US3445790A - Ferrite waveguide device having magnetic return path within the waveguide - Google Patents

Description

May 20, 1969 .c. B..SCHNEIDER 3,4 0

' FERRITE WAVEGUIDE DEVICE HAVING MAGNETIC RETURN PATE'WITHIN THE WAVEGUIDE Filed July 15, 1966 Sheef/ of 2 MN? l 38 22 44 54 50 /T f I /[//////////f////A// /l/ I INVENTOR. cYRlL B. SCHNEIDER ATTORNEYS y 0, 1969 c. B. SCHNEIDER 3,445,790

FERRITE WAVEGUIDE DEVICE HAVING MAGNETIC I RETURN PATH WITHIN THE WAVEGUIDE Sheet L of 2 Filed July 15, 1966 50/ FIG.-9

INVENTOR.

52 60 62 GYRIL B. SCHNEIDER BY v l I F414 ad. W

. k I 8 52 ATTORNEYS United States Patent 3,445,790 FERRITE WAVEGUIDE DEVICE HAVING MAGNETIC RETURN PATH WITHIN THE WAVEGUIDE Cyril B. Schneider, Oxnard, Calif., assignor to E & M Laboratories, a corporation of California Filed July 15, 1966, Ser. No. 565,527 Int. Cl. H03h 5/06 7/38 U.S. Cl. 33324.1 14 Claims ABSTRACT OF THE DISCLOSURE Ferrite microwave devices of compact external size are provided by an arrangement incorporating permanent magnets and magnetic path members as parts of or within the waveguide walls. In a rectangular waveguide, the waveguide interior is reduced in height through the use of transition sections within which permanent magnets are disposed in each broad wall of the waveguide. A magnetic return path disposed within an adjacent narrow wall of the waveguide completes the magnetic flux path which internally extends through the ferrite element. Temperature compensation is selectively provided through the use of ferromagnetic elements within the wall member and adjacent the permanent magnets. Undesirable resonance and increased bandwidth in ferrite microwave devices generally are minimized through the employment of an improved dielectric slab. The slab is configured to have minimum thickness at its edges which abut the waveguide walls and a smooth transition along the electric field lines to an intermediate thickness providing a desired total volume of dielectric material.

This invention relates to microwave devices and more particularly, to devices of the type utilizing magnetized ferrite elements for control of propagated waves.

Conventional microwave waveguide ferrite isolators normally include a C-shaped magnet mounted outside the wave-guide section of the isolator and may have pole pieces extending within the waveguide section to establish the desired magnetic field on the ferrite. Most conventional waveguide isolators are rather bulky due to the large magnet required. With operational microwave systems that are to be modified, space limitations frequently prevent or restrict addition of isolators and similar components at needed locations without disassembly and redesign.

Where isolators are to be physically located near other magnetic components, such as klystrons or magnetrons, the magnetic field of the isolator may adversely affect the operation of these components. In such cases the isolators typically are magnetically shielded, as by steel housings enclosing the externally mounted magnet. This shielding considerably increases component size and weight and reduces the magnetic efficiency due to partial absorption of the magnetic energy. The result may be the need for an even larger magnet to provide the necessary internal field strength.

In many applications of ferrite components, a wide bandwidth is extremely important, with a large number of requirements covering the full waveguide bandwidth. A limiting fatcor in broad bandwidth units is the presence of resonance spikes which are caused by higher order waveguide modes excited by a high loading factor or by sharp discontinuities within the waveguide. When these resonance spikes lie in the frequency range of the propagated wave, they advesely afiect the electrical characteristics. Frequently these spikes limit the useable range of the ferrite device. Where spikes occur within the frequency range of interest, it is necessary to take such 3,445,790 Patented May 20, 1969 ice steps as increasing the ferrite length, reducing the load thickness, or using suppressors to reduce the spike level. Since the spike cannot be completely eliminated, electrical characteristics, such as isolation, VSWR, and insertion are degraded.

