Surface mountable circulator/isolator and assembly technique

[0001] This application is a continuation-in-part of U.S. application Ser. No. 10/005,520, filed Dec. 7, 2001, which is herein incorporated in its entirety by reference.

[0002] The invention relates to microwave ferrite devices, and more particularly, to a surface mountable circulator/isolator design and assembly technique.

[0003] Increasing demands for high signal power and bandwidth capacity in modern communication networks impose stronger limitations on the allowed level of intermodulation distortion (IMD). A typical level of IMD is about 75 dBc for existing high power circulators, which is not sufficient for providing the desired degree of inter-channel isolation. The suppression of IMD decreases the interference between the adjacent communication channels and leads to the higher quality of operation. Therefore, the development of a circulator/isolator that is capable of handling high input power while maintaining a low IMD would be highly desirable.

[0004] A major contributor to IMD in microwave ferrite devices, such as circulators/isolators, is the non-linear phenomenon of ferromagnetic resonance. The closer the frequency of ferromagnetic resonance (FMR) is to the operating frequency range, the larger is the signal distortion.

[0005] Another contributor to the IMD is a non-uniform design. Specifically, the more portions of different conducting materials used in a device design, the worse the device performs in terms of IMD. For example, in surface mountable devices, separate conductors are typically used to electrically connect the center conductor to contact ports of the device. Moreover, it is difficult to provide tight coplanarity in such a design because the contact ports are distinct, separate parts from the connecting conductors. Such a non-uniform contact can contribute to increased IMD levels.

[0006] Another problem associated with the microwave ferrite devices is poor alignment. In more detail, typical circulators/isolators include a number of layers such as ferrites, a center conductor, magnets, pole pieces, ground plates, and temperature compensators. These layers are generally referred to as a stack. During manufacturing of a ferrite device, the layers are stacked onto one another, and manually manipulated by a technician during an alignment process before the layers are fixed into place. As the ground planes are generally the widest layers, it is difficult to properly align the narrower layers, such as the ferrites and center conductor. As such, alignment error is difficult to avoid.

[0007] Generally stated, the overall performance of the circulator/isolator device is a function of alignment. In addition, the shaping of the center conductor can be such that a low IMD level is achieved. The center conductor is usually shaped to match the circulator's impedance to that of a transmission line. Such impedance matching enables efficient transfer of energy between the device ports. The tuning elements typically include quarter-wave transformer arms and open-end tuning stub resonators symmetrically situated between the arms. With proper alignment, the open-end tuning stub resonators can fully extend to the perimeter of its surrounding layers, thereby enabling further improvement of IMD performance.

[0008] One common alignment technique employs a well in a housing, where the layers of a device can be stacked. The diameter of the well is slightly larger than the widest layer to accommodate the elements of the stack during manufacturing. The sides of the well are slotted allowing a manual push-stick alignment of the circuit. However, such a technique does not effectively solve the alignment error problem. In addition, thermal stress caused by differing coefficients of thermal expansion associated with the stack layers is further exacerbated by alignment error, thereby causing further deterioration of device performance.

[0009] The lack of coplanarity gives rise to other problems as well. In particular, large-scale production of ferrite devices implicates simple mechanical designs that are compatible with automated pick-and-place assembling and mounting technology. The proper pick-and-place of a device having a non-uniform, non-coplanar mounting base is inhibited. Thus, the manufacturing process may require more complicated and/or costly placement processes. Moreover, reliable electrical contact with a host system (e.g., a mother board or chassis level card) requires that the connecting leads and mounting base of a circulator/isolator be rigid and coplanar. Typically, an overall coplanarity of the mounting base should be within a few mils.

[0010] Thus, both electrical and mechanical parameters of a circulator/isolator device should be suitable for pick-and-place processing in both the device assembly, as well as population of the device on a host system. What is needed, therefore, is a highly manufacturable and reliable circulator/isolator device that has a co-planar mounting surface and is capable of maintaining a low IMD.

