US3453563A - Microwave energy phase shifter wherein the output energy is polarized in the opposite sense from the input energy - Google Patents

Description

35am WWW Mtg-Wm mass 'REFEREHQE July 1, 1969 3,453,563

MICROWAVE ENERGY PHASE SHIFTER WHEREIN THE OUTPUT ENERGY IS Sheet of 2 HA. MAURER POLARIZED IN THE OPPOSITE SENSE FROM THE INPUT ENERGY Filed March 2, 1967 PROGRAMMER QHE mEEPEou TRANSMITTER FIG 1 COLLIMATED AND STEERED BEAM COLLIMATED DIVERGENT BEAM PROGRAMMER TRANSMITTER RECEIVER AND STEERED BEAM FIG. 2

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8. NE IE [1| I- e woz o Emit 3+ 5 2 58 m 635 y 1, 1 H. A. MAURER MICROWAVE ENERGY PHASE SHIFTER WHEREIN THE OUTPUT ENERGY IS POLARIZED IN THE OPPOSITE sENsE FROM THE INPUT ENERGY Filed March 2, 1967 Sheet 2 of 2 INVENTOR HANS A. May/m? ar 2 5 M ATTORNEY n M oom M53". me: Om

MICROWAVE ENERGY PHASE SHIFTER WHEREIN THE OUTPUT ENERGY IS POLARIZED IN THE OPPOSITE SENSE FROM THE INPUT ENERGY Hans A. Maurer, Tarzana, 'Calif., assignor to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed Mar. 2, 1967, Ser. No. 620,027

"Int- Cl. H03h 7/18, /00

US. Cl. 333-3l 2 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF INVENTION The present invention relates to analog ferromagnetic or ferrite phase shifting devices adaptedto alter in a desired manner the propagation characteristics of transmitted and received high frequency electromagnetic Wave energy across the planar wave front of an electronically scanned phased array antenna. In recent years such antennas have achieved considerable usage in the long range communication as well as radar fields in view of the rapid scanning rates attainable without the use of any mechanical rn'ovable components. Planar antennas of considerable height and length utilize a considerable number of phase shifting elements to collimate and steer high electromagnetic wave energy in a predetermined wave front. Such phase shifters commonly employ discrete bodes of a ferromagnetic material which are magnetized generally in a longitudinal or axial direction by external electrical coils to vary the microwave permeability characteristics of the selected material. A good discussion pf the applicable antenna systems as well as prior art phase shifter devices of the ferromagnetic type may be found in the reference Survey of Electronically Scanned Aptennas, Parts 1 and 2, by Harold Shnitki'n, The Microwave Journal, December 1960, pp. 67-72 and January 1961, pp. 57-64.

In view of the fact that the invention to be described is dealing with the variable microwave permeability "of magnetized ferromagnetic bodies the term ferromggnetic shall be interpreted to include all metallic or insulating materials which exhibit a natural frequency of precession as a function of the magnitude of an applied DC field and an RF orthogonal magnetic field interacts with the precessing electron spins in determining the microwave permeability of a selected material. Such materials also refer to ferrites as well as the garnet types of materials and generically the term ferromagnetic shall include all such materials.

The behavior of discrete ferromagnetic bodies when magnetized and disposed in the path of electromagnetic energy with respect to the interaction phenomenon has been extensively described in the article entitled The Elements of Nonreciprocal Microwave Devices by C. Lester Hogan, Proceedings of the I.R.E., October 1956, pp. 1345-1368. It is therefore known that a circularly polarized electromagnetic wave interacts with the direc- 3,453,563 Patented July 1, 1969 tion of precession of the aligned electron spin axis of a magnetized ferromagnetic body to produce a first value of microwave permeability which is directly related to the off-diagonal components of the ferromagnetic permeability tensor. A wave propagated in the opposite direction interacts with the magnetized body to a lesser degree and produces a second value of microwave permeability. In view of the differences in accordance with the direction of wave propagation microwave ferromagnetic phase shifters are inherently nonreciprocal devices which imposes stringent requirements on operation of phased array antenna systems.

For the purposes of further clarification of this description of the invention, the term circularly polarized in reference to the electrical wave energy shall be considered to be the electric field of such waves which can be resolved vectorially into two orthogonal components of equal amplitude apart in space and 90 apart in time. It shall further be of interest in the discussion of the polarization sensitivities of the electromagnetic wave energy to point out that the term right-hand circular polarization is defined as an electromagnetic g'wave which is propagated in a manner similar to that of the ri-ghthand screw so that when traveling away from the observer the observed direction of rotation is clockwise. The term left-hand circular polarization will be considered as being in the opposite direction of rotation or counterclockwise.

