Abstract:
A 90 degree splitter which covers a wide frequency range of 1500 to 2500 Mhz in a small footprint of only 0.2 inches by 0.2 inches. This device does not use any capacitors which greatly simplifies the construction and lowers the cost in comparison to conventional splitters.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to hybrid splitters and more particularly to microwave 90 degree splitters.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventional ninety degree couplers are typically large, having a footprint substantially larger than two inches by two inches.  
           [0005]    A conventional 90 degree splitter is shown in FIG. 1. It consists of two transformers T 1  and T 2  and four capacitors C 1 , C 2 , C 3  and C 4 . Typically, the transformer is made by winding twisted wires onto a one hole toroid core. Transformer T 1  has wires  11  and  12 . Transformer T 2  has wires  13  and  14 . The connection between two transformers is usually made by soldering the wires from the two transformers together with solder joints SJ 1  and SJ 2  and then to a grounded capacitor C 3 , C 4  or welding the wires to a common metal pad which has a capacitor connected to a ground G.  
           [0006]    Various examples of power splitters are known in the art. U.S. Pat. Nos. 4,789,845, 4,173,742, 4,182,996 and 5,430,418 show power splitters.  
           [0007]    As the frequency of operation increases, the values of the capacitors goes down and it becomes difficult to realize them as lumped elements. In general C 3  and C 4  are smaller than C 1  and C 2 .  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a ninety degree splitter that incorporates no capacitors.  
           [0009]    It is an object of the present invention to provide a wire wound, wide band ninety degree splitter that is functional above one gigahertz.  
           [0010]    The present invention is a ninety degree splitter which covers a wide frequency range of 1500 to 2500 MHz in a small footprint of only 0.2 inches by 0.2 inches. This device does not use any capacitors which greatly simplifies the construction and lowers the cost in comparison to conventional splifters.  
           [0011]    The capacitors are eliminated by substituting inter-winding capacitance in the transformers used in the splitter. This eliminates the capacitors, and reduces related process such as extra soldering and welding. The result is a lower cost device with high frequency performance exceeding that obtained with conventional devices utilizing lumped capacitors.  
           [0012]    The present invention provides a power splitter that includes a transformer with a core. A first winding ( 21 ), a second winding ( 23 ), a third winding ( 22 ) and a fourth winding ( 24 ) are wound on the core. The first and second windings are coupled to the third and fourth windings, such that the inter-winding capacitance between the windings form a third and fourth capacitance in FIG. 1. C 3  and C 4  are eliminated in lower frequency application.  
           [0013]    A further embodiment of the present invention provides a power splitter that includes a transformer with a core. A first winding ( 31 ), a second winding ( 32 ) and a third winding ( 33 ) are wound on the core. The first winding is coupled to the second winding, such that the inter-winding capacitance between the first and second winding forms a first and a second capacitance. The inter-winding capacitance between the first, the second and third winding forms a third and a fourth capacitance in FIG. 1. All four capacitors are eliminated in high frequency applications. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic of a prior art ninety degree splitter.  
         [0015]    [0015]FIG. 2 is a schematic of a first embodiment of the present invention.  
         [0016]    [0016]FIG. 3 is a schematic of a second embodiment of the present invention in which no tuning capacitors are employed. 
     
    
       [0017]    It is noted that the drawings of the invention are not to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. The invention will be described with additional specificity and detail through the use of the accompanying drawings. In the drawings like numbering represents like elements between the drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring to FIG. 2, a 90 degree power splitter assembly  20  is shown. Splitter assembly  20  has a transformer T 3 . Transformer T 3  is formed by winding wires  21 ,  22 ,  23  and  24  on a magnetically permeable core. All four wires are twisted together to form a twisted four wire line, the center portion of which is wound on the toroid to form TP 3 . The ends of the twisted four wire line are unwound. Then wires  21  and  23  are twisted together at each end of the twisted four wire line to form twisted pairs TP 4  and TP 5  respectively.  