Accordingly, it is an object of the present invention to provide an improved microwave device for accomplishing energy absorption, phase shift or dispersion with superior control and efiiciency.

It is an object of the present invention to provide an improved microwave device which has reduced size and weight, nominal magnetic shielding, and increased operational bandwidth.

It is an object of the present invention to provide an improved microwave ferrite isolator of relatively small size and light weight having improved magnetic genera- .tion, higher magnetic field strength, improved operating characteristics over a larger bandwidth, and an improved dielectric load device.

It is an object of the present invention to provide an improved dielectric load device for eliminating undesirable resonances within the operating frequency bandwidth in a ferrite microwave device.

These and other objects in accordance with the present invention may be accomplishedby providing an improved waveguide device having tapered internal conductive wall members providing a waveguide section of reduced height and including permanent magnets which establish a substantial magnetic field in a ferrite disposed between the wall members. The magnets, which are magnetically coupled by a magnetic conductor disposed within an adjacent narrow wall of the waveguide device, reside completely within the broad walls, providing a compact unit of regular waveguide size. The magnetic conductor provides a return magnetic path between the magnets and additionally defines a path of relatively low impedance to propagated electromagnetic wave energy. Ample magnetic shielding, the need for which is decreased by confining the magnets completely within the waveguide section of the device, is provided by the waveguide section and the magnetic conductor, resulting in more efiicient use of the magnets to provide high field strength efliciency.

In accordance with particular aspects of the invention, the size and configuration of the magnets in conjunction with the wall members may be varied to provide the magnetic characteristics desired. In one arrangement, each magnet is installed within a wall member at a central portion intermediate the tapered ends of the wall member with a small thickness of the high electrical conductivity wall member between each magnet and the ferrite defining the interior broad walls of reduced height within the waveguide. In other arrangements in accordance with the invention, the magnets are shaped to comprise a substantial part of or all of the wall members, a layer of high electrical conductivity material on the magnet surfaces defining the interior broad walls of reduced height. A ferromagnetic element may be included in each wall member adjacent the magnet to provide temperature compensation as desired.

In accordance with a further aspect of the invention, an improved dielectric load slab is provided in conjunction with the ferrite to eliminate undesirable resonances within the operational bandwidth of the microwave device, thereby providing broader bandwidth. The thickness of the dielectric load slab, in the direction normal to the electric field, is made relatively large at portions intermediate the broad walls and relatively small at .the edges adjacent the broad walls. The thicknesses are chosen to provide a desired total volume of dielecertic material. It has been found that the minimum thickness at the edges and the smooth transition along the electric field lines effectively reduce or eliminate undesirable resonance spikes within a relatively broad bandwidth of operating frequencies.

A better understanding of the invention may be had by reference to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective exploded view, partially broken away, of a system employing a microwave device in accordance with the invention;

FIG. 2 is a side elevational view of the microwave device shown in FIG. 1;

FIG. 3 is an end view, taken along the lines 3-3 of FIG. 2;

FIG. 4 is a perspective view of a preferred arrangement of a wall member in accordance with the invention used in the microwave device of FIG. 1;

FIG. 5 is a perspective view of another wall member arrangement in accordance with the invention;

FIG. 6 is a perspective view of another wall member arrangement in accordance with the invention;

FIG. 7 is a perspective view of yet another wall member arrangement in accordance with the invention;

FIG. 8 is a top view of a combined ferrite and dielectric load slab arrangement in accordance with the invention;

FIG. 9 is a side view of the arrangement of FIG. 8; and

FIG. 10 is an end view of the arrangement of FIG. 8.

