US2787765A

US2787765A - Magnetically controlled ferrite phase shifter having birefringent properties

Info

Publication number: US2787765A
Application number: US304609A
Authority: US
Inventors: Arthur G Fox
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1952-08-15
Filing date: 1952-08-15
Publication date: 1957-04-02
Anticipated expiration: 1974-04-02

Description

A1911] 2, 1957 A. G. FOX 2,787,765

MAGNETICALLY CONTROLLED FERRITE PHASE SHIFTER HAVING BIREFRINGENT PROPERTIES Filed Aug. 15, 1952 2 Sheets-Sheet 1 uvvavron A. 6. FOX

AT ORNEV April 2, 1957 2,787,765

A. G. F OX MAGNETICALLY CONTROLLED FERRITE PHASE SHIFTER HAVING BIREFRINGENT PROPERTIES Filed Aug. 15, 1952 2 Sheefs-Sheet 2 lA/l ENTOk A. 6. FOX 1 ATT RNEV phone Laboratories, Incorporated, New York, N. Y., "a corporation of New York Application August 15, 1952,"Serial No. 304,609 11 Claims. "c'l. sea -i1 This'in'vention relates to guided electromagnetic transmission systems and, mere particularly, to phase changing or phase shifting devic'es for use' in such systems.

"It 'is'an object of the invention to introduce an easily adjustable value of phase shift which may be either leading or lagging, fixed or continuouslyvariable, to energy conveyed along said systems.

Continuously variable phase changers by means of which the phase of an output'wave may be shifted with respect to the input wave are an essential component in "the electrornagnetic wave transmission art. Such phase changers heretofore have involved mechanically moving parts and were, therefore, inherently restricted tolimited degrees ofphase shift and to relatively low speeds of possible variation.

'Another object oftlie invention isto shift the phase "at an electromagnetic Wave over a range may l excec'd one cycle of phase shift 'by an entirely electrical- 1y, controlledfphase changer. h o

, I t 'is'a further object of the invention to vary the value of'phase shiftintroduced at an arbitrarily rapid rate.

"Inaccordance with the invention, the'unus'ual prop- "erties of ferromagnetic materials in the' presence of'excitingmagnetic fields are utilized. In one embodiment, including the several variations thereof to be described fin det ail hereinafter, linearly polarized "waves a're converted to circularly polarized waves, applied to an element of ferromagnetic material which excited by'a transverse'magnetic field, and then recenve rted to linearly polarized waves. The instantaneous phase shift iutroduced by this/combination dependsjupon the instantaneous angular relationship of the applied field to the polar- "ization of the waveenergy. Special-features of the invention are found in the means forj electrically, rapidly and continuously varying' this angular 'relationship'to terre'spshain w vary the ihtrbducdphase shift.

These and other objects and features of the present invention, thenature of the invention and its advantages, will appear more fully upon consideration of the various specific illustrative embodiments shown in the accompanying drawings and of the following detailed description of these drawings.

In the drawings: I p Fig. 1 is a perspective view of a variable phase'shifter,

inaccordance with theinvention, for introducing a variafble phase shift to electrical energy traversing therehr h; a M r V Fig. Zjis a schematic representation, given forthe purp o seof explanation, of a portion of the phase-shift'erof Fi 1; v

iig. 3 represents an alternative variationof thephase shifter in Fig.1,'in accordance with theinventiomtby' illustrating a structure which may *be substituted for certain components of -Fig;--l; y

" Fig. 4 illustrates suitable means for producinganelecjtrically' controlled rotating magnetic field, in accordance with the invention, which "may be incorporatedin the phase shifter'of Fig. 1;

tangular guides

12 and 13.

7 2,787,765 Patented Apr. :2, 45957 2 Fig. S :is a perspective view'of aphase shifter, inaccordance with the invention, for introducing a rapidly varying, electrically controlled phase shift to electromagnetic wave energy; and

Figs. 6A and 6B represent alternative modifications of Fig. S,in accordance with the invention.

In more detail, Fig. 1 illustrates an embodiment of a variable phase shifter-in accordance with the invention comprising a section of waveguide 11, which maybe of circular cross-section, interposed between suitable transmission means for supporting linearly polarized electromagnetic waves and for applying these waves with a-givenipolarization to guide 11. These transmission means are illustrated in'the embodiment of Fig.1 as sec tions of

rectangular wave guides

12 and 13 which each tapersmoothly and gradually into the circular crosssection of guide ilto which they'are integrally connected.

