Shim-tuned coaxial cable impedance transformer

Information

  • Patent Grant
  • 6664868
  • Patent Number
    6,664,868
  • Date Filed
    Wednesday, December 19, 2001
    23 years ago
  • Date Issued
    Tuesday, December 16, 2003
    21 years ago
Abstract
A shim-tuned transformer for matching the impedance of a generator and a load coupled to the generator via a transmission line. The transformer includes an outer conductor having an inner surface and an inner conductor positioned within the outer conductor. The transformer further includes at least one shim disposed on the inner surface of the outer conductor and encircling the inner conductor. The at least one shim is slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention relates generally to impedance matching transformers and, more particularly, to a shim-tuned coaxial cable impedance transformer.




2. Description of the Related Art




A generator, such as a transmitter, for example, is typically designed to operate into a specific impedance of a network. However, a load (e.g., an antenna) that is coupled to the generator usually does not provide the specific impedance in which the generator is designed to operate.




When the impedance of the load and the impedance as seen by the generator are equal, maximum power is transferred from the generator to the load over a transmission line coupling the generator to the load. If a mismatch between the impedances of the load and generator occurs, however, the power that is not transferred to the load may be returned towards the generator through the transmission line. These rearward-traveling waves may combine with their respective forward-traveling waves along the transmission line, and because of the phase differences along various positions within the line, may cause standing waves in the transmission line by the alternate cancellation and reinforcement of the voltage and current distributed along the transmission line. The larger the standing waves that occur along the transmission line, the greater the mismatch of the impedance of the load that is coupled to the generator.




In an attempt to compensate for this impedance mismatch between the generator and the load, series-tuned transformers, such as slug-tuned transformers, for example, have been used. These particular transformers, however, have been historically difficult to accurately construct and calibrate, thus resulting in a very limited improvement, if any, in impedance matching a generator to a load. Slug-tuned transformers are typically problematic because relatively large frequency shifts make it very difficult to match high standing wave ratio (SWR) values of the transmission line. Additionally, the slugs within the slug-tuned transformers cannot be changed or adjusted within the transformer without disassembly of the transformer. Accordingly, the slug-tuned transformer is difficult to calibrate as a result of the need to disassemble the transformer to replace and/or adjust the slugs.




The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.




SUMMARY OF THE INVENTION




One aspect of the present invention is seen in a transformer for matching the impedance of a generator and a load coupled to the generator via a transmission line. The transformer includes an outer conductor having an inner surface and an inner conductor positioned within the outer conductor. The transformer further includes at least one shim disposed on the inner surface of the outer conductor and encircling the inner conductor. The at least one shim is slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load.




Another aspect of the present invention is seen in a system. The system comprises a generator for generating a signal and a load for receiving the signal generated by the generator. The system further includes a transformer coupled between the generator and the load. The transformer includes an outer conductor having an inner surface and an inner conductor positioned within the outer conductor. The transformer further includes at least one shim disposed on the inner surface of the outer conductor and encircling the inner conductor. The at least one shim is slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load.




Another aspect of the present invention is seen in a method for matching the impedance of a generator to a load coupled to the generator via a transmission line. The method comprises providing an outer conductor having an inner surface and providing an inner conductor positioned within the outer conductor. The method further comprises providing at least one shim disposed on the inner surface of the outer conductor and encircling the inner conductor, the at least one shim being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:





FIG. 1

shows a simplified block diagram of a wireless transmission network, including a shim-tuned transformer for impedance matching a transmitter to an antenna in accordance with one embodiment of the present invention;





FIG. 2

illustrates a more detailed representation the shim-tuned impedance matching transformer of

FIG. 1

;





FIGS. 3A-C

provide a cross-sectional view of portions of the shim-tuned impedance matching transformer of

FIG. 2

according to one embodiment of the present invention;





FIG. 3D

provides a detailed representation of the shims of the impedance matching transformer of

FIG. 2

incorporating mating teeth formed on the edges of the shims for combining the shims with one another;





FIG. 4

provides a cross-sectional view of the shim-tuned impedance matching transformer of

FIG. 2

according to one embodiment of the present invention; and





FIG. 5

illustrates a process for designing the shim-tuned impedance transformer of

FIG. 2

according to one embodiment of the present invention.











