Nov. 6, 1962 W. A. HUGHES 3,063,027 HIGH POWER MICROWAVE ISOLATOR Filed Feb. 14, 1955 WMl.”ar/7%,. .. ‘i: // // 43 Jaw/m. , Will/d4 A/l/éé/ii, 21 JV ma. 1 Irma/£14 3,063,027 Patented Nov. 6, 1962 I 2 The novel features which are believed to be character istic of the invention, both as to its organization and 3,063,027 ‘ HEGHPOWER MICRUWAVE ISOLATOR Willard Aiien Hughes, Los Angeles, Caiiii, assignor to Hughes Aircraft Company, Culver City, Caii?, a cor poration of Delaware Filed Feb. 14, 1955, Ser. No. 487,996 2 Claims. (Cl. 333-242) This invention relates to waveguides for unidirectional microwave transmission, and more particularly to a broadband high power waveguide isolator. Many utilizations of microwave energy require a power source which is very stable in amplitude and frequency method of operation, together with further objects and advantages thereof, will be better understood from‘ the 5 following description considered in connection with the accompanying drawing in which a number of embodi ments of the invention are illustrated by way of example. It is to be expressly understood, however, that the draw ing is for the purpose of illustration and description only, 10 and is not intended as a de?nition of the limits of the invention. In the drawing: FIG. 1 is a perspective cut-away view of a simpli?ed embodiment of the invention to aid in the explanation of output. For example, the usual microwave generators the invention; are susceptible to deterioration with respect to frequency FIG. 2 is a cross-sectional view through a practical em and amplitude output if the nature of the load varies. It 15 bodiment of the invention; follows that their stability is deleteriously affected if FIG. 3 is a cross-sectional view of a second practical energy is re?ected from a load which varies in impedance. embodiment of the invention; Accordingly, it is highly desirable to isolate the micro FIG. 4a is a longitudinal sectional along the centerline wave energy generator from the load. It is also desir of a third embodiment of the invention; FIG. 4b is a cross-section taken through the embodi ment of FIG. 4a at the plane designated as 4b; wave from the load.‘ FIG. 5 is a cross-section of a fourth practical embodi In the prior art this was most closely achieved by ment of the invention; and mounting one or more ferrite specimens in a waveguide FIG. 6 is a cross-section of a ?fth practical embodi and subjecting them' to an externally applied static mag 25 merit of the invention. netic ?eld. In one form of load isolator a ferrite speci Referring now to the drawing, in which like numbers men, preferably ‘of rectangular cross section, is asym~ able to provide such isolation with a low insertion loss while at the same time exhibiting high loss to the re?ected represent like elements in the different ?gures, it will be metrically mounted in a rectangular waveguide parallel to its longitudinal axis. The static traverse magnetic 30 assumed for purposes of explanation that it is desired to pass energy from left to right through the isolator. In ?eld is provided by a relatively large permanent magnet the cause of simplicity certain structural details have located outside of the waveguide. The magnetic ?eld is been omitted from the ?gures. For example, secured channeled through the ferrite, causing the ferrite to pro to each end of the isolator but omitted from the draw vide high attenuation for wave energy passing through it in one direction and low attenuation for wave energy 35 ings is a suitable waveguide ?ange for coupling the de vice of this invention to other equipment. traversing it in the opposite direction. Referring speci?cally to FIG. 1, microwave energy is It is an object of the present invention to provide a impressed upon opening 10 of waveguide 12 from a micro microwave isolator of the type described above which is wave source in a manner well known in the art. Wave relatively compact and at the same time is capable of guide 12 may be a length of conventional waveguide of handling a large magnitude of power. 40 the character adapted to be used at the desired microwave It is another object of the present invention to provide frequency. Ferrite strips 14 and 16 are in a conventional a high power microwave isolator that is relatively broad manner rigidly secured to the inner horizontal surfaces band in its operation and not frequency sensitive. of waveguide section 12 and are interposed along plane The desired isolation is achieved in accordance with this invention in the following manner. In a section of 45 15, which is the plane of circular polarization of the H ?eld of the traveling microwave. Permanent magnet 18 waveguide a slender ferrite strip is placed longitudinally is constructed and placed so that “north” pole face 20 in a plane of circular polarized H ?eld. This plane in the and “sent ” pole face 22 focus transverse to the wave waveguide is one parallel to the electric ?eld and its lo guide a narrow magnetic ?eld along the plane 15 through cation may be calculated by methods well known in the ferrite strips 14 and 16 which are, as shown, of substané art. It is the plane in which the transverse component tially the same length as the pole faces and of cross of the H ?eld is