Patent Description:
Below resonance circulators and isolators are devices that are designed for applications from three Gigahertz (<NUM>) to over <NUM>. Such circulators and isolators may be used in radio and radar frequency applications such as radar scanners, high-definition radio transmitters, or the like.

Conventional circulators may have potential drawbacks to their design. For example, these circulators may be relatively lossy outside of a narrow bandwidth, resulting in relatively high field loss. Additionally, these circulators may include an epoxy that is cured at a relatively low temperature, resulting in damage to the circulator during processing of the circulator.

Thus, there is a need in the art for below resonance circulators that provide relatively low field loss at a larger bandwidth, and that can be processed without resulting in damage to the circulators. <CIT> discloses a nonreciprocal circuit element and communication apparatus. <CIT> discloses a below resonance circulator and method of manufacturing the same. <CIT> discloses another non-reciprocal circuit device such as an isolator or a circulator.

Aspects of the invention are recited in the independent claims and preferred features are recited in the dependent claims.

Disclosed herein is a broadband microstrip ferrite circulator or isolator. The broadband microstrip ferrite circulator or isolator further includes a dielectric substrate having an opening therein. The broadband microstrip ferrite circulator or isolator further includes a ferrite disc positioned within the opening of the dielectric substrate. The broadband microstrip ferrite circulator or isolator further includes a conductor having three contacts extending therefrom, the conductor being positioned on the ferrite disc. The broadband microstrip ferrite circulator or isolator further includes a magnet. The broadband microstrip ferrite circulator or isolator further includes a spacer positioned between the conductor and the magnet.

Also disclosed is a broadband microstrip circulator. The broadband microstrip circulator includes a conductive carrier. The broadband microstrip circulator further includes a planar dielectric substrate defining an opening therein. The broadband microstrip circulator further includes a planar ferrite component located within the opening defined by the planar dielectric substrate. The broadband microstrip circulator further includes a conductor located adjacent to the planar ferrite component such that the planar ferrite component is located between the conductor and the conductive carrier. The broadband microstrip circulator further includes a magnet located such that the conductor is located between the magnet and the planar ferrite component.

Also disclosed is a method of manufacturing a circulator. The method includes forming a pre-circulator structure by stacking, in order, a carrier, a first adhesive, a dielectric substrate having an opening therein, a ferrite disc in the opening of the dielectric substrate, a second adhesive, a conductor having a center portion with three legs extending therefrom, a third adhesive, a spacer, a fourth adhesive, and a magnet. The method further includes applying pressure to the pre-circulator structure and heating the pre-circulator structure with the pressure applied to a temperature in order to cure the first adhesive, the second adhesive, the third adhesive, and the fourth adhesive.

Other systems, methods, features, and advantages of the present invention will be or will become apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the present invention. In the drawings, like reference numerals designate like parts throughout the different views, wherein:.

Described herein are below resonance circulators (which may also be referred to as isolators) and methods for manufacturing such circulators. The circulators are formed with an independent center conductor and without an external compressive force, such as a housing. The circulators further include a single ferrite element without any film metallization thereon. Various components of the circulators may be coupled together using an adhesive, such as a low loss nonconductive microwave epoxy (e.g., a low loss nonconductive sheet epoxy).

The circulators described herein have various advantages over conventional circulators. Use of a single non-metallized ferrite element and use of the independent center conductor reduces a total quantity of components relative to conventional circulators.

Furthermore, use of the microwave adhesives reduces or eliminates a need for a housing. The reduced quantity of components and the lack of a housing may reduce manufacturing costs of the circulator. The particular designs disclosed herein result in a relatively high-performance circulator that is compatible with tape and reel packaging.

Additionally, the circulators disclosed herein may be processed at a sufficiently high temperature that the adhesives survive the curing process and any soldering process without any structural damage. The circulators also provide desirable characteristics over a relatively broad bandwidth, such as between <NUM> Gigahertz (GHz) and <NUM>. The circulators may provide a functional bandwidth of at least <NUM> percent (<NUM>%) in any area within this range, or even outside of this range. For example, if the target bandwidth is <NUM>, the circulators may provide a functional bandwidth of between <NUM> and <NUM>. This results in relatively low field loss of the circulators.

