Patent Publication Number: US-11658380-B2

Title: Tuning elements with reduced metal debris formation for resonant cavity filters

Description:
CLAIM OF PRIORITY 
     The present application is a 35 U.S.C. 371 national stage application of PCT International Application No. PCT/EP2019/068679, filed on Jul. 11, 2019, which claims the benefit of and priority from U.S. Provisional Patent Application No. 62/696,959 entitled “ Tuning Elements With Reduced Metal Debris Formation For Resonant Cavity Filters ” filed on Jul. 12, 2018, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     FIELD 
     The present invention relates generally to communications systems and, more particularly, to filters that are suitable for use in cellular communications systems. 
     BACKGROUND 
     Cellular base stations are known in the art and typically include, among other things, baseband equipment, radios and antennas.  FIG.  1    is a simplified, schematic diagram that illustrates a conventional cellular base station  10 . As shown in  FIG.  1   , the cellular base station  10  includes an antenna tower  30  and an equipment enclosure  20  that is located at the base of the antenna tower  30 . A plurality of baseband units  22  and radios  24  are located within the equipment enclosure  20 . Each baseband unit  22  is connected to a respective one of the radios  24  and is also in communication with a backhaul communications system  44 . Three sectorized antennas  32  (labelled antennas  32 - 1 ,  32 - 2 ,  32 - 3 ) are located at the top of the antenna tower  30 . Three coaxial cables  34  (which are bundled together in  FIG.  1    to appear as a single cable) connect the radios  24  to the respective antennas  32 . In many cases, the radios  24  are located at the top of the tower  30  instead of in the equipment enclosure  20  in order to reduce signal transmission losses. 
     Cellular base stations can use phased array antennas  32  that include a linear array of radiating elements. Typically, each radiating element is used to (1) transmit radio frequency (“RF”) signals that are received from a transmit port of an associated radio  24  and (2) receive RF signals from mobile users and pass these received signals to the receive port of the associated radio  24 . Duplexers are typically used to connect the radio  24  to each respective radiating element of the antenna  32 . A “duplexer” refers to a known type of three-port filter assembly that is used to connect both the transmit and receive ports of a radio  24  to an antenna  32  or to one or more radiating elements of multi-element antenna  32 . Duplexers are used to isolate the RF transmission paths to the transmit and receive ports of the radio  24  from each other while allowing both RF transmission paths access to the radiating element(s) of the antenna  32 . 
       FIG.  2    is a perspective view of a conventional duplexer  50 .  FIG.  3    is a perspective view of the conventional duplexer  50  of  FIG.  2    with the cover plate  78  removed therefrom.  FIG.  4    is a perspective view of the duplexer  50  of  FIGS.  2 - 3    with the top cover and resonators removed to more clearly show the cavities within the filter housing. 
     Referring to  FIGS.  2 - 4   , the conventional duplexer  50  includes a housing  60  that has a floor  62  and a plurality of sidewalls  64 . An interior ledge  66  is formed around the periphery of the housing  60 . Internal walls  68  extend upwardly from the floor  62  to divide the interior of the housing  60  into a plurality of cavities  70 . Coupling windows  72  are formed within the walls  68 , and these windows  72  as well as openings between the walls  68  allow communication between the cavities  70 . Internally-threaded columns  74  and resonating elements  76  are provided within the housing  60 . The resonating elements  76  may include, for example, dielectric resonators or coaxial metal resonators, and may be mounted onto selected ones of the internally threaded cavities  74 . A cover plate  78  acts as a top cover for the duplexer  50 . Screws  80  are used to tightly hold the cover plate  78  into place so that the cover plate  78  continuously contacts the interior ledge  66  and the top surfaces of the walls  68 . 
     The duplexer  50  further includes an input port  82 , an output port  84  and a common port  86 . The input port  82  may be attached to an output port of a transmit path phase shifter (not shown) via a first cabling connection  83 . The output port  84  may be attached to an input port of a receive path phase shifter via a second cabling connection  85 . The common port  86  may connect the duplexer  50  to one or more radiating elements of the antenna (not shown) via a third cabling connection (not shown). A plurality of tuning screws  90  are also provided. The tuning screws  90  may be adjusted to tune aspects of the frequency response of the duplexer  50  such as, for example, the center frequency of the notch in the filter response. It should be noted that the device of  FIGS.  2 - 4    illustrates two duplexers that share a common housing, which is why the device includes more than three ports (the device includes a total of six ports, although all of the ports are not visible in the views of  FIGS.  2 - 4   ). 