equal to the longitudinal component of section very small compared With the waveguide cross the H ?eld of the traveling microwave. An external section. transverse static magnetic ?eld is caused to be focused Referring now to FIG. 2, permanent magnet 18, shown through the ferrite. With this con?guration a forward going microwave signal has a circularly, with a positive 55 in cross~section, is placed around waveguide'lz in such a manner that the transverse static magnetic ?eld is sense, polarized H ?eld and the ferrite exerts no absorp focused along plane 15 representing the plane of circular’ tion effect upon it. Thus, the insertion loss is extremely polarization of the H ?eld. Ferrite strips 14 and 16 low. The backward going microwave signal in the same are secured to the inside walls of waveguide 12 as shown plane has a circularly, With a negative sense, polarized H so as to be interposed in the transverse magnetic ?eld ?eld and is absorbed by the precessional resonance of the along plane 15. electrons in the ferrite. The undesired re?ected micro Referring now to FIG. 3, permanent magnet i8 is wave energy is then converted to heat by precessional again shown to substantially surround waveguide section damping losses and the heat is absorbed into the wall of 12 and pole faces 25} and 22 again focus the transverse the waveguide. The physical theory concerning the magnetic ?eld along plane 15 which coincides with ‘the phenomenon of positively and negatively circularly polar ized magnetic ?elds is a rectangular TEN) mode in a certain plane in the waveguide and the dependence of I the sense of the circular polarization upon direction of 65 plane of circular polarization of the propagating magnetic ?eld. Longitudinally dividing waveguide section 12 into three substantially equal volumes having substantially equal cross-sections are secured brass cooling ?ns 24 and 26. As in the previous embodiment, ferrite strips propagation is discussed in “The Microwave Gyrator,” Bell System Technical Journal, January 1952, pages 1.—3l, 70 14 and 16 are mounted along the inside Wall of wave by C. L. Hogan. guide 12 in the plane 15 of circular polarization. Mount ed in the same plane and on the opposite surfaces of brass 3,063,027 .51. For purposes of description of the operation of the invention it will be assumed that the waveguide is excited in the TB“, mode. The operation of the invention is not disturbed by this mode. The electric and magnetic ?elds '3 cooling ?n 24 are ferrite strips 27 and 28; and likewise on the opposite surfaces of brass cooling ?n 26 and coin cident with plane 15 are mounted ferrite strips 29 and 30. Ferrite strips 27—30 are of substantially the same dimen sions as strips 14 and 16. are set up as usual with the transverse electric ?eld across the narrow dimension of the cross-section of the wave Referring to FIGS. 4a and 4b there is shown in sec tion an embodiment of the invention which utilizes a guide and the alternating magnetic ?elds across the greater dimension of the cross-section of the waveguide and along the length of the waveguide. The electrons in microwave impedance transformer having a broadband impedance matching characteristic. The transformer comprises steps 32, 34, 35, 35', 34’, 32’ (left to right) in the horizontal walls of waveguide section 31. Ferrite strips 14' and 16’ are secured along the length of the narrowest portion of waveguide 31 in proportionally the 10 the ferrite strips have an average magnetic moment which same position of the cross-section as in the other embodi ments of the invention. The ferrite strips may here be smaller in cross-section than are strips 14 and 16 in the previous embodiment. Permanent magnet 18’ with attached pole faces 29 and 22 is placed in a manner to provide the narrow trans verse magnetic ?eld along plane 15 through ferrite strips 14’ and 16' across the height of the waveguide section 31. Glass or other dielectric seals 36 and 36' are placed across waveguide section 31 at opposite ends of the isolator in a manner so as to sustain a pressure differential between the space inside the isolator and the outside waveguide. Referring now to FIG. 5, magnet 18 is again shown to substantially surround waveguide 12, and pole faces 20 and 22 focus a transverse magnetic ?eld through the wave is random in the absence of the external magnetic ?eld. When permanent magnet 18 is in place to establish the transverse external ?eld along plane 15, the average magnetic moment tends to line up with the external ?eld which is established. In addition, the alternating mag netic ?elds, due to the waveguide excitation, cause this average magnetic moment to process. This processing of the average magnetic moment is attended by the pro duction in the ferrite of magnetic ?elds which tend to reinforce the alternating magnetic ?elds. The precession frequency depends upon the strength of the external ?eld and when the precessional frequency is made equal to the propagating microwave frequency, precessional resonance occurs. Under these conditions microwave energy travelling left to right in waveguide section 12 in FIG. 1 is not effected by the precessional resonance and passes un attenuated to the load or other utilization device of the microwave