Referring to <FIG>, an exemplary circulator <NUM> is shown. The circulator <NUM> may include a carrier <NUM>, a dielectric substrate <NUM> defining an opening <NUM> therein, a ferrite disc <NUM> located in the opening <NUM>, a conductor <NUM>, an insulator <NUM>, and a magnet <NUM>. The carrier <NUM> may be conductive and may function as a ground plane. The carrier <NUM> may include a plurality of ground members (not shown) extending outward from the carrier <NUM>, or may function as a ground member and be electrically connected to ground of an element upon which the circulator <NUM> is mounted, such as on a circuit board.

The dielectric substrate <NUM> may include various materials such as a ceramic, Kapton, microwave board materials such as resin-impregnated glass, a low loss microwave substrate, or the like. The dielectric constant of the dielectric substrate <NUM> may be, for example, between <NUM> and <NUM>, between <NUM> and <NUM>, or about <NUM>. Where used in this context, "about" refers to the referenced value plus or minus <NUM>% of the referenced value. The dielectric constant of the dielectric substrate <NUM> may be selected based on the requirements of a system in which the circulator <NUM> is used.

The various components of the broadband circulator <NUM> can be formed in the shape of a circle, a triangle, a rectangle, a square, and/or combinations thereof. The shapes of the components can vary depending on the performance needs of the broadband circulator. In that regard, the opening <NUM> of the dielectric substrate <NUM>, along with the ferrite disc <NUM>, may have any shape. For example, the opening <NUM> and the ferrite disc <NUM> may have a round shape, as shown, an oval shape, a square shape, a triangular shape, or the like. In addition, the dielectric substrate <NUM> may have any shape such as square (as shown), circular, triangular, or the like. The ferrite disc <NUM> may contact the dielectric substrate <NUM> or may be separated from the dielectric substrate <NUM> by a gap.

By placing the ferrite disc <NUM> within the opening <NUM>, the functional bandwidth provided by the circulator <NUM> is increased, by as much as <NUM>% or more. Additionally, this configuration of the ferrite disc <NUM> within the opening <NUM> results in lower field loss than other circulator designs.

The ferrite disc <NUM> may be biased by the magnet <NUM> to create a chamber within the ferrite disc <NUM>. As will be described below, this chamber is where operations on the signals occur. Unlike ferrite elements used in conventional microstrip circulators, the ferrite disc <NUM> may be non-metallized meaning it may have no plating positioned thereon. Additionally, the dielectric substrate <NUM> is non-metallized.

The conductor <NUM> is designed to receive and output signals of the circulator <NUM>. In that regard, the conductor <NUM> includes a plurality of legs, e.g., three legs <NUM>, that each correspond to a signal path of the circulator. Each of the three legs <NUM> may be spaced apart by approximately <NUM> degrees. In various embodiments, each leg may be spaced an equidistance apart from one another. In some embodiments, each of the three legs <NUM> may be spaced apart by any distance between <NUM> degrees and <NUM> degrees, or between <NUM> degrees and <NUM> degrees, or between <NUM> degrees and <NUM> degrees. The three legs <NUM> may be oriented in any configuration such as a "T" configuration (as shown in <FIG>), a "Y" configuration (as shown in <FIG>), an "L" configuration, or the like.

The insulator <NUM> may insulate the center conductor <NUM> from the magnet <NUM>. In some embodiments, the insulator <NUM> may include a sleeve or a spacer. In that regard, the insulator <NUM> may include any insulator such as plastic, ceramic, or the like.

As mentioned above, the magnet <NUM> may bias the ferrite disc <NUM> to create the chamber within the ferrite disc <NUM>.

In operation, a signal may be received by a first leg <NUM>. As the signal travels inward along the first leg <NUM>, it may be received within the chamber of the ferrite disc <NUM> where it may resonate. Based on the direction of bias of the ferrite disc <NUM> (which is controlled by the polarity of the magnet <NUM>), the signal may be output as a null signal on a second leg <NUM> or on a third leg <NUM>, and may be output as a signal that closely resembles the input signal on the other of the second leg <NUM> or the third leg <NUM>. In some embodiments, the circulator <NUM> may be designed to operate between <NUM> gigahertz (GHz) and <NUM>, between <NUM> and <NUM>, between <NUM> and <NUM>, or the like.

