenna feed
US3530483A (en) * 1967-07-13 1970-09-22 Csf Multimode monopulse horn antenna

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2981946A (en) * 1947-09-30 1961-04-25 Rca Corp Antenna feed system
US2994869A (en) * 1950-05-23 1961-08-01 Orville C Woodyard Microwave antenna system
US3423756A (en) * 1964-09-10 1969-01-21 Rca Corp Scanning antenna feed
US3530483A (en) * 1967-07-13 1970-09-22 Csf Multimode monopulse horn antenna

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2626926A1 (de) * 1976-06-16 1977-12-29 Licentia Gmbh Verfahren zur steuerbaren strahlschwenkung bei reflektorantennen
FR2594260A1 (fr) * 1981-05-22 1987-08-14 Thomson Csf Source primaire hyperfrequence pour antenne a balayage conique et antenne l'incorporant.

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GB1362926A (en) 1974-08-07

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