105 that is disposed over or laminated to the top ferrite disc 102. The top circuit stack 103 also includes a central portion 108 of a conductor layer on the top side of the top dielectric layer 105. The central portion 108 of the conductor layer has a circular shape and an outer edge 125, which matches with the diameters of the ferrite discs 102 and 104. The central portion 108 forms a top ground layer or ground plane 108. In the disclosure, the central portion and the top ground layer or top ground plane are used interchangeably.

The top circuit stack 103 also includes a central circular portion and three connecting wings 114A-C, each connecting wing including a portion of the conductor layer on top of the same top dielectric layer, which extends from the central circulator portion. The connecting wings 112A-C can be folded to connect the top ground plane 108 on the top side to a bottom ground plane under a bottom of the circulator device 100. It will be appreciated by those skilled in the art that the number of wings may vary with the design of the circulator. For example, if the circulator has four ports, there will be four wings.

Middle circuit stack 101 is inserted between the top ferrite disc 102 and the bottom ferrite disc 104. Middle circuit stack 101 includes a middle dielectric layer 106 having a circular shape with edge 126. Middle circuit stack 101 also includes circulator circuit 107 placed on both sides of the middle dielectric layer 106. The circulator circuit 107 includes a first circuit portion 110 on the top side of the middle dielectric layer 106. The first circuit portion may be the main circuit or conductor circuit formed on the top side. In the disclosure, the first circuit portion, the main circuit or conductor circuit are used interchangeably. The main circuit or conductor circuit 110 can be formed of one or more metals, such as gold, silver, copper, aluminum, or tin, or a combination of metals such as copper with tin plating, or copper with silver plating, among others. The first circuit portion 110 is also referred to as top coupling circuit 110. The main circuit 110 includes Y-junction conductors, unconnected circuitry, circuitry connected to the ground, and circuitry connected to ports.

The circulator circuit 107 also includes a second circuit portion 118 on the bottom side or backside of dielectric layer 106, e.g., the bottom coupling circuit 118. The second circuit portion 118 is also referred to as bottom coupling circuit 118 or bottom coupling elements. The bottom coupling circuit 118 may include coupling elements, such as shunt capacitors, which can be used to tune the circulator device 100 to operate at a lower frequency.

The top and bottom coupling circuits 110 and 118 can be different from each other. For example, the bottom coupling circuit 118 is different from the main circuit 110. The bottom coupling circuit 118 can help achieve the desired performance and operation frequency without the need to increase the ferrite disc size.

Middle circuit stack 101 also includes three connecting wings 112A-C connected to the coupling conductor circuit 110 by respective connecting portions 120. The connecting wings 112A-C can be folded to connect both the coupling conductor circuit 110 and the coupling conductor circuit 118 on both the top and bottom sides of the middle dielectric layer 106 to create a mounting surface 304 of the circulator device 100.

To fully utilize the area of the ferrite, main circuit 110 can have features (e.g., port matching stubs or resonator stubs) as close to the edge of the ferrite disc as possible. However, as the circulator circuit 107 including main circuit 110 and coupling circuit 118 approaches the edges 124 and 122 of the top and bottom ferrite discs 102 and 104 when assembled, the effective dielectric constant changes dramatically due to proximity to air. Thus, the closer the circulator circuit 107 is toward the edges 124 and 122 of the top and bottom ferrite discs 102 and 104, the accuracy of the placement of the main circuit 110 relative to the ferrite discs becomes more critical for the performance of the circulator.

A condensed view of the circulator device in FIG. 1 according to one aspect of the disclosure is depicted in FIG. 2. As shown in FIG. 2, the top circuit 103, the top ferrite disc 102, the middle circuit stack 101, and the bottom ferrite disc 104 are placed together. The top ferrite disc 102 may have the same diameter as the bottom ferrite disc 104. Edge 124 of the top ferrite disc 102 is aligned with edge 122 of the bottom ferrite disc 104. Edge 125 of the top ground plane 108 is aligned with edge 124 of the top ferrite disc 102. Edge 126 of the middle dielectric layer 106 is aligned with edge 124 of the top ferrite disc 102 and edge 122 of the bottom ferrite disc 104.

It will be appreciated by those skilled in the art that the wings may have any shape as long as they fit together. When the wings are all folded together, the wings would substantially fill the area below the ferrite disc. For example, the wings may be oddly shaped as long as they fit together.

The middle circuit stack 101 includes connecting wings 112A-C connected to a central circular portion by respective connecting portions 120. The top circuit stack 103 includes connecting wings 114A-C connected to the central circular portion 108 by respective connecting portions or flex connections 121. The connecting portions or flex connections 120 are configured to have the length extending to the bottom of the bottom ferrite disc 104, for example, the length is equal to or slightly larger than the combined thickness of the top ferrite disc 102 and the bottom ferrite disc 104.