[0011] One embodiment of the present invention provides a passive microwave device. The device includes a printed circuit board having a plurality of conductive ports, a ground portion, and at least three aligning holes that are configured to receive alignment pins of an assembly fixture. A housing is secured on the ground portion of the printed circuit board, and includes a bottom portion having three or more centering slots. Each centering slot corresponds to one of the aligning holes of the printed circuit board. The device further includes a stack that has a center conductor that is configured with three or more aligning portions that are each adapted to couple with a corresponding alignment pin of an assembly fixture.

[0012] The device may further include a pressing cover that is disposed on top of the stack, and configured to tightly fit into an inner perimeter of the housing. A locking cover may also be disposed on the pressing cover, and configured with a number of teeth spaced on its periphery. In such an embodiment, the locking cover is rotated during the manufacturing process so that the teeth engage flair slots defined in the housing thereby locking the stack in place. The printed circuit board has a stack side and a host side, and may further include a plurality of metallized via holes that electrically and thermally couple the stack side to the host side.

[0013] Likewise, the conductive ports and ground portion of the printed circuit board each have a stack side and a host side. Each conductive port can be configured with a metallized pad on its host side that is substantially coplanar with the ground portion of the host side. In general, each aligning portion of the stack is disposed on the stack's periphery and is configured with a surface adapted to couple with a corresponding alignment pin of an assembly fixture. In one particular embodiment, the center conductor includes a plurality of tuning stub resonators in symmetrical relation to one another, and each aligning portion is disposed on an end of a respective tuning stub resonator.

[0014] The center conductor may further include a plurality of transformer arms in symmetrical relation to one another, where each arm has an end portion that is electrically and mechanically connected to a respective conductive port on the stack side of printed circuit board. The stack may further include at least one of a ground plane, a magnet, a ferrite, a pole piece, and a temperature compensator. Some such stack elements may have at least three alignment holes configured to receive alignment pins of an assembly fixture. Other stack elements may have a common shape that allows minimal play when the element is placed between alignment pins of an assembly fixture.

[0015] In one such embodiment, the stack includes a ferrite element on at least one side of the center conductor, and the center conductor further includes tuning stub resonators and transformer arms in symmetrical relation to one another. Each tuning stub resonator is extended to an edge of the one or more ferrite elements in a radial direction. The center conductor may also include transformer arms in symmetrical relation to one another. Each tuning stub resonator is extended toward its neighboring transformer arms in an azimuthal direction. In operation, such an embodiment enables 30-degree rotation of the standing wave pattern to be maintained and low IMD.

[0016] Another embodiment of the present invention provides a method for manufacturing a circulator/isolator device. The method includes placing a printed circuit board on an assembly fixture having three or more alignment pins, the printed circuit board having at least three aligning holes that are configured to receive the alignment pins of the assembly fixture. The method further includes placing a housing on a central ground portion of the printed circuit board, the housing including a bottom portion having three or more centering slots. Each centering slot corresponds to one of the alignment pins of the assembly fixture. The method further includes placing a stack in the housing between the alignment pins of the assembly fixture. The stack includes a center conductor that is configured with three or more aligning portions that are each adapted to couple with a corresponding alignment pin of the assembly fixture.

[0017] The method may further include disposing a pressing cover on top of the stack, where the pressing cover is configured to tightly fit into an inner perimeter of the housing. The method may also include disposing a locking cover on top of the pressing cover, where the locking cover is configured with a number of teeth spaced on its periphery. The method can proceed with rotating the locking cover so that the teeth engage flair slots defined in the housing thereby locking the stack in place, and securing the locking cover with a bonding material (e.g., solder or epoxy).

[0018] The method may continue with placing a circulator/isolator device produced by the method on a host system thereby contacting coplanar conductive ports and a ground portion of the printed circuit board with corresponding contacts of the host system. The center conductor may further include a plurality of transformer arms in symmetrical relation to one another, where the method continues with electrically and mechanically connecting an end portion of each transformer arm to a respective conductive port on the printed circuit board.