One arrangement in accordance with the invention may conveniently be described as it is constructed in conjunction with rectangular waveguide devices and as used as a non-reciprocal isolator in a waveguide system. When constructed in this form and for this purpose, the device as shown in FIG. 1 may consist of an isolator 10 posi tioned between a pair of rectangular waveguide sections 12, 14. The waveguide sections 12, 14 illustrate only in a general way the manner in which the isolator 10 is coupled to associated system units. Those skilled in the art will recognize the many applications for an isolator, as for example, isolation of a transmitter from a receiver in conjunction with circulator or duplexing apparatus. Thus, by way of example, the arrangement of FIG. 1 is illustrated as having a transmit forward direction, in which direction an input from the waveguide section 12 passes through the isolator 10 with low attenuation and reflection, and a load or reverse direction in which direction microwave energy provided by the waveguide section 14 is greatly attenuated by the isolator 10. Each waveguide 12, 14 includes an associated flange 16 or 18, respectively, by which the waveguide may be coupled to the intermediate isolator 10.

Details of the isolator 10 may be seen with greater clarity in the views of FIGS. 2 and 3, to which reference may now 'be made. A rectangular waveguide section 20, which is made of any conventional waveguide material, such as aluminum, has broad walls 22, 24 and narrow walls 26, 28 all of which correspond in size to the standard waveguide sections 12, 14. At each end, the isolator 10 may be provided with flanges 30, 32 for coupling to the associated flanges 16, 18 of the standard height waveguide sections 12, 14 so as to provide an electrically unified structure. The isolator 10 is reduced in height by a pair of wall members 34, 36 mounted on the broad walls 22, 24 and provided with tapered end portions 38. The wall members 34, 36 are substantially coextensive with the interior broad walls 22, 24 of the waveguide section and have a thickness normal to the broad walls which increases inwardly from the opposite ends to a maximum at a central portion 40, the inner surface 42 of which defines the reduced height broad walls of the waveguide section. The wall members 34, 36 may be fashioned of any appropriate high electrical conductivity material, aluminum being preferred because of its light weight and ease of fabrication. The characteristic impedance of the unloaded reduced height waveguide section provided by the wall members 34, 36 may be selected to provide r 4 matching with the associated standard height waveguide sections thereby eliminating the need for an impedance matching section.

The wall members 34, 36, respectively, as best seen in FIGS. 3 and 4, include magnets 44, 46 mounted within accommodating apertures in the central portion 40 adjacent the narrow wall 26 of the waveguide section 20. The thickness of the magnets 44, 46 between opposite, substantially parallel, rectangular surfaces thereof, which dimension also defines the depth of the accommodating apertures, is slightly less than the thickness of the wall members 34, 36 at the central portion 40. With one of the rectangular surfaces defining a portion of the outer surface of the wall member in contact with the broad wall 22 or 24, a relatively thin portion of the conductive material of each wall member lies adjacent the other rectangular surface of the magnets, to define that part of the inner surface 42 providing an RF path for microwave energy. The lengths of the magnets 44, 46 and the accommodating apertures in a direction parallel to the central axis of the waveguide section 20 are slightly less than the length of the central portion 40. In width, the magnets and the accommodating apertures extend in directions normal to the narrow Walls from the edge of the wall member adjacent the narrow wall 26 along at least half the width of the wall member.

A combined ferrite-dielectric load slab arrangement 48, which includes a ferrite slab 50 and a dielectric load slab 52, is mounted on the inner surfaces 42 of the wall member 34, 36 approximately midway between the narrow walls 26, 28. The magnets 44, 46 provide a static magnetic field of selected direction through the ferrite slab 50. A magnetic coupling member 54 which comprises a portion of the narrow wall 26, extends along the width of the wall 26 and abuts the magnets 44, 46 at its opposite ends to provide a return path for the magnetic flux flow flowing between the magnets. The coupling member 54, which may be fashioned of appropriate magnetic material, such as steel, is preferably in the shape of a bar having a thickness comparable to the thickness of the narrow wall 26 and a width in the longitudinal direction of the waveguide section substantially equal to the magnet dimensions in the same direction. Additional material thickness may be added when necessary to avoid magnetic saturization. As thus constructed, the coupling member 54 is disposed completely within and forms a part of the narrow wall 26. In addition to providing a return magnetic path, the coupling member 54 provides an RF path of substantially low impedance within the waveguide section because of its relatively small dimension in the longitudinal direction. The compact arrangement of the magnets 44, 46 and the member 54 in conjunction with the waveguide section 20 frequently obviates the need for external magnetic shielding, the magnetic flux produced by the magnets being almost entirely confined Within the waveguide section and the coupling member 54. This results in increased magnetic efiiciency and small magnets can be used to provide a given magnetic field strength because of the absence of shielding loss.