While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.




DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS




Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.




Turning now to the drawings, and specifically referring to

FIG. 1

, a simplified block diagram of a transmission network


100


, employing a shim-tuned transformer, is shown in accordance with one embodiment of the present invention. In the illustrated embodiment, the transmission network


100


may be used for a variety of wireless applications including, but not necessarily limited to, AM, FM, SSB, TV, satellite, cellular, and PCS communications. In addition to the aforementioned examples, it will be appreciated that the transmission network


100


may operate in accordance with various other wireless transmission protocols without departing from the spirit and scope of the present invention. It will further be appreciated that the transmission network


100


may alternatively take the form of a receiving network for receiving signals either in addition to or in lieu of transmitting signals.




In one embodiment of the present invention, the transmission network


100


, in one of its simplest forms, comprises a transmitter


105


for generating signals, a transmission line


115


for carrying the signals generated by the transmitter


105


, and an antenna


120


for sending the signals generated by the transmitter


105


via a wireless communication medium to a receiver station (not shown). Although the network


100


of

FIG. 1

is provided in the form of a transmission network, its application is not so limited. It will be appreciated that the transmitter


105


may take the form of any type of signal generator and the antenna


120


may take the form of any type of load. Accordingly, the transmission network


100


illustrated in

FIG. 1

need not necessarily be limited to a wireless transmission network, but may take on a variety of other forms where the need for impedance matching a signal generator to a load is desirable.




In accordance with one embodiment of the present invention, the transmission line


115


that couples the transmitter


105


to the antenna


120


is provided in the form of a coaxial cable, such as RG8A coaxial cable, for example. It will be appreciated, however, that the transmission line


115


may include various other types of known transmission lines in lieu of a coaxial cable without departing from the spirit and scope of the present invention.




When the load impedance of the antenna


120


(i.e., the load) and the characteristic impedance Z


0


(as seen from the transmitter


105


) are equal, maximum power is transferred via the transmission line


115


to the antenna


120


. If a mismatch of these impedances occurs, however, the power that is not transferred via the transmission line


115


to the antenna


120


may be returned towards the transmitter


105


. These rearward-traveling waves may combine with their respective forward-traveling waves on the transmission line


115


, and because of the phase differences along various positions within the transmission line


115


, may cause standing waves in the transmission line


115


by the alternate cancellation and reinforcement of the voltage and current distributed along the transmission line


115


.




To compensate for the impedance mismatch of the transmitter


105


and the antenna


120


that may occur, the transmission network


100


is provided with a shim-tuned transformer


110


. In accordance with the illustrated embodiment, the shim-tuned transformer


110


substantially matches the characteristic impedance as seen from the transmitter


105


to the load impedance of the antenna


120


to maximize the power that is transferred from the transmitter


105


to the antenna


120


via the transmission line


115


.




Turning now to

FIG. 2

, a more detailed representation of the shim-tuned transformer


110


is shown in accordance with one embodiment of the present invention. The transformer


110


comprises an outer conductor


205


and a center conductor


210


that is disposed lengthwise within the outer conductor


205


. In the illustrated embodiment, the outer conductor


205


takes the form of a copper tube. It will be appreciated, however, that the outer conductor


205


may be constructed out of other suitable conductive materials, as opposed to copper, without departing from the spirit and scope of the present invention. According to one embodiment of the present invention, the outer conductor


205


is provided with an elongated opening or slot (not viewable in

FIG. 2

) that runs lengthwise along the top surface of the outer conductor


205


. The functionality of this slot formed on the outer conductor


205


will be appreciated as the description proceeds.