       FIGS.  5 A and  5 B  are perspective views of some conventional tuning screws shown mounted in top covers of respective filters. Referring to  FIG.  5 A , a tuning screw  100  is shown mounted in a top cover  120  of a filter housing. The top cover  120  has a plurality of apertures  130  extending therethrough, which may be threaded (two apertures  130  are depicted in  FIG.  5 A , one of which has the tuning screw  100  inserted therein). A threaded nut  140  may be provided above each aperture  130 . Tuning screws  100  can be threaded through the respective apertures  130  (only one tuning screw  100  is shown). The tuning screws  100  can readily be threaded further into or further out of the threaded apertures  130 , and hence into or out of the cavity of the filter, and the nuts  140  may be used to fix the screws  100  in a desired position, which may facilitate very precise tuning of the filter. In other embodiments a thicker top cover  120  may be used that has threaded apertures formed therein, which may eliminate the need for separate threaded nuts  140 . 
     Referring to  FIG.  5 B , a cover  170  of a filter housing is depicted that includes a self-locking tuning screw  150  mounted therein. The self-locking tuning screw  150  is mounted in a threaded aperture  180  in the cover  170  (a second threaded aperture  180  is illustrated in  FIG.  5 B  that does not have a tuning screw  150  therein). The self-locking tuning screw  150  may operate in the same fashion as the tuning screw  100  discussed above. 
     SUMMARY 
     According to some embodiments of the present disclosure, a resonant cavity filter includes a housing having a resonator therein, and a tuning element including an elongated pin member having a conductive outer surface. The tuning element is mounted for insertion of the elongated pin member into an interior of the resonator. The conductive outer surface includes a contact portion by which the elongated pin member is secured in a desired position to adjust a frequency response of the resonant cavity filter, where the contact portion is free of threading. 
     In some embodiments, the tuning element further includes a turret member having an opening therein that is aligned with the interior of the resonator. The elongated pin member extends through the opening in the turret member for the insertion into the interior of the resonator and is secured by an interference fit between the contact portion and the turret member. 
     In some embodiments, the turret member includes a plurality of fingers respectively positioned around a perimeter of the opening therein. The fingers are flexible and/or elastic to grip the contact portion of the elongated pin member therebetween to secure the elongated pin member in the desired position. 
     In some embodiments, the tuning element further includes a ring-shaped member having an inner surface that is shaped to mate with outer surfaces of the fingers such that acceptance of the fingers into the ring-shaped member causes the fingers to grip the contact portion of the elongated pin member therebetween. 
     In some embodiments, the outer surfaces of the fingers define a tapered shape, and the inner surface of the ring-shaped member is tapered to mate with the tapered shape of the fingers. 
     In some embodiments, the outer surfaces of the fingers include an external thread pattern, and the ring-shaped member is a nut having an internal thread pattern on the inner surface thereof that is configured to mate with the external thread pattern. 
     In some embodiments, first portions of the outer surfaces of the fingers include the external thread pattern, and second portions of the outer surfaces of the fingers are tapered relative to the first portions. 
     In some embodiments, the second portions of the outer surfaces of the fingers are tapered from a dimension corresponding to a diameter defined by the inner surface of the ring-shaped member to a dimension greater than the diameter. 
     In some embodiments, the ring-shaped member has an elasticity sufficient to cause the fingers to grip the contact portion of the elongated pin member therebetween responsive to acceptance of the fingers into the ring-shaped member. 
     In some embodiments, the turret member has a threaded hole in a sidewall thereof that is configured to accept a screw-shaped member, and the screw-shaped member is configured to be laterally threaded into the threaded hole to contact the contact portion to secure the elongated pin member in the desired position. 
     In some embodiments, the housing further includes a top cover with an aperture therein that is aligned with the interior of the resonator, and the turret member is mounted on the cover with the opening therein coaxially aligned with the aperture. 
     In some embodiments, the turret member includes an extended base portion that extends through and beyond the aperture in the top cover and into the interior of the resonator. 
     In some embodiments, the aperture in the top cover is tapered in a direction away from the interior of the resonator. The turret member includes an external thread pattern protruding outside of the aperture opposite the resonator, which is configured to mate with an internal thread pattern of a nut. Outer surfaces of the fingers are tapered to mate with the aperture such that acceptance of the fingers into the aperture responsive to tightening of the nut around the external thread pattern of the turret causes the fingers to grip the contact portion of the elongated pin member therebetween. 
     In some embodiments, the opening in the turret member includes an internal thread pattern and is tapered toward the interior of the resonator, and the tuning element further includes an elastic ring and a nut that are sized to fit within the opening in the turret member, with the nut having an external thread pattern that is configured to mate with the internal thread pattern. The elongated pin member extends through the elastic ring and the nut for the insertion into the interior of the resonator, and tightening the nut advances the elastic ring into the opening and toward the interior of the resonator causing compression of the elastic ring against the contact portion to secure the elongated pin member in the desired position. 
