US2913687A - Dielectric support for ferrites in waveguide devices - Google Patents

Description

Nov. 17, "1959 E. STR-UMWASSER DIELECTRIC SUPPORT FOR FERRITES IN WAVEGUIDE DEVICES Filed March 2, 1955 United States Patent() f DIELECTRIC SUPPORT FOR FERRITES WAVEGUIDE DEVICES ErieStrumwasser, Los Angeles, Calif assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application March 2, 1955, Serial No. 491,613 6 Claims, Cl. 333-98 This invention relates to high power ferrite microwave devices, and more particularly to a supporting component for the ferrite element in such devices. f

In ferrite microwave devices such as isolators, attenuators, and modulators in which the ferrite member is supported within a section of waveguide by supports fabricated of a dielectric -plastic material such as polytetrafluoroethylene (Teflon), no special problems are encountered regarding arcing betweenthe dielectric and ferrite when the microwave power-being handledis of the order of a few watts. However, such a configuration is susceptible to voltage breakdown between the ferrite and the dielectric supportwhen the power being transferred through the device is of the order of hundreds of kilowatts. This arcing occurs primarily at the points of maximum electric field and results from the finite air gap between dielectric and ferrite due to imperfect mechanical. contact between support and ferrite, or I ;because the materials near the contact area are distorted by localized heating.

It is,.ther efore, an object of this invention to substantially eliminate arcing between the ferrite, member and its dielectricsupport in a ferrite microwave device.

Briefly, this is achieved by cutting away a portion of the. dielectric support from the ferrite in that area inwhich. the electric field gradient is maximum, thereby creating. a greater air gap and less tendency for-arcing between the ferrite. and the dielectric in the areaof greatest electric. field gradient.

The. novel features which are believed to be characteristic of the invention, both as to its organization and methodflof operation, together with further objects and advantages thereof, will be better understood from the.

following description considered in connection with the accompanying drawing in which several embodiments of the invention are illustrated by Way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of thelimits of the inven tion.

In the drawing:

Fig-1 is a perspective view of one embodiment of the dielectric supports for a ferrite memberin accordance with this invention;

Fig. 2 is a perspective view of a second embodimen of the invention;

Fig. 3 is an end viewof the supportof Fig. 2 at the input end of a ferrite waveguide device; 7

Fig. 4 is a cross-section through the dielectric support of Fig. 2 atthe line 4 of Fig. 2;

Fig. 5 is an end View of the support of Fig. 2 at the output end of the waveguide device; and

Fig. 6 is a perspective view of a dielectric support in accordance with this invention in a practical embodiment of a waveguide ferrite device.

Referring now to the drawing, in which like numbers represent like elements in the difierent figures it will be assumed for purposes of illustration and description 2,913,687 Patented Nov. 17, 1959,

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that it is desired to pass energy from left to right through the. waveguide ferrite device. In the cause of simplicity, certain structural details have been omitted from the figures. For example, secured to each end of each divice is, a suitable waveguide flange for coupling the device to other equipment. Also'omitted from the drawing is the conventional means external to the waveguide for providing a longitudinal magnetic field through the ferrite along its length. 3

Referring specifically to ,Fig. l, vertically polarized microwave energy is impressed upon opening 10 ofcircular waveguide section 12 from a microwave source in a manner well known in the art.Ferrite cylinder 14 is symmetrically supported along the length ofwaveguide 12 by annulardielectric discs 16, 18 and 20 which are in turn transversely supported at intervals along the length-of \t/aveguide 12. The number of discs is determined by the structural requirements of supporting the ferrite; and their exact position along the ferrite is determined by optimum impedance match considerations. In Fig. 1a three disc support configuration is assumed. A suitable external longitudinal magnetic field causes the vertical plane of polarization to be Faraday rotated as the energy traverses alongferrite cylinder 14 so that the plane of polarization when the energy passes dielectric disc ,20 is at an angle 0 with respect to the vertical. Thus, the plane of polarization of the energy rotates in a clockwise direction, as indicated by the arrows in Fig. 1.