Rectangular guides Hand 13 will accept or support only linearly-polarized waves in which the electric vector, which determines the plane of polarization of the wave,

is parallel to the short side of the rectangular Wave guide.

The dimension of guide 11 is preferably chosen so that only the "various polarizations of the dominant TEn mode in circular guide can be propagated. By means of the smooth transitionfrom

rectangular guides

12 and 13 to circular guide La TEw mode, in either rectangular guide 12 M13 may be coupled to and from the T1311 mode in circular-guide 11 which has-a similar or parallel "polarization. ;It is obvious to one skilled in the art that any of a number of other Well-known couplingmeans having polarization selective transmission characteristics may be employed-in lieu of

rectangular guides

12 and 13 to couple a'linearly'polarized wave tothe proper polarization in circular guide 11.

in plaues inclined-at acute angles off-45 degrees to the plane of polarization of wave energy supported in rec- Surrounding guide-11in the vicinity of element 35 is a means for producing a=constant transverse-magneticfield passing through element 15 in a plane inclined at a variable angle 6 'toathe plane of polarization of wave energy supported in

guides

12 and 13. As illustrated-in Fig. 1, these fieids may be supplied by permanent magnet structures having concentrated pole pieces N and S bearing against the outside wall of guide 11 along narrow, oppositely disposed areas. Thus. the'magn'etic fields for elements i4 and r6 are supplied by magnet structures 17 and l8,"respectively, each having their pole pieces inclined at a fixed 45 degree angle. 'The field fo-r element 15 is supplied by magnet 19 Which"isrotatably mounted on guide 111 to provide for *the' variable angle 0.

-El'ements 14, "15 and '16 may each be blocks of fer- "-ro'magnetic'material or the type exhibiting a Faradayeffect rotation when in the presence of a longitudinal magnetizingffield. These materials comprise aniron .spinel oraferrite. 011 the basis of their electrical properties, a particularlysuitable designationaof this class of materials is igyromagnetic to designate materials having electrons capable ofbeing aligned byan external magnetic field'and capable of exhibiting the precessional motion of a gyroscopic pendulum. As a specific example, elements 14, 15 and 16 may each be cylindrical blocks of nickel-zinc ferrite prepared in the manner disclosed in the copending application of C. L. Hogan, Serial No. 252,432 filed October 22, 1951, which matured into United States Patent No. 2,748,353, May 29, 1956. It has been determined that when these materials are excited by a transverse magnetic field, they exhibit a permeability constant of one value to electromagnetic energy components polarized parallel to the exciting magnetic field and a different value to electromagnetic energy components polarized perpendicular to the field. This effect may theoretically be explained by the assumption that the ferromagnetic material contains unpaired electron spins which tend to line up with the applied magnetic field. An electromagnetic wave having its magnetic vector in the direction of the magnetic field (the electric vector perpendicular to the magnetic field) will be unable to reorient the electron spins to any appreciable extent and, hence, will see a permeability close to unity regardless of the strength of the magnetic field. A wave having its magnetic vector at right angles to the magnetic field will cause the electron spins to precess about the axis of the magnetic field in synchronism with the applied electromagnetic wave. a permeability substantially different from unity because the precessing spins now yield a component of radio frequency flux density along the waves magnetic vector. The amount of difference from unity will be determined by the strength of the magnetic field.

Since the phase velocity of a wave passing through a material depends upon the permeability of the material, a wave traversing the ferromagnetic material of element 12 with its electric vector polarized parallel to the magnetic field will exhibit a higher phase velocity than the wave polarized perpendicular to the magnetic field. An element having this property, namely, the ability to transmit two sets of waves polarized at right angles to one another with different speeds, will produce two different phase delays for the two polarizations and, accordingly, may be termed a differential phase shift element. The value of this phase shift difference for a ferromagnetic element is approximately proportional to the thickness of the material traversed by the waves and to the intensity of the magnetization to which the material is subjected. It may be shown by mathematical analysis provided the frequency of the wave energy is substantially greater than the gyromagnetic resonance frequency of the ferromagnetic material, that this phase difference expressed in radians is substantially given by the expression it]. 7 114 112E111] 2 in which I is the thickness of the material in meters, 5 is the dielectric constant of the material, is its permeability without exciting magnetic field, M is the saturation magnetization of the material, H is the exciting magnetic field, 0. represents the frequency of the wave energy and 7 is the spectroscopic splitting factor of the material. In accordance with the invention, the differential phase shifts of elements if. and 16 are made equal to 90 degrees and the differential phase shift of element is made equal to 180 degrees, by properly choosing the thickness of the elements and the strength of the magnetic field applied to each, either by calculations in accordance with the above expression, or by adjustments on an empirical basis.