     In some embodiments, the housing further includes a top cover with an aperture therein that is aligned with the interior of the resonator, and the conductive outer surface of the elongated pin member is expandable to contact a sidewall of the aperture to secure the elongated pin member in the desired position by an interference fit with the contact portion. 
     In some embodiments, the elongated pin member includes a hollow opening extending along a major axis thereof within the conductive outer surface thereof. 
     In some embodiments, the tuning element further includes a screw-shaped member, and the hollow opening in the elongated pin member is tapered and is configured to accept the screw-shaped member. Insertion of the screw-shaped member into the hollow opening causes expansion of the contact portion of the conductive outer surface to contact the sidewall of the aperture to secure the elongated pin member in the desired position. 
     In some embodiments, the hollow opening includes an internal thread pattern that is configured to mate with a thread pattern of the screw-shaped member, and an end of the elongated pin member opposite the hollow opening is closed. 
     In some embodiments, the elongated pin member further includes an elastic inner portion defining the hollow opening and including the conductive outer surface thereon. The elastic inner portion is configured for compression during insertion of the elongated pin member into the aperture, and for expansion responsive to release of the compression to secure the elongated pin member in the desired position by the interference fit with the contact portion. 
     In some embodiments, the elongated pin member includes an elongated bar member extending within a hollow opening in the conductive outer surface. The hollow opening has a varying width and the elongated bar member has a wider portion at an end thereof proximate the interior of the resonator, and retraction of the elongated bar member into the hollow opening causes expansion of the contact portion to contact a sidewall of the turret member to secure the elongated pin member in the desired position. 
     In some embodiments, the turret member includes an external thread pattern protruding outside of the aperture opposite the resonator, and the tuning element is a nut having an internal thread pattern on the inner surface thereof that is configured to mate with the external thread pattern. 
     According to some embodiments of the present disclosure, a resonant cavity filter includes a housing having a resonator therein and a top cover with an aperture therein that is aligned (e.g., coaxially) with an interior of the resonator, and a tuning element. The tuning element includes an elongated pin member that is mounted for insertion through the aperture in the top cover and into the interior of the resonator. The tuning element is fixed in a desired position by an interference fit with a contact portion on a conductive outer surface of the elongated pin member, without rotational friction. 
     In some embodiments, the contact portion is free of a thread pattern. 
     In some embodiments, the tuning element further includes a turret member mounted on the top cover and having an opening therein that is coaxially aligned with the aperture. The elongated pin member extends through the opening in the turret member for the insertion through the aperture and into the interior of the resonator. 
     In some embodiments, the turret member includes a plurality of fingers respectively positioned around a perimeter of the opening therein. The fingers are flexible to clamp the contact portion of the elongated pin member therebetween to fix the elongated pin member in the desired position. 
     In some embodiments, first portions of outer surfaces of the fingers include an external thread pattern, and second portions of the outer surfaces of the fingers are tapered from a dimension corresponding to a diameter defined by the first portions to a dimension greater than the diameter. 
     In some embodiments, the turret member includes a threaded hole in a sidewall thereof that is configured to accept a screw-shaped member. The screw-shaped member is configured to be laterally threaded into the threaded hole to pin the contact portion between the screw-shaped member and a sidewall of the opening in the turret member to fix the elongated pin member in the desired position. 
     In some embodiments, the conductive outer surface of the elongated pin member is expandable to contact a sidewall of the aperture or a sidewall of the turret to secure the elongated pin member in the desired position. 
     In any of the above embodiments, the resonant cavity filter may be a duplexer or a diplexer. 
     Further features, advantages and details of the present disclosure, including any and all combinations of the above embodiments, will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the embodiments that follow, such description being merely illustrative of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a simplified, schematic diagram of a conventional cellular base station. 
         FIG.  2    is a perspective view of a conventional duplexer. 
         FIG.  3    is a perspective view of the conventional duplexer of  FIG.  2    with the cover plate removed therefrom. 
         FIG.  4    is a perspective view of the duplexer of  FIGS.  2 - 3    with the top cover and resonators removed. 
         FIGS.  5 A- 5 B  are perspective views of a conventional tuning screw and a conventional self-locking tuning screw, respectively. 
         FIG.  6    is a perspective view of a resonant cavity filter including tuning elements according to embodiments of the present invention. 
         FIG.  7 A  is a perspective view of a tuning element according to embodiments of the present invention. 
         FIG.  7 B  is an exploded perspective view of the tuning element of  FIG.  7 A . 
         FIG.  7 C  is an enlarged perspective view of a perforated turret member shown in  FIG.  7 B . 
         FIG.  8    is a schematic cross-sectional view of the turret portion and retaining nut of the tuning element of  FIG.  7 A . 
