Patent Application
20100277258
Various exemplary embodiments relate generally to capacitive input coupling and, more particularly, to tuning a capacitive input coupler.
Many systems use cavity filters to define resonant frequencies for microwave or radio frequency (RF) signals. Such cavities may have an enclosed space surrounded by at least one electrically conductive wall. The dimensions of this enclosed space and the interaction of the electromagnetic waves that embody the signals with the at least one electrically conductive wall define particular frequencies.
A cavity filter is not useful without means for coupling energy into the cavity and from the cavity, so a coupler may be added to transfer a portion of the energy from the cavity filter to an external location. A simple coupler could be a direct metal to metal connection, such that the coupler directly taps energy from the conductive walls of the cavity.
However, such DC-grounded tapping has a number of drawbacks. For example, due to non-linearity in the electromagnetic waves at the metal-to-metal contacts, Passive Inter-Modulation (PIM) signals may appear when signals pass from the cavity walls into a conductive junction. Such degradation in performance is particularly likely when a conductive wall of a cavity is directly linked to a metallic coupler. PIM signals raise a number of issues, including distortion of a desired signal that may potentially degrade system performance.
PIM may be avoided, to some extent, by high quality workmanship, such that the metallic conductor is precisely soldered to a cavity wall. However, even one skilled in metallurgy may be unable to perfectly shape the junction, so some PIM signals will persist. Thus, an alternative solution may be needed that does not involve a metal-to-metal junction.
One alternative is to place a dielectric between the metallic wall of the cavity and the external conductor. Fixed capacitive tapping may use a coaxial structure. However, such a structure is not easily tunable, so it can only tap a set amount of energy from a cavity filter.
Another conventional method requires insertion of tuning screws into a microwave cavity. While rotating a screw to vary the depth of its penetration into the cavity does achieve tuning, it may be difficult to duplicate such tuning when the environment requires adjustment of a very large coupling range with a single design. Thus, it would be beneficial to have a tuning technique for a cavity that was repeatable, resulting in identical coupling each time the technique was used in the same way in a cavity having the same dimensions.
For the foregoing reasons and for further reasons that will be apparent to those of skill in the art upon reading and understanding this specification, there is a need for a capacitive coupling technique that is both easily tunable and adequately reduces PIM.
In light of the present need for an improved technique for capacitive coupling from a cavity filter, a brief summary of various exemplary embodiments is presented. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various exemplary embodiments, but not to limit the scope of the invention. Detailed descriptions of a preferred exemplary embodiment adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections.
In various exemplary embodiments, a filter may provide tunable capacitive input coupling, the filter including one or more of the following: a housing having at least one conductive wall that defines a cavity operating at a default frequency; a conductive element extending inside the cavity from the at least one conductive wall along an axis; and a tuning assembly disposed adjacent the at least one conductive wall and separated from the conductive element by a tunable distance. The tuning assembly may include: a hollow sleeve inserted into a recess having a specified depth along the at least one conductive wall parallel to the axis, the hollow sleeve comprising a non-conductive material and having a particular depth; a wire having a first end inserted fully within the hollow sleeve to the particular depth and a second end bent in a direction orthogonal to said axis, thereby having the capacitive input coupling fixed to a value that is proportional to the particular depth; and a dielectric disposed circumferentially around the first end of the wire, the dielectric retaining the first end of the wire within the hollow sleeve at the particular depth.
In addition, in various exemplary embodiments, the particular depth may be determined through manual testing. Furthermore, in various exemplary embodiments, the wire may be L-shaped, having a bend so that the first end and the second end are orthogonal.
In various exemplary embodiments, the cavity may have a rectangular shape. Alternatively, the cavity may have a cylindrical shape. In various exemplary embodiments, the conductive element may have a cylindrical shape.
In various exemplary embodiments, the dielectric may compress the first end of the wire, thereby holding the wire in a fixed position. In various exemplary embodiments, the specified depth of the hollow sleeve may correspond to a default level of capacitive coupling for the cavity and the default frequency of the cavity.
In various exemplary embodiments, the sleeve may be inserted to the particular depth to tune a cavity to operate at a new level of coupling different from the default coupling, the particular depth being less than the specified depth. In various exemplary embodiments, the sleeve may further comprise a locking portion, the locking portion protruding outside of the recess and holding the sleeve in a fixed position within the recess.