Although the magnetic field provided by the magnets 44, 46 is static in the sense that it does not vary widely with time, it nevertheless is affected by changes in temperature both outside and inside the waveguide section 20. Therefore, a pair of compensator elements 55, 57 are respectively disposed adjacent the magnets 44, 46 to provide temperature compensation as necessary. The strength of the magnetic field varies inversely with the temperature, and the compensator elements 55, 57 comprise ferromagnetic material having a negative coefficient of permeability, preferably within a temperature range in which the microwave device is to be operated. The compensator elements 55, 57 which reside within accommodating apertures in the wall members 34, 36 extend outwardly from the edges of the magnets 44, 46 opposite the narrow wall 26 a uniform distance along the entire length of the magnets in a direction parallel to the axis of elongation of the waveguide section 20. The compensator elements 55, 57 shunt magnetic flux from the adjacent magnets 44, 46 about the internal ferrite to an extent dependent upon their permeability. Because of the negative coefiicient of permeability of the compensator elements, the degree of shunting for a given temperature is always such as to provide substantially the same field strength within the ferrite slab 50.

The magnets 44, 46 in conjunction with the coupling member 54 provide a magnetic field source which is completely contained within the outside dimensions of the waveguide section 20 of the isolator 10. This arrangement, therefore, provides a waveguide component which is light in weight and compact, and therefore particularly useful where space limitations are paramount, although it should be understood that the arrangement is useful with any waveguide system. The arrangement is particularly useful with waveguide systems already constructed and wherein it is determined that certain waveguide components, such as isolators, are necessary. Thus an already assembled Waveguide system can be provided with isolators in accordance with the present invention by simply removing a section of waveguide approximately equal in length to the length of the isolator 10 and attaching the flanges 16, 18 for receiving the isolator. Because the outside dimensions are approximately the same as those of the standard waveguide, no space problems are presented.

The isolator 10 in accordance with the present invention operates in well-known fashion to provide resonance absorption and thereby attenuation of the electromagnetic wave energy traveling in a particular direction through the isolator. The direction of the magnetic field provided by the magnets 44, 46 in conjunction with the sense of rotation of the magnetic intensity vector in the region of the ferrite slab 50 provides a strong interaction at the gyromagnetic resonant frequency with the spinning electrons in the ferrite slab, resulting in the absorption of the microwave energy and dissipation of the energy as heat.

Alternative arrangements of the wall members 34, 36 in accordance with the present invention are shown in FIGS. 5, 6 and 7. In the arrangement shown in FIG/5, the magnet 44 has a configuration similar to that of FIG. 4 except that its thickness is substantially equal to the thickness of the central portion 40 of the wall member. One rectangular surface of the magnet 44 is plated or coated with a suitable conductive material 56, such as copper, to define a part of the inner surface 42 providing a uniform RF path. The arrangement of FIG. 5 provides magnetic properties similar to those of the arrangement shown in FIG. 4, and is somewhat easier to manufacture because of the relative ease with which a section of the wall member may be cut out to accommodate the magnet.

In the alternative arrangement shown in FIG. 6, the magnet 44, and accordingly the accommodating aperture therefor, comprises approximately one-half the width of the wall member 34 along the entire length thereof and have a thickness approximately equal to the wall member thickness both at the central portion 40 and at the tapered end portions 38. The appropriate surfaces of the magnet 44 including the inner surfaces of the tapered end portions 38 are plated or coated with the conductive material 56 to provide a uniform RF path. The wall member arrangement of FIG. 6 provides larger magnets and thereby greater field strength, at the expense of some increased stray magnetic leakage to the outside of the isolator 10'.