The 'centerfholes in annular discs 16, 18 and20, are of substantially the same diameter asferrite cylinder 14 which is supported bysaid center holes. According to this example, disc16 hascutouts 22 Which are approximately circular Twith centers on t me at the angle 9 passing, through the center of disc 16; and in this example their diameters are approximately half that offerrite cylinder 14 and their centers are approximately on the circumference of the center hole in disc 16. The exact size and geometry of the cutouts are determined by the consideration ofsufficiently decreasing the gradient in the area Where arcing would otherwise occur while disturbing the symmetry of the device as little as possible; because the greater the assymmetry seen. by the reflected energy, the greater the ellipticity given to the reflected energy as it passes back throughDisc 20 isplaced at the output side offerrite cylinder 14 and is rotated about the ferrite, cylinder to the angle Thusthe cutouts are coincident with a line passing through the center of the ferrite and parallel to the plane of polarization so as to provide an air gap between ferrite and dielectric in the area of highgradient of the electric field.

Referring to Fig. 2 in which an embodiment is shown which utilizessolid cylinder 24 of dielectric. to supportferrite cylinder 14.Dielectric cylinder 24 with a cylindrical bore along its. axis of the same diameter as ferrite cylinder. l4twhich is supported therein is, in this example, the same length asferrite cylinder 14.Dielectric cylinder 24 along its length substantially fills circular waveguide section 12 and is supported therein.Cutouts 26 in this embodiment are spiral grooves of substantially the same cross-section ascutouts 22 of Fig. l. .The groove cutoutsspiral continuously and at a constant pitch along the lengthof the dielectric cylinder out is rotated to the same angle.

is rotated at an angle at the output end ofdielectric cylinder 24. Thus, for a 90 rotation of the plane of polarization of energy, it may be seen (in Figs. 3 to 5) that thecutout portions 26 lie parallelto the electric vector E along the path of the microwave energy. At what may be considered the input end, before rotation, the plane of polarization may be considered to be vertical, with the device in the relative. position of Figs. 2 and 3. Halfway along thedielectric cylinder 14, both the electric vector and thecutouts 26 are inclined at an angle with respect to the vertical. After full rotation, as shown in Fig. 5, the electric vector E is displaced at an angle 0' from the vertical but still bisects thecutouts 26.

Referring to Fig. 6, a practical embodiment is shown which is adapted for use ina high power, force cooled microwave isolator. In this embodiment the dielectric box support 28 has perforated holes 29 through 38 to allow the flow of a suitable coolant past ferrite cylinder 40. Holes 41 and 42 are of the same diameter as ferrite cylinder 40 and support cylinder 40 which passes through the holes. Square waveguide section 44 supports dielectric box support 28, the inside height and width dimensions of waveguide section 44 being substantially equal to the height and width dimensions of dielectric box support 28. Ferrite cylinder 40 has pointed ends which extend beyond the input and output ends of dielectric support 28. The plane of polarization at the input end of ferrite cylinder 40 is vertical, is caused to be rotated 8 to the right at the input end ofbox 28, 37 at the output end of box 28, and 45 at the output end of ferrite cylinder 40. Cutouts 46, geometrically similar tocutouts 22 of Fig. 1, are accordingly rotated 8 as shown in Fig. 6. Likewise cutouts 48 are geometrically similar tocutouts 22, but are rotated 37 as shown.

3 Thus, in all the embodiments of the invention shown, the respective cutouts are adapted to provide a larger gap between the dielectric support and the ferrite cylinder in that area in which the electric field gradient is highest; and this area is determined by the direction of the plane of polarization which in these waveguide ferrite devices is caused to rotate as the traveling energy passes along the length of the device.

