US3099806A - High-power resonance absorption isolator having ferrite slab offset from polepieces so as to be non-uniformly magnetized - Google Patents

Description

y 1963 L. A. BLASBERG ETAL 3,099,806

HIGH-POWER RESONANCE ABSORPTION ISOLATOR HAVING FERRITE SLAB OFFSET FROM POLEPIECES so AS TO BE NONUNIFORMLY MAGNETIZED Original Filed March 15, 1956 zimz 5 i I i A Eras.

United States The present invention relates to microwave devices and is a continuation of copending application, Serial No. 572,176, Lawrence A. Blasberg et al., High-Power Resonance Absorption Isolator, filed March 15, 1956, now abandoned. More particularly, it relates to a nonreciprocal isolator adapted to be used in microwave transmission means to permit the passage of electromagnetic energy therethrough in one direction and to prevent the passage of such energy in the opposite direction.

In a microwave system it is customary to interconnect the various components thereof by means of reciprocal transmission means such as hollow waveguides. Due to this reciprocal nature characteristic, electromagnetic energy may be propagated through the transmission means with equal facility in either direction. Since the output power, the frequency, and the frequency stability of a microwave generator are normally dependent in some degree on the load into which it is working, it is desirable to place a nonrcciprocal isolator in the otherwise reciprocal transmission means. Such an isolator should permit the free passage of electromagnetic energy propagating in the forward direction but should completely absorb energy propagating in the reverse direction.

Although isolators of a Wide variety have been provided, one of the most efiicient types are those employing a gyroresonant or ferrite element for absorbing the electromagnetic energy. Such a member is asymmetrically positioned in a section of waveguide so that the plane of circular polarization of the electromagnetic energy will pass therethrough. In addition, a biasing magnetic field is created in the gyroresonant or ferrite clement substantially transverse to the direction of propagation and parallel to the plane of circular polarization. As a result, electromagnetic energy propagating in one direction and having a frequency equal to the gyroresonant frequency will be coupled into the electron spins and absorbed thereby.

Heret-ofore, it has been customary for the biasing flux field within the gyroresonant or ferrite member to be homogeneous or of uniform density. This in turn will insure the gyroresonant frequency being substantially uni form in all portions of the gyroresonant or ferrite member. Although such prior art isolator devices have been effective to absorb electromagnetic energy traveling in the reverse direction, their ability to effectively do so is confined to a narrow band of frequencies centered around the gyroresonant frequency. As the difference between the gyroresonant frequency and the frequency of the electromagnetic energy increases, the amount of isolation rapidly decreases.

It is now proposed to provide a more eificient gyroresonant isolator which will provide :a higher degree of isolation over a wide band of frequencies than has heretofore been possible. More particularly, this is to be accomplished by providing an isolator in which a gyroresonant or ferrite member is disposed in a waveguide and a heterogeneous flux field extends transversely therethrough. Since the flux density of this field varies transversely of the gyroresonant or ferrite member, the gyroresonant freatent U Patented July 30, 1963 ice quency inside of the member may be made to vary transversely thereof so as to correspond to the transverse position of the plane of circular polarization. As a result, even though the frequency of the electromagnetic energy may vary, as the plane of circular polarization moves it will always be located in the portion of the ferrite member where gyroresonance is occurring. This in turn will insure the isolator providing a high degree of isolation over a wide band of frequencies.

FIG. 1 is a schematic perspective view of an embodiment of the device of the present invention;

FIGS. 2 and 3 are cross-sectional schematic views of the device of FIG. 1;

FIG. 4 is a cross-sectional plan View of the device of FIG. 1 with dashed lines representative of the magnetic fieid of a wave being propagated from a generator to a load; and

FIG. 5 illustrates the magnetic field distribution in a plane transversely across the waveguide in the device of FIG. 1.

Referring now to the drawings, FIGS. 1, 2 and 3 show an embodiment of an isolator 10 which is adapted to unidirectionally attenuate energy reflected from a load so that it does not return to the microwave generator from whence it originated. The isolator 10* comprises a section 12 of conventional rectangular waveguide having flanges 14 and 16 to enable it to be inserted in the waveguide interconnecting a microwave generator with its associated load.