Referring now to

FIG. 3A

, a cross-sectional view of a portion of the shim-tuned transformer


110


is provided. The outer conductor


205


encircles the center conductor


210


, and a slot


305


is formed therein lengthwise along the top surface of the outer conductor


205


so as to provide an elongated opening between the inside and outside of the outer conductor


205


.




Referring back to

FIG. 2

, the transformer


110


comprises a pair of shims


215


,


220


, in accordance with one embodiment, that are moveably disposed on the inner surface of the outer conductor


205


. The shims


215


,


220


(as illustrated in

FIG. 2

) are viewed as if one could see through the outer conductor


205


; although in reality, the shims


215


,


220


reside on the inner surface of the outer conductor


205


and are not viewable from the outside surface of the outer conductor


205


. Although two shims


215


,


220


are illustrated in

FIG. 2

, it will be appreciated that the number of shims


215


,


220


disposed on the inner surface of the outer conductor


205


may vary. For example, the transformer


110


may include three, four, or more shims


215


,


220


disposed on the inner surface of the outer conductor


205


without departing from the spirit and scope of the present invention. In an alternative embodiment, the shims


215


,


220


may be configured with mating teeth


320


(

FIG. 3D

) on each mating end of the shims


215


,


220


such that the shims


215


,


220


may be joined in a “locking” relationship so as to form one shim


215


,


220


using various standard shim lengths. It will further be appreciated that the shims


215


,


220


may be joined using other types of mating mechanisms, as opposed to the mating teeth herein described, without departing from the spirit and scope of the present invention.




The spacing between the shims


215


,


220


is adjustable, along the outer conductor


205


to substantially match the characteristic impedance as seen by the transmitter


105


and the load impedance of the antenna


120


of the transmission network


100


. Once the proper spacing between the shims


215


,


220


is set, the shims


215


,


220


may then be moved as a unit along the outer conductor


205


to substantially match the impedances. Accordingly, both the spacing between the shims


215


,


220


and their location along the outer conductor


205


are adjustable.




Referring to

FIG. 3B

, a cross-sectional view of a portion of the transformer


110


is shown where at least one of the shims


215


,


220


is disposed therein. In the illustrated embodiment, the shim


215


,


220


takes the form of a cylindrical shape and is disposed on the inner surface of the outer conductor


205


so as to encircle the center conductor


210


.




Turning now to

FIG. 4

, a side view perspective of the shim-tuned transformer


110


is shown in accordance with one embodiment of the present invention. The shims


215


,


220


disposed on the inner surface of the outer conductor


205


respectively include header tabs


415


,


420


that rise through the slot


305


that runs lengthwise along the top of the outer conductor


205


. The header tabs


415


,


420


permit the shims


215


,


220


to be moved along the inside surface of the outer conductor


205


by sliding their respective header tabs


415


,


420


along the slot


305


that runs along the top of the outer conductor


205


. A cross-sectional perspective view of the header tabs


415


,


420


are shown in

FIG. 3B

, protruding from the slot


305


of the outer conductor


205


.




The header tabs


415


,


420


permit movement of the shims


215


,


220


within the outer conductor


205


to calibrate the transformer


110


to match the characteristic impedance and the load impedance of the antenna


120


without the inconvenience of disassembling the transformer


110


. In accordance with one embodiment, the movement of the header tabs


415


,


420


may be performed by human interaction. Alternatively, the transformer


110


may be configured with a motor-driven mechanism (not shown) to move the header tabs


415


,


420


of the transformer


110


.




According to one embodiment of the present invention, a thin coat of polytetrafluroethylene (PTFE) may be applied to the inner surface of the outer conductor


205


to facilitate movement of the shims


215


,


220


along the inner surface of the outer conductor


205


. PTFE is commercially made available by Dupont as Teflon®. It will be appreciated, however, that other types of coating materials that are suitable for facilitating the movement of the shims


215


,


220


within the outer conductor


205


may be used in lieu of PTFE without departing from the spirit and scope of the present invention.