         FIG.  9 A  is a cross-sectional view of the tuning element of  FIG.  7 A  inserted into a top cover of and extending into a resonator of a resonant cavity filter of  FIG.  6    in order to tune the frequency response of the filter. 
         FIG.  9 B  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  10 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  10 B  is an exploded perspective view of the tuning element of  FIG.  10 A . 
         FIG.  11    is a perspective view of a resonant cavity filter including tuning elements according to still further embodiments of the present invention. 
         FIG.  12 A  is a cross-sectional view of the tuning element of  FIG.  11    inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  12 B  is an exploded perspective view of the tuning element of  FIG.  12 A . 
         FIG.  13 A  is a cross-sectional view of a tuning element according to yet further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  13 B  is an exploded perspective view of the tuning element of  FIG.  13 A . 
         FIG.  14 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  14 B  is perspective view of the tuning element of  FIG.  14 A . 
         FIG.  15 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  15 B  is perspective view of the tuning element of  FIG.  15 A . 
         FIG.  15 C  is an enlarged perspective view of the tuning element of  FIG.  15 B . 
         FIG.  16 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  16 B  is perspective view of the tuning element of  FIG.  16 A . 
         FIG.  16 C  is an enlarged perspective view of the turret member of  FIG.  16 B . 
         FIG.  17 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  17 B  is an enlarged view of a portion of the tuning element of  FIG.  17 A . 
         FIG.  18 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. 
         FIG.  18 B  is an enlarged perspective view of the turret member of  FIG.  18 A . 
     
    
    
     DETAILED DESCRIPTION 
     Passive Intermodulation (“PIM”) distortion is a known effect that may occur when multiple RF signals are transmitted through a communications system. PIM distortion may occur when two or more RF signals encounter non-linear electrical junctions or materials along an RF transmission path. Such non-linearities may act like a mixer, causing new RF signals to be generated at mathematical combinations of the original RF signals. If the newly generated RF signals fall within the bandwidth of existing RF signals, the noise level experienced by those existing RF signals may be effectively increased. When the noise level is increased, it may be necessary reduce the data rate and/or the quality of service. 
     PIM distortion can be a significant interconnection quality characteristic for an RF communications system, as PIM distortion generated by a single low quality interconnection may degrade the electrical performance of the entire RF communications system. Thus, ensuring that components used in RF communications systems generate acceptably low levels of PIM distortion may be desirable. In particular, minimizing and controlling the effects of PIM distortion may be used to achieve high end performance. PIM performance may also be a recognized market differentiator and provides competitive advantage, enabling increased data transfer efficiency. 
     PIM can be generated by many factors. One possible source of PIM distortion may be due to inconsistent metal-to-metal contact along an RF transmission path. For example, conventional tuning screws for a resonant cavity RF filter form metal-to-metal contacts where the metal screws are threaded into a mating metallic nut of the filter housing. It is standard practice to tune the RF filter to a desired frequency response through the careful placement of apposite tuning screws in a position that provides the desired tuning effect. This process slowly brings the filter from detuned to tuned condition by continuous re-touching of screws position. Given the strong RF interactions within each screw and other screws, the tuner may continuously move one screw, then move another screw, and subsequently move the same screw or screws multiple times. 
     However, microscopic loose metal particles may be created by adjustment of the tuning screws in the resonating cavities of the filter. The creation of such metal particles typically occurs during the tuning phase of the filter, as a purpose of tuning screws is to provide a method of adjusting the frequency response of the filter in a desired fashion based on the depth to which the screw is inserted within the filter cavity. These repeated rotations of the screws can create the metal particles that fall into filters cavities and generate PIM. In particular, the plating on the screws or related threaded holes (silver, copper or other well conductive metals) may be scraped on the surface and small flakes and debris may be generated. 
     Pursuant to embodiments of the present invention, resonant cavity filters are provided that have improved tuning elements. The resonant cavity filters may be duplexers, diplexers, combiners, or the like, which are suitable for use in cellular communications systems and other applications. The filters and tuning elements may be designed so that the metal-to-metal contacts resulting from threading between the components or members of the tuning elements are effectively outside of the adjacent filter cavity, so that metal shavings and/or metal debris that may be formed due to contact and/or adjustment of the components are less likely to fall within the housing of the filter, where such metal shavings/debris may give rise to PIM distortion. 