Also, a middle ground 116 and mounting pads 128 are formed on the top side of the middle dielectric layer 106. The mounting pads 128 are physically separated and electrically isolated from the middle ground 116 by a dielectric portion 115. A portion of the middle ground 116 and mounting pads 128 are positioned on the connecting wings 112A-C.

FIG. 3A is a top view of the circulator device of FIG. 1 according to one aspect of the disclosure. FIG. 3B is a bottom view of the circulator device of FIG. 3A according to one aspect of the disclosure. As shown in FIG. 3A, the circulator device 100 is fully assembled. The dielectric layers 106 and 105 may be flexible. The circulator device 100 can be formed by folding connecting wings 112A-C and 114A-C of both middle and top circuit stacks 101 and 103 including middle and top dielectric layers, respectively. The connecting wings 112A-C of the middle circuit stack 101 and connecting wings 114A-C of the top circuit stack 103 including respective dielectric layers 106 and 105 can be folded under the bottom ferrite disc 104 to provide vertical connections for the circulator circuit 107 including Y-junction conductors and the ground, respectively. The top circulator circuit 107 including the top coupling circuit 110 and the bottom coupling circuit 118 connects to a mounting surface of the circulator by flex connection 120. Also, circulator device 100 includes the top ground layer 108 on top of the top dielectric layer 105. The top ground layer 108 connects to a bottom ground layer (not shown) of the circulator device by flex connections 121.

In some variations, the flex circuits may be glued to the ferrites.

In other variations, in the case of thermal plastic dielectrics, the flexible circuits can be heated and pressed to the ferrites. Heating and pressing the ferrites and the thermal plastic dielectric can create a laminate where the thermal plastic dielectric bonds with the two ferrites and thus holds the ferrites together.

As shown in FIG. 3B, the connecting wings 112A-C from the middle circuit stack 101 and the connecting wings 114A-C from the top circuit stack 103 are shaped to form a circular shape by a combination of the connecting wings 112A-C with connecting wings 114A-C. Each of connecting wings 112A-C from the middle circuit stack 101 is alternately placed between two connecting wings 114A-C from the top circuit stack 103. There are no overlaps between the neighboring connecting wings, but small gaps 302 between the neighboring connecting wings.

Circulator device 100 also includes mounting pads 128 and middle grounds 116 on top of the middle dielectric layer 106. The middle grounds or middle ground layers 116 and mounting pads 128 are formed on the same dielectric layer 106 as the main circuit 110 including Y-junction conductors. The mounting pads and a portion of the middle ground 116 are positioned on the connecting wings 112A-C. Both mounting pads 128 and middle grounds 116 are also folded under the bottom ferrite disc 104 to create a bottom surface or a mounting surface 304 that includes mounting pads and middle ground 116 on folded connecting wings 112A-C and top ground 108 on folded connecting wings 114A-C. A folded connection 306 connects the bottom ground to the top of the middle dielectric layer 106 and then provides ground connection through vias 512 for the bottom coupling circuit 118. The vias 512 are illustrated in FIG. 1 and FIGS. 5A-5B. As such, the top ground and middle ground at the bottom surface 304 can connect to a bottom ground of the circulator device. The mounting pads that are connected to the Y-junction conductors as shown in FIG. 1 are also on the bottom surface, which can be placed on a mounting surface. The flexibility of the dielectric layers 106 and 105 allows the folding of the circulator circuit and top ground layer to eliminate the need for vias, sidewall metallization, and connection pins that are commonly used for vertical connections or interconnections of conventional circulators.

A side view of the circulator device of FIGS. 3A and 3B according to one aspect of the disclosure is depicted in FIG. 4. As shown in FIG. 4, the connecting wings 114A-C of the top circuit stack 103 can be folded to connect the top ground plane 108 to a bottom ground plane under the bottom ferrite disc 104 by flex connections, which extend vertically outside the edge 124 of the top ferrite disc 102 and the edge 122 of the bottom ferrite disc 104.

A flat permanent magnet 402 is disposed over the top ground layer or top ground plane 108, which is disposed over the top ferrite disc 102. The magnet 402 serves as a direct current (DC) magnetic bias source. The magnet 402 may be glued to the central portion 108 or the top ground plane 108. Thus, magnet 402 does not have electrical contact with the top ground plane 108.

In some variations, there may be a soft-magnetic (e.g., ferrous metal) disc and/or a non-magnetic spacer disc between the magnet 402 and the top ground plane 108.

