The subject matter described herein relates to circulators and isolators used in RF devices, and more particularly to an integrated circulator or isolator having a packaging configuration suited for use with phased array antenna systems and other RF devices where space and packaging limitations preclude the use of conventional circulators or isolators.
In phased array antennas, radar systems and various other forms of electronic sensor and communications systems or subsystems, ferrite circulators and isolators provide important functions at RF front end circuits of such systems. Typically, such devices, which can be broadly termed “non-reciprocal electromagnetic energy propagation” devices, are used to restrict the flow of electromagnetic wave energy to one direction only to/from an RF transmitter or RF receiver subsystem. Circulators and isolators can also be used for directing transmitting and receiving electromagnetic energies into different channels and as frequency multiplexers for multi-band operation. Other applications involve protecting sensitive electronic devices from performance degradation or from damage by blocking incoming RF energy from entering into a transmitter circuit.
A conventional microstrip circulator device consists of a ferrite substrate with RF transmission lines metalized on the top surface to form three or more ports. A ground plane is typically formed on the backside of the substrate, as illustrated in
A circulator device uses the gyromagnetic properties of the ferrite material, typically yttrium-iron-garnet (YIG), for its low loss microwave characteristics. The ferrite substrate is biased by an external, static magnetic field from a permanent magnet. The magnetization vector in the ferrite substrate processes in only one circular direction, thus forming a non-reciprocal path for electromagnetic waves to propagate, as indicated by arrows in
A phased array antenna is an antenna formed by an array of individual active module elements. In applications involving phased array antennas, each radiating/reception element can use one or more such ferrite circulators or isolators in the antenna module. However, incorporating any device into the already limited space available on most phased array antennas can be an especially challenging task for the antenna designer. The space limitations imposed in phased array antennas is due to the fact that the spacing of the radiating/reception elements of the array is determined in part by the maximum scan angle that the antenna is required to achieve, and in part by the frequency at which the antenna is required to operate. For high performance phased array antennas, this spacing is typically close to one half of the wave length of the electromagnetic waves being radiated or received. For example, a 20 GHz antenna would have a wavelength of about 1.5 cm or 0.6 inch, thus an element spacing of merely 0.75 cm or 0.3 inch. This spacing only gets smaller as the antenna operating frequency increases. Thus, a conventional circulator device (e.g., a conventional microstrip circulator) has physical size constraints in all 3 dimensions due to its having a ferrite substrate with metalized RF transmission lines on the substrate and a permanent magnet attached therewith.
As a consequence, a conventional microstrip circulator/isolator requires mounting on a phased array module circuit board made of a non-magnetic substrate material totally different from that of the ferrite substrate. Complicating matters further, the size of the ferrite circulator/isolator does not scale down as the operating frequency increases because of the need for a stronger permanent magnet with the increasing operating frequency. The need for a stronger permanent magnet is harder to meet due to material constraints. Furthermore, wire bonding connections are required for connecting conventional circulator/isolator ports with the rest of a microwave circuit. Accordingly, the packaging of a conventional circulator/isolator becomes more and more difficult and challenging within phased array antennas as the operating frequency of the antenna increases or its performance requirements (i.e., scan angle requirement) increases. These same packaging limitations are present in other forms of RF devices where there is simply insufficient space to accommodate a conventional circulator or isolator.
Accordingly, circulator/isolator assemblies may find utility in RF communication applications.
In one aspect, a circulator/isolator assembly to operate within a first frequency range is disclosed that includes a first magnetic substrate having a first surface and a second surface and a first ground plane formed on the first surface, a dielectric layer disposed adjacent the first magnetic substrate, the dielectric layer comprising a multi-port junction circuit disposed on a first side of the dielectric layer and dimensioned to be resonant within the first frequency range, the multi-port junction circuit comprising a conductive disk coupled to a plurality of RF transmission traces, a first RF transmission trace forming an input port and a second RF transmission trace forming an output port, a ground plane disposed on a second side of the dielectric layer, and a first magnetic cylinder disposed proximate the multi-port junction circuit of the dielectric layer, such that the first magnetic cylinder excites a circular, unidirectional magnetic flux field in the first magnetic substrate that limits electromagnetic wave propagation to a single direction of the multi-port circuit junction circuit.
In another aspect, an antenna assembly is disclosed. The assembly includes a first radiating element, a second radiating element, and a circulator/isolator assembly that includes a first magnetic substrate having a first surface and a second surface and a first ground plane formed on the first surface, a dielectric layer disposed adjacent the first magnetic substrate, the dielectric layer comprising a multi-port junction circuit disposed on a first side of the dielectric layer and dimensioned to be resonant within the first frequency range, the multi-port junction circuit comprising a conductive disk coupled to a plurality of RF transmission traces, a first RF transmission trace forming an input port and a second RF transmission trace forming an output port, a ground plane disposed on a second side of the dielectric layer, and a first magnetic cylinder disposed proximate the multi-port junction circuit of the dielectric layer, such that the first magnetic cylinder excites a circular, unidirectional magnetic flux field in the first magnetic substrate that limits electromagnetic wave propagation to a single direction of the multi-port circuit junction circuit.