For purposes of explanation of operation of the embodiments of Fig. 1 and Fig. 2, it will be assumed thatcircular waveguide section 12 is being excited in the conventional TE mode and further that the energy incident upon input opening is vertically polarized. Thus, it is clear that when the energy impinges upon the input end offerrite cylinder 14 the areas of maximum electric field' gradient will be in a plane passing through the center of the ferrite cylinder and parallel to the electric field vector wherecutouts 22 are situated. The ferrite cylinder is supported by that portion of the center hole of dielectric disc 16 which has not been altered by thecutouts 22. Thus, there is a larger gap betwen dielectric and ferrite in the area of high field gradient; and undesired arcing is thereby prevented. When the microwave energy reaches dielectric support 16 the plane of polarization has already rotated to angle 0 and the cut- The Faraday rotation of the plane of polarization is in a conventional manner effected by an externally caused longitudinal field along the ferrite cylinder. When the microwave energy reaches dielectric supporting disc 18, the plane of polarization of the energy has been rotated to an angle In order to prevent arcing at this support, disc 18 is rotated to the same angle When the microwave energy reachesdisc 20 at the output end offerrite cylinder 14 the plane of polarization of the energy has been rotated to the angle 0 and dielectric supportingdisc 20 is accordingly rotated so that the cutouts acre coincident with the areas which would otherwise have a high electric field gradient. As the microwave energy passes beyonddisc 20, it is further rotated to the angle 0 in the remainder of the ferrite.

The operation of the embodiment of Fig. 2 is substantially the same as that of Fig. 1 except that thedielectric cylinder 24 continuously supportsferrite cylinder 14 along its length instead of by spaced dielectric discs. In this embodiment thespiral groove cutouts 26 are adapted to provide a larger gap at all points along the ferrite cylinder at which a high field gradient would otherwise occur. In this embodiment the total angle of Faraday rotation is 0', and therefore the total angle of the spiral ofcutouts 26 is 0'.

In the practical embodiment of Fig. 6 it will again be assumed that the energy incident upon the input of waveguide section 44 is vertically polarized. For purposes of impedance matching, ferrite cylinder 40 is pointed at each end. In this practical embodiment the total angle of Faraday rotation is 45 so that energy reflected from a load at the output end of waveguide section 44 will be rotated another 45 as it passes back through the device so that any refiected energy appearing at the input end of waveguide section 44 will be of orthogonal polarization to the normal input polarization. Since it is desired to support the ferrite cylinder at points along its greatest diameter, the ferrite rod with its pointed ends is made to extend beyond each end of the dielectric box support 28. Thus, some amount of Faraday rotation of the plane of polarization of the incident microwave energy will have already occurred when the energy reaches the input end of dielectric box support 28, and the cutouts therein are accordingly rotated by the angle equal to that amount of Faraday rotation of the microwave energy at that point. In a practical embodiment that angle is 8. Likewise, the amount of Faraday rotation which has occurred in the ferrite when the energy has reached the output end of support 28 is not the full 45 but rather 37, and the cutouts 48 are accordinglyplaced at an angle of 37. The remaining 8 of rotation of the angle of polarization of the microwave energy occurs after the microwave energy has left the output end of support 28 and before the energy leaves the output pointed end of ferrite cylinder 40.

In the practical embodiment of Fig. 6 power levels of up to 300 kilowatts have been transmitted through the device into a variable phase 2:1 mismatch, and no arcing occurred between the ferrite and dielectric supports.

Other advantages provided by this invention are the ease and simplicity of adapting the new dielectric supports to existing waveguide ferrite devices and thereby increasing their power handling capacity. A further ad,- vantage is that in a force cooled waveguide ferrite device, the cutouts permit the coolant to flow past portions of the ferrite which would normally be in contact with dielectric supporting material and thereby permit better and more uniform cooling thus preventing localized differential heating effects from damaging the ferrite material and resulting in a further increase in power handling capacity.

What is claimed is:

1. In a unidirectional waveguide device employing a pencil shaped ferrite element for rotating the plane of polarization of microwave energy conducted through the waveguide device, the ferrite element being substantially smaller in cross section than the waveguide, means supporting the ferrite element in the waveguide device, said means comprising: a solid dielectric element supporting and partially encompassing the ferrite element and being in contact therewith along that portion of the surface of said ferrite element across which there is appreciably no change in electric field intensity, portions of said dielectric supporting element being cut out and'the surface spaced apart from that portion of the surface of said ferrite element across which there exists the greatest field intensity and at which there would otherwise exist an excessive electric field gradient.