     More generally, the metal-to-metal contact at the threading between components of the tuning element may be eliminated and/or otherwise provided non-adjacent to openings in the cover for the filter housing, such that the creation of such small metal particles from the metal-to-metal contact is reduced and/or is prevented from falling into the corresponding resonating cavity of the filter. In some embodiments, tuning elements may include a conductive pin member (rather than a conventional screw) with a non-threaded contact portion on its outer surface. As used herein, non-threaded refers to the absence of a thread pattern (or “threading”) on the described surface. The pin member can be moved up and down (i.e., into and out of the filter cavity) and secured by the contact portion or otherwise fixed in a desired position in a stable manner, while at the same time providing a good electrical contact. For example, in some embodiments the tuning element may include an intervening turret member that is configured to accept the pin member within an opening or aperture above the filter cavity, and to guide the pin member into or out of the interior of the resonator. In some embodiments, the pin member itself may be configured to expand its outer diameter to be secured by the contact portion directly in the aperture above the filter cavity. Thus, by removing the interface between threading patterns from a space that is gravitationally adjacent the filter cavity, resonant cavity filters and tuning elements according to embodiments of the present invention may provide improved PIM distortion performance as compared to conventional resonant cavity filters. 
       FIGS.  6 - 9 A  illustrate a tuning element  200  according to embodiments of the present invention as well as a portion of a resonant cavity filter  250  that includes the tuning element  200 . In particular,  FIG.  6    is a perspective view of a resonant cavity filter including tuning elements  200  according to embodiments of the present invention.  FIG.  7 A  is a perspective view of one of the tuning elements  200  of  FIG.  6   .  FIG.  7 B  is an exploded view of the tuning element  200  of  FIG.  7 A .  FIG.  7 C  is an enlarged perspective view of a perforated turret member  240  shown in  FIG.  7 B .  FIG.  8    is a schematic cross-sectional view of the turret member  240  and retaining nut  260  of the tuning element  200  of  FIG.  7 A .  FIG.  9 A  is a cross-sectional view of the tuning element  200  of  FIG.  7 A  inserted into a top cover of and extending into a resonator  270  of one of the resonant cavity filters  250  of  FIG.  6    in order to tune the frequency response of the filter  250 . 
     Referring now to  FIGS.  6  and  9 A , the resonant cavity filter  250  includes a housing  264  that has a top cover  262 . Screws  280  are used to tightly hold the top cover  262  in place. A plurality of resonators  270  such as, for example, metallic coaxial resonators, are disposed within cavities  268  of the filter  250 . Each resonator  270  may have one or more sidewalls  272  (for example, a generally cylindrical shaped sidewall) that define an open interior  274 . The top cover  262  includes a plurality of openings or apertures  263  that are aligned (e.g., coaxially aligned) with the interiors  274  of respective resonators  270 . Tuning elements  200  are mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the apertures  263  and into the interiors  274  of the respective resonators  270 . Although described and illustrated herein primarily with reference to coaxial insertion of the tuning element into the resonator  270 , it will be understood that the tuning element can be out of concentricity or even beside the resonator  270  and still provide the desired tuning effects described herein. 
     As shown  FIGS.  7 A,  7 B, and  9 A , the tuning element  200  includes an elongated pin member  230 . In some embodiments, the pin member  230  may be a metallic rod that has a cylindrical shape so that an outer surface  231  thereof forms a single continuous sidewall. The pin member  230  includes a conductive material and has a contact portion  222  on the outer surface  231 . The contact portion  222  refers to a portion of the outer surface  231  of the pin member  230  by which the pin member  230  is secured in a desired position to adjust a frequency response of the filter  250 . For example, the pin member  230  may be secured by an interference or friction fit at the contact portion  222  via a clamping mechanism (as shown in the embodiments of  FIGS.  6 - 10  and  16   ), a pinning mechanism (as shown in the embodiments of  FIGS.  11 - 12   ), and/or an expansion/contraction mechanism (as shown in the embodiments of  FIGS.  13 - 15  and  17   ). At least the contact portion  222  on the outer surface  231  of the pin member  230  is free of an external thread pattern (or “external threading”), such that the pin member  230  can be inserted through one of the apertures  263  and can be moved into and out of the interior  274  of the underlying resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     As shown in the embodiments of  FIGS.  7 A- 7 C,  8 , and  9 A , the tuning element  200  further includes a turret member  240  having an opening  210  therein that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 . The opening  210  extends completely through the turret member  240  and has a diameter that is sufficient or is otherwise is sized to accept the pin member  230  and guide the pin member  230  into or out of the interior  274  of the resonator  270 , e.g., by sliding the pin member  230  within the opening  210 . A base  265  of the turret member  240  is sized to fit in the aperture  263  for mounting on the cover  262 . The turret member  240  may be mounted on the top cover  262  by screw fit, press fit, soldering, or other mounting technique. When mounted by screw fit, the base  265  of the turret member  240  may include an external thread pattern that matches a thread pattern of the aperture  263  in the cover  262 . However, the turret members  240  may be mounted on the top cover  262  before assembly with the remainder of the housing  264  or otherwise such that any metal particles created by the mounting of the turret member  240  on the top cover  262  may be prevented from entering or may be emptied from the interiors  274  of the resonators  270  before tuning by insertion of the pin members  230 . 
