Patent Grant
7164903
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.
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.
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.
The three impedance-transformer transmission lines 101–103 are typically each one-quarter wavelength long at some desired frequency fo. 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 Zin, the output impedances Zout1, Zout2 and Zout3 and the desired power split between the outputs 106–108. In one embodiment, when the impedances Zin, Zout1, Zout2, and Zout3 are all equal, and an equal power split is desired, then Z1=Z2=Z3=√{square root over (3)}Zin and R1=R2=R3=3Zin.
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
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.
In the three-way Wilkinson power divider 200, the resistor 207 crosses the output transmission line 210.
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>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.
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