Abstract:
The hybrid junction includes four electrically conductive planar windings, circular or rectangular, arranged so as to lie along an imaginary spherical or cylindrical surface. Each of the four electrically conductive windings is rotated from adjacent windings by about forty-five degrees. The four electrically conductive windings are electrically insulated from each other and each include a respective signal port. The hybrid junction automatically splits and/or sorts signals. Signals applied to any port will split equally between the opposite port pairs. One output signal will be in-phase with the input signal, and the other output signal will be shifted by 0 or 180 degrees from the input signal. The input signal is split equally, output coupling may be half power or loose, and there is isolation between the output ports. The hybrid junction operates over a broad bandwidth.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of communications, to sorting and routing signals, and to the field of transformers and related methods. 
   BACKGROUND OF THE INVENTION 
   An important form of radio frequency (RF) power divider is the 3db hybrid coupler which is described in a number of references including Chapter 13 entitled “TEM-Mode, Coupled-Transmission-Line Directional Couplers, and Branch-Line Directional Couplers” of a book whose title is “Microwave Filters, Impedance-Matching Networks And Coupling Structures” by Matthaei, Young and Jones. The 3db hybrid coupler has two input ports and two output ports. With one input connected to a terminating impedance matched to the system characteristic impedance, a signal at the other input produces signals at the two outputs of the coupler each of which contains approximately one-half of the power engendered by the input signal (neglecting insertion loss). Depending on device form and connections, the outputs may differ in phase from each other by 0, 90, or 180 degrees. The 90 degree phase type sometimes is called a quadrature hybrid. 
   The Magic-T or Rat-Race hybrid ring circuit is another type, which throughout the past has been optimized with the purpose of obtaining a higher bandwidth (&gt;40%). Various approaches to increase the bandwidth include using non-flat technology instead of the middle wave length line (asymmetric part) of the ring. The resulting ring is more symmetrical and the bandwidth is only limited by the interconnection of the quarter length wave sections. The hybrid ring can be described as a divider or 180 degree coupler, and is particularly useful in mixer and coupling signal circuits. 
   Generally then, the 0 degree hybrid coupler is a four-port network available from a number of manufacturers in a wide variety of package types, ranging over a frequency spectrum of 10 kHz to 18 GHz. The traditional function of a 0 degree hybrid coupler is to split an input signal into two equal amplitude, isolated 0 degree outputs or to combine to similarly phased, equal amplitude signals into a single output. 
   Operationally, a 0 degree hybrid coupler is a symmetrical network in that signals applied to any port will split equally between the opposite port pairs. An input signal applied to port  1  will split equally between ports  2  and  3 . The output signals from ports  2  will be in-phase with the input signal at port  1 . The input signal is split equally so that the two resulting output signals. An important natural characteristic of a 0 degree hybrid coupler is its reaction to mismatches. In the case of a common input mismatch, all reflections are directed to the isolated port  4 , and as a result system match is not affected when port  4  is terminated in its characteristic impedance. The same condition holds true for output mismatches, reflections are directed to the isolated port  4 . The standard hybrid coupler may also be used to combine two signals at ports  2  and  3  into an output signal at port  1 . 
   U.S. Pat. No. 1,458,193, entitled “Multiple Balancing Arrangement For Multiplex Transmission”, to Osbourne, describes a transformer type of the hybrid junction. In this type, transformer windings are tapped to create uncoupled ports, in like fashion to bridge circuits, such as the Wheatstone Bridge. Tapped winding hybrid transformers have found wide application, especially in telephone repeaters. One such 2 way amplifier, or “repeater”, is described by Wright in U.S. Pat. No. 1,515,643, entitled “Transmission Circuits”. This hybrid became key to long distance telephony, and they remain in use today, as for instance to reduce earpiece “sidetone” in telephone handsets to comfortable levels. 
   Unfortunately however, limitations can arise in tapped winding hybrid transformers. The multiplicity of windings is complex: a magnetic circuit or “core” is needed to ensure coupling between all, and in essence, 6 windings are required. Any number of difficulties can upset symmetry, causing unbalance. For instance, if the taps are not at the midpoint of the winding turns, or the magnetic core has a void, isolation between ports  1  and  4  is reduced. And since winding techniques vary, intricate care may be required in practice to achieve high isolation. 
   Hybrid junctions of the transformer type generally require a magnetic circuit or ferrite core, which limits frequency response. They may not operate above say 1 Ghz, or are narrowband above this. They also have limited power ratings and complex geometry, such as six windings and many cores. 