The apparatus thus far described serves to introduce a time phase shift to electromagnetic wave energy transmitted therethrough of two times the angle 0. If 0 is continually varied by rotation of magnet 19 a continuous change in phase will be produced. This operation may most easily be analyzed by following the path of a linearly Such a wave will see polarized wave introduced by way of guide 12 and leaving the phase shifter by way of guide 13. The effect of degree differential phase shift element 14 is to convert this linearly polarized wave into a clockwise rotating circularly polarized wave. A complete and detailed explanation of this effect is given in my copending application Serial No. 301,726, filed July 30, 1952. The clockwise rotating circularly polarized waves are then applied to the degree differential phase shift element 15. In order to understand the effect of element 15 upon these waves, certain properties of a 180 degree differential phase shift section must be examined. This examination may most readily be made with reference to the schematic representation of Fig. 2 which shows the 180 degree differential phase shift element 15 separated from the other components of Fig. 1.

Referring therefore to Fig. 2, the axis A designates the plane of wave energy of greatest phase velocity, i. e., under the conditions described above, the electric polarization of wave energy parallel to the exciting magnetic field while the axis B designates the plane of wave energy of smaller phase velocity, i. e., the electric polarization of wave energy perpendicular to the exciting magnetic field.

Assume first that linearly polarized waves represented by vector E are being introduced from the left of the section, and these waves are polarized at anangle 0 clockwise from axis A. Vector E may be resolved into components a and b along axes A and B, as shown on Fig. 2. Since the A-axis component travels at higher speed than the B-axis componennupon emerging from the other end of the section, b lags behind a by 180 degrees or one-half wavelength. Hence, at the position of a the B-axis component will be pointing in the opposite direction from b, as indicated by 12. Now, when a and b" are added vectorially, the resultant will be a linearly polarized wave represented by E polarized at an angle 0 counterclockwise from the A axis. Thus, the effect of a 180 degree differential phase shift section upon linearly polarized waves is to cause a rotation of the angle of polarization in the direction of the A axis by 20, or twice the angle between the A axis and the input polarization. (The B axis could equally well have been chosen as the reference axis, and the same result would have been obtained.) If the input polarization remains fixed, rotation of the phase shift axes by angle 0 will cause a rotation of the plane of the output polarization by twice 0.

Instead of a linearly polarized input, however, a clockwise-rotating circularly polarized wave is applied to element 15. This circularly polarized wave may be thought of. as a linearly polarized vector which, however, is rotating in the clockwise direction. Since the angle between this input vector and axis A is constantly increasing in the clockwise direction, the analysis of the linearly polarized wave above shows that the angle of the output vector is constantly increasing in the counterclockwise direction. It is, therefore a property of the 180 degree differential phase element that it converts clockwise circularly polarized waves into counterclockwise circularly polarized waves. Furthermore, an examination of the field patterns existing at a particular instant in time will indicate that the instantaneous angle of the output vector of the circularly polarized wave will depend upon the instantaneous angle of the input vector with respect to the principal axes of the section. Therefore, by rotating the phase shift axis of the section by an angle 0 the instantaneous output polarization will be rotated by an angle 20.

The circularly polarized waves emerging from element 15 are reconverted into linearly polarized waves by the 90 degree differential phase shift element 16. As disclosed in my abovementioned copending application, the emerging linear wave is polarized at an angle of 45 degrees to the planes of phase shift of element 16 and is, therefore, in the proper orientation for passage out guide 13. The instantaneous phase of this wave in guide 13 depends upon the time of transmission through element 16 and also upon the instantaneous phase of the wave at the input of element 16. But the instantaneous phase of the input circularly polarized wave depends upon, and is the same as, its instantaneous polarization or orientation at the input of element 16.