[0019] In one embodiment, the center conductor includes a plurality of transformer arms and tuning stub resonators in symmetrical relation to one another, where the method further includes the preliminary step of forming the center conductor so that its tuning stub resonators extend toward its neighboring transformer arms in the azimuthal direction, and extend to the edge of ferrite elements included in the stack.

[0020] Another embodiment of the present invention provides a method for manufacturing a stack for a circulator/isolator device. The method includes placing stack elements including at least one of a ground plane, a magnet, a ferrite, a pole piece, and a temperature compensator, into an assembly fixture having three or more alignment pins. Each stack element has one of at least three alignment holes configured to receive the alignment pins of the assembly fixture, or a common shape that allows minimal play when the element is placed between the alignment pins of the assembly fixture. The method may further include securing the stack elements by bending inter-laced periphery fingers of upper and lower ground plane stack elements, thereby forming a final stack assembly.

[0021] Another embodiment of the present invention provides an assembly fixture for manufacturing circulator/isolator devices. The fixture includes a body, and three or more alignment pins that extend vertically from a top surface of the body. The pins are adapted for at least one of: coupling with corresponding holes and slots of elements included in a circulator/isolator device being assembled; and limiting radial movement of circulator/isolator device components disposed between the alignment pins. In one embodiment, the length of the pins is slightly less than the device's height so as to allow a cover to rest on the assembly without contacting the pins. In another particular embodiment, there are three alignment pins, two of which have a fixed position, and the third pin has an adjustable position.

[0022] The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.

[0023] FIG. 1a is an exploded perspective view of the ferrite device structure configured in accordance with one embodiment of the present invention.

[0024] FIG. 1b illustrates the surface mount or host side of the structure illustrated in FIG. 1a.

[0025] FIG. 2 illustrates the stack of a circulator/isolator device configured in accordance with one embodiment of the present invention.

[0026] FIG. 3 graphically illustrates a function of the splitting factor versus frequency for two different values of an external magnetic field.

[0027] FIG. 4 illustrates a stack center conductor configured in accordance with one embodiment of the present invention.

[0028] FIG. 5 illustrates a cross-sectional view of an assembled circulator/isolator device configured in accordance with one embodiment of the present invention.

[0029] FIG. 6 illustrates a perspective view of a partially assembled circulator/isolator device that is installed in an assembly fixture in accordance with one embodiment of the present invention.

[0030] FIGS. 7a and 7b illustrate side and top views respectively of an assembly fixture configured in accordance with one embodiment of the present invention.

[0031] Embodiments of the present invention enable an inexpensive, high power circulator/isolator device having efficient IMD and temperature performance. A readily manufacturable sheet metal housing and coplanar mounting surface reduce requirements for precision machining, and allow the utilization of automated pick-and-place assembling and installation techniques. In addition, alignment of device materials, such as the stack, is maintained.

[0032] Device Structure

[0033] FIG. 1a is an exploded perspective view of the circulator/isolator device structure configured in accordance with one embodiment of the present invention. The structure includes a printed circuit board (PCB) 1, a housing 2, a stack 3, a pressing cover 4, and a locking cover 5. The stack 3 is shown in its assembled state, and includes a number of components that will be discussed in reference to FIG. 2.

[0034] The PCB 1 can be a conventional printed circuit board that is masked and etched with a pattern suitable for the particular application for which the device is intended. For example, the PCB 1 can be a two side copper clad dielectric of FR-4 type material. This particular embodiment includes three conductive ports 1a for a circulator application, or two ports 1a for an isolator application. Such ports can be used for input and output of microwave energy. As port usage is the primary difference between the circulator and isolator applications, this disclosure is presented in the context of circulators so as to provide a more complete description. However, the principles of the present invention are equally applicable to isolator applications.