     As shown in greater detail in  FIGS.  7 C,  8 , and  9 A , the turret member  240  includes a plurality of fingers  216  respectively positioned around a perimeter of the opening  210  therein. Although illustrated with reference to four fingers  216  by way of example, it will be understood that fewer or more fingers  216  may be included in some embodiments. The fingers  216  are flexible and/or elastic to grip the contact portion  222  of the pin member  230  therebetween, in order to secure the pin member  230  in the desired position to adjust the frequency response of the filter  250 . For example, in the embodiments of  FIGS.  7 A- 7 C,  8   , and  9 A, the tuning element  200  includes a ring-shaped member (illustrated as an internally-threaded nut  260 ) having an inner surface  261  that is shaped to mate with outer surfaces of the fingers  216 . Acceptance of the fingers  216  into the nut  260  (e.g., by tightening or otherwise moving the nut  260  towards the base  265  of the turret member  240 ) causes the fingers  216  to grip the contact portion  222  of the pin member  230  therebetween. 
     The outer surfaces of the fingers  216  may define a tapered shape, and the inner surface  261  of the nut  260  may be shaped to mate with the tapered shape of the fingers  216 . In particular, as shown in greater detail in  FIGS.  8  and  9 A , outer surfaces of the fingers  216  respectively include an external thread pattern  217 , and the nut  260  includes an internal thread pattern  267  on the inner surface  261  thereof that mates with the external thread pattern  217  of the fingers  216 . That is, the fingers  216  include both a tapered portion and a threaded portion  217 , and the inner surface  261  of the nut  260  includes a complementary tapered portion and threaded portion  267 . In some embodiments, the tapered portion of the fingers  216  may define a width or diameter that is greater than the threaded portions  217 . In some embodiments, the tapered portions and the threaded portions may be combined, that is, the tapered portions of the fingers  216  may include a thread pattern, and the inner surface  261  of the nut  260  may be correspondingly shaped for mating. The external thread pattern  217  of the fingers  216  is outside of the aperture  263  in the cover  262  and is otherwise not vertically aligned with the internal cavity  274  of the resonator  270 . 
     As such, the turret member  240  may be secured or otherwise mounted to the cover  262  above the aperture  263  such that the opening  210  in the turret member  240  is aligned with the interior  274  of the resonator  270 , and the pin member  230  may be inserted into the opening  210  in the turret member  240  and may be raised and lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (illustrated by the up-and-down arrows in  FIG.  9 A ) to a desired position to adjust the frequency response of the filter  250 . The pin member  230  may be secured in the desired position by rotating the nut  260  (illustrated by the rotating arrow in  FIG.  9 A ) such that the nut  260  tightens around the fingers  216  of the turret member  240 , which deforms the fingers  216  to clamp the contact portion  222  of the outer surface  231  of the pin member  230  (illustrated by left and right arrows pointing toward the pin member  230  in  FIG.  9 A ). The metal-to-metal contact created by the clamping mechanism  216 ,  260 , which is free of internal threading aligned with the interior  274  of the resonator  270 , may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  230  to tune the resonant filter  250 . 
     Also, as the external thread pattern  217  of the fingers  216  is outside of the aperture  263  and is otherwise not vertically aligned with the internal cavity  274  of the resonator  270 , any metal particles created by the rotational friction between the threading  267  on the internal surface  261  of the nut  260  and the external surfaces of the fingers  216  may not be introduced into the interior  274  of the resonator  270 . That is, in some embodiments, the tuning element  200  may include an externally-threaded perforated turret member  240  with elastic fingers  216  that define a tapered shape around an opening or bore  211  therein, which can be used to mechanically fix a pin member  230  at a desired position by contact with a non-threaded contact portion  222  of the pin member  230 . 
     As shown in  FIGS.  8  and  9 A , the outer diameter of the turret member  240  may be greater than the aperture  263  into the filter cavity  274 , such that the external threading  217  of the turret member  240  is outside of or otherwise not adjacent to the interior of the filter cavity  274 . A corresponding nut  260 , internally tapered on inner surface  261  as well, can be screwed onto the turret member  240  to oblige the fingers  216  to move towards the internal opening  210  and secure the pin member  230  at a desired position in the opening  210  when the nut  260  is tightened. Such a configuration moves the threaded connection away from the openings  210 ,  263  that are aligned with the interior  274  of the resonator  270 . This may help reduce or prevent metal shavings or debris that may be cut from the threading on the fingers  216  and/or nut  260  when the nut  260  is loosened or tightened from falling into the interior  274  of the resonant cavity filter  250 , where such metal shavings or debris otherwise might serve as a source of PIM distortion. 