energy. Energy reflected from the utiliza guide coincident with plane 15. Ferrite strips 14 and 16 tion device, however, has circularly polarized magnetic are placed as before along the inside wall of waveguide 30 fields of opposite sense along plane 15 and in this case 12 coincident with plane 15. The strips are here made precessional resonance occurs to absorb substantially all with a substantially half round cross-section. In addition, the re?ected energy in the ferrite strips 14- and 16 by cooling ?ns 3S and 40 are secured on the outside of wave precessional damping losses and the energy is absorbed guide section 12 along the length of the isolator coincident as heat in the wall of the waveguide. with plane 15 and are adapted to conduct and radiate heat Referring now to FIG. 3, it is seen that the brass cool away from the ferrite strips 14, 16 and waveguide 12. ing ?ns 24 and 26 of their attached ferrite strips 27 Referring now to FIG. 6, waveguide section 12 with through 30 cause the device to be capable of absorbing ferrite strips 14 and 16 and pole pieces 20 and 22 are and dissipating even higher amounts of energy ‘by virtue shown in substantially the same con?guration as in FIG. 40 of the function of the cooling ?ns to conduct heat with 2. However, the magnet 18” is reversed to encircle the the outside waveguide walls. The principle of operation, opposite side of waveguide 12; and external cooling ?ns however, remains exactly the same because the cooling 43 in the form of a length of channel 44 are secured along ?ns are at right angles to the electric vector in the wave the length of waveguide section 12. guide and do not effect the magnetic vector because the Referring to FIGS. 3 and 5, it is seen that slots 41 and fins are made of brass. 42 are cut substantially through the waveguide to allow The device shown in FIG. 4 is an embodiment of the the pole faces to be in closer proximity to the ferrites for invention which utilizes an impedance transformer to purposes of improving the focusing of the transverse mag netic ?eld through the ferrite strips and along plane 15 reduce the dimensions of the waveguide in the region of the ferrite strips so that a smaller magnet may be used within the waveguide. The depth of the slot may be the due to the reduced magnetic gap between waveguide entire thickness of the waveguide wall or any fraction 50 surfaces through the ferrite strips 14' and 16’. The vol thereof. The horizontal dimensions are substantially ume enclosed between glass seals 36 and 36’ may be those of the ferrite strips. As shown in FIG. 3, pole faces either evacuated or pressurized to preclude arcing across 20 and 22 are accordingly shaped with tongue projections the reduced waveguide dimension. This embodiment has of the same dimensions which are inserted into their re the further advantage of providing an even lower inser spective slots. The embodiment according to FIG. 5 55 tion loss because less ferrite material is required to utilizes iron cooling ?ns 38 and 40 for pole faces; and achieve a given attenuation. there are adapted to ?t directly into the slots. _ The embodiment of FIG. 5 utilizes external cooling The permanent magnets adapted for use in the inven ?ns to increase the power dissipating capabilities of the tion may be, for compactness and efficiency, of the well isolator. Because of the proximity of ?ns 38 and 40 known Alnico type or any similar material having like 60 to the ferrite strips 14 and 16, heat is readily conducted characteristics. The ferrite strips utilized are fabricated from the ferrite strips to the cooling ?ns. In this embodi of material suitable for precessional resonance at micro ment the cooling ?ns function also as magnetic pole faces Wave frequencies. For example, ferrites of the general and thus are shaped in a conventional manner to focus formula XFe 203 in which X is a bivalent metal ion are a strong magnetic ?eld along plane 15 through the ferrite particularly useful for this purpose. A suitable ferrite 65 strips. The half-round cross-section of ferrite strips 14 is described in the patent to Luhrs, No. 2,644,930 which and 16 provides the advantage of decreasing the tendency consists of 25 moles of manganese oxide, 25 moles of of the microwave energy to are between the ferrites be zinc oxide and 50 moles of ferric oxide. The mixture is sintered at 1300 degrees C. The composition and man ner of making ferrites having the necessary structure are 70 cause of the rounded surfaces. Also the rounding pro vides a broader band of operation because of internal described in the RCA Review No. 17 for September, 1950 by R. L. Harvey et al. Substances capable of exhibiting demagnetization due to the rounded geometry. Referring to the embodiment according to FIG. 6, cool the precessional absorption phenomenon at microwave ford another practical means for dissipating the heat from ing ?ns ‘43 attached as a channel 44 to the waveguide af frequencies are known in the art as ferro-magnetic dielec 75 the ferrite strips. Magnet 18” is reversed from the pre tries. 5 3,063,027 vious embodiments in order that the external cooling ?ns of channel 44 may be closer to the ferrite strips. 