It has become well known that rotation of the plane of polarization as well as phase shift of waves itransmitted through ferromagnetic ty'pe devices are functions of left and right-hand circularly polarized phase constants, fully and completely described in an article by N. Sakiotis and H.. N. Chait, entitled, Ferrite at Microwaves, Proceedings of the I.R.E., vol. 41, pp. 87-93, January 1953. With the disposition of a ferromagnetic body within a circular waveguide section for supporting circularly polarized waves and a unidirectional current applied to the windings of the external solenoid surrounding the waveguide a positive coil current and right-hand circular polarization will result in advancing the phase of the electromagnetic waves while a negative current will result in a phase delay. The term phase delay, of course, implies that the effective electrical length of the over-all phase shifting device has become longer due to the changes in the microwave permeability of the ferromagnetic material and phase advance; is simply negative phase delay. Conversely, left-hand circular polarization results in an output which is delayed in phase for positive currents and advanced in phase for a negative current. Since different values of phase shift are obtained for the positive and negative currents it may be noted that reversing the sense of the input circular polarization between righthand and left-hand has the same effect upon the phasecurrent characteristics as reversing of the coil currents.

Since present day ferromagnetic phase shifting devices are inherently nonreciprocal a need exists for a transmission and reflection type phase shifter for phased array antenna systems which is insensitive to the polarization of the waves transmitted through the device in either direction. Such polarization insensitivity will greatly enhance the value of all intelligence reflected from distant targets and assist in the rejection of rain clutter as a limitation in target definition.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention a phase shifting device is disclosed which is Wholly reciprocal. The device as will be hereinafter described in further detail embodies a plurality of discrete ferromagnetic bodies arranged in tandem combined with a polarization sense inversion structure spatially separating the bodies. An axial DC internal magnetizing field is applied to the respective bodies in exactly the same direction in a series-aiding manner. The resultant phase shift of propagated electromagnetic wave energy through the in-line ferromagnetic phase shifting bodies will be a net difference in phase shift for propagation of energy in either direction. The arrangement disclosed herein provides for a phase shift of an incoming circularly polarized electromagnetic wave traversing the first ferromagnetic body. After passing through the intermediate structure the polarization is reversed and the second in-l-ine ferromagnetic body subtracts the complementary phase shift from the first phase shift provided that both ferromagnetic bodies are excited with the same level of magnetic excitation.

The invention will be described with reference to a so-called lens-type array antenna system as well as a coupled or corporate fed type array antenna. It is expressly understood that the selection of the appropriate current values as well as the length of the ferromagnetic bodies shall be in accordance with well known principles to achieve a resultant differential phase shift and explicit teachings in that direction need not be incorporated in this description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention as well as the details of the construction of a preferred embodiment will be readily understood after consideration of the following detailed specification and reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a corporate fed type transmission array antenna system;

FIG. 2 is a diagrammatic presentation of a lens-type array antenna system;

FIG. 3 is a diagrammatic illustration of the embodiment of the present invention;

FIG. 4 is a graph illustrative of the phase-current characteristics of an illustrative embodiment of the invention; and

FIG. 5 is an isometric view with external structure partially broken away of an antenna phase shifting device in accordance with the teachings of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2, two systems utilizing a transmission type phase shifting device are illustrated. The array antenna 2 comprises a plurality of the analog phase shifters 4 of the type to be hereinafter described. A high power electromagnetic wave generator, shown generally as transmitter 6, is disposed in-line with the array antenna with the energy being distributed through a system of corporate fed networks indicated generally by the numeral 8. The signals indicated by the arrows are fed into one end of the phase shifters 4 and in view of the fact that circularly polarized energy may be preferred for such systems the requisite polarization deter mination means are of course provided in the corporate feed network. The individual phase shifting devices 4 are provided with electrical coils to provide a DC magnetic biasing field in the ferromagnetic material. The phase shifters are initially set for the desired phase shift by adjusting the coil currents through a computerized pro grammer 12 so that the effective electrical length across the surface of the array antenna will provide a collimated energy wave front designated by the letter A with the beam direction being designated by the arrow B. The dotted lines with the accompanying arrows are indicated in this illustration to show the direction of uncollimated energy propagated through the transmission type device without any accompanying phase shift for steering the resultant beam wave front in any desired manner.