As pointed out above with particular reference to Fig. 2, this instantaneous orientation depends in turn upon the incidence angle of the wave at the input'of element 15 with the principal planes of phase shift therein. Since the position of these planes are determined by the applied magnetic field, when the field is rotated through angle 6, a total angle displacement of 20 Will be introduced between the rotating electric vector found at the output of element 14 and the vector found at the input to element 16. Thus, a time phase of 20 is introduced between the linearly polarized wave in guide 12 and the linearly polarized Wave in guide 13. This time phase is in an advanced sense if the angle 6 is in the direction of rotation of the circularly polarized wave leaving element 14. or is in retarded sense if 0 is in the opposite direction. All that has been said holds for any state of polarization of the input of element 15 so it also holds at any instant if the planes of phase shift of element 15 are continuously rotated. There is then no limit to the range of phase control obtainable and continuous rotation of magnet 19 will cause continuous retardation or advancement of the phase. Also continuous rotation of magnet 19 at a constant speed will cause a fixed increase or decrease in the frequency of the transmitted wave. Furthermore, waves passing through the assembly of Fig. 1 will suffer the same phase shift regardless of the direction of transmission therethrough.

While the ferromagnetic means for converting between linearly polarized waves and circularly polarized waves of my above-mentioned copending application have been shown in Fig. 1 by way of illustration, it should be noted that other converters or transducers may be employed. for example, Fig. 3 shows a 90 degree difi'erential phase shift section which may replace elements 14 or 16 and their associated magnetic fields. In Fig. 3 the phase shift section comprises two oppositely positioned metal fins 3t) and 31, each extending perhaps one-fourth of the way across wave-guide section 32 which would replace a length of guide 11 of Fig. 1. Fins 30 and 31 produce a kind of capacitative loading and, accordingly, reduce the velocity of wave energy polarized parallel to the fins, the principal plane of phase shift of the section. The lengths of fins ill and 31 are such that a 90 degree phase shift is intro duced to this wave energy relative to the wave. energy polarized perpendicular to the fins. Each of fins Eltl and 31 may be tapered or introduced by a quarter wave transformer to prevent reflection loss at the edges thereof. When the plane of fins 3t) and 31 is oriented at an angle of degrees with respect to the linear polarization in guide 12, this wave energy is converted into circularly polarized waves.

in the embodiment of Fig. 1, the angle at which the transverse magnetic field is applied to element 15 i varied by physically rotating magnet 19 upon guide 11 by suitable mechanical means. A special feature ofthe invention resides in the combination by which the applied magnetic field is rotated electrically.

Referring to Fig. 4, an electromagnetic field source is shown which may replace magnet 19 of Fig. 1. As illustrated in Fig 4, this source comprises a magnetic core structure as having, for example, four internally directed pole pieces 41, 42, 43 and 44, preferably equally displaced to bear upon the periphery of guide 11 along narrow oppositely disposed longitudinal lengths of the outside wall thereof when structure 40 is incorporated into. Fig. l in place ofmagnet 19. Upon pole pieces 41, 4 2, 43 and 44 are placed turns of wire constituting solenoids 45, 4.6, i! and d8, respectively. QpposltesolenoidsdS and 47 are connected together to a source49 of exciting alternating current. The remaining solenoids 4.6 and 48 are connected together to source 49 through phase shifter 50 introducing a degree time phase to the currents supplied to solenoids 46 and 48 with respect to the current supplied to solenoids 45 and 47. Shifter 50 may be simply a circuit of passive reactance elements proportioned to produce the desired 90 degree lead or lag in current. The resultant magnetic field produced by the sum of the field from 45 and 47, and 46 and 48, will rotate about the longitudinal axis of structure 4-0 at the frequency of source 49. Thus, a continuously variable phase shifter is provided which is entirely electrically controlled and which involves no moving parts. The phase change produced will be 41rradians per cycle of the frequency of source 49.

The rotating magnetic field produced by either permar nent magnet 39 of Fig. l or the electromagnetic of Fig. 4 is suitable for exciting element 15 within guide 11 if, the phase is to be changed slowly requiring a slow orientation of the magnetic field. However, if the phase is to he changed rapidly and continuously as might be required for continuous scanning in radar equipments, eddy currents set up in the conductive walls of guide 11 would tend to prevent the magnetic field from penetrating the ferromagnetic element therein. In the embodiment of the invention shown in Fig. 5 this ditficulty is avoided.