2. In a waveguide isolator device employing an elongated ferrite element for rotating the plane of polarization of microwave energy conducted through the waveguide device, means supporting the ferrite element in the waveguide device, said means comprising: a plurality of dielectric supporting discs each being transversely supported at different points along the length of the waveguide device and each of said discs substantially filling the cross-section of the interior of said waveguide device, said discs each having central openings to allow passage and support of the elongated ferrite element therethrough, portions of the inner surfaces of said discs thereby being in contact with said ferrite element, the area of said contact being substantially confined to that portion of the surface of said ferrite element across which there is no appreciable electric field intensity, there being cut outs adjacent the central opening in each disc between the ferrite element an' each dielectric disc along the associated portion of the surface of said ferrite element across which there would otherwise be a large electric field gradient.

3. In a waveguide isolator device employing a pencil shaped ferrite element having a cross section small compared with that of the waveguide for rotating the plane of polarization of microwave energy conducted through the waveguide device, means supporting the ferrite element in the waveguide device, said means comprising: a solid dielectric cylinder substantially filling said waveguide device, said cylinder having a bore along its axis, said bore providing support for said .ferrite element; a pair of cut-away grooves along the length of said bore, said grooves being symmetrically opposite each other along the length of said bore and made coincident at all points along the length of said waveguide device with a line passing through the axis of said device parallel to the electric field vector, the lateral dimensions of said cut-away grooves beingdetermined by optimum considerations between providing rigid support for said fer rite element, providing an airgap sufficient to preclude voltage breakdown in the area near the surface of'said ferrite in which there would otherwise be a high electric field gradient, and maintaining the angular symmetry along the centerline of said device.

4. In a high power waveguide microwave isolator device employing an elongated ferrite element having a cross section small compared with that of the waveguide for rotating the plane of polarization of microwave energy conducted through the waveguide microwave iso lator device, means supporting the ferrite element in the isolator device comprising: a right parallelepiped dielectric box fabricated of thin slabs of solid dielectric, the exterior dimensionsof said box being such that said box wave isolator device; said box including supporting holes centered about the center of the lateral surfaces of said box, said supporting holes being adapted to support the ferrite element along the length of said device, said supporting holes providing contact between dielectric and ferrite along that part of the surface of said ferrite across which there is no appreciable electric field intensity, the supporting holes having cut out portions to define a gap between dielectric and ferrite in that area in which there would otherwise be a large electric field gradient, thus providing support for said ferrite element while precluding voltage breakdown in said area, said box being otherwise perforated in a manner to allow passage of coolant past the surfaces of said ferrite element.

5. In a unidirectional waveguide device employing a ferrite element substantially smaller in cross section than the waveguide device and extending longitudinally along and inside the waveguide device, means for supporting the ferrite element in the waveguide device comprising: a dielectric member within said Waveguide device, said dielectric member having an internal aperture therein encompassing said ferrite element with a portion of the surfaces defining said internal aperutre restraining said ferrite element from movement, said dielectric member being in contact with at least portions of the inner walls of said waveguide device, the internal aperture of said dielectric member having cutout portions defining gaps between said dielectric member and said ferrite element in the area of high electric field intensity within said waveguide device.

6. A microwave device comprising: a hollow waveguide for propagating electromagnetic wave energy having an electric field with a principal initial plane of polarization; means including a ferrite element longitudinally disposed within said hollow waveguide for rotating the plane of polarization of microwave energy within said waveguide, the rotation proceeding continuously along the length of the ferrite element; and dielectric support means within said hollow waveguide and at least partially encompassing said ferrite element, said dielectric support means being in contact with the interior walls of said hollow waveguide and in contact with portions of the surface of the ferrite element, there being cut out portions in the dielectric adjacent the ferrite element, the cut out portions extending in a plane parallel to the plane of polarization of the energy within the waveguide at the difrerent'points along the length of the ferrite element.

References Cited in the file of this patent Guided Waves, Applied Scientific Research, vol. 13, No. 2, July 27, 1953, pages 142-144.

Sullivan et al., New Type Microwave Switch, Journal of Applied Physics, vol. 26, No. 10, October 1955, pages substantially fills the interior of said waveguide micro- -1283-

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