Abstract:
An integrated N-way Wilkinson power divider is described. In one embodiment, the N-way Wilkinson power divider uses a conductor layer with a cross-over (or cross-under) resistor insulated from the conducting layer by an insulating bridge. In one embodiment, the width of the transmission line underneath a cross-over resistor is adjusted to improve performance In one embodiment, a three-way Wilkinson power divider is formed using microstrip transmission lines on a single-layer substrate that supports the microstrip transmission lines, dielectric insulators, and resistors.

Description:
BACKGROUND 
   1. Field of the Invention 
   The invention relates to N-way Wilkinson power dividers for splitting or combining power in a radio frequency circuit. 
   2. Description of the Related Art 
   A Wilkinson power divider is a passive electronic device that splits a single RF input signal into two (n=2) or more (n≧3) in-phase output RF signals. Such devices can also be used in the opposite direction to combine multiple in-phase RF signals into a single RF output. The details of design and operation for these devices are well known. Such devices are typically realized using resistors and impedance-transformer sections of RF transmission line (such as coaxial line, microstrip, stripline, etc.) in various configurations. 
   In many applications, especially for high-volume and low-cost component production, it is desirable to construct Wilkinson power dividers using inexpensive assembly methods and materials such as sputtered, printed or etched circuits on a flat substrate and using planar transmission lines (e.g. microstrip, stripline, etc.). Realizing n-way (where n≧3) Wilkinson power dividers is difficult and expensive, requiring the use of circuits assembled from multiple substrate layers and/or the use of discrete resistors rather than printed or etched resistors. These costs and difficulties have limited the usefulness of N-way Wilkinson power dividers. 
   SUMMARY 
   The present invention solves these and other problems by providing integrated Wilkinson power dividers on a single substrate layer, resulting in substantially-reduced manufacturing cost. In one embodiment, an n-way (where n≧3) Wilkinson power divider is fabricated on a single substrate layer which supports transmission-line sections and resistors, including one or more output transmission-line conductors that cross one or more resistors. The cross-over (or cross-under) resistors are supported by the substrate layer and are insulated from the transmission-line conductors by a relatively thin local dielectric insulator formed by printing, etching etc. In one embodiment, the width of at least one transmission line section is adjusted where it passes under a resistor in order to improve electrical performance of the device. 
   In one embodiment, a three-way Wilkinson power divider is constructed as an integrated-type circuit on a substrate, such as, for example, alumina, Teflon, plastic, etc. Integrated microstrip transmission-line structures are formed on the substrate using conductive inks and printing techniques. Integrated resistors are formed on the substrate using resistive ink and printing techniques, and an integrated insulating area between a transmission-line conductor and a resistor is formed using printing-type techniques. 

   
     BRIEF DESCRIPTION OF FIGURES 
       FIG. 1  is a schematic diagram of a three-way Wilkinson power divider. 
       FIG. 2  shows an implementation of the three-way Wilkinson power divider where a resistor crosses an output transmission line. 
       FIG. 3  shows an exploded view of the three-way Wilkinson power divider shown in  FIG. 2 . 
       FIG. 4  shows an implementation of the three-way Wilkinson power divider where a resistor crosses a impedance-transformer transmission line. 
   

   DETAILED DESCRIPTION 
   Although typically referred to as a power divider, a Wilkinson power divider can also be used as a combiner to combine multiple input RF signals into a single RF output. Accordingly, the present disclosure refers to a Wilkinson power divider with the understanding that the term power divider also encompasses a power combiner. 
     FIG. 1  is a schematic diagram of a three-way (n=3) Wilkinson power divider  100 . The power divider  100  includes an input  105  having a driving-point impedance Z in , and three outputs  106 – 108 , having respective driving point impedances Z out1 , Z out2  and Z out3 . Three impedance-transformer transmission lines  101 – 103  having respective transmission-line characteristic impedances Z 1 , Z 2  and Z 3  are provided between the input  105  and the outputs  106 – 108 , respectively. Three resistors  112 – 114  (having resistance R 1 , R 2  and R 3 , respectively) are provided between outputs  106  and  107 ,  107  and  108 , and  108  and  106  respectively. 