Referring to Fig. 5 a phase changer is shown which is electrically identical so far as its principles of operation are concerned to the phase changer disclosed with ref erence to Fig. 1. In the embodiment of Fig. 5, however, the conductive shield is removed by employing the alldielectric wave guide techniques as disclosed in my copending application Serial No. 274,313, filed March 1, 1952.

As there disclosed, electromagnetic Wave energy, when properly launched upon a strip or red of all-dielectric material, i. e., a rod without a conductive shield, will he guided by the rod with a portion of the energy conducted in a field surrounding the rod. it has been determined that they ferromagnetic materials herein considered may also serve as guiding structures. liecause these materials have a much higher index of refraction than the more commonly employed dielectric materials, a sufficient amount of the wave energy will travel within the ferremagnetic material to be substantially affected by its permeability. Therefore, a differential phase shift will. he introduced to the energy by the planes of difierent per. meability.

In Fig. 5 dominant mode ener y in rectangular metallic guide 51 is coupled to dielectric guide 52 of round cross-section by means of horn 53 comprising a flared out end of guide 51. Dielectric rod 52 is pushed through horn 53 to extend several Wavelengths into guide 51. The match between guide 51. and guide 52 is improved by providing a taper 54, extending along several wavelengths of the portion of guide 52 within guide it. Guide 52 may consist of any dielectric material having a dielectric constant substantially different from that of air, such as polyflex, polyethylene, tomention only two specific materials. Guide 52 is joined, as a continuation thereof, to rod 55 of ferromagnetic material having a round cross-- sectional dimension similar to that of guide 52.

Since, as noted above, ferromagnetic guide 55 has a much higher index of refraction than the adjoining dielec tric guide 52, a tapered joint 56 extending along several wavelengths is. desirably employed at the point of tunetion of two materials to prevent excessive radiation losses; A similar taper 57 connects the other end of ferromagnetic rod 55 to dielectric guide 58 which. is connected.

by. horn 5:9 to. rectangular metallic guide 6t).

Permanent magnet structures 61 and 61', which may be identical to structures 17 and 18 of Fig. l, are located at spaced points on red 55 with their pole pieces inclined;

51 and 60. Interposed between magnets 61 and 61 are four

solenoids

62, 63, 64 and 65 which may be symmetrically arranged upon a suitable supporting structure about the center portion of rod 55. Opposite solenoids are connected together in pairs to sources of exciting current in the same manner as disclosed with reference to the structure in Fig. 4 to produce a rotating magnetic field transverse to the center portion of rod 55. When the strength of the magnetic field supplied by magnets 61 and 61. is adjusted to produce a 90 degree differential phase shift in the portion of rod 55 excited by these magnets, and when the field strength supplied by

solenoids

62, 63, 64 and 65 is adjusted to produce a 180 degree differential phase shift in the center portion of rod .55, the single ferromagnetic element 55 serves the three functions of converting the linearly polarized wave into a circularly polarized wave, rotating the instantaneous polarity of the circularly polarized wave, and reconverting the rotated circularly polarized wave into a linearly polarized wave. Each of these functions is exactly similar to the corresponding function described above with reference to Fig. 1.

By way of illustrating the applications of the all-dielectric wave guide techniques to the present invention, each of the three functions describedabove were performed in a single ferromagnetic element. However, it should be noted that separate ferromagnetic elements may be used each separated from the other by a section of dielectric guide. On the other hand only the 180 degree differ ential section may comprise an unshielded ferromagnetic element while the 99 degree sections preceding and following it may be situated beyond

dielectric guides

52 and 58 for example, within

metallic guides

51 and 60 and may comprise therein phase shift means of the types illustrated in Fig. l or Fig. 3, for example. Horns 53 and 59 and tapers 54 would still be employed to launch the now circularly polarized waves upon the dielectric wave guides 52 and 58.