[0035] The PCB 1 further includes at least three aligning holes 1b and a plurality of the metallized via holes 1c. The aligning holes 1b are configured to receive alignment pins of an assembly fixture. The metallized via holes 1c electrically and thermally couple the stack side of the PCB to the host side, and operate to dissipate heat and provide a robust ground portion. The metallized surface of the PCB 1 (indicated by the dotted area) is partially removed from the ports 1a thereby forming short metallized pads 1d on the stack side of the PCB 1, as shown in FIG. 1a, and long metallized pads 1e on the host side of the PCB 1 as illustrated in FIG. 1b. Note how the long metallized pads 1e run out to the edge of the ports 1a. These metallized pads 1e allow robust, coplanar contact points that electrically and mechanically couple to contact points of a host system during a manufacturing pick-and-place operation.

[0036] PCB 1 can be, for example, drilled or stamped to form the aligning holes 1b and the via holes 1c, which can then be metallized. Conventional masking/etching processes can be used to remove unwanted metal for the surface of the PCB 1. Numerous processes can be employed to form the PCB 1, and the present invention is not intended to be limited to any one such process or type of PCB 1.

[0037] The housing 2 includes side portions 2a each configured with an open flair slot 2b, and a bottom portion configured with alternating centering slots 2c and relief openings 2d. In one embodiment, the housing 2 is made from a single piece of sheet metal (e.g., steel or aluminum). The sheet metal can be milled, stamped, or otherwise cut to a pattern so as to form the side portions 2a, open flair slots 2b, centering slots 2c, and relief openings 2d. The side portions 2a can then be bent up to a perpendicular position relative to the bottom portion as shown. With such an embodiment, no secondary machining of the housing 2 is required.

[0038] In the formed housing 2 of this particular embodiment, the lower horizontal portion of the flair slots 2b are substantially parallel to the bottom of the housing. This will allow the pressing cover 4 and teeth 5a of locking cover 5 to fully engage the slots 2b. Note that the slots 2c, the openings 2d, and the side portions 2a are equally spaced and symmetrically positioned relative to the central axis of the housing 2. Centering slots 2c have inner edges that are closest to the central axis of the housing 2. These inner edges of slots 2c correspond to the aligning holes 1b. Thus, corresponding alignment pins of an assembly fixture can be used to ensure that the centering slots 2c are in proper alignment with the PCB 1. In addition, each relief opening 2d coincides with a respective conductive port 1a location on the PCB 1. As such, the housing 2 will not impinge upon the location of the ports 1a.

[0039] The stack 3 includes a set of elements suited to the particular application. For instance, in the case of a circulator, the stack 3 could include a center conductor, two ferrite disks (one on each side of the center conductor), one or more magnets, upper and lower pole pieces, a temperature compensator, and upper and lower ground planes. Note that, depending on the application, some of the elements included in the stack 3 may be unutilized. Further note that additional elements may be employed in a particular device design depending on given specifications.

[0040] As can be seen in this embodiment, the stack 3 includes three port connectors or transformer arms of the center conductor extending downward. End portions of each arm electrically and mechanically connect to a respective short metallized pad 1d on the stack side of the PCB 1. Via holes 1c through each pad can be solder filled or otherwise metallized so that an electrical connection is formed at the contact point between each transformer arm and the corresponding short metallized pad 1d. Electrical contact is also made between each transformer arm and a respective long metallized pad 1e by way of one or more via holes 1c associated with each port 1a. In addition, the stack 3 center conductor includes a number of aligning portions (only one shown in FIG. 1a) disposed on its periphery. Each aligning portion has a half-moon or concave surface that is adapted to couple with a corresponding alignment pin of an assembly fixture. Specific embodiments of the stack 3 and its center conductor will be discussed in reference to FIGS. 2 and 4, respectively.