FIG. 2 is illustrative of another transmission type of array antenna system wherein the transmitter is spatially di p sed with r spect to the ar ay ant n a with he e gy being directed by means of a transmission horn 14 to illuminate one end of the phase shifting device 4 with a diverging beam pattern indicated by numeral 16. The divergent rays are collimated and converted into a planar wave front of uniform phase as indicated by letter A with the beam direction indicated by arrow B. In this embodiment both a transmitter and receiver 18 have been collectivly diagrammatically represented since it will be evident that duplexing operation is permissible with the energy of the returning reflected signals being picked up at one end of the transmission type phase shifter and due to the reciprocal operation of such devices the energy will be propagated and reflected back towards the horn 14. Through the utilization of suitable two-mode transducer means together wit-h appropriate switching networks the return signals will be coupled to the receiver.

To achieve an understanding of the present embodiment of the invention reference is now directed to FIG. 3. The phase shifting device comprises a first ferrite body member 20 having a predetermined length in accordance with the desired value of phase shift desired. This body member will also be referred to as rod No. 1 and an axial magnetic field indicated by the arrow 22 is provided by a unidirectional current source coupled to electrical coil 24 which encircles the ferrite body member in a clockwise direction. A second ferromagnetic body member 26 is provided with an internal magnetic field indicated by arrow 28 which is applied by means of the coil winding 30. It is noted therefore that the two ferromagnetic body members 20 and 26 may be considered to be magnetically coupled in that the internal DC magnetization field ex" tends in a similar direction. Between the respective ferromagnetic body members a polarization sense inverter 01' rotator structure such as a 1r or 2 component delaying device is disposed and generally designated as 32. For the purposes of the remainder of the specification the ferromagnetic body member 26 will also be referred to as rod No. 2. The polarization inversion section 32 shall designate structure which provides for the direction of rotation of a circularly polarized wave to be reversed upon leaving body member 20. Therefore, if the input energy is right-hand circularly polarized wave energy it will be reversed and emerge from the over-all phase shifting device as left-hand circularly polarized wave energy.

The net resultant differential phase shift and its in dependence with respect to the polarization of the energy being transmitted through the device will best be under-- stood by reference now to FIG. 4 wherein the phasecurrent characteristics of the in-line tandem arrangement of two ferromagnetic bodies separated by a polarization sense inverter will be explained. The coordinates of the illustrative graph are phase shift along the vertical axis and current I along the horizontal axis. Curve 34 is a plot of the phase-current characteristics of the righthand circularly polarized wave energy (RH?) and as previously noted for negative current values a phase delay is provided while for positive current a phase advance is indicated. As is Well known in the art the term phase advance or negative phase delay is defined as a shortening of the electrical length of the phase shifter while phase delay implies that the electrical length of the phase shifter has become longer. Curve 36 indicates the phase-current characteristics for left-hand circular polarization (LHP) with a phase advance for negative coil currents and a phase delay for positive currents. In the description of the phase array antenna system it is preferred that the passive analog phase shifting elements be preset at a given value of coil current indicated by the symbol I and the dotted line 38 has been plotted for this value.

With right-hand circularly polarized input energy and positive current the first ferromagnetic body member designated rod No. 1 will provide a phase advance indicated by dotted line 42. The signals then traverse the polarization sense inverter section which converts the right-hand circularly polarized energy into left-hand circularly polarized energy. Upon traversing rod No. 2 we note that a phase delay b value is impressed upon the Wave energy as indicated by dotted line 40. The total phase shift through the transmission device then will be a phase delay as indicated by dotted line 44. It will also be evident that if a short circuit plate were placed behind one port of the device it could be adapted to a reflection type array and then we would have a traverse up and down with resultant net phase shift T= [2+1]- If left-hand circular polarization were applied to the phase shifter instead of right-hand circular polarized energy, rod No. 1 would provide a phase delay and the second ferromagnetic body or rod No. 2 would provide a phase advance for the same direction of coil current. Stated in another manner, the roles of the two rods Nos. 1 and 2 would be reversed but the phase shift through the device will still be a phase delay This latter condition will be exemplary of the returning signals to the antenna from outer space which would then be received by the output end and first contact ferromagnetic body member 26. It can be readily seen, therefore, that the phase shifting device is wholly reciprocal from the standopint of both current polarity and the polarization. For both transmission and reception then a linear superposition of the two complementary phase shift values occurs which are associated with one level ofmagnctic excitation. The invention described therefore will work equally well with either polarization of electromagnetic wave energy and hence reference is made to the fact that the said device is polarization insensitive.

FIG. 5 illustrates a preferred embodiment of the reciprocal phase shifting device of the present invention in a transmission or lens-type array antenna system. The reciprocal phase shifter 50 comprises a first ferromagnetic body member 52 axially disposed within hollow pipe circular waveguide 54, conventionally used for supporting circularly polarized waves, by dielectric means 56, such as Teflon, quartz or like materials. The internal DC magnetic field producing means comprises a solenoid 60 encircling the circular waveguide 54 and being energized by means of leads 62 connected to a unidirectional voltage source.