   What is needed then, is a more simple and uncomplicated hybrid junction, one that obtains 4 ports from 4 untapped windings, with or without a core, in the optimum geometry. There also remains, a need to identify a Euclidian or symmetric form of hybrid transformer with windings superimposed about a single point space. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing background, it is therefore an object of the present invention to provide a broadband hybrid junction, such as a coupler or transformer, with a spherical or cylindrical geometry and spatial superposition of windings. The broadband junction is without tapped windings or bridging, and a magnetic core may be omitted. 
   This and other objects, features, and advantages in accordance with the present invention are provided by a hybrid junction including four circular electrically conductive windings arranged so as to lie along an imaginary spherical surface. Each of the four circular electrically conductive windings is spaced from adjacent windings by about forty-five degrees. The four circular electrically conductive windings are electrically insulated from each other and each includes a respective signal port. 
   Each of the circular electrically conductive windings may include a plurality of turns. Also, a core may be included within the four circular electrically conductive windings. The core may be one of a solid dielectric material, a gas dielectric material and a nonconductive magnetic material. The diameter of the imaginary spherical surface is preferably electrically small, being 1/20 of a wavelength or less in diameter. Each of the signal ports may preferably lie along an equator of the imaginary spherical surface, and each of the signal ports may be a coaxial signal port or a waveguide signal port. Furthermore, the signal ports are preferably connected to define a 180 degree coupler or a 0 degree coupler. 
   A method aspect is directed to a method of making a hybrid junction including forming four circular electrically conductive windings arranged so as to lie along an imaginary spherical surface, and spacing each of the four circular electrically conductive windings from adjacent windings by about forty-five degrees. The method also includes electrically insulating the four circular electrically conductive windings from each other, and providing a respective signal port for each of the four circular electrically conductive windings. 
   The method may also include providing a core within the four circular electrically conductive windings, wherein the core is a solid dielectric material, a gas dielectric material or a nonconductive magnetic material. Also, each of the signal ports may be preferably provided along an equator of the imaginary spherical surface and the signal ports may be balanced twisted pair, coaxial signal ports or with transitions, waveguide ports. 
   Objects, features, and advantages in accordance with the present invention are also provided by a hybrid junction including a cylindrical core with vias, and four rectangular (or square) electrically conductive windings wound therein. Each of the four rectangular electrically conductive windings is spaced from adjacent windings by about forty-five degrees. The four rectangular electrically conductive windings are electrically insulated from each other, and each includes a respective signal port. 
   The cylindrical core may be provided within the four rectangular electrically conductive windings, and the core may be a solid dielectric material, a gas dielectric material or a nonconductive magnetic material. Core length (l) and diameter (d) may be approximately equal, and the core of electrically small size, 1/20 wavelengths or less, such that (l=d)&lt; 1/20 wavelengths. Also, each of the signal ports may be a twisted pair transmission line, formed from the winding wires. The signal ports are preferably connected to define a 0 degree coupler or a 180 degree coupler, by reversing connection polarities. 
   Another method aspect is directed to a method of making a hybrid junction, including winding four rectangular electrically conductive windings in situation, after the cylindrical core has been constructed. Each of the four rectangular electrically conductive windings being rotated from adjacent windings by about forty-five degrees. Further, the method includes electrically insulating the four rectangular electrically conductive windings from each other, and providing a respective signal port for each of the four rectangular electrically conductive windings. 
   Another method may include providing a core within the four rectangular electrically conductive windings, after the windings are formed, the core being solid dielectric sections, a gas dielectric material or a nonconductive magnetic powder. The core may also be sectioned or comprised of wedges, to permit post winding assembly, and the four rectangular windings may be substantially planar. Finally, the signal ports may be twisted pair, coaxial signal ports or transitions to waveguide structures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view schematic diagram of a hybrid junction according to a first embodiment of the invention. 
       FIG. 2  is a top view of the hybrid junction of  FIG. 1 . 
       FIG. 3  is an isometric view of a cylindrical core according to another embodiment of the invention. 
       FIG. 4  is a transparent view of the cylindrical core, of the hybrid junction of  FIG. 3 . 
       FIG. 5  is an isometric view of the cylindrical core including windings, of the hybrid junction of  FIG. 3 . 
       FIGS. 6A-6D  are schematic diagrams illustrating the splitting of signals of the hybrid junction according to the invention. 
       FIG. 7  is a schematic diagram illustrating the hybrid junction of the invention operating as a duplexer for a transmitter and receiver. 
       FIGS. 8A-8B  are graphs of coupling between two windings, in amplitude and phase, measured as a function of angular rotation. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments. 