   The three impedance-transformer transmission lines  101 – 103  are typically each one-quarter wavelength long at some desired frequency f o . The impedances of the impedance-transformer transmission lines  101 – 103  and the values of the resistors  112 – 114  are calculated using established formulas that depend on the input impedance Z in , the output impedances Z out1 , Z out2  and Z out3  and the desired power split between the outputs  106 – 108 . In one embodiment, when the impedances Z in , Z out1 , Z out2 , and Z out3  are all equal, and an equal power split is desired, then Z 1 =Z 2 =Z 3 =√{square root over (3)}Z in  and R 1 =R 2 =R 3 =3Z in . 
   Until now, a three-way Wilkinson power divider has been relatively expensive to manufacture due to the need for at least one of the transmission lines, such as the transmission line  102  in  FIG. 1 , to cross over or under a resistor, such as the resistor  114 . To satisfy this requirement, it has been necessary to use one or more extra layers of substrate material and/or to use some non-integrated components such as discrete resistors. 
     FIG. 2  shows an implementation of the three-way Wilkinson power divider  200  on a grounded dielectric substrate  201 . The Wilkinson power divider  200  has an input transmission line  202  that is provided to a first end of each of three impedance-transformer transmission lines  203 – 205 . A second end of the impedance-transformer transmission line  203  is provided to an output transmission line  209 . A second end of the impedance-transformer transmission line  204  is provided to an output transmission line  210 . A second end of the impedance-transformer transmission line  205  is provided to an output transmission line  211 . A first terminal of a resistor  206  is provided to the junction between the impedance-transformer transmission line  203  and the output transmission line  209 . A second terminal of the resistor  206  is provided to the junction between the impedance-transformer transmission line  204  and the output transmission line  210 . A first terminal of a resistor  207  is provided to the junction between the impedance-transformer transmission line  203  and the output transmission line  209 . A second terminal of the resistor  207  is provided to the junction between the impedance-transformer transmission line  205  and the output transmission line  211 . A first terminal of a resistor  208  is provided to the junction between the impedance-transformer transmission line  204  and the output transmission line  210 . A second terminal of the resistor  208  is provided to the junction between the impedance-transformer transmission line  205  and the output transmission line  211 . In one embodiment, the impedance-transformer transmission lines  203 – 205  are all substantially the same length. In one embodiment, the impedance-transformer transmission line  204  includes one or more curved sections to adjust the length of the impedance-transformer transmission line  204  to substantially match the length of the impedance-transformer transmission lines  203  and  205 . 
   The resistor  207  crosses the output transmission line  210  at a crossing region. The resistor  207  is insulated from the output transmission line  210  by a dielectric insulator  212  provided between the resistor  207  and the output transmission line  210  in the crossing region. In one embodiment, the resistor  207  crosses over the output transmission line  210 . In one embodiment, the resistor  207  crosses under the output transmission line  210 . The dielectric insulator  212  can be any dielectric insulator, such as, for example, glass, plastic, air, epoxy, polymeric materials, elastomers, etc. In one embodiment, the dielectric insulator  212  is formed using Metech 7600 material. The presence of the dielectric insulator  212  and/or the resistor  207  near the output transmission line  210  will perturb the transmission line impedance of the output transmission line  210  and also cause some coupling between the output transmission line  210  and the resistor  207 . In one embodiment, the width of the output transmission  212  is adjusted (increased and/or decreased) to improve performance of the power divider  200 . In one embodiment, performance is improved by reducing the transmission line width in the crossing region and thereby providing more nearly uniform transmission-line characteristic impedance through the crossing region. In one embodiment, operation is improved by reduction of capacitive RF signal coupling with the resistor  210  due to the reduction in overlapping area. 