Referring again to

FIG. 4

, once the proper spacing of the shims


215


,


220


is determined, a pre-sprung shielding material


430


may be placed within the slot


305


of the outer conductor


205


to prevent the header tabs


415


,


420


, and their respective shims


215


,


220


, from shifting within the outer conductor


205


of the transformer


110


. Referring to

FIG. 3C

, a cross-sectional view of a portion of the transformer


110


is shown. The shielding material


430


is pressed into the slot


305


of the outer conductor


205


to substantially prevent the shim header tabs


415


,


420


of their respective shims


215


,


220


from shifting within the slot


305


of the outer conductor


205


once the transformer


110


is calibrated for optimal impedance matching.




When it is desired to adjust the spacing of the shims


215


,


220


within the transformer


110


, the shielding material


430


may be removed from the slot


305


of the outer conductor


205


. Subsequent to removing the shielding material


430


from the slot


305


, the spacing of the shims


215


,


220


may then be adjusted by sliding the shim header tabs


415


,


420


along the slot


305


of the outer conductor


205


. When the desired position of the shims


215


,


220


is achieved by moving their respective shim header tabs


415


,


420


along the slot


305


of the outer conductor


205


, the shielding material


430


may then be pressed into the remaining gaps of the slot


305


(i.e., the gaps in the slot


305


adjacent the shim header tabs


415


,


420


) to prevent the shims


215


,


220


from shifting within the outer conductor


205


of the transformer


110


once calibrated.




According to one embodiment, the transformer


110


is further provided with connectors


440


on each end of the outer conductor


205


to permit connection of the transformer to the transmission line


115


of the transmission network


100


. In one embodiment, the connectors


440


are of the quick-change type, and the connectors


440


are fastened to the outer conductor


205


of the transformer


110


by set screws


445


. It will be appreciated, however, that the type of connectors


440


used for coupling the transformer


110


to the transmission line


115


and the manner in which the connectors


440


are fastened to the outer conductor


205


may vary without departing from the spirit and scope of the present invention.




In accordance with one embodiment of the present invention, the overall length of the shim-tuned transformer


110


is the sum of one-half the wavelength needed for phase adjustments, the optimum distance between the shims


215


,


220


, and the combined length of the shims


215


,


220


. Adjustments may be made with conventional impedance matching instruments such as watt meters, impedance bridges, and the like. By shortening the overall length of the outer conductor


205


, the length of the shims


215


,


220


, and reducing the spacing between the shims


215


,


220


may widen the bandwidth of the shim-tuned transformer


110


. This will, of course, limit the standing wave ratio (SWR) reducible to unity. The lengths of the shims


215


,


220


may be cut shorter by a factor of 1/(ε)


½


, where ε is the velocity factor, to compensate for the slower speed of the electrons through the transformer dielectric in comparison to the speed of the electrons in air. For example, ε is typically measured at 0.66 for a transmission line


115


including RG8A coaxial cable.




Several different characteristic impedances may be produced for the transmission network


100


using the shim-tuned transformer


110


by varying the thickness of the shims


215


,


220


. For example, a shim gauge of 15 is 0.0673 inches thick. When the shims


215


,


220


(using gauge 15) are inserted within the outer conductor


205


having an outer diameter of 0.5 in., it reduces the inside diameter of the outer conductor


205


and produces a shim impedance (z


t


) of 40.69 Ω and a characteristic impedance Z


t


of 0.814. Alternatively, a shim gauge of 7 is 0.1793 inches thick, and when the shim


215


,


220


(using gauge 7) is inserted within the outer conductor


205


it reduces the inside diameter of the outer conductor


205


by producing a shim impedance (z


t


) of 21.17 Ω and a characteristic impedance Z


t


of 0.423. From these examples, it will be appreciated that the impedance may be altered by using different thicknesses of the shims


215


,


220


, inner diameters of the outer conductor


205


, and inner wire gauges for the center conductor


210


.