       FIG.  9 B  is a cross-sectional view of a tuning element  200 ′ according to further embodiments of the present invention inserted into a top cover of and extending into a resonator of a resonant cavity filter in order to tune the frequency response of the filter. Referring now to  FIG.  9 B , and as similarly shown in  FIG.  9 A , the resonant cavity filter  250  includes a housing  264  that has a cover  262 . A resonator  270  is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  that define an open interior  274 . The top cover  262  includes an opening or aperture  263 , and a tuning element  200 ′ is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . The tuning element  200 ′ includes an elongated conductive pin member  230  having a contact portion  222  that is used to secure the pin member  230  in a desired position to adjust a frequency response of the filter  250 . At least the contact portion  222  on the outer surface  231  of the pin member  230  is free of threading, such that the pin member  230  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     As shown in the embodiments of  FIG.  9 B , the tuning element  200 ′ further includes a turret member  240 ′ having an opening  210 ′ therein that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 , with a diameter that is sufficient or is otherwise is sized to accept the pin member  230  and guide the pin member  230  into or out of the interior  274  of the resonator  270 . A base  265 ′ of the turret member  240 ′ is sized to fit in the aperture  263  for mounting on the cover  262 , and may be mounted on the cover  262  by screw fit, press fit, soldering, or other mounting technique, as similarly described above with reference to the turret member  240  of  FIGS.  6 - 9 A . 
     As shown in greater detail in  FIG.  9 B , the turret member  240 ′ includes a plurality of fingers  216 ′ respectively positioned around a perimeter of the opening  210 ′ therein. The fingers  216 ′ are flexible and/or elastic to grip the contact portion  222  of the pin member  230  therebetween, in order to secure the pin member  230  in the desired position to adjust the frequency response of the filter  250 . That is, the turret member  240 ′ may be similar in structure to the turret member  240  of  FIG.  9 A  in some aspects. However, in contrast to the embodiments of  FIG.  9 A , the fingers  216 ′ are free of threading on the outer surfaces thereof. The tuning element  200 ′ further includes a ring-shaped member (also referred to herein as ring  260 ′) having an inner surface  261 ′ that is shaped to mate with outer surfaces of the fingers  216 ′. The outer surfaces of the fingers  216 ′ may define a tapered shape. At least one of the ring  260 ′ or the fingers  216 ′ has an elasticity that is sufficient such that acceptance of the fingers  216 ′ into the ring  260 ′ (e.g., by pushing or otherwise moving the ring  260 ′ towards the base  265 ′ of the turret member  240 ′) causes the fingers  216 ′ to grip the contact portion  222  of the pin member  230  therebetween. 
     As such, the turret member  240 ′ may be secured or otherwise mounted to the top cover  262  above the aperture  263  such that the opening  210 ′ in the turret member  240 ′ is aligned with the interior  274  of the resonator  270 , and the pin member  230  may be inserted into the opening  210 ′ in the turret member  240 ′ and may be raised and lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (illustrated by the up-and-down arrows in  FIG.  9 B ) to a desired position to adjust the frequency response of the filter  250 . The pin member  230  may be secured in the desired position by pushing the ring  260 ′ (illustrated by the down arrow in  FIG.  9 B ) toward the base  265 ′ of the turret  240 ′ such that the ring  260 ′ deforms the fingers  216 ′ to clamp the contact portion  222  of the outer surface of the pin member  230  (illustrated by left and right arrows pointing toward the pin member  230 ). In some embodiments, the fingers  216 ′ may define an annular groove on the outer surfaces thereof, and the nut  260 ′ may include an annular ring on the inner surface  261 ′ thereof (or vice versa). 
     That is, in some embodiments, the tuning elements  200 ′ may include a perforated turret  240 ′ having non-threaded, tapered elastic fingers  216 ′. A corresponding elastic ring  260 ′, internally tapered and non-threaded as well, can be pushed onto the turret  240 ′ to accept the fingers  216 ′ and oblige the fingers  216 ′ to move towards the internal opening  210 ′ to fix the inserted pin member  230  in a desired position. The metal-to-metal contact created by the clamping mechanism  216 ′,  260 ′ at the contact portion  222 , which is free of a threading pattern aligned with the interior  274  of the resonator  270 , may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  230  to tune the resonant filter  250 . 