   Referring initially to  FIGS. 1 and 2 , a hybrid junction  10 , and associated method of making, according to a first embodiment will now be described. The hybrid junction  10  includes four circular electrically conductive windings  12  (WINDINGs  1 - 4 ) arranged so as to lie along an imaginary spherical surface  14 . Each of the planes of the four circular electrically conductive windings  12  is spaced or rotated from adjacent windings by about forty-five degrees. The four circular electrically conductive windings  12  are electrically insulated from each other (e.g. by spacing or a dielectric at the crossing points) and each includes a respective signal port  16  (PORTs  1 - 4 ). Each signal port  16  may have two terminals  18 , as is common. 
   Each of the circular electrically conductive windings  12  may include a plurality of turns. Also, a core  22  may be included within the four circular electrically conductive windings. The core may be one of a solid dielectric material, a gas dielectric material (e.g. air) or a nonconductive magnetic material. For example, a permeable magnetic core may be used at lower frequencies such as less than 2000 MHz. The diameter of the imaginary spherical surface  14  is preferably less than 1/20 wavelengths, 
   The entire hybrid junction  10  may be enclosed in a spherical shell  24 , which contains a fill material  28 . For instance, the hybrid junction  10  may be immersed in granules of ferrite powder, with spherical shell  24  providing the containment. Fill material  28  may provide an enhanced magnetic circuit for the H fields of windings  12 . Spherical shell  24  may be conductive, insulator, magnetic, or dielectric. When conductive however, shell  24  can shield the hybrid junction  10  from ambient fields, electric or magnetic, such those from say nearby power wiring. Note that in  FIG. 2 , an alternative view of the  FIG. 1  embodiment, spherical shell  24  and fill material  28  are not shown. This is simply for the sake of drawing clarity, and spherical shell  24  and fill material  28  may be present in  FIG. 2 . 
   Each of the signal ports  16  may preferably lie along an equator  20  of the imaginary spherical surface  14 , and each of the signal ports may be a balanced port, such as twisted pair, a coaxial signal port or with transitions, a waveguide signal port. Furthermore, the signal ports are preferably connected to define a 0 degree coupler, or a 180 degree coupler, by reversing connections to terminals  18 , as may be appreciated by those skilled in the art. 
   A method aspect is directed to a method of making a hybrid junction  10  including forming four circular electrically conductive windings  12  arranged so as to lie along an imaginary spherical surface  14 , and spacing each of the four circular electrically conductive windings from adjacent windings by about forty-five degrees. The method also includes electrically insulating the four circular electrically conductive windings  12  from each other (e.g. by providing spacing or a dielectric at the crossing points). The method includes providing a respective signal port  16  for each of the four circular electrically conductive windings  12 . 
   The method may also include providing a core  22  within the four circular electrically conductive windings  12 , wherein the core is preferably a nonconconductive magnetic material: solid, liquid, or gas. If conductive, the core material may be of insulated laminations, as is common in power transformers. The core  22  material may also have equal dielectric permittivity and magnetic permeability (μ=ε), forming an isoimpedance material, with a 377 ohm characteristic impedance matching free space. 
   A hybrid junction  30  according to another embodiment, which may be preferential for manufacturing purposes, will be described with reference to  FIGS. 3-5 . The hybrid junction  30  includes a core  40 , which may be any combination of magnetic or dielectric materials. Typically, at lower frequencies, core  40  is a nonconductive magnetic material such as ferrite or E iron, and core  40  is small relative to wavelength. Core  40  is configured with holes  44 , which may be eight in number, to form vias. Holes  44  are arranged on a circular baseline, typically having a radius 0.25 that of the diameter of core  40 , and they go all the way through the core  40 , forming vias or pathways. Core  40  may also sectioned, e.g. into wedges, to facilitate its assembly in place, after windings  46  have been constructed. 
   Holes  44  are be used to receive windings  46 . Each winding is substantially planar, with the wires jumping to opposite rather than adjacent holes. There are no connections where the wires cross, and the windings may be made of, for instance, enameled magnet wire. The two wire ends from each winding become terminals  52 , forming a respective port  50 , and may connected to an electrical network, as will be appreciated by those skilled in the art. Connections to terminals  52  may be reversed to provide a 0 or 180 degree phase hybrid as desired. 
   Optionally, the two wire ends, or “leads”, from each winding may be twisted together, as they egress from core  40 , to form a balanced transmission line of controlled characteristic impedance. This may be done on any embodiment of the present invention. 
   The hybrid junction of the present invention includes rotationally offset winding planes which are preferably at about 45 degrees. As would be appreciated by those skilled in the art, performance of the hybrid junction would degrade with angles that varied further from 45 degrees. No center taps are needed and a magnetic core is not needed. The geometries of the hybrid junction are optimally spherical, as in the  FIG. 1  embodiment, because of the circular windings. The cylindrical core embodiment, of  FIGS. 3-5 , may however be preferred for manufacturing purposes. The  FIG. 1  embodiment conveys the theoretically ideal geometry for the present invention, a cross plane hybrid transformer. 