[0041] During device assembly, the pressing cover 4 is disposed on the top of the stack. The pressing cover 4 may be made from the same material as the housing 2, but need not be. In one embodiment, the cover 4 is a polygonal flat layer of sheet metal having as many sides as the housing 2. The cover 4 is configured to tightly fit into the inner perimeter of the housing 2, and more particularly, to engage the housing 2 slightly above the lower horizontal portion of the flair slots 2b. It will be appreciated that the actual shape of the housing 2 and cover 4 can vary, and that the present invention is not intended to be limited to any one shape.

[0042] A locking cover 5 is disposed on top of the pressing cover 4, and is configured with teeth 5a. In this particular embodiment, these teeth 5a are equally spaced on the periphery of the cover 5. The slots 2b in the housing 2 accept the teeth 5a. Just as with the cover 4, the locking cover 5 may be made from the same material as the housing 2. The stack 3 and the cover 4 are securely fastened in the housing 2 when the cover 5 is turned, thereby locking the stack 3 in place. There are two holes 5b in the locking cover 5 to receive a rotation tool tips. After rotating the locking cover 5 into position, a bonding material (e.g., solder or glue) can be applied to the holes 5b so as to secure locking cover 5 to cover 4.

[0043] Stack Configuration

[0044] FIG. 2 illustrates the stack of a circulator/isolator device configured in accordance with one embodiment of the present invention. In this example, the stack includes (from bottom up) a bottom ground plane, a lower pole piece, a lower ferrite disk, a center conductor (also referred to as a circuit herein), an upper ferrite disk, a top ground plane, an upper pole piece, a magnet, and temperature compensators. Additional layers may be included, such as magnets, ground planes, and pole pieces, depending on the application.

[0045] The lower and upper pole pieces can be steel or some other ferromagnetic material. The circuit is typically copper, but can be any suitable conductor depending on the application. Note that the pole pieces, ferrites, magnet, and temperature compensator have substantially the same shape in this embodiment. This common shape allows minimal play when such stack elements are placed between the alignment pins of an assembly fixture. Further note that each of the three transformer arms of the circuit extend beyond the perimeter of the bottom ground plane so that they can be connected to respective short pads 1d of the PCB 1. Further note that the aligning portions of the circuit (not shown in FIG. 2) correspond to alignment pins of the assembly fixture such that the circuit effectively has substantially the same size as that of the pole pieces, ferrites, and magnet.

[0046] The top and bottom ground planes of this example are each configured with three alignment holes adapted to receive the alignment pins of an assembly fixture. This allows the stack to be pre-assembled in a self-aligning fashion in accordance with the principles of the present invention. Further note that the ground planes are the widest elements in the stack, and fully cover the ferrite elements. These ground planes may be, for example, silver plated copper, or other non-ferrous material depending on the desired electrical properties. Inter-laced fingers on the perimeters of the ground planes can be bent into secure the layers of the stack, thereby forming a final stack assembly as illustrated in FIG. 1a.

[0047] A secondary assembly procedure utilizing similar self-alignment principles of the present invention can then be used to assemble the pre-fabricated stack into a circulator/isolator device as shown in FIG. 1a. Note that the secondary assembly procedure employs an assembly fixture having alignment pins that are farther apart than the alignment pins of the fixture used to assemble the stack. This will allow the pre-fabricated stack to properly fit within the pins of the assembly fixture of the secondary procedure.

[0048] In alternative embodiments, a single assembly procedure is employed, where the stack layers are assembled as part of the overall device assembly. In such an embodiment, the inter-laced fingers on the perimeters of the ground planes can be eliminated so that no bending need be performed. In another embodiment, the ground planes of the stack can be of the same shape as the other stack layers (e.g., pole pieces and ferrites) so that they fit within the aligning pins of the assembly fixture. In such cases where the interlaced fingers are not included on the ground planes, the stack layers are effectively secured in place once the locking cover 5 is installed.