In some variations, magnet 402 may be ceramic magnets or rare earth metal magnets.

The connecting wings 112A-C of the middle circuit stack 101 can be folded such that connecting portions or flex connections 120 extend vertically outside the edge 122 of the bottom ferrite disc 104 and the mounting pads 128 are positioned under the bottom of the bottom ferrite disc 104 after folding, as shown in FIG. 3B. The mounting pads can be positioned on a mounting surface 304 of the circulator. The mounting surface includes the folded connecting wings 112A-C which are alternately positioned with the folded connecting wings 114A-C. The connecting portions 120, rather than vias, connect the circulator circuit 107 to the mounting surface 304 of the circulator.

Isolator

In some variations, the top coupling circuit 110 may include a resistive element when the circulator is configured to be an isolator.

The isolator is a two-port device, which is often a three-port or four-port circulator with one or two ports terminated with a resistive element, such that unwanted incoming power on an output port (e.g., reflections) is directed to the resistive element and then dissipated as heat.

The isolator can be formed by terminating one of the ports of the circulator with a proper matching load. The termination is built inside the circulator device. The termination can be built on either the top or bottom sides of the middle dielectric layer.

In some variations, the matching load can be realized as a resistive layer or resistive element on either surface of the dielectric layer. The resistive element can be designed to terminate one of the circulator ports and thus turn the circulator into an isolator.

Since the resistive element is built inside the circulator device, the design of the disclosed circulator offers a great saving on space and does not take extra space outside the circulator device.

A top view of the first portion of the circulator circuit on the top side of the middle dielectric layer of FIG. 1 according to one aspect of the disclosure is depicted in FIG. 5A. As shown in FIG. 5A, an isolator 500 includes an input port 506 and an output port 508 and a resistive element 504 that terminates one of the three ports and turns the circulator into the isolator. The isolator 500 includes a top coupling circuit 110 on the top side of the middle dielectric layer 106. The top coupling circuit 110 includes Y-junction conductors. Also, the input port 506 and the output port 508 are positioned near edge 126 of the middle dielectric layer 106, as shown in FIG. 5A. Also, the top coupling circuit 110 includes circuit Y-junction conductors.

A bottom view of the second portion of the circulator circuit on the bottom side of the middle dielectric layer of FIG. 1 according to one aspect of the disclosure is depicted in FIG. 5B. As shown in FIG. 5B, the isolator 500 includes the bottom coupling circuit 118 on the bottom side of the middle dielectric layer 106, which may include two shunt capacitors or tuning capacitors 510 positioned under the input port 506 and output port 508, respectively. The capacitors 510 can be connected to vias 512 through connections 502. The first circuit portion or top coupling circuit 110 connects to the second circuit portion or the bottom coupling circuit 118 through folded connections 306A-C (shown in FIG. 3B) and vias 512 in the middle dielectric layer 106. For example, the folded connections 306A-C connect the middle grounds 112A-C (that are folded to be under the bottom of the bottom ferrite) to the top of the middle dielectric layer 106. Ground connections for tuning capacitors 510 are provided through vias 512. Specifically, vias 512 connect the tuning capacitors 510 on the bottom of the middle dielectric layer 106 to the top of the middle dielectric layer 106. The vias 512 connect to the middle grounds through the folded connections.

It will be appreciated by those skilled in the art that the number of shunt capacitors may vary with the type of circulators depending on the number of ports.

In some variations, the circulator may include three ports and is configured to be an isolator. The top coupling circuit may include a resistive element and Y-junction conductors. The bottom coupling circuit may include two shunt capacitors positioned under the input port and output port, respectively.

In other variations, the circulator may include three ports and is configured to be an isolator. The top coupling circuit may include two shunt capacitors positioned under the input port and output port, respectively (not shown). The bottom coupling circuit may include a resistive element and Y-junction conductors (not shown).

In some variations, the circulator includes three ports and is not configured to be an isolator. The top coupling circuit may include Y-junction conductors. Three mounting pads are on the same side as the Y-junction conductors. The bottom coupling circuit may include one, two, or three shunt capacitors positioned to be under the mounting pads.

In some variations, the circulator includes three ports and is not configured to be an isolator. The bottom coupling circuit may include Y-junction conductors. Three mounting pads are on the same side as the Y-junction conductors. The top coupling circuit may include one, two, or three shunt capacitors positioned to be under the mounting pads.

In some variations, the circulator includes four ports and is not configured to be an isolator. The top coupling circuit may include Y-junction conductors. Four mounting pads are on the same side as the Y-junction conductors. The bottom coupling circuit may include one, two, three, or four shunt capacitors positioned to be under the mounting pads.