In another aspect, a method to channel one or more communication signals through a transmit/receive module in a wireless communication system comprises receiving one or more communication signals in the transmit/receive module and passing the communication signal through at least one communication channel comprising a circulator/isolator assembly. The circulator/isolator assembly comprises a first magnetic substrate having a first surface and a second surface and a first ground plane formed on the first surface, a dielectric layer disposed adjacent the first magnetic substrate, the dielectric layer comprising a multi-port junction circuit disposed on a first side of the dielectric layer and dimensioned to be resonant within the first frequency range, the multi-port junction circuit comprising a conductive disk coupled to a plurality of RF transmission traces, a first RF transmission trace forming an input port and a second RF transmission trace forming an output port, a ground plane disposed on a second side of the dielectric layer, and a first magnetic cylinder disposed proximate the multi-port junction circuit of the dielectric layer, such that the first magnetic cylinder excites a circular, unidirectional magnetic flux field in the first magnetic substrate that limits electromagnetic wave propagation to a single direction of the multi-port circuit junction circuit.
The features, functions and advantages discussed herein can be achieved independently in various embodiments described herein or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.
The detailed description is described with reference to the accompanying figures.
In the following description, numerous specific details are set forth to provide a thorough understanding of various embodiments. However, it will be understood by those skilled in the art that the various embodiments may be practiced without the specific details. In other instances, well-known methods, procedures, and components have not been illustrated or described in detail so as not to obscure the particular embodiments.
Various examples of circulator assemblies are described and claimed in commonly assigned U.S. Pat. Nos. 5,256,661, 7,495,521, and 8,344,820, all to Chen, et al, the disclosures of which are incorporated herein by reference. In brief, this application describes alternate constructions of circulator assemblies which may be used in phased array antenna structures.
The first magnetic substrate 220 has first surface 222, which appears as the upper surface in
In one embodiment, the first magnetic substrate 220 is formed from a material that comprises yttrium iron garnet ferrite (YIG) substrates that are formed in a planar configuration. Other suitable materials for the first magnetic substrate 220 may include ferrites such as spinel or hexagonal, which are chosen depending on the required operational frequency and other performance parameters. Please note that ferrites exhibit excellent ferromagnetic properties, e.g., susceptible to induction, non-conductive, and low loss materials and that other ferromagnetic substrate materials may also be utilized for the first magnetic substrate 220.
In one embodiment, a top surface 226 includes a first ground plane is formed on the first surface 222 of the first magnetic substrate 220. In some embodiments the top surface 226 includes a ground plane formed as a metalized layer on the first surface 222 of the first magnetic substrate 220. In the embodiment depicted in
The first magnet 250 may also vary in dimensions depending upon the strength of the magnetic field that is needed. In one embodiment, the magnet 250 has a height of about 0.1 inch (2.5 mm) and a diameter of about 0.1 inch (2.5 mm). While shown as a circular magnet, the first magnet 250 could comprise other shapes such as triangular, rectangular, octagonal, etc. Similarly, the first magnetic substrate 220 and/or the multi-port junction circuit 236 could also comprise other shapes such as triangular, rectangular, octagonal, etc. The magnetic field strength of the magnetic 250 may vary considerably to suit a specific application, but in one implementation is between about 1000 Gauss-3000 Gauss. For millimeter wave applications (30 GHz-60 GHz), the strength of the magnetic field may be as high approximately 10,000 Gauss. Any magnet that can provide such field strengths without affecting the microwave fields (thus being non-conductive) may be utilized. Electromagnets could potentially be used for many applications for reduced magnetic strength requirements. Permanent bar magnets widely available commercially from a number of sources could also be used for many applications.
A dielectric layer 230 is disposed adjacent first magnetic substrate 220. In some embodiments the dielectric layer 230 may be a portion of a printed circuit board (PCB) or any other conventional microwave substrate. By way of example, the dielectric layer 230 may be formed from a polytetrafluoroethylene (PTFE) material or a ceramic-based material such as alumina. The dielectric layer 230 comprises a multi-port junction circuit 236 coupled to a plurality of RF transmission traces 238a, 238b, 238c, which may be collectively referred to herein by reference numeral 238. The end portion of the transmission traces 238 may be considered input/output ports through which RF energy may be transmitted. The multi-port junction circuit 236 and transmission traces 238 may be formed on a surface of the dielectric layer 230 or may be embedded in the dielectric layer 230.
The assembly 210 may be assembled by positioning the first magnetic substrate 220 and the first magnet 250 proximate the multi-port junction circuit 236 of the dielectric layer 230, which may be part of a microwave circuit assembly. The first magnet 250 excites a circular, unidirectional magnetic flux field in the first magnetic substrate 220 that limits electromagnetic wave propagation to a single direction the multi-port circuit junction 236 such that RF energy can flow in only one circular direction (unidirectional) between the ports defined by the RF transmission traces 238.