Next in line is the polarization sense inverter 64 which in the illustrative preferred embodiment comprises a 11' or M2 conductive plate member 66 angularly disposed along the wave propagation path defined by an extension of the circular waveguide 54 and designated 68. Matching transformer means such as illustratively a dielectric member 70 provides for the matching of the impedances of the ferromagnetic body 52 and the half-wave plate section 64. The input end of the over-all phase shifting element 50 is enclosed by a radiating element 72 preferably of a material having the impedance characteristice required to transform the free space electromagnetic energy to be propagated to the impedances of the circular waveguide. A material which as been widely accepted for this purpose is Rexolite or other similar composition materials.

Disposed in-line with the aforementioned components is the second ferromagnetic body section including the rod member 74 centrally positioned by dielectric means 76 within the circular waveguide 78. Solenoid 80 wound in substantially the same manner as the solenoid 60 is externally connected by means of leads -82 to the suitable unidirectional voltage source means. In accordance with the teachings of the invention the internal DC magnetic field provided by this solenoid member is similar in direction and magnitude to that provided for the first ferromagnetic body member. A dielectric spacer member 84 is disposed at one end of the ferromagnetic body member 74. A radiating element 86 is disposed at the output end of the over-all phase shifting device which would be the appropriate designation for the transmission cycle and the receiving end for the reflected signal returning. Members 84 and 86 are fabricated of similar materials as members 70 and 72. There is thus disclosed an exemplary preferred embodiment of an arrangement of two ferromagnetic body members in tandem and spaced apart by a polarization sense inverter structure to achieve reciprocal polarization insensitive operation in a phase array antenna system. In operational models a large number of the phase shifting elements similar to that shown in FIG. 5 together with appropriate circuitry for programming the phase shift value desired will be arranged along the planar wave front of the array antenna. It should be understood that while the invention has been described with relation to hollow pipe circular waveguides it will be equally applicable to other transmission line configurations having suitable polarization conversion means to the desired circularly polarized wave energy. Moreover, it will be obvious to those skilled in the art that any suitable polarization sense inverter means may be employed between the tandem pair of ferromagnetic body members. Accordingly, it is intended that all modifications, alterations or variations as may be practiced are included within the scope and spirit of the invention.

What is claimed is:

1. A transmission type ferromagnetic phase shifter comprising:

a section of waveguide transmission line for propaga= tion of circularly polarized electromagnetic wave eny;

first and second spatially separated body members of a ferromagnetic material arranged in tandem along the longitudinal axis of said waveguide;

means including energizing coils concentrically wound said waveguide adjacent to each of said ferromagnetic body members with a direct current in said coils being directed in a series-aiding manner to yield an internal magnetization excitation field of similar direction and magnitude within each of said body members; I

said circularly polarized energy traversing said first body member being oriented vectorially in one predetermined plane of polarization to yield a value of electrical phase shift;

means comprising a one-half wavelength polarization inverter member positioned between said first and second body members for rotating the propagated energy vectorially by to reverse the plane of polarization;

said energy traversing said second body member receiving another predetermined value of electrical phase shift;

the total combined phase shift value, of energy transmitted through the device in either direction being the net difference between the respective phase shifts provided by the first and second body members and having the opposite sense of polarization orientation from the wave energy first incident upon said wave-= guide section.

2. A variable electrical phase shifting device of electromagnetic wave energy comprising:

a section of circular waveguide;

first and second body members of a ferromagnetic material disposed in-line along the longitudinal axis of said waveguide;

said first and second body members being spatially separated by one-half Wavelength of the transmitted energy with a diametrically disposed conductive vane member positioned therein;

electrical coils concentrically wound around said waveguide adjacent to each of said ferromagnetic body members with said coils being interconnected in a series-aiding manner to result in an internal DC magnetization excitation field being directed axially Within said waveguide in substantially the same direction and level of excitation in each of said ferromagnetic body members;

7 said wave energy traversing said first body member being oriented vectorially in one predetermined plane of polarization and receiving a value of electrical phase shift; said wave energy traversing said second body member receiving another predetermined value of electrical phase shift; the total combined electrical phase shift value of energy transmitted through the device being the net diflerence between the respective phase shifts provided by the first and second body members and having a sense of polarization opposite to the polarization orientation originally impinging upon the circular waveguide section.

References Cited UNITED STATES PATENTS 3,089,104 5/1963 Allen 333-24.1 X 3,090,015 5/1963 Scharfman 33324.l X 3,212,031 10/1965 Reggia ct a1 333-241 X

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