   Referring to  FIGS. 6A-6D , the operative results of the hybrid junction  10 ,  30  automatically splitting and/or sorting signals will be described. Port  1  couples equal magnitude and opposite phase to Ports  2  and  3 , with no coupling to Port  4 . Port  2  couples equal magnitude and opposite phase to Ports  1  and  4 , with no coupling to Port  3 . Port  3  couples equal magnitude and opposite phase to Ports  1  and  4 , with no coupling to Port  2 , i.e. S 13 =−S 43  and S 23 =0. Port  4  couples equal magnitude opposite phase to Ports  2  and  3 , with no coupling to Port  1 . The hybrid junction is reciprocal and all ports are completely matched. The function also my be written in algebraic form: 
   
     
       
         
           
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   As background, the operation of a simplified two winding educational system will be described.  FIGS. 8(A , B) are graphs of the measured coupling between two windings as a function of their angular displacement. Only two windings are present in the  FIG. 8(A , B) educational system, they are operated together as a transformer, and one winding is rotated out of the plane of the other as in a variometer (variable transformer). The data is normalized to the case of the two windings being coplanar. Attention is called to the fact the phase advances by approximately 180 degrees as the rotated winding passes between 90 to 180 degrees physical rotation. This is important to the operation of this invention, as will be seen in the theory of operation. 
   A theory of operation for the complete invention will now be described. Referring to  FIG. 2 , winding  1  is driven by a RF (radio frequency) potential. Windings  1  and  4  are orthogonal to each other, such that magnetic fields from winding  1  do not curl through the aperture of winding  4 . In the present invention, perpendicular windings are uncoupled from each other. 
   Continuing the theory of operation, windings  2  and  3  are however coupled to winding  1 , as they are not orthogonal to  1 . The magnetic fields from winding  1  curl equally through the aperture of windings of  2  and  3 , causing equal power division to them, since there is symmetry about the plane of  4 . Now windings  2  and  3  can of course couple to winding  4 , as well as to  1 , and isolation between  1  and  4  is desired. Notice however, that the plane of winding  3  is rotated 315 degrees clockwise from the plane winding  1 , such that winding  3  has “passed through” the plane of winding  1 , causing a 180 degree phase shift has to occur in its induced fields. Thus, although windings  2  and  3  do couple individually to winding  1 , fields from  2  and  3  are 180 degrees out of phase with each other, and they cancel out in  4 . Thus,  2  and  3  refer 180 out of phase in  4  and  1 , in combination causing isolation between  4  and  1 . 
   The present invention may form a loose or tight coupler, depending on the magnetic flux density produced by the windings. Either tight or loose couplers can be advantageous, depending on requirements. Loose coupling is advantageous say for instrumentation, by reducing disturbance to the connected network. For tighter coupling, windings ( 12 ,  46 ) can contain a large number of turns N, core ( 22 ,  40 ) can be of large diameter, or core ( 22 ,  40 ) can have high magnetic permeability. In general, the inductive reactance of windings ( 12 ,  46 ) should be 4 or more times greater than the circuit impedance into which they are connected, as is common in RF transformer design. 
   Windings  12 , of hybrid junction  10  (spherical core), and windings  46  of hybrid junction  30  (cylindrical core) are operable in two modes relative to size and resonance: electrically small nonresonant or electrically large self resonant. Generally, the preferred mode is nonresonant windings, as is typical in transformers. However for requirements such as high power levels, self resonant windings may be beneficial. Such a hybrid is of larger physical size and heat dissipation. Depending on turns N, winding technique, and distributed capacitance, the length of the wire used in a self resonant winding may be about 0.2 to 0.45 wavelengths. The instantaneous bandwidth of resonant windings is narrow, approximately 0.5 to 2 percent, but they may be made tuneable. 
   Windings ( 12 ,  46 ) are in general short solenoids. However, informal scramble winding is sufficient for low frequency requirements. If multiple winding layers are needed, at higher frequencies, bank winding may be used to raise frequency response. 
   The port connections for the present invention can be telephone lines, with the windings wires forming a twisted pair, or coaxial cables to antennas, or with transitions waveguides to RADARS. The hybrid junction can be described as a transformer, coil, coupler, magic-T or phantom circuit. The hybrid junction may be used in telephones, RF mixers, Superheterodyne receivers, circular polarized antennas, transmit-receiver TR duplexers, bi-directional amplifiers/repeaters, undersea cables and ignitions, for example. As illustrated in  FIG. 7 , the hybrid junction  10 ,  30  may operate as a duplexer for a transmitter and receiver using the same antenna. 
   Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.