In some variations, the circulator includes four ports and is not configured to be an isolator. The bottom coupling circuit may include Y-junction conductors. Four mounting pads are on the same side as the Y-junction conductors. The top coupling circuit may include one, two, three, or four shunt capacitors positioned to be under the mounting pads.

In other variations, the circulator may include four ports and is configured to be an isolator. The top coupling circuit may include a resistive element and Y-junction conductors. The bottom coupling circuit may include three shunt capacitors positioned aligned with three mounting pads.

In some variations, the top and middle dielectric layers 105 and 106 can be formed of, but not limited to, a polymer such as a polyimide, polytetrafluoroethylene (PTFE), a fiber-reinforced polymer, such as epoxy glass re-enforced material, or ceramic materials, among others.

The disclosed folded circulator device is quite different from the circulator by Bunce's circulator (see U.S. Pat. No. 8,183,952, entitled “Surface Mountable Circulator,” by Graeme Bunce et al., issued on May 22, 2012). Bunce's circulator uses Y-conductor arms extended to an edge via for interconnects. Bunce's circulator uses vias for interconnects rather than using the disclosed flex connections 120 and 121 to serve as interconnects. Also, Bunce's circulator does not use the backside for coupling elements. Moreover, Bunce's circulator does not contain any resistive elements.

Fabrication

FIG. 6 is a flow chart illustrating the steps for fabricating a circulator device according to one aspect of the disclosure. The circulator device includes example circulator device 100.

Method 600 for fabricating the disclosed circulator device includes forming a first circuit stack 101 comprising a first circuit portion 110 of a circulator circuit 107 on a first side of a first dielectric layer 106 and a second circuit portion 118 of the circulator circuit 107 on a second side of the first dielectric layer 106 opposite to the first side, wherein the second circuit portion 118 is different from the first circuit portion 110 at operation 602.

In some variations, forming the circulator circuit 107 may include using a pre-fabricated flexible PCB layer with copper foil on both sides and forming the elements of top coupling circuit 110 and bottom coupling circuit 118 using standard PCB fabrication methods. For example, main circuit 110 may be etched on the top side of the PCB layer or dielectric layer, and the bottom coupling circuit 118, such as tuning elements, may be etched on the backside of the dielectric layer.

In some variations, forming the circulator circuit 107 may include depositing a seed layer on a top and a bottom of the first dielectric layer 106 by sputtering to form top and bottom seeded surfaces. In some embodiments, the seed layer may be chromium, titanium, or tungsten, among others. In particular, chromium binds well to both the dielectric and copper.

In some variations, forming the circulator circuit 107 may also include plating a metal on the top and bottom seeded surfaces over the first dielectric layer 106 to form top and bottom plated layers.

The main circuit or conductor circuit 110 may be formed on the top side of the middle dielectric layer 106. Coupling circuit 118 may be formed on the backside of the middle dielectric layer 106. Ground 116 and mounting pads 128 are formed on the same dielectric layer 106 as the main circuit 110.

The resistive sheet may be added under the conductor. The resistive sheet can be in the form of commercially available copper foils with an embedded resistive sheet, such as Ohmega Ply™ or Ticer™, pre-fabricated onto one or both sides of a flexible PCB material and formed using standard PCB processes or the resistive element may be formed selectively onto a formed circuit by an additive process such as sputtering, screen printing or inkjet printing of resistive materials.

In some variations, the resistive element may be formed on a face of one or both of the ferrites 102 or 104 in an area facing the main circuit 110 or a bend piece of the main circuit 110, preferably the combination having a good thermal path and cost compromise for the application.

Method 600 also includes forming a second circuit stack 103 comprising a second dielectric layer 105 and a top ground layer 108 disposed over the second dielectric layer, the second circuit stack comprising a second plurality of connecting wing 114A-C configured to be foldable at operation 604.

In some variations, the top and middle dielectric layers 105 and 106 can be formed of, but not limited to, polymers such as a polyimide, PTFE, fiber-reinforced polymers, such as epoxy glass re-enforced material, or ceramic materials, among others.

In some variations, forming the top ground layer 108 on the top dielectric layer 105 may include plating a metal on the seeded surface over the second dielectric layer.

In some embodiments, the metal used for ground planes, the top and bottom coupling circuits, and mounting pads have high conductivity, such as copper, silver, gold, aluminum or tin, among others.

In some variations, a metal seed layer may include chrome and copper which may be sputtered on the first and second dielectric layers.

In some variations, the seeded dielectric layers may be copper plated. The circulator circuit may be formed from the plated copper.