In accordance with a preferred embodiment of the invention, ferrite slabs 1 8 and 20 are disposed contiguous to opposite inner surfaces of the respective broad sides of the section 12 of rectangular waveguide intermediate the center lines and corresponding edges thereof. The ferrite slabs 18 and 20* are of the order of 70 mils thick and from one-fourth to one-half the width of the section 12 of waveguide in width. In general, the length of the ferrite slab 22 along the longitudinal axis of the waveguide is not critical and, for X-band, may be within the range of from 0.75 to 2.0 inches or longer and the edges of the slabs may be tapered, as shown, so as to minimize the standing-wave-ratio resulting from the insertion of the isolator 10 into the waveguide. Further, any ferrite material which can be made to exhibit gyroresonance throughout the desired band of frequencies within which operation is intended may be employed for the slabs 18, '20. As a practical matter, however, it is desirable to employ ferrite materials which have high resistivities so as to the insertion loss in the Wave propagated in the forward direction. Examples of ferrite materials which have been suitable for slabs 18, 20* are ferrites known commercially as General Ceramic R1 or Ferroxcu'be 106.

The apparatus for producing the asymmetrical magnetic field distribution across the waveguide section 12 includes pole pieces 22, 24 and permanent magnet 26. The pole pieces 22, 24- extend between the flanges 14, 16 and are inserted through apertures in the waveguide section 12 which are disposed directly opposite each other in the broad sides thereof and oriented so as to be parallel to the longitudinal axis of the waveguide. Further, the apertures are 0.150 inch wide and disposed along one side of the waveguide over the edges of ferrite slabs 18, 20 nearest the side of the waveguide. The face of each of the pole pieces 22, 24 is made flush with the respective inner surface of the broad side of waveguide section 12. In the present embodiment, the pole pieces 22, 24 are made of 0.150 inch thick Armco iron so as to completely fill the apertures through the waveguide, 0.125 inch of the face of each of the pole pieces 22, 24 being covered by the corresponding ferrite slab 20, 18, respectively.

The permanent magnet 26 is of the horseshoe type and may, for example, be composed of a magnetic material known commercially as Alnico V. In order to achieve the magnetic flux distribution in accordance with the present invention, the horseshoe magnet is disposed wave generator to the load, it is evident that the magnetic field presented to point A is rotating in a clockwise direction with respect to the applied static magnetic field, as viewed in the drawing. Electromagnetic energy reflected over the portion of Waveguide including the center lines 5 from the load would, therefore, be propagated back toof the broad sides thereof so that the pole pieces of the wards generator 14 and, accordingly, would present a magnet 26 are contiguous to the pole pieces 22, 24 as magnetic field at point A that rotates in the counterparticularly illustrated in FIG. 2. The magnetic field clockwise direction with respect to the applied static magdistribution thus produced is represented by the charnetic field. In accordance with the invention, the polarity acteristic 30 of FIG. 5. Referring to FIG. 5, a partial of the magnetic field produced by magnet 26 is poled cross section of the device of FIG. 1 including the ferrite so as to couple to the aforementioned magnetic field rotatslab 20, pole piece 22, and a portion of the Waveguide ing in the counterclockwise direction. In addition to section 12 is shown for the purpose of referencing maghe characteristics of the ferrite material actually employed, netic field intensity versus position across the wavethe frequencies at which gyroresonance occurs is deterguide, 15 mined by the direct-current magnetic field. Inasmuch as In accordance with the present invention, the magnetic the intensity of the magnetic field varies considerably field intensity as represented by characteristic must across the ferrit slab Z2, attenuation in the backward dipass through or equal that intensity required to effect reotion is effected over a broad range of frequencies. gyroreso-nance within the ferrite slabs 18, 20 along a Representative performance characteristics of an X- plane whe ther is ub tantially pu e circular polariza- 2O band rectangular waveguide resonance absorption isolator tion. Inthe present case, a plane of this type is located made in accordance with the present invention are tabumidway between the center lines and the respective edges lated below:

Waveguide Length of Weight of Ferrite Ferrite Peak Band Insertion Isolation, Back-t0- height, in. device, in. magnet length, in. used powers Width, loss, db db front absorpused, oz. used, kw. percent tion ratio 0. 500 i 1. 75 I 20 1.6 106 350 15 5.5 220 240 l of the broad sides of the waveguide. The exact location Typical performance characteristics of the above-menof: the plane will vary as function'of the frequency of the tioned 350 kw. high-power resonance absorption isolator electromagnetic energy being propagated in the waveover a 10% frequency band in the X band region are: guide (a) A voltage standing wave ratio less than 1.09; In event .Uhalt 1 Slabs arefomPosed of (b) An insertion loss of from 0.41 to 0.51 decibels General Ceramic R-l or Ferroxcube 106 ferrite matekl-iowatts peak: d n p power inpu an rial, the s t fi Intensity eflect gyroreaonance P ((3) Isolation of from 23 to 30 decibels with 30 kilowatts theX band region is of the order of 4000 gauss. Also, in I k b 1Q d pea ac. war power.

proceeding toward the center line from the nearest point H h at hi h gymq-esonmce in h f it material is the characteristics of the resonance absorption isolator effected, the magnetic field intensity progressively decreases have been measured as function of 1lempemtllm fromuntil the intensity at the center line is substantially less R The insertion 1088 is decreased 0.3 than that required to produce gyroresonance, F h db and the isolation 3.5 db in this temperature range. The in the event that the ferrite slab should extend across Chang? resonance field Strength of the feI'IliTe gecmetfy the center line, the intensity of the magnetic field across 15 F 'p r f by a change in field T ng h f 1116 the-center line is made less than that required to produce magnetic F with temperature- This gi a m imum gyroresonance so as not to effect bidirectional attenuaof m with tempfilftltum- This nim m detion. Althou-ghthe permanent magnet 26 has been shown tumng to Similar Gillie t mperatures of the and described in connection with the device of FIG. 1, three ferwgmasmti; matem'al's in the magnetic circuit. the use of an electromagnet to establish a magnetic field Ferroxcwba 105 ferrite Armco iron and AlHiCO V P rmain accordance with the present invention is considered s-{ all haw/Curie temperatures f approximately to be within the scope of the teachings of the present f specification. Also, it is understood that the height of What 1S 1wned 133 the waveguide Section 12 may be reduced to decrease 1. Aunidirectional microwave transmission device comthe reluctance of the path of the magnetic flux and thus Pnsmg: flf t a concomitant decrease in the Weight of the Pep (a) a rectangular waveguide including a pair of opposite manem magnet 2 broad walls and a pair of opposite narrow walls;

In Operation, electromagnafic energy is propagated by (b) a magnet having a different pole piece adjacent Waveguide, including the section 12 f a microwave each broad wall of said waveguide at a location disgenerator to load in the TELO mode at a group velocity, Vg taut from a first narrow wall of said waveguide beas indicated in the cross sectional plan Vie/W of the device tween the center of the surfaces of the broad walls of FIG. 1 shown in FIG. 4. In FIG. 4, dashed lines 32, a second narrow Wall of said ide; 34 3 and 3 are representative of the field configura (c) and an elongated slab of gyroresonant material distions of the magnetic fi ld of the pmpagated Wave. AS posed longitudinally within said Waveguide substanggnemuy known these field configurations move through tially parallel to said broad walls thereof, said slab the Waveguide at the group velocity, Vg. Thus, the actual having a transverse width greater than" the width of magnetic field presented to a point such as A in the fer- 130.16 pieces adjacent said Waveguide? said Slabrite slab 20 is represented successively by vectors a, b, emendlil'g transverse.ly across the Interior of 5 c, d, e and 3. There is a plane of circular polarization that w l f i toward sald fi narrow wall from 3 P extends longitudinally of the waveguide where the vectors g dlsfliced i said first e Wall from the will rotate with uniform velocity; i.e., the energy is cirs gf 0' t 6 P0 6 pieces closest to Sam Second narrow y P Q Thls P121116 W111 move tlansvfifs'ely of 2. A unidirectional microwave transmission device comthe waveguide as the frequency of the energy varies. i