Each of the legs <NUM> of the conductor <NUM> may be bent such that a bottom surface of each of the legs <NUM> is relatively flush with a bottom surface of the carrier <NUM>. In that regard, the circulator <NUM> may be mounted on a circuit board. The circulator <NUM> may be electrically and mechanically coupled to the circuit board by applying solder to a joint between the circuit board and the carrier <NUM>, and by applying solder to a joint between the circuit board and each of the legs <NUM>. In that regard, each of the legs <NUM> may also be electrically connected to a corresponding signal trace, and the carrier <NUM> may be electrically connected to a ground trace.

As shown in <FIG>, various adhesives may be used between adjacent components. In particular, a first adhesive <NUM> may be positioned between the carrier <NUM> and the dielectric substrate <NUM> and between the carrier <NUM> and the ferrite disc <NUM>. A second adhesive <NUM> may be positioned between the dielectric substrate <NUM> and the conductor <NUM> and between the ferrite disc <NUM> and the conductor <NUM>. A third adhesive <NUM> may be positioned between the conductor <NUM> and the insulator <NUM>. A fourth adhesive <NUM> may be positioned between the insulator <NUM> and the magnet <NUM>.

The adhesives <NUM>, <NUM>, <NUM>, <NUM> may be used to bond the various components of the circulator <NUM> together. In that regard, use of the adhesives <NUM>, <NUM>, <NUM>, <NUM> reduces or eliminates the need for a housing, thus reducing an overall weight and cost of the circulator <NUM>.

Some or all of the adhesives <NUM>, <NUM>, <NUM>, <NUM> may include low loss microwave adhesives. In particular, the first adhesive <NUM>, the second adhesive <NUM>, and the third adhesive <NUM> may include a low loss microwave adhesive, and the fourth adhesives <NUM> may include a structural adhesive. In some embodiments, the fourth adhesive <NUM> may also or instead include a microwave adhesive, or the first, second, and third adhesives <NUM>, <NUM>, <NUM> may include a structural adhesive. In some embodiments, the microwave adhesive may be used as the second adhesive <NUM>. In these embodiments, other adhesives may be used between the other components of the circulator <NUM>. In some embodiments, each of the adhesives <NUM>, <NUM>, <NUM>, <NUM> may include one or more of a microwave adhesive or a non-microwave adhesive.

It is desirable for the microwave adhesives <NUM>, <NUM>, <NUM> to have certain characteristics in order to improve performance of the circulator <NUM>. In particular, it is desirable for the microwave adhesives to have one or more of the following characteristics:.

An exemplary microwave adhesive suitable for use in the circulator <NUM> may include ULTRALAM® <NUM>, available from Rogers Corporation of Rogers, CT.

The carrier <NUM> may include a conductive metal. In some embodiments, the metal may include a magnetic material such as steel, stainless steel, Kovar, Silver, Gold, Copper, or the like. In some embodiments, the carrier <NUM> may be metallized. In particular, the carrier <NUM> may include plating, such as silver plating or gold plating, in order to reduce insertion loss of signals.

The magnetic properties of the carrier <NUM> may function to attract magnetic fields generated by the magnet <NUM>. By attracting such magnetic fields, the carrier <NUM> increases the likelihood that the magnetic fields travel in a direction perpendicular to a first side <NUM> and a second side <NUM> of the ferrite disc <NUM>. Stated differently, the carrier <NUM> increases the likelihood that the magnetic fields travel straight through the ferrite disc <NUM> from the first side <NUM> to the second side <NUM>. Causing the magnetic fields to travel perpendicular to the sides <NUM>, <NUM> of the ferrite disc <NUM> increases the performance of the circulator <NUM>.

The shape of the carrier <NUM> may be square, rectangular, circular, oval, or the like. The thickness of the carrier <NUM> may vary based on the application. For example, the thickness of the carrier may be between <NUM> and <NUM> or between <NUM> and <NUM>.

The ferrite disc <NUM> may have any shape, such as square, rectangular, circular, oval, or the like. In some embodiments and as shown, the ferrite disc <NUM> may have a circular shape. The circular shape may be desirable as it is cheaper to produce a circular ferrite disc than a ferrite disc having a different shape. Thus, the circular shape may result in a reduced cost of the circulator <NUM>.