In various exemplary embodiments, a tuning assembly may comprise: a hollow sleeve inserted into a recess having a specified depth along the at least one conductive wall parallel to an axis, the hollow sleeve comprising a non-conductive material and having a particular depth; a wire having a first end fully inserted within the hollow sleeve to the particular depth and a second end bent in a direction orthogonal to said axis, thereby having the capacitive input coupling fixed to a value that is proportional to the particular depth; and a dielectric disposed circumferentially around the first end of the wire, the dielectric retaining the first end of the wire within the hollow sleeve at the particular depth.
In various exemplary embodiments, the particular depth may be determined through manual testing. In various exemplary embodiments, the wire may be L-shaped, having a bend so that the first end and the second end are orthogonal.
In various exemplary embodiments, the dielectric may compress the first end of the wire, thereby holding the wire in a fixed position. In various exemplary embodiments, the specified depth of the recess may correspond to a default level of capacitive coupling.
In various exemplary embodiments, the sleeve may be inserted to the particular depth to tune a cavity to operate at a new level of coupling different from the default coupling, the particular depth being less than the specified depth. In various exemplary embodiments, the sleeve may further comprise a locking portion, the locking portion protruding outside of the recess and holding the sleeve in a fixed position within the recess.
In various exemplary embodiments, a method of assembling a filter includes one or more of the following steps: providing a housing with at least one conductive wall that defines a cavity; placing a conductive element within the cavity, the conductive element mounted on the at least one conductive wall and extending from the at least one conductive wall into the cavity along an axis; mounting a tuning assembly on the at least one conductive wall, the tuning assembly separated from the conductive element and having an internal recess with a specified depth parallel to the axis; inserting a non-conductive sleeve into the internal recess to a particular depth; inserting a first end of a wire fully into the sleeve to the particular depth, the wire having a second end bent in a direction orthogonal to the axis; and placing a dielectric around the first end of the wire to maintain the wire at the particular depth in the sleeve, thereby defining a tuned distance for capacitive coupling between the wire and the conductive element.
In various exemplary embodiments, the method may further comprise performing manual testing to determine the particular depth. In various exemplary embodiments, the method may further comprise inserting the sleeve to the particular depth to tune the cavity to operate at a new coupling different from a default coupling, the particular depth being less than the specified depth.
In order to better understand the various exemplary embodiments, reference is made to the accompanying drawings, wherein:
Referring now to the drawings, in which like numerals refer to like components or steps, there are disclosed broad aspects of various exemplary embodiments.
As depicted in
Filter 100 also has a conductive element 120 extending orthogonally from bottom portion 110a into the cavity. In
Tuning assembly 130 may be disposed along one side wall 110b of the cavity. Although tuning assembly 130 does not physically touch conductive element 120, it has a virtual connection due to capacitive coupling. As will be described in greater detail below, a designer may vary the distance between conductive element 120 and tuning assembly 130 to change the amount of capacitive coupling.
While tuning assembly 130 may be disposed in a corner of a filter, as shown in
During manufacture, tuning assembly 200 is fabricated with a hollow recess 210. Recess 210 may be cylindrical in shape, but other shapes may be applicable, as will be apparent to those having ordinary skill in the art. The specified depth of recess 210 should be designed for subsequent tuning of a cavity resonator.
Sleeve 220 fits into recess 210 within tuning assembly 200. Sleeve 220 may be pushed fully into recess 210, corresponding to a specified depth set during manufacture, or sleeve 220 may be inserted only to a particular depth within the recess. This procedure may permit repeated use of identical sleeves 220 in cavities to produce similar coupling characteristics.
Sleeve 220 may be fabricated from a non-conductive material, such as Teflon™. Sleeve 220 may also be cylindrical in shape, having a long axis that is parallel to the long axis of conductive element 120, as depicted in
Locking portion 230 may ensure that sleeve 220 only reaches a predetermined depth within recess 210. Exemplary locking portion 230, as depicted in
A designer may wish to change the coupling from its default level. The default level of capacitive coupling corresponds to the specified depth of recess 210. Thus, a designer would create a sleeve 220 having a particular depth, using manual testing to determine if that particular depth was appropriate for the desired operating frequency of the resonant cavity. This depth may be specified by determining the proper location of locking portion 230 along sleeve 220.
Wire 240 may be L-shaped, bent so that a first end of wire 240 fits securely within sleeve 220. A second end of wire 240 may form a right angle, extending orthogonally toward element 120, as depicted in
A specified depth of sleeve 220 may correspond to a particular level of capacitive coupling designed for a cavity. Therefore, a manufacturer may design a plurality of cavities to have identical sleeves, thereby ensuring that those sleeves 220 may produce a default coupling within the cavities when wire 240 is fully inserted into those sleeves 220. However, it should be apparent to those skilled in art that such determination of an appropriate depth for sleeve 220 may be determined at times other than manufacture. For example, sleeve 220 could be adjusted prior to installation of the cavities in a work environment.