As noted above, tapered joints 56 and 57 are employed to prevent mismatches between the dielectric guides 52 and 53 and the ferromagnetic rod 55. As illustrated in Fig. 5 these tapers comprise conical points on the ends of

guides

52 and 58 which fit into corresponding conical depressions in the ends of rod 55. Other methods of matching the materials may be employed. For example, the index of refraction of the dielectric material of guides 2 and 53 would be made the same as the index of refraction of the ferromagnetic material. This would tend to maintain the external field of the energy conveyed along the combination at a constant diameter. Alternatively, if the index of refraction of the magnetic material is higher than that of the dielectric material, the field of the energy may be maintained constant by providing the dielectric rod with a proportionately larger diameter than the diameter of the magnetic rod as shown in Figs. 6A and 6B. The transition between the two diameters may be made, for example as shown in Fig. 6A, by providing the dielectric rods 81 and 32 with conical points, such as 83, to lit within a corresponding impression in magnetic rod 84. The center core of rods 31 and 32 may then be drilled out or otherwise removed. In Fig. 6B the transition is made by providing conical points of equal taper upon the three

rods

85, 86 and 8'7 and then providing corresponding conical. impressions in dielectric rods 85 and to receive the

points

58 and 89, respectively, of magnetic rod 87.

The phase shifters of Figs. 1 and 5 are both reciprocal as has been noted, i. c., the same phase shift is introduced to wave energy transmitted in either direction therethrough. Thus, if waves'transmitted through the shifters a first time are reflected back by a mismatched termination, the reflected waves will have suffered twice the phase shift of a single traversal. Both phase shifts will be either in a lagging sense or both in a leading sense.

. in Fig. l the ferromagnetic elements therein have been illustrated by way of specific example, as cylindrical blocks of material substantially filling the interior space of the metallic shield wave guide. It should be noted, however, that the effect of the ferromagnetic material on electromagnetic waves continues if the material fills only a portion of this space. Furthermore, in order to prevent or cut down deflections from the faces of the elements, it may be found desirable to employ conical or otherwise tapered transition members, which members may be of dielectric material or of ferromagnetic material on one or both sides of the elements in accordance with usual practice.

In all cases, it is understood that the above-described arrangements are simply illustrative of a small number of many possible specific embodiments which can rep resent applications of the principles of the invention. Numerous and varied other arrangements can readily be devised in accordance with said principles by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. Variable phase shift apparatus for the transmission of electromagnetic wave energy comprising a pair of degree differential phase shift sections, an element of gyromagnetic material interposed between said sections, electromagnetic solenoids disposed about said element to produce a magnetic field extending transversely through said element, the strength of said magnetic field and the thickness of said element being proportioned to produce a degree differential delay between components of said wave energy polarized parallel to said field and compo nents of said wave energy polarized perpendicular to said field.

2. Apparatus for the transmission of electromagnetic wave energy comprising in combination, means on the input side for converting said wave energy from linear to circular polarization, means on the output side for reconverting to linear polarization, an interposed element of gyromagnetic material in the path of said circularly polarized waves, and means for applying a magnetic field to said element in a direction transverse to the direction of propagation of said wave energy, the strength of said field falling outside the region of ferromagnetic resonance for said element at a frequency within the operating range.

3. Apparatus for the transmission of electromagnetic wave energy comprising in combination, a source ofilinearly polarized electromagnetic wave energy, an input means coupled to said source for converting said wave energy from linear to circular polarization, an output means for reeonverting to linear polarization, an element of gyromagnetic material interposed between said input and output means in the path of said circularly polarized waves, and means for applying a magnetic field to said element in a direction transverse to the direction of prop agation of said wave energy, the strength of said field falling outside the region of ferromagnetic resonance for said element at a frequency within the operating range.

4. Variable phase shift apparatus for the transmission of electromagnetic wave energy comprising in combination, means on the input side for converting said wave energy from linear to circular polarization, means on the output side for reconverting to linear polarization, an interposed ele ent of gyromagnetic material in the path of said circularly polarized waves, and means for applying a magnetic field to said element in a direction transverse to the direction of propagation of said wave energy and for rotating said transverse field about the axis of the direction of propagation of said waves through said element.

5. Variable phase shift apparatus for the transmission of electromagnetic wave energy comprising in cornbination, a source of linearly polarized electromagnetic wave energy, an input means coupled to said source for con-' verting said wave energy from linear to circular polarization, an output means for reconverting to linear polarization, an element of gyromagnetic material interposed between said input and output means in the path of said circularly polarized waves, and means for applying a magnetic field to said element in a direction transverse to the direction of propagation of said wave energy and for rotating said transverse field about the axis of the direction of propagation of said wave energy through said element.