         [0019]    Where wire  21  of the twisted four wire line is wound around the core, a winding W 5  is formed. Similarly, wire  22  forms a winding W 7 , wire  23  forms a winding W 6  and wire  24  forms a winding W 8 . It is noted that the length of wires  22  and  24  wound around the core is shorter than the length of wires  21  and  23 . This results in windings W 7  and W 8  being shorter than windings W 5  and W 6 , or in other words, windings W 7  and W 8  have less turns than windings W 5  and W 6 .  
         [0020]    Wire  21  has two ends  21 A and  21 B. Wire  22  has two ends  22 A and  22 B. Wire  23  has two ends  23 A and  23 B. Wire  24  has two ends  24 A and  24 B. A capacitor C 1  is connected between wire ends  21 A and  23 A. A capacitor C 2  is connected between wire ends  21 B and  23 B. Wires  22  and  24  have their ends connected to a ground G. Wire  22  has ends  22 A and  22 B connected to ground G. Wire  24  has ends  24 A and  24 B connected to ground G.  
         [0021]    The new 90 degree power splitter shown in FIG. 2 has a simpler structure than that shown in FIG. 1. It contains only one transformer and two capacitors. The transformer is made by winding twisted wires to perform the function of two transformers as well as two of the capacitors found in a conventional 90 degree power splitter. The transformer supporting this type of structure functions at higher frequencies because of the reduced capacitance. In place of the two grounded capacitors C 3  and C 4 , which are lumped elements, twisted four wire line TP 3  which is part of the transformers, is substituted. The inter-winding capacitance of TP 3  serves as a distributed capacitance. This structure has been used on one application to support a high frequency range of 220 to 300 MHz in a practical splitter. In the frequency range above 200 MHz, C 3  and C 4  of FIG. 1 can be realized as distributed capacitors using twisted magnet wires as shown in FIG. 2.  
         [0022]    Referring to FIG. 3, another embodiment of a 90 degree power splitter assembly  30  is shown. Splitter assembly  30  has a transformer T 4 . Transformer T 4  is formed by winding wires  31 ,  32 , and  33  on a magnetically permeable core. The core may be a toroid or may be square. Wires  31 ,  32  and  33  are twisted together to form a twisted three wire line TP 6 . Wires  31  and  32  are twisted together at both sides of TP 6  to form twisted pairs TP 7  and TP 8 . The twisted three wire line TP 6  is wound onto the core and TP 7  and TP 8  are wound onto the core on their respective sides of TP 6 .  
         [0023]    Where wire  31  is wound around the core, a winding W 9  is formed. Similarly, wire  32  forms a winding W 10  and wire  33  forms a winding W 11 . It is noted that the length of wire  33  wound around the core is less than that of wires  31  and  32 . This results in winding W 11  being shorter than windings W 10  and W 9  or in other words, winding W 11  has less turns.  
         [0024]    Wire  31  has two ends  31 A and  31 B. Wire  32  has two ends  32 A and  32 B. Wire  33  has two ends  33 A and  33 B. No capacitors are present as they are in FIGS. 1 and 2. Wire  33  has its ends connected to a ground G. Wire  33  has ends  33 A and  33 B connected to ground G.  
         [0025]    The 90 degree power splitter assembly  30  shown in FIG. 3 is a simpler version of that shown in FIG. 2. This is a high frequency 90 degree power splitter, in which the capacitors C 1  and C 2  are eliminated by the inter-winding capacitance of the transformer T 4 . The whole 90 degree power splitter appears as a simple single transformer. The structure performs over a wide bandwidth at high frequency. The structure also has less components and less connections. This design makes it possible to place the unit in a small case with a footprint of only 0.2 inches by 0.2 inches. Experimental units have been built successfully which cover the frequency range of 1500 to 2500 MHz.  
         [0026]    Although the illustrated embodiment showed a transformer structure for a 90 degree power splitter. It is contemplated to use the transformer structure for other phase angles and other types of signal handling devices such as filters, traps and combiners.  
         [0027]    While the invention has been taught with specific reference to these embodiments, someone skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope as such.