In one embodiment of the present invention, the shim-tuned transformer


110


having a length of 1.25 wavelengths with the shims


215


,


220


having a total of one-fourth wavelengths (i.e., one-eighth wavelengths each) and having a ratio of shim impedance (z


t


) to a characteristic impedance (Z


0


) of 0.4 can match a transmission line


115


having a 40:1 voltage SWR. The minimum SWR occurs when the two shims


215


,


220


are placed within the outer conductor


205


such that the spacing between them are conjugate and the shims


215


,


220


are adjusted as a unit over the 1.25 wavelength distance of the shim-tuned transformer


110


.




Turning now to

FIG. 5

, a process


500


for designing the shim-tuned transformer


110


is provided in accordance with one embodiment of the present invention. The process


500


commences at block


505


where the resistance and the reactance of the antenna


120


is determined. According to one embodiment, the resistance and reactance of the antenna


120


may be calculated with a Numerical Electromagnetic Code method of moments antenna-modeling tool such as EZNEC 3.0, which is available by EZNEC Antenna Software, Beaverton, Oreg. At block


510


, the size of the center conductor


210


is determined to match the output impedance of the transmitter


105


. In the illustrated embodiment, the size of the center conductor


210


is selected based upon the current handling requirements at the RF frequency in which the transmitter


105


is tuned.




The process


500


continues at block


515


where the inside diameter of the outer conductor


205


is determined from the gauge size used for the outer conductor


205


. At block


520


, the thickness of the shims


215


,


220


are determined based upon the outer diameter of the outer conductor


205


.




At block


525


, the amount of spacing between the shims


215


,


220


is calculated using a Smith Chart® or Smith software, such as WinSmith®, available from Nobel Publishing Company, Atlanta, Ga. The transformer


110


is then constructed at block


530


and the spacing between the shims


215


,


220


and the location of the shim assembly along the outer conductor


205


is adjusted for optimal impedance matching between the transmitter


105


and the antenna


120


.




The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.