       FIG.  10 A  is a cross-sectional view of a tuning element  200 ″ according to further embodiments of the present invention inserted into a top cover  262  of and extending into a resonator  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter  250 .  FIG.  10 B  is an exploded perspective view of the tuning element  200 ′ of  FIG.  10 A . As shown in  FIGS.  10 A and  10 B , the arrangement of elements and clamping mechanism is similar to that of the tuning element  200  of  FIG.  9 A , and as such, repeated description thereof will be omitted. However, in  FIGS.  10 A and  10 B , the base  265  of the turret  240  further includes an extended base portion  265 ″ that extends through and beyond the aperture  262  in the top cover and into the filter  250 . In some embodiments, the extended base portion  265 ″ may protrude into the interior  274  of the resonator  270 . As such, in the embodiments of  FIGS.  10 A- 10 B , the tuning effect provided by the tuning element  200 ″ may attributed primarily to the extended base portion  265 ″, while additional or fine tuning may be attributed to adjustment of the pin member  230  into or out of the resonator  270 . Such a tuning element  200 ″ may provide improved RF stability in addition to the improved PIM performance as discussed above. 
       FIG.  11    is a perspective view of a resonant cavity filter  250  including tuning elements  300  according to still further embodiments of the present invention.  FIG.  12 A  is a cross-sectional view of the tuning element  300  of  FIG.  11    inserted into a top cover of and extending into a resonator of a resonant cavity filter  250  in order to tune the frequency response of the filter.  FIG.  12 B  is an exploded view of the tuning element  300  of  FIG.  12 A . 
     As shown in  FIGS.  11  and  12 A- 12 B , the resonant cavity filter  250  includes a housing  264  that has a top cover  262 . A resonator  270  such as, for example, a metallic coaxial resonator, is disposed within a cavity  268  of the filter  250 . The resonator  270  may have one or more sidewalls  272  (for example, a generally cylindrical shaped sidewall) that define an open interior  274 . The top cover  262  includes an opening or aperture  263  that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 . 
     A tuning element  300  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . The tuning element  300  includes an elongated pin member  330 . The pin member  330  includes a conductive material and has a contact portion  322  on its outer surface  331  that is used to secure the elongated pin member  330  in a desired position to adjust a frequency response of the filter  250 . At least the contact portion  322  on the outer surface  331  of the pin member  330  is free of threading, such that the pin member  330  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     The tuning element  300  further includes a turret member  340  having an opening  310  therein that is aligned with the interior  274  of the resonator  270 . The opening  310  extends completely through the turret member  340  and has a diameter that is sufficient or is otherwise sized to accept the pin member  330  and guide the pin member  330  into or out of the interior  274  of the resonator  270 , e.g., by sliding the pin member  330  within the opening  310 . The opening  310  may be free of internal threading. A base  365  of the turret member  340  is sized to fit in the aperture  263  for mounting on the cover  262 . The turret member  340  may be mounted on the cover  262  by screw fit, press fit, soldering, or other mounting technique, as similarly described above with reference to the turret members  240  and  240 ′ of  FIGS.  9  and  10   . 
     As shown in  FIGS.  11  and  12 A- 12 B , the turret member  340  includes a threaded hole  362  in a sidewall thereof, which is sized and otherwise configured to accept a laterally-extending screw-shaped member  360  (also referred to herein as a fixing screw). That is, the threading of the threaded hole  362  mates with the threading of the screw-shaped member  360 . The screw-shaped member  360  is thus configured to be laterally threaded into the threaded hole  362  to contact a contact portion  322  of the pin member  330  and mechanically fix the pin member  330  in the desired position (e.g., by tightening or otherwise moving the fixing screw  360  through the threaded hole  362  to contact the pin member  330 ). For example, the fixing screw  360  may wedge or pin the contact portion  322  of the pin member  330  between an end of the fixing screw  360  and a sidewall of the opening  310  in the turret member  340 . The laterally threaded hole  362  may be inclined (rather than extending parallel) with respect to the surface of the top cover  262  in some embodiments, for example, inclined toward or away from the top cover  262 . Similar to the embodiments of  FIGS.  6 - 10   , at least the contact portion  322  of the pin member  330  does not include or is otherwise free of threading on the outer surface  331 . 
     As such, the turret member  340  may be secured or otherwise mounted to the cover  262  above the aperture  263  such that the opening  310  in the turret member is aligned with the interior  274  of the resonator  270 , and the pin member  330  may be inserted into the opening  310  in the turret member  340  and may be raised and lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (illustrated by the up-and-down arrows in  FIG.  12 A ) to a desired position to adjust the frequency response of the filter  250 . The pin member  330  may be secured in the desired position by rotating the fixing screw  360  (illustrated by the rotating arrow in  FIG.  12   ) such that the fixing screw  360  moves toward and contacts the pin member  330  at the contact portion  322  (illustrated by the arrow pointing toward the pin member  330  in  