Method 600 may also include forming a device stack comprising a bottom ferrite layer, the first circuit stack disposed over the bottom ferrite layer, a top ferrite layer disposed over the first circuit stack, and the second circuit stack disposed over the top ferrite layer at operation 606.

Method 600 may also include folding the first plurality of connecting wings of the first circuit stack to a bottom of the bottom ferrite layer at operation 608.

Method 600 may also include folding the second plurality of connecting wings of the second circuit stack to the bottom of the bottom ferrite layer to form the circulator device having a bottom surface at operation 610.

In alternative variations, the method may include 3D printing the circulator circuit 107 on both sides of the dielectric layer and 3D printing the vertical connection to the mounting surface.

In some variations, the middle dielectric layer 106 can be formed of the ceramic material while both the top and bottom coupling circuits are printed or sputtered. Then, a side metallization on the dielectric material and the ferrites may be used to connect the coupling circuits 110 and 118 to a mounting surface 304 under the bottom ferrite layer 104. It is understood that a selective plating process may be used to form patterns in metallization. For example, the middle dielectric layer 106 and the bottom ferrite layer 104 may be side metallized to provide signal paths for the circulator circuit to a mounting surface 304. The top and middle dielectric layers 105 and 106 and the top and bottom ferrite layers 102 and 104 may be side metallized to provide electrical paths for the top ground layer to a bottom ground layer at a bottom of the device.

A method for fabricating a circulator device may include forming a first circuit stack comprising a first circuit portion of a circulator circuit on a first side of a first dielectric layer and a second circuit portion of the circulator circuit on a second side of the first dielectric layer opposite to the first side, wherein the second circuit portion is different from the first circuit portion.

The method may also include forming a second circuit stack comprising a second dielectric layer and a top ground layer disposed over the second dielectric layer.

The method may also include plating a first edge portion of a bottom ferrite layer to provide signal paths from the first circuit portion and the second circuit portion to a mounting surface of the circulator device. The method may also include plating an edge portion of the top ferrite layer and a second edge portion of the bottom ferrite layer to provide an electrical path from the top ground layer or a middle ground layer to a bottom ground layer.

The method may further include forming a device stack comprising a bottom ferrite layer, the first circuit stack disposed over the bottom ferrite layer, a top ferrite layer disposed over the first circuit stack, and the second circuit stack disposed over the top ferrite layer.

Applications

The 5G mobile phone network works by way of a plurality of base stations, often arranged in cell towers or on buildings. A typical base station contains an array of transceiver modules or blocks arranged to work in a MIMO configuration to maximize performance and flexibility. A MIMO configuration may have many transceivers, such as 64 transceivers. Each transceiver includes a circulator to direct the amplified transmitting signal to the antenna and direct the received signal from the antenna to the receiver, while blocking the transmitting signal from entering the receiver, thus allowing for a full duplex operation.

The circulators may be either clockwise or counterclockwise, the direction is set by a statically applied magnetic bias. In a clockwise circulator, if a signal is applied to a port, then the signal will exit the next port in a clockwise direction while the next port in a counterclockwise direction is isolated, i.e., the next port sees no signal. And vice versa if the circulator is in a counterclockwise direction. The circulator is thus a non-reciprocal device with at least 3 ports. The circulators include a ferrite material, which, when magnetically biased, causes non-reciprocal operation.

The ferrite circulators are often used as a duplexer as in the example of the 5G base stations. The circulator may also be used to protect/isolate equipment. For instance, an amplifier applies a signal to one port, an antenna is connected to the following port in the direction of operation, and termination is connected to the last port, if in this configuration the antenna becomes damaged or disconnected, then the reflected power will go to the termination instead of back into the amplifier and thus protect the amplifier from overload. For this type of protective operation, the circulator may have a built-in termination and is then referred to as an isolator. The operation of circulators can be compared to a revolving door with three entrances and one mandatory rotating sense.

The circulator can be configured to operate at a reduced frequency. For example, at least one of the first circuit portion and the second circuit portion may include one or more shunt capacitors configured to tune the circulator to the reduced frequency of operation. The reduced frequency of operation may be in a range from 2300 MHz to 2700 MHZ.

In some variations, a method of using the circulator may include tuning one of the first circuit portion or the second circuit portion to a reduced operation frequency ranging from 2300 MHz to 2700 MHZ.

For example, typically existing circulators operate in a frequency around 4000 MHz. In contrast, various embodiments or aspects, the presently disclosed device is configured to operate in a reduced frequency around 2500 MHz without increasing the size of the circulator or the diameter of the ferrites.