In the arrangement of FIG.'7, the entire wall member 34 is comprised of the magnet 44, the inner surfaces again being coated or plated with the conductive material 56. Like the arrangement of FIG. 6, the wall member of FIG. 7 provides greater magnetic field strength at the expense of increased flux leakage to the outside of the isolator 10.

The details of the improved dielectric load slab 52 in conjunction with the associated ferrite slab 50 are shown in FIGS. 8, 9 and 10. The dielectric load slab 52 which is fashioned of any appropriate dielectric material, such as Al-300, has a volume chosen to produce the desired loading effect within the isolator 10. Conventional dielectric load slabs are typically 6-sided with a rectangular cross section, with one of the larger surfaces being abutted against the ferrite slab.

Certain undesirable resonances present in isolators employing conventional ferrite-dielectric load slab combinations within a reasonably narrow bandwidth produce non-uniform resonant absorption at various different frequencies thereby limiting the bandwith within which desirable operation can be accomplished. The undesirable resonances affect the insertion loss, the voltage standing wave ratio, the isolation, and other important electrical characteristics of the isolator. It has been found that the undesirable resonances are shifted out of the desired broad frequency band of operation by substantially reducing the thickness of those portions of the dielectric load slab adjacent the interior walls of the isolator while at the same time increasing the thickness of the load slab at central portions thereof as necessary to provide the desired volume of dielectric material for proper loading.

Accordingly, the improved dielectric load slab 52 is comprised of an elongated element of dielectric material having a planar base surface 58 for receiving the ferrite slab 50; the overall length of the load slab being somewhat greater than the ferrite slab 50 with the opposite ends. extending therebeyond. The width of the load slab 52 in a direction parallel to the plane of the base surface 58 and normal to the axis of elongation increases in linear fashion inwardly from points at the opposite ends of the load slab to a maximum uniform width along a central region 60 disposed between the identical tapered end regions 62. The thickness of the load slab 52 in a direction normal to the plane of the base surface 58 is a uniform minimum at the outer edges of the load slab in the width direction. The thickness increases in linear fashion inwardly to a maximum thickness region lying within a plane normal to and intersecting the plane of the base surface at the central axis thereof. The maximum thickness of the' load slab 52 is uniform along the central region 60 thereby defining a line parallel to the central waveguide axis. At the end regions 62 the maximum load slab thickness decreases linearly from the uniform thickness of the central region 60 to the uniform minimum thickness, thereby defining planes which extend between the ends of the central region and the opposite ends of the load slab 52. The overall load slab thicknesses are chosen to provide the desired volume of dielectric material for best operation. It has been found that best results are obtained when the variations in thickness are made gradual and the outer surfaces are relatively smooth and without abrupt discontinuity.

The improved dielectric load slab 52, as illustrated in FIGS. 8, 9 and 10, has resulted in isolators of shorter length and improved electrical characteristics, and is useful for many applications utilizing confined wave propagation. Devices in accordance with the invention utilize a smooth transfer into a highly dielectric loaded media, along the electric field lines. The thin edge of the dielectric member acts as a field concentrator and provides better directional control of the electric field by acting to insure perpendicularity at the end points of the electric fields. This may be regarded as a shaping effect that provides a smooth transition into the media. Tendencies to produce or support higher order modes are minimized by reduction of the coextensive facing surfaces between the waveguide wall and the dielectric media. The additional discontinuity introduced by the cement employed along the edges of the dielectric is also minimized by this configuration. Although a fiat taper of the thickness is illustrated, it will be appreciated that other configurations, such as curvilinear variations, could also be used for like effect.