In either case, the designer will have flexibility to insert sleeve 220 firmly into recess 210 in tuning assembly 200. Inserting sleeve 220 further into recess 210 may increase the distance between the second end of wire 240 and conductive element 120, thereby reducing the capacitive coupling. Conversely, withdrawing sleeve 220 from recess 210 may decrease the distance between the second end of wire 240 and conductive element 120, strengthening the capacitive coupling.
Dielectric 250 may surround the first end of wire 240. Dielectric 250 may be fabricated from a non-conductive plastic, such as polyethylene terephthalate (PET). When wire 240 is inserted into sleeve 220, sleeve 220 may exert a compression force on wire 240 and dielectric 250, thereby holding wire 240 in a fixed position within sleeve 220. This fixed position may be the position at which wire 240 and dielectric 250 are inserted completely into sleeve 220, such that the depth of wire 240 is at the particular depth of sleeve 220 within recess 210.
Wire 240 may pass directly through a central axis of dielectric 250, being aligned with the middle of sleeve 220. However, it should be apparent to those skilled in the art that wire 240 may be disposed in other positions. Regardless of the actual location of wire 240 relative to dielectric 250, dielectric 250 should firmly hold wire 240 in place after it has been moved to an appropriate position in sleeve 220. Thus, locking portion 230 may encompass or otherwise engage the outer perimeter of recess 210, locking both sleeve 220 and dielectric 250 into recess 210 at a particular depth.
The designer may perform testing when creating sleeve 320 to correlate the shape of sleeve 310 to the desired capacitive coupling. Locking portion 330 may prevent sleeve 320 from being inserted beyond a particular depth in recess 310. Dielectric 350 may prevent wire 340 from wobbling within sleeve 320. Dielectric 350 may fill all space between wire 340 and sleeve 320 or only part of that space.
In step 420, the designer places a conductive element within the cavity and mounts the conductive element on a wall so that it extends from that wall into the cavity along an axis. The conductive element may, for example, have the shape of a cylindrical post. Like the wall, the conductive element may be made of metal.
In step 430, the designer mounts a tuning assembly on the wall, the tuning assembly being separated from the conductive element and having an internal recess parallel to the axis. The tuning assembly may be cylindrical in shape. The recess may have a specified depth based upon default capacitive coupling levels.
In step 440, manual testing may be performed to determine a particular depth for insertion of the sleeve into the recess. The sleeve may be cylindrical in shape. The sleeve may entirely fill the recess to obtain the default level of capacitive coupling. Alternatively, the designer may shape the sleeve so that it only fills the recess to a particular depth, performing testing to make sure that the sleeve is shaped to match this target.
In step 450, the designer inserts the sleeve into the recess once testing is finished. The locking portion of the sleeve, which may be constructed to match the contour of the outer perimeter, will engage once the sleeve is inserted to the particular depth within the recess having the specified depth. Because the locking portion is wider than the width of the recess, the locking portion will prevent any further insertion, locking the sleeve to the particular depth within the recess.
In step 460, the designer fully inserts a first end of a wire into the sleeve to a particular depth. The wire may have a second end bent in a direction orthogonal to the axis. The wire is fully inserted until it reaches the end of the sleeve. At this point, the locking portion of the sleeve ensures that the wire and the sleeve cannot be pushed any further into the recess, fixing both at their current positions.
In step 470, a dielectric is placed around the first end of said wire to maintain the wire at the particular depth in the sleeve, thereby defining a tuned distance for capacitive coupling between the wire and a conductive element. The method ends in step 475.
Thus, according to the foregoing, various exemplary embodiments provide a reliable and efficient method for capacitively coupling energy into or from a cavity filter. More particularly, the various exemplary embodiments provide a technique for tuning capacitive coupling in a reliable manner.
It should be apparent that the foregoing description of a cavity filter is only exemplary. Thus, the teachings of this disclosure are equally applicable to any system where selection of a particular frequency is important. For example, the teachings of this disclosure could be applied to any system that transfers electrical energy in a capacitive manner. Other suitable substitutes will be apparent to those of ordinary skill in the art.
Although the various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications may be implemented while remaining within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the invention, which is defined only by the claims.