6. Variable phase shift apparatus for the transmission of electromagnetic wave energy comprising in combination, means on the input side for converting said wave energy from linear to circular polarization, means on the output side for reconverting to linear polarization, an interposed element of gyromagnetic material in the path of said circularly polarized waves, and means for applying a magnetic field to said element in a direction transverse to the direction of propagation of said wave energy and for rotating said transverse field about the axis of the direction of propagation of said waves through said element, the strength of said field falling outside the region of ferromagnetic resonance for said element at a fre quency within the operating range.

7. Variable phase shift apparatus for the transmission of electromagnetic wave energy comprising in combination, a source of linearly polarized electromagnetic waves, an input means coupled to said source for converting said wave energy from linear to circular polarization, an output means for reconverting to linear polarization, an ele ment of gyromagnetic material interposed between said input and output means in the path of said circularly polarized Waves, and means for applying a magnetic field to said element in a direction transverse to the direction of propagation of said wave energy and for rotating said transverse field about the axis of the direction of propagation of said waves through said element, the strength of said field falling outside the region of ferromagnetic resonance for said element at a frequency within the operating range.

8. Variable phase shift apparatus for the transmission of linearly polarized electromagnetic wave energy comprising in combination, means on the input side for converting said wave energy from linear to circular polarization, means on the output side for reconverting to linear polarization, an interposed element of gyromagnetic material in the path of said circularly polarized waves, and a plurality of separately excited solenoids disposed about said element to produce a resultant magnetic field passing through said element in a direction transverse to the direction of propagation of said wave energy and at a variable angle dependent upon the rela tive excitation of said solenoids.

9. Variable phase shift apparatus for the transmission of linearly polarized electromagnetic wave energy comprising in combination, means on the input side for converting said wave energy from linear to circular polarization, means on the output side for reconverting to linear polarization, an interposed element of gyromagnetic material in the path of said circularly polarized waves, and a plurality of separately excited solenoids disposed about said element to produce a resultant magnetic field passing through said element in a direction transverse to the direction of propagation of said wave energy and at a 10 variable angle dependent upon the relative excitation of said solenoids, the strength of said field falling outside the region of ferromagnetic resonance for said element at a frequency within the operating range.

10. Variable phase shift apparatus for the transmission of linearly polarized electromagnetic wave energy comprising in combination, a source of linearly polarized electromagnetic wave energy, input means coupled to said source for converting said wave energy from linear to circular polarization, output means for reconverting to linear polarization, an element of gyromagnetic material interposed between said input and output means in the path of said circularly polarized waves, and a plurality of separately excited solenoids disposed about said element to produce a resultant magnetic field passing through said element in a direction transverse to the direction of propagation of said wave energy and at a variable angle dependent upon the resultant excitation of said solenoids.

11. Variable phase shift apparatus for the transmission of linearly polarized electromagnetic wave energy comprising in combination, a source of linearly polarized electromagnetic wave energy, input means coupled to said source for converting said wave energy from linear to circular polarization, output means for reconverting to linear polarization, an element of gyromagnetic material interposed between said input and output means in the path of said circularly polarized waves, and a plurality of separately excited solenoids disposed about said element to produce a resultant magnetic field passing through said element in a direction transverse "to the direction of propagation of said wave energy and at a variable angle dependent upon the resultant excitation of said solenoids, the strength of said field falling outside the region of ferromagnetic resonance for said element at a frequency within the operating range.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,123 King Apr. 16, 1940 2,402,948 Carlson July 2, 1946 2,438,119 Fox Mar. 23, 1948 2,464,269 Smith Mar. 15, 1949 2,483,818 Evans Oct. 4, 1949 2,548,889 Kester Apr. 17, 1951 2,607,849 Purcell Aug. 19, 1952 2,629,079 Miller Feb. 17, 1953 2,644,930 Luhrs July 7, 1953 2,650,350 Heath Aug. 25, 1953 OTHER REFERENCES Publication I, Sakiotis et al.: Microwave antenna ferrite applications," Electronics June 1952, pp. 156-166. (Copy in Division 69.)

Hewitt: M. W. absorption in ferromagnetic semiconductors, Physical Review, vol. 73, No. 9, May 1, 1948, pages 1118-19. (Copy in Division 69 333-246.)

Hogan: Faraday effect at M. W. frequencies, Bell Technical Journal, vol. 31, pages 1-31, January 1951. (Copy in Division 69 333-246.)

Beljers et al.: Magnetic losses in ferrites at U. H. R, Journal of Applied Physics, vol. 22, No. 12, December 1951, page 1506.