In one particular arrangement in accordance with the invention, an isolator was fashioned with a 4 brass body, and a ferrite slab made of Nf-llA. A load slab made of Al-300 and having the approximate proportions shown in FIGS. 8, 9 and 10 was used without a mode suppressor. The ferrite slab used measured 3.260" long, 0.6 17" wide, and 0.022" thick. The load slab was 4.800 long, 0.617" wide at the central region, and had end regions 1.125" long. The load slab thickness varied from a uniform minimum of 0.050" to a maximum of 0.225" at the central region. The following isolator characteristics were found:

Isolation (minimum) decibels 31 Isolation (maximum) d0 58 Insertion loss (maximum) do 0.75 Insertion loss (minimum) d0 0.60 VSWR (maximum) 1.09 VSWR (minimum) 1.04

Although there have been described specific arrangements of a waveguide device and a dielectric load in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangement falling within the scope of the annexed claims should be considered to be a part of the invention.

What is claimed is:

1. A microwave device comprising the combination of a waveguide section having a pair of members defining opposite broad wall means; a pair of magnet means, each disposed within a different one of said pair of members for providing a magnetic field between the wall means; means disposed within a third wall member of the waveguide section and coupled to the pair of magnet means to provide a return magnetic path; and ferrite means disposed within said magnetic field and within the waveguide section.

2. The invention as set forth in claim 1 wherein said pair of opposite members have a substantially standard exterior dimension and converge from the opposite ends of the waveguide section to define a central, interior portion of reduced height.

3. The invention as set forth in claim 1 and including in addition magnetic means coupled to said magnets for providing temperature compensation.

4. A microwave device in accordance with claim 1 further including dielectric load means disposed adjacent and extending beyond the opposite ends of said ferrite means in a direction parallel to the axis of elongation of the waveguide section.

5. A microwave device in accordance with claim 4 wherein said ferrite means has a broad surface and said dielectric load means comprises a member having a broad surface substantially coextensive with the broad surface of the ferrite means, a thickness in a direction normal to the broad surface which tapers from a central region to a minimum at the opposite edges of the broad surface, and a width which tapers at opposite ends of the member.

6. A microwave isolator for use with a system having selected height waveguides, the isolator including in combination a waveguide section of standard exterior dimensions arranged to be coupled at its opposite ends to the selected height waveguides and having a pair of broad wall members defining a hollow interior of substantially rectangular cross-section and reduced height at a central portion thereof; a pair of magnet means, each contained substantially completely within a different one of the opposite broad wall members in the central portion of the waveguide section; means disposed entirely within a narrow wall of the Waveguide section and coupled to said magnet means for providing a magnetic path between the magnet means; a ferrite slab disposed adjacent the opposite broad wall members between the magnet means; and a dielectric load slab disposed adjacent the ferrite slab, said dielectric load slab having a thickness which is less at those portions thereof adjacent the pair of opposite broad wall members than at those portions at the central regions thereof.

7. The invention as set forth in claim 6 above, wherein a pair of magnetic elements having a negative temperature coefficient of permeability are inset into said opposite broad wall members adjacent the different ones of said magnets to provide temperature compensation therefor, wherein said load slab thickness increases with increasing distance from the broad walls to a maximum thickness at a point approximately equidistant from the broad wall members.

8. A microwave device for use with a system having selected height waveguides, the device including in combination a waveguide section corresponding in exterior cross-sectional dimension to the selected height waveguides; a pair of aluminum wall members mounted on the opposite interior broad walls of the waveguide section, said wall members having a width substantially equal to the width of the broad walls and a thickness normal to the broad walls which increases inwardly from opposite ends of the waveguide section to a uniform maximum thickness at a central portion, the inner surfaces of the central portions of the wall members defining a pair of facing planar conductive walls between which lies a region of reduced height within the waveguide section; each of said wall members having an aperture therein, said aperture having a length such that it extends along at least a substantial portion of the length of the wall member central portions in a direction parallel to the central axis of the waveguide section, a Width normal to a narrow wall such that it extends from the narrow wall along at least half the total width of the wall member, and a depth normal to the interior broad walls of the Waveguide section such that it extends from the adjacent interior broad wall over a substantial portion of the total Width of the wall member, a pair of permanent magnets each residing within and coextensive with the aperture of a different one of the wall members; ferrite means disposed adjacent the facing planar conductive walls of the wall members between the magnets; and a magnetic element in abutting relation to each of said magnets, said magnetic element being disposed completely within and forming a part of a narrow wall of the waveguide section thereby providing a return magnetic path between the magnets and a radio-frequency path of relatively low impedance for microwave energy within the waveguide section.

9. A microwave device in accordance with claim 8 further including a separate temperature compensator inset into each of said wall members adjacent the permanent magnet therein, each temperature compensator comprising a ferromagnetic element having a negative temperature coefficient of permeability, said element extend ing outwardly from the edges of the magnets opposite the magnetic element and adjacent the ferrite means to form a magnetic shunt path between the magnets.

10. A microwave device in accordance with claim 8 wherein each of the apertures within the wall members has a length less than the length of the central portion of the associated wall member and a width approximate ly one-half the total width of the wall members.

11. A microwave device in accordance with claim 8 wherein each of the apertures within the Wall members has a length substantially equal to the total length of the associated wall member and the portion of each Wall member extending between the magnet and the wall member inner surface in a direction normal to the interior broad Walls of the waveguide section comprises a relatively thin layer of conductive material providing a uniform RF path.

12. A microwave device in accordance with claim 8 wherein each of the apertures within the wall members has a width substantially equal to the total width of the associated wall member, the wall member comprising a relatively thin layer of conductive material, the outer surface of which defines the opposite interior broad walls of the waveguide section.

13. A microwave device in accordance with claim 8 further including a dielectric load slab mounted adjacent the ferrite means, said load slab comprising an elongated element of dielectric material having a planar base surface for abutment against the ferrite means, said base surface having a central axis parallel to the axis of elongation of the element, said element having a width in a direction normal to the central axis of and parallel to the plane of the base surface which increases inwardly from points at opposite ends of the element to a maximum uniform thickness along a central region of the element equidistant from the opposite ends, said element further having a thickness which extends from the base surface in a direction normal to the plane thereof, said thickness being a maximum at a maximum thickness plane normal to and intersecting the plane of the base surface at the central axis thereof, said thickness decreasing with increased distance from the plane of maximum thickness on opposite sides thereof a uniform minimum thickness at the outer extremes of the element in the width direction, the maximum thickness of the element defining a line within the maximum thickness plane which is parallel to the axis of elongation of the element along the central region and which slopes to points removed from the base plane by a distance equal to the minimum uniform thickness at the opposite ends of the element.

14. In a microwave device having ferrite means disposed within a waveguide section, an improved dielectric load slab comprising an elongated element of di electric material having a planar base surface abutting against the ferrite means, said base surface having a central axis parallel to the axis of elongation of the element, said element having a width in a direction normal to the central axis of and parallel to the plane of the base surface which increases inwardly from points at opposite ends of the element to a maximum uniform thickness along a central region of the element equidistant from the opposite ends, said element further having a thickness which extends fom the base surface in a direction normal to the plane thereof, said thickness being a maximum at a maximum thickness plane normal to and intersecting the plane of the base surface at the central axis thereof, said thickness decreasing with increased distance from the plane of maximum thickness on opposite sides thereof to a uniform minimum thickness at the outer extremes of the element in the width direction, the maximum thickness of the element defining a line within the maximum thickness plane which is parallel to the axis of elongation of the element along the central region and decreasing linearly from opposite ends of the central region to the opposite ends of the element to define planes which extend therebetween.

References Cited UNITED STATES PATENTS 2,956,245 10/1960 Duncan 33324.2 2,989,709 6/ 1961 Seidel et al.

3,273,082 9/1966 Chiron 333-24.1 X 3,304,521 2/1967 Freibergs et :al 333-24.2 3,355,680 11/1967 Saltzman et al. 3331.1

HERMAN KARL SAALBACH, Primary Examiner.

PAUL L. GENSLER, Assistant Examiner.

Us. 01. X.R. 333 24.2, 34

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