The assembly 210 shown in
The circuit traces 238 and junction circuit 236 may be formed on a first side of the dielectric material layer 230 using conventional circuit printing techniques. In some embodiments the junction circuit 236 has a diameter indicated by D1 on
Advantageously, as illustrated in
In some embodiments one or more circulator assemblies (e.g., circulator/isolator 210) may be incorporated into a phased array antenna. Referring to
Referring to
At operation 515 the communication signal is passed through a communication channel in the transmit/receive module which comprises a circulator/isolator assembly. As described herein, the circulator/isolator assembly comprises a first magnetic substrate having a first surface and a second surface and a first ground plane formed on the first surface, a dielectric layer disposed adjacent the first magnetic substrate, the dielectric layer comprising a multi-port junction circuit coupled to a plurality of RF transmission traces, one of the traces forming an input port and a different one of said traces forming an output port, and a first magnet disposed proximate the multi-port junction circuit of the dielectric layer, such that the first magnet excites a circular, unidirectional magnetic flux field in the first magnetic substrate that limits electromagnetic wave propagation to a single direction of the multi-port circuit junction circuit.
Thus, described herein are novel structures for circulator/isolator assemblies which may be used in conjunction with phased array antennas. In accordance with the description provided herein, a circulator/isolator assembly may be constructed with the multi-port junction circuit 236 and the RF traces 238 disposed on the dielectric layer. This enables the multi-port junction circuit 236 and the RF traces 238 to be printed as a component of a circuit board rather than placed separately as a component of the substrate. In addition, this allows the use of a plain substrate layer 220. Advantageously, unlike a conventional circulator having a 3-port Y-junction circuit traces deposited on a ferrite substrate, the novel structure for a circular/isolator (e.g., circulator/isolator assembly 210) shares a same non-magnetic substrate with a printed circuit board containing one or more transmit/receive (T/R) channels. In addition, a ferrite substrate with only a metalized ground plane on one side can now be simply placed on top of a multi-junction circuit (e.g., multi junction trace) to achieve circulator/isolator functionality, e.g., unidirectional capability. Furthermore, advantageously, the disclosed circulator/isolator combined with prior art patents (e.g., 7,256,661, 7,495,521) incorporated by reference in their entirety will provide multi-channel functionality in a compact space; thus, this circulator/isolator device reduces antenna system overall footprint.
One skilled in the art will recognize that connections (e.g., ground connections, RF transmission connections) between the top surface 226 and the second surface 234 may be provided by metalized vias outside of the multi-port junction circuit 236 and RF transmission lines 238 (e.g., RF transmission traces). Alternatively, other mechanisms such as a metal casing wrapping the top surface 226 and the second surface 234 together without getting too close to the ports of 238 so as to provide needed connectivity there between.
At operation 620 a dielectric material is selected for the dielectric layer 230. Suitable materials include Rogers RO4003 laminate materials. As described above with reference to
At operation 625 the shape and size of the junction circuit 236 is selected. In some embodiments the shape and size of the junction circuit 236 is selected such that the circular dielectric resonator structure has a TM110 mode resonance frequency that matches the operating frequency requirement selected in operation 610.
By way of example, the theoretical approximate formula for the microstrip dielectric resonator diameter is given by equation (1):
where R is the radius of the metal junction disk, c is the speed of light in free space, f is the frequency of the resonance, Dk is the effective dielectric constant of the ferrite material. By way of example, for a design frequency of f=17.36 GHz, and a ferrite material having a dielectric constant Dk=12, therefore the radius R is found to be 0.0575 in, so the diameter is 0.115 in.
At operation 630 the line width of the circuit traces 238 may be determined. In some embodiments the line width of the circuit traces may be selected to match a desired characteristic impedance, e.g., 50 ohms.
In some embodiments design modifications (operation 635) may be implemented to accommodate mechanical packaging and integration of the circulator/isolator assembly 210. By way of example, the structure may be tuned using simulation software to achieve a desired RF performance. At operation 640 a biasing magnet is selected and at operation 645 the circulator/isolator assembly 210 is assembled.
Reference in the specification to “one embodiment” or “some embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an implementation. The appearances of the phrase “in one embodiment” in various places in the specification may or may not be all referring to the same embodiment. Each of the steps described in the above method are part of a sample exemplary embodiment. The order, positioning, and break-down of the steps of the above described method are exemplary only, e.g., each of the above disclosed steps are interchangeable, reorderable, replaceable, removable, and combinable. As such, this method is indicative of one exemplary process for manufacturing a circulator/isolator in accordance with the teachings of the specification.
Although embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that claimed subject matter may not be limited to the specific features or acts described. Rather, the specific features and acts are disclosed as sample forms of implementing the claimed subject matter.
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20150011168 A1 | Jan 2015 | US |