The ferrite disc <NUM> may have a diameter. In some embodiments, the diameter may be between <NUM> millimeters (mm) and <NUM>, between <NUM> and <NUM>, or between <NUM> and <NUM>.

The ferrite disc <NUM> may have a thickness. In some embodiments, the thickness may be between <NUM> and <NUM>, between <NUM> and <NUM>, or between <NUM> and <NUM>.

Unlike conventional circulators, the ferrite disc <NUM> of the circulator <NUM> may function without being metallized. The step of applying a metal plating to a ferrite disc may be relatively expensive. In that regard, forming the ferrite disc <NUM> of the circulator <NUM> without metallization results in significant cost savings when manufacturing the circulator <NUM>.

The conductor <NUM> may include a conductive metal. In some embodiments, the metal of the conductor <NUM> may be nonmagnetic. For example, the conductor <NUM> may include brass, copper, beryllium copper, gold, silver, or the like. In some embodiments, the conductor <NUM> may be metallized. In that regard, the conductor <NUM> may be plated such as with silver or gold. Such metallization of the conductor <NUM> may reduce insertion loss, thus increasing performance of the circulator <NUM>.

As described above, the conductor <NUM> may include three legs <NUM> extending therefrom. The conductor <NUM> may further include resonators <NUM> positioned between each of the three legs <NUM>. The conductor <NUM> may include between one and four resonators positioned between each of the legs <NUM>. As shown in FIG. <NUM>, the conductor <NUM> includes two resonators <NUM> positioned between each of the legs <NUM>.

The resonators <NUM> may dictate the operating frequency of the circulator <NUM>. The resonators <NUM> may further aid in impedance matching of the circulator <NUM> by adding capacitance. In some embodiments, the resonators <NUM> may provide impedance matching for frequencies within <NUM>%, or <NUM>%, or <NUM>% of a desired bandwidth. In order to achieve the desired effect, it is desirable for a diameter of the resonators <NUM> to be equal or less than a diameter of the magnet <NUM>.

Use of the microwave adhesive as the second adhesive <NUM> between the ferrite disc <NUM> and the conductor <NUM> provides several advantages. For example, use of the microwave adhesive eliminates the need to include any thin or thick film deposition on the ferrite disc <NUM>, thus reducing the manufacturing cost of the circulator <NUM>.

The insulator <NUM> may include any insulating material. For example, the insulator <NUM> may include a plastic, a ceramic, a rubber, or the like. It is undesirable for the magnet <NUM> to contact the conductor <NUM>. In that regard, the insulator <NUM> insulates the magnet <NUM> from the conductor <NUM>. In some embodiments, the insulator <NUM> may function as a spacer. In some embodiments, the insulator <NUM> may include another shape, such as a sleeve positioned around the magnet <NUM> or around a portion of the conductor <NUM>.

The insulator <NUM> may include a metal or other conductor positioned on some or all of a top surface <NUM>. The metal may operate as a ground plane. In some embodiments, the metal may include copper or brass etched on to the insulator <NUM>. Through experimentation, it was determined that use of the metal on the portion of the surface <NUM> alleviates current induced on the magnet <NUM>. Accordingly, inclusion of the metal reduces losses experienced by the circulator <NUM>.

The magnet <NUM> may include any magnetic material. For example, the magnet <NUM> may include samarium cobalt, ceramic barium ferrite, alnico, neodymium, or the like. The magnet <NUM> may include any shape such as a square, rectangle, triangle, circle, oval, or the like. It may be desirable to use a circular magnet as it is less expensive to form a circular magnet than any other shape. Accordingly, use of a circular magnet may result in reduced manufacturing costs.

Turning to <FIG>, a method <NUM> for forming a circulator, such as the circulator <NUM> of <FIG>, is shown. In block <NUM>, the method <NUM> includes acquiring a carrier, a dielectric substrate with an opening therein (or forming the opening), a ferrite disc, a conductor, an insulator, a magnet, a microwave adhesive, and a structural adhesive. The carrier, the dielectric substrate, the ferrite disc, the conductor, the insulator, and the magnet may be formed or purchased in their final shape. For example, these components may be formed by stamping, forging, or other processes known in the art. The microwave adhesives and the structural adhesives may be purchased in sheet form or in fluid form or may be manufactured using processes known in the art.