6 tion of the magnetic ?eld within the waveguide; a second embodiment of FIG. 5, the following speci?cations were plurality of ferrite strips secured along the interior walls of said waveguide section also coincident with the plane of circular polarization in the magnetic ?eld; an external including ?anges; the inside dimensions of the waveguide focused along and throughout said plane of circular polar ization. .070” x 1.7" and were placed so that their centerlines 2. A microwave isolator device in which the effect of microwave energy loss through heat dissipation due to In a speci?c structure constructed according to the used: The brass waveguide section was 3" in overall length 5 magnet adapted to provide a transverse magnetic ?eld were 1.122" by .497"; the ferrite strips Were .100" x were .220” from the closest vertical wall; cooling fin-pole pieces 38 and 40 were of soft pure iron .18” x .55" x 1.7” each with a tongue .062" x 1.7" inserted through a lon electron precessional resonance damping losses in a fer rite substance is utilized to allow propagation of micro wave energy in a waveguide in one direction and preclude gitudinal slot of the same dimensions in the waveguide propagation of the microwave energy in the opposite walls to make actual contact with the ferrite strips along their entire length; the magnet was horseshoe in cross 15 direction, said device comprising: a length of rectangular waveguide being adapted to be excited in the plane polar section and 1.7" long and cast of Alnico V material; the ized mode and having thereby a plane throughout the magnetic ?eld at the pole faces was 3700 Gauss and at length of the waveguide section along which the magnetic the surface of the ferrites opposite the pole faces, 3300 Gauss. vector is circularly polarized; a pair of slender ‘ferrite Using a pulsed carrier over the band from 8500 ki1o~ 20 strips secured along the length of said waveguide section in contact with the inner surface of opposite walls thereof megacycles to 9500i kilomegacycles, the pulses being 2.4 along said plane and having a semi-circular cross-‘section, micro-seconds in width and of 4-15 cycles repetition rate the curved portions of said strips facing each other and continuous duty, the attenuation in the forward direction the vilat portions of said strips being disposed perpendicu was .5 db while the attenuation in the reverse direction was 12 dbil db over the above band. Thus an attenua 25 lar to said plane; a permanent magnet external to the waveguide for producing a transverse magnetic ?eld along tions ratio of nearly 30‘ to l in db was achieved while transferring power peaks of ‘greater than 300 kilowatts the plane of circularly polarized magnetic ?eld through and average power of greater than 300 watts. Other advantages over the prior art are that a lower said ferrite strips; cooling ?ns external to said waveguide section and attached thereto consisting of a material suit able for serving also as pole faces for said magnet and voltage standing wave ratio (VSWR) is seen by the micro wave circuitry on the input side of the isolator; the iso lator of this invention operates over a considerably broader band and is, therefore, much less frequency sensitive; the insertion loss of the device is negligible (.5 db); and the power handling capabilities are at least 100 times better than in the prior art systems. It is also seen that the device is simple in construction so as to o?er economic advantages. being attached thereto, each of said cooling ?ns being secured to said waveguide coincident with the plane of circular polarization external to said waveguide section and being secured thereto in a manner such that each of said cooling ?ns is a?ixed to one of said ferrite strips for conducting heat therefrom into space. References \Cited in the ?le of this patent What is claimed is: 1. A waveguide isolator device utilizing the principle of magnetic precessional resonance and the inherent energy dissipation associated therewith in a ferrite sub stance for unidirectionally absorbing microwave energy propagating within the waveguide, said isolator device comprising: a section of rectangular waveguide being 45 adapted to be excited in a conventional plane polarized mode; a number or" cooling ?ns, said cooling ?ns being thin heat conductive nonpermeable sheets supported along the length of said waveguide internal thereto and dis posed parallel to the magnetic ?eld in a manner to avoid 50 disturbance of the electric ?eld; a ?rst plurality of ferrite strips supported along and in contact with said cooling ?ns and made coincident with a plane of circular polariza UNITED STATES PATENTS 2,643,296 Hansen ______________ __ June 23, 1953 2,648,047 2,748,353 2,745,069 2,767,380 2,776,412 2,777,906 2,844,789 2,849,684 Hollingsworth _________ __ Aug. 4, Hogan _______________ __ May 29, Hewitt ________________ __ May 8, Zobel ________________ __ Oct. 16, Sparling _______________ __ Jan. 1, Shockley _____________ __ Jan. 15, Allen ________________ __ July ‘22, Miller _______________ __ Aug. 26, 1953 1956 1956 1956 1957 1957 1958 1958 OTHER REFERENCES Journal of Applied Physics, vol. 24, No. 6, June 1953, pages 816-817. Fox et al.: “Behavior and Applications of Ferrites,” Bell Technical Journal, vol. XXXIV, No. 1, January 1955.