Claims
  • 1. A transformer for matching the impedance of a generator and a load coupled to the generator via a transmission line, comprising:an outer conductor having an inner surface; an inner conductor positioned within the outer conductor; a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load; and a coating material applied to the inner surface of the outer conductor to facilitate the sliding of the shims along the inner surface of the outer conductor.
  • 2. The transformer of claim 1, wherein the coating material applied to the inner surface of the outer conductor comprises polytetrafluroethylene.
  • 3. A transformer for matching the impedance of a generator and a load coupled to the generator via a transmission line, comprising:an outer conductor having an inner surface and an outer surface, the outer conductor having a slot formed lengthwise along the outer surface of the outer conductor, the slot providing an opening between the inner and outer surfaces of the outer conductor; an inner conductor positioned within the outer conductor; and a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load, the shims include including a pair of shims each including a respective header tab attached thereto and protruding through the slot formed within the outer conductor, the edges of the pair of shims including mating teeth for mating the pair of shims together by a locking relationship of their respective mating teeth by movement of their respective header tabs towards one another.
  • 4. A transformer for matching the impedance of a generator and a load coupled to the generator via a transmission line, comprising:an outer conductor having an inner surface and an outer surface, the outer conductor having a slot formed lengthwise along the outer surface of the outer conductor, the slot providing an opening between the inner and outer surfaces of the outer conductor; an inner conductor positioned within the outer conductor; and a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load, the shims including a header tab attached thereto that extends through the slot of the outer conductor, movement of the header tab along the slot formed in the outer conductor causing the shim attached thereto to slide along the inner surface of the outer conductor, movement of the header tab being restricted by a shielding material placed within the slot of the outer conductor adjacent the header tab.
  • 5. The transformer of claim 4, further comprising a connector attached to each end of the outer conductor, wherein the connector couples the transformer to the transmission line between the generator and the load.
  • 6. The transformer of claim 4, wherein a spacing between the shims and a position of the shims relative to the outer conductor are adjustable for matching the impedance of the generator and the impedance of the load.
  • 7. The transformer of claim 4, wherein the shims are separately slideable along the inner surface of the outer conductor.
  • 8. The transformer of claim 4, wherein the outer conductor and inner conductor of the transformer form a coaxial cable.
  • 9. The transformer of claim 4, wherein the generator is a transmitter and the load is an antenna.
  • 10. A system comprising:a generator for generating a signal; a load for receiving the signal generated by the generator; and a transformer coupled between the generator and the load, the transformer including: an outer conductor having an inner surface and an outer surface, the outer conductor having a slot formed lengthwise along the outer surface of the outer conductor, the slot providing an opening between the inner and outer surfaces of the outer conductor; an inner conductor positioned within the outer conductor; and a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load, the shims including a pair of shims each including a respective header tab attached thereto and protruding through the slot formed within the outer conductor, the edges of the pair of shims including mating teeth for mating the pair of shims together by a locking relationship of their respective mating teeth by movement of their respective header tabs towards one another.
  • 11. A system, comprising:a generator for generating a signal; a load for receiving the signal generated by the generator; and a transformer coupled between the generator and the load, the transformer including: an outer conductor having an inner surface and an outer surface, the outer conductor having a slot formed lengthwise along the outer surface of the outer conductor, the slot providing an opening between the inner and outer surfaces of the outer conductor; an inner conductor positioned within the outer conductor; and a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load, the shims including a header tab attached thereto that extends through the slot of the outer conductor, movement of the header tab along the slot formed in the outer conductor causing the shim attached thereto to slide along the inner surface of the outer conductor, movement of the header tab being restricted by a shielding material placed within the slot of the outer conductor adjacent the header tab.
  • 12. The system of claim 11, wherein the transformer further comprises a connector attached to each end of the outer conductor, wherein the connector couples the transformer to the transmission line between the generator and the load.
  • 13. The system of claim 11, wherein the system comprises a wireless transmission system and the generator includes a transmitter and the load includes an antenna.
  • 14. The system of claim 11, wherein the outer conductor and inner conductor of the transformer form a coaxial cable.
  • 15. The system of claim 11, wherein the shims are separately slideable along the inner surface of the outer conductor.
  • 16. The system of claim 11, wherein a spacing between the shims and a position of the shims relative to the outer conductor are adjustable for matching the impedance of the generator and the impedance of the load.
  • 17. A system, comprising:a generator for generating a signal; a load for receiving the signal generated by the generator; and a transformer coupled between the generator and the load, the transformer including: an outer conductor having an inner surface; an inner conductor positioned within the outer conductor; and a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load; and a coating material applied to the inner surface of the outer conductor to facilitate the sliding of the shims along the inner surface of the outer conductor.
  • 18. The system of claim 17, wherein the coating material applied to the inner surface of the outer conductor comprises polytetrafluroethylene.
  • 19. A method for matching the impedance of a generator to a load coupled to the generator via a transmission line, comprising:providing an outer conductor having an inner surface and an outer surface; forming a slot lengthwise along the outer surface of the outer conductor, the slot providing an opening between the inner and outer surfaces of the outer conductor; providing an inner conductor positioned within the outer conductor; and providing a plurality of shims disposed on the inner surface of the outer conductor and encircling the inner conductor, the shims being slideable along the inner surface of the outer conductor for matching the impedance of the generator and the impedance of the load, the shims including header tabs attached thereto that extend through the slot of the outer conductor, movement of the header tabs along the slot formed in the outer conductor causing the shims attached thereto to slide along the inner surface of the outer conductor movement of the header tabs being restricted by a shielding material placed within the slot of the outer conductor adjacent the header tabs.
  • 20. The method of claim 19, further comprising:moving the shims relative to each other.
  • 21. The method of claim 19, further comprising:adjusting a spacing between the shims and a position of the shims relative to the outer conductor for matching the impedance of the generator and the impedance of the load.
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Number Name Date Kind
2900610 Allen et al. Aug 1959 A
3340485 Caron Sep 1967 A
3792385 Napoli et al. Feb 1974 A
5545949 Bacher Aug 1996 A