In block <NUM>, the microwave adhesive and the structural adhesive may be cut into their desired shapes. For example and with brief reference to <FIG>, each of the first adhesive <NUM>, the second adhesive <NUM>, and the third adhesive <NUM> may be cut to have the desired shape from the sheet of microwave adhesive. Likewise, the first adhesive <NUM>, the second adhesive <NUM>, and the third adhesive <NUM> may have substantially similar diameters (i.e., within <NUM>%, or within <NUM>%, or within <NUM>% of each other). The fourth adhesive <NUM> may be cut to have the desired shape from the sheet of structural adhesive.

Returning reference to <FIG>, the carrier and the conductor may optionally be metallized in block <NUM>. For example, the carrier and the conductor may be plated with gold, silver, tin, copper, or the like.

In block <NUM>, some of the components may be stacked on top of each other to form a pre-circulator structure. For example, the carrier may be positioned on a surface. A first microwave adhesive may be positioned on the carrier, and the dielectric substrate with the ferrite disc located in the opening may be positioned on the first microwave adhesive. A second microwave adhesive may be positioned on the combined dielectric material and ferrite disc and the conductor may be placed on the second microwave adhesive. A third microwave adhesive may be positioned on the conductor and the insulator may be positioned on the third microwave adhesive. The structural adhesives and the magnet may not be placed with the other components at this point.

In block <NUM>, the pre-circulator structure may be cured in order to bond the components together. It is desirable for pressure to be applied to the components during the bonding process to ensure effective coupling between the components. In that regard, pressure may be applied to the pre-circulator structure at the same time heat is applied to bond the pre-circulator structure. The pressure may be applied, for example, using a clamp having ends that sandwich components from the carrier to the insulator.

For example, the applied pressure may be between <NUM> Kilopascals (kPa) and <NUM> kPa, between <NUM> kPa and <NUM> kPa, or between <NUM> kPa and <NUM> kPa. The applied temperature may be between <NUM> degrees Celsius (C) and <NUM> degrees C , between <NUM> degrees C and <NUM> degrees C , or between <NUM> degrees C and <NUM> degrees C.

The pressure may be applied during the entire heating phase. For example, the pre-circulator structure may be exposed to the high temperatures for <NUM> minutes and may remain exposed to the pressure for an additional <NUM> minutes after removal of the heat.

After the pre-circulator structure is cured, a structural adhesive may be stacked on the pre-circulator structure and the magnet may be stacked on the structural adhesive in block <NUM>. For example, the structural adhesive may include Ablebond® <NUM>, available from Henkel of Dusseldorf, Germany.

In block <NUM>, the combination of the pre-circulator structure, the structural adhesive, and the magnet may be cured. For example, the combination may be exposed to relatively high temperatures in order to cause the structural adhesive to bond to the insulator and the magnet. For example, the combination may be exposed to temperatures between <NUM> degrees C and <NUM> degrees C or between <NUM> degrees C and <NUM> degrees C.

After the structural adhesive has bonded to the magnet and the insulator, formation of the circulator may be complete.

Claim 1:
A microstrip circulator or isolator (<NUM>), comprising:
a carrier (<NUM>);
a dielectric substrate (<NUM>) defining an opening (<NUM>) therein and being non-metallized;
a first low loss microwave adhesive (<NUM>) for attaching the dielectric substrate (<NUM>) to the carrier (<NUM>);
a ferrite disc (<NUM>) located within the opening (<NUM>) defined by the dielectric substrate (<NUM>);
a conductor (<NUM>) located adjacent to the ferrite disc (<NUM>) such that the ferrite disc (<NUM>) is located between the conductor (<NUM>) and the carrier (<NUM>);
a second low loss microwave adhesive (<NUM>) for attaching the conductor (<NUM>) to the dielectric substrate (<NUM>) and to the ferrite disc (<NUM>); and
a magnet (<NUM>) located such that the conductor (<NUM>) is located between the magnet (<NUM>) and the ferrite disc (<NUM>).