[0049] Other stack configurations are possible, and the present invention is not intended to be limited to any one such configuration. Rather, any number of stack configurations can be implemented in accordance with the principles of the present invention so as to provide a self-aligning assembly process. For example, another embodiment of the present invention may employ an assembly fixture having twelve alignment pins, with two pins for bracing each side of a hexagonal shaped stack. In such a case, the stack layers would have a common shape so as to fit within the alignment pins of the fixture. Alternatively, the ground planes of the stack could be configured with twelve alignment holes that correspond to the fixture's alignment pins. In any case, a self-aligning assembly process is enabled. In this sense, the alignment of the device layers and componentry is inherent in the design.

[0050] The effective diameter of the stack, whether pre-fabricated or not, should correspond to the diameter of the circle that is tangential to the inner edges of the centering slots 2c of housing 2. Centering and alignment of stack 3 elements in the housing 2 is thereby enabled, as well as lower IMD. The stack elements are configured with alignment holes or other constructive features that facilitate alignment with the alignment pins of the assembly fixture.

[0051] 30-Degree Rotation of Standing Wave Pattern Restoration

[0052] FIG. 3 graphically illustrates a function of the splitting factor k/ versus frequency for two different values of an external magnetic flux. Curve 6 shows that at the operation frequency range f_oper, the splitting factor provides a 30-degree rotation of the standing wave pattern required for circulation action. The separation between the frequency of ferromagnetic resonance and the operation frequency is equal to f₁f_oper. One way to decrease IMD is to keep this difference as large as possible. This can be achieved by increasing the external biasing magnetic field from H₁ to H₂. This will shift the curve 6 into a new position 7, thereby increasing the spacing to f₂f_oper. With this frequency shift, however, the splitting factor at a given operation frequency range f_oper will be diminished and the required 30-degree rotation of the standing wave pattern will not be achieved. As will now be explained, embodiments of the present invention enable restoration of the 30-degree rotation at the enhanced magnetic field.

[0053] Stack Center Conductor

[0054] FIG. 4 illustrates a stack center conductor configured in accordance with one embodiment of the present invention. The center conductor 8 includes three transformer arms 8b and three tuning stub resonators 8c. Each of the transformer arms 8b are in symmetrical relation to one another, and are substantially 120 degrees from each other. This symmetry equally applies to the tuning stub resonators 8c. The transformer arms 8b can be used for impedance matching (e.g., to a 50 ohm line). Also, an aligning portion 8a is disposed on the end of a respective tuning stub resonator 8c. Each aligning portion 8a has a concave surface that substantially corresponds with a respective inner edge 2c of the housing 2, as well as the alignment pins of an assembly fixture.

[0055] Such a self-aligning center conductor design enables the tuning stubs 8c to be fully extended to the perimeter of the stack. By enabling the extension of the tuning stub resonators 8c, the 30-degree rotation at the enhanced magnetic field can be restored. More specifically, the lowest IMD, corresponding to the highest frequency offset, can be achieved with a center conductor 8 having its tuning stub resonators 8c maximally extended toward the neighboring transformer arms 8b in the azimuthal direction, and extended to the edge of the ferrite elements in the radial direction. With such a configuration, the 30-degree rotation of the standing wave pattern corresponding to the largest allowed frequency offset can be maintained. Increased magnetic field and reduced IMD are also provided.

[0056] Note the actual shape and size of the center conductor, including its transformer arms 8b and tuning stub resonators 8c, depends on factors such as the desired frequency of operation and the desired level of IMD suppression. For instance, the narrower the tuning stub resonators 8c, the higher the frequency of operation. Numerous other center conductor 8 configurations are possible in light of this disclosure, and the present invention is not intended to be limited to any one such configuration. A typical range of operating frequencies for common circulator/isolator applications is, for example, 100 MHz to 30 GHz.

[0057] Assembled Device

[0058] FIG. 5 illustrates a cross-sectional view of an assembled circulator/isolator device configured in accordance with one embodiment of the present invention. The housing 2 can be secured to the ground portion of PCB 1 by, for example, solder or another electrically conductive bonding material. The stack 3 is disposed inside the housing 2 and is enclosed by the pressing cover 4. The locking cover 5 is disposed on a top of the cover 4, with its teeth 5a being received by the flair slots 2b. Thus, the stack 3 is held in place with a compression force resulting from turning (e.g., during the assembly process) the locking cover 5, which moves the teeth 5a along the slanted upper edges of flair slots 2b in the housing 2. When the cover 5 is rotated into position, a drop of solder or glue can be applied throughout the holes 5b as previously explained.