   The transmission lines  202 – 205  and  209 – 211  and the resistors  206 – 208  are disposed on the grounded dielectric substrate  201 . In one embodiment, the dielectric substrate  201  comprises materials with relatively low loss at RF, such as, for example, alumina, Teflon, plastic, etc. The transmission lines  202 – 205  and  209 – 211  can be formed by etching (e.g., photo etching) processes and/or by depositing (e.g., by photo masking, printing, etc.) conductive materials such as, for example, metals and/or conductive inks. In one embodiment, a conductive ink such as, for example, Metech 3524 is used. The resistors  206 – 208  can be formed by etching (e.g., photo etching) processes and/or by depositing resistive materials such as, for example, metals and/or resistive inks. In one embodiment, a resistive ink such as, for example, Metech 9000 series thick-film material is used. 
     FIG. 3  shows an exploded view of the three-way Wilkinson power divider  200  shown in  FIG. 2 . In  FIG. 3 , the resistor  207  is shown as passing over the output transmission line  210 . As discussed above, the resistor  207  can also pass under the output transmission line  210 .  FIG. 3  also shows a ground plane  301  for the grounded dielectric substrate  201 . 
   In the three-way Wilkinson power divider  200 , the resistor  207  crosses the output transmission line  210 .  FIG. 4  shows a three-way Wilkinson power divider  400 , where the resistor  207  crosses a impedance-transformer transmission line  404 . The power divider  400  includes the grounded substrate  201  and the transmission lines  202 ,  203 , and  205  as configured in  FIG. 2 , and the resistor  207  as configured in  FIG. 2 . The second end of the impedance-transformer transmission line  203  is provided to an output transmission line  409 . The second end of the impedance-transformer transmission line  205  is provided to an output transmission line  411 . In the power divider  400 , the impedance-transformer transmission line  204  is replaced by a straightened impedance-transformer transmission line  404  which crosses the resistor  207  and is provided to an output transmission line  410 . The impedance-transformer transmission line  404  is insulated from the resistor  207  by a dielectric insulator  412 . 
   In the power divider  400 , a first terminal of a resistor  406  is provided to the junction between the impedance-transformer transmission line  203  and an output transmission line  409 . A second terminal of the resistor  406  is provided to the junction between the impedance-transformer transmission line  404  and the output transmission line  410 . A first terminal of a resistor  408  is provided to the junction between the impedance-transformer transmission line  404  and the output transmission line  410 . A second terminal of the resistor  408  is provided to the junction between the impedance-transformer transmission line  205  and the output transmission line  411 . In one embodiment, the impedance-transformer transmission lines  203 ,  205 , and  404  are all substantially the same length. In one embodiment, the width of the impedance-transformer transmission line  404  is reduced in the crossing region to compensate for impedance variations caused by the dielectric insulator  412  and/or the resistor  207 . The dielectric insulator  414  is similar to the dielectric insulator  212  and can be constructed from the same types of materials. 
   Although described above in connection with a particular embodiment of the present invention, it should be understood the description of the embodiment is illustrative of the invention and are not intended to be limiting. Thus, for example, although the specific examples provided here were for a single-stage 3-way Wilkinson power dividers, it should understood that the principle of allowing resistors to cross transmission lines by using dielectric insulators can be used to construct N-way Wilkinson power dividers where N&gt;2 having one or more stages. Moreover, the N-way Wilkinson power dividers can be constructed such that resistors cross resistors by using dielectric insulators. Moreover, the practice of integrating resistor—resistor, resistor-transmission line, and/or transmission line-transmission line crossing by using dielectric insulators and adjusted line widths in the crossing regions as described above can be used to construct other RF circuits involving combinations of resistors and/or transmission lines. The adjustment in line width can be an adjustment of a width of a transmission line and/or an adjustment of a width of a resistor line. One of ordinary skill in the art will recognize that a change in a width of a resistor line will change a resistance of the resistor and such change can be compensated by changing a length of the resistor line and/or changing a width of the resistor line outside the crossing region. Accordingly, various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined in the appended claims.