Inasmuch as the field configurations represented by (a) a rectangular waveguide including a pair of opdashed lines 32, 34, 35, 38 are progressing from the microposite broad walls and a pair of opposite narrow walls and having substantially oppositely disposed longitudinal slots in said broad walls thereof, said slots being noncentrally disposed between said narrow walls thereof;

(b) a magnet having a different pole piece adjacent each broad wall of said waveguide and extending into the slots in said broad walls;

( c) and an elongated ferrite slab disposed longitudinally within said waveguide substantially parallel to said broad walls thereof, said slab extending transversely across the interior of said waveguide from said slots toward the narrow wall farthest from said slots, the transverse width of said slab being greater than the width of said pole pieces extending into said slots, said slab only partially overlaying the ends of said pole pieces disposed within said slots.

3. A unidirectional microwave transmission device comprising:

(a) a rectangular waveguide including a pair of 0pposite broad walls and a pair of opposite narrow walls;

(11) a magnet having a different pole piece adjacent each broad wall of said waveguide at a location distant from a first narrow wall of said waveguide between the center of the surfaces of the broad walls and a second narrow wall of said waveguide;

(c) and a pair of elongated ferrite slabs disposed longitudinally within said waveguide substantially parallel to said broad walls thereof, a different one of said slabs being adjacent each broad wall of said waveguide, said slabs extending transversely across the interior of said waveguide toward said first narrow wall from a position displaced toward said first narrow wall from the edges of the pole pieces closest to said second narrow wall.

4. A unidirectional microwave transmission device comprising:

(a) a rectangular waveguide including a pair of opposite broad walls and a pair of opposite narrow walls and having substantially oppositely disposed longitudinal slots in said broad walls thereof, said slots being noncentrally disposed between said narrow walls thereof;

(b) a magnet having a different pole piece adjacent each broad wall of said waveguide and extending into the slots in said broad walls;

(c) and a pair of elongated slabs of gyroresonant material disposed longitudinally within said waveguide substantially parallel to said broad wall-s thereof, a different one of said slabs being adjacent each broad wall of said waveguide, said slabs extending transversely across the interior of said waveguide from said slots toward the narrow wall farthest from said slots, the transverse width of said slabs being greater than the width of said pole pieces extending into said slots, said slabs only partially overlaying the ends of said pole pieces disposed within said slots.

5. A unidirectional microwave transmission device comprising:

(a) a rectangular waveguide including a pair of opposite broad walls and a pair of opposite narrow walls and having substantially oppositely disposed longitudinal slots in said broad walls thereof, said slots being noncentrally disposed between said narrow walls of said waveguide;

(11) a magnet having a different pole piece adjacent each broad wall of said waveguide and extending into the slots in said broad w-alls;

(c) and a pair of elongated ferrite slabs disposed 1ongitudinally within said waveguide substantially parallel to said broad walls thereof, a different one of said slabs being adjacent each broad wall of said waveguide, said slabs extending transversely across the interior of said Waveguide from said slots toward the narrow wall farthest from said slots, the transverse width of said slabs being greater than the width of said pole pieces extending into said slots, said slabs only partially overlaying the ends of said pole pieces disposed in said slots.

References Cited in the file of this patent UNITED STATES PATENTS 2,776,412 Sparling Ian. 1, 1957 2,806,972 Sensiper Sept. 17, 1957 2,849,684 Miller Aug. 26, 1958 OTHER REFERENCES Fox et al.: Bell System Technical I ournal, J an. 1955, pages 42-53.

Claims (1)

1. A UNIDIRECTIONAL MICROWAVE TRANSMISSION DEVICE COMPRISING: (A) A RECTANGULAR WAVERGUIDE INCLUDING A PAIR OF OPPOSITE BROAD WALLS AND A PAIR OF OPPOSITE NARROW WALLS; (B) A MAGNET HAVING A DIFFERENT POLE PIECE ADJACENT EACH BROAD WALL OF SAID WAVEGUIDE AT A LOCATION DIS TANT FROM A FIRST NARROW WALL OF SAID WAVEGUIDE BETWEEN THE CENTER OF THE SURFACES OF THE BROAD WALLS AND A SECOND NARROW WALL OF SAID WAVEGUIDE;

Images