[0059] FIG. 6 illustrates a perspective view of a partially assembled circulator/isolator device that is installed in an assembly fixture in accordance with one embodiment of the present invention. This particular fixture includes a base 9 and three pins 10. Location of the pins 10 relative to each other coincides with that of the holes 1b in the PCB 1, slots 2c in the housing 2, and concave portions 8a of the center conductor 8. The shape of the stack elements is such that their placement between the alignment pins 10 allows minimal radial play. The length of the pins 10 on the base 9 is slightly less than the height of the stack 3. In this way, the cover 4 can rest on the stack without contacting the alignment pins 10. Thus, the locking cover 5 can be engaged when the assembly is still in the fixture and properly aligned.

[0060] In this embodiment, the end portions of the transformer arms 8b of the center conductor 8 are bent down and soldered to the short metallized pads 1d of the PCB 1, as shown on FIG. 6 with the dash-dot lines. Conductors from a host system to which the device is installed are electrically connected to the long metallized pads 1e. These connections are electrically continuous to the short pads 1a and transformer arms 8b by way of the metallized via holes 1c.

[0061] The ground portion on the host side of the PCB 1 is adapted to make contact with the ground of a host system. During the installation of the device into the host system using a pick-and-place method, the device's metallized pad 1e of each conductive port and the ground portion (e.g., remaining metallized surface of the PCB host side) have to be simultaneously connected to their respective system contacts. Each of these electrical contacts on the device's host side are substantially coplanar with one another so as to allow such a connection. With manufacturing and assembly techniques as described herein, the coplanarity, as well as stack flatness, are substantially maintained thereby providing a high performing device.

[0062] As will be appreciated, other benefits are also realized by employing the principles of the present invention. For instance, in operation, a temperature variation of the device takes place, particularly in high power applications. The difference in coefficients of thermal extension between the stack 3 and housing 2 is compensated for by the spring action of the teeth 5a within a proportional segment of the stress-strain curve. The resistance of the cover 5 to bending in areas other than the teeth 5a is much greater. Therefore, during those variations the portion of cover 5 that contacts the stack 3 remains substantially flat and continues to provide relatively uniform and unchanging pressure on the stack 3. Thus, a stable performance of the device, including a low IMD if desired, is preserved over a broad range of temperatures.

[0063] Alignment Fixture

[0064] FIGS. 7a and 7b illustrate side and top views respectively of an assembly fixture configured in accordance with one embodiment of the present invention. As can be seen, the fixture of this embodiment includes a base 9 and three alignment pins 10 extending vertically from the upper surface of the body 9. The position for each of pins 10a is fixed in the base 9, while the position of pin 10b is adjustable. In particular, pin 10b is positioned on a slider 9a, which is adapted to slide in a groove 9c formed in the surface of base 9. The adjustable nature of pin 10b allows for some flexibility when assembling a circulator/isolator device or stack to reduce radial play. Once pin 1b is in the desired position, a thumb screw 9b (or other suitable retaining mechanism) can be tightened to secure pin 10b in position.

[0065] Other fixture configurations will be apparent in light of this disclosure, and the present invention is not intended to be limited to any one such configuration. Rather, any fixture having three or more alignment pins that can be employed to automatically align the layers of a circulator/isolator device or stack during the assembly process can be configured in accordance with the principles of the present invention. The size of the base 9, as well as the spacing between the pins 10, can vary depending on the size of the device being manufactured.

[0066] The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure. For example, the principles of the present invention can be employed in the assembly of any device that requires alignment of its layers, and need not be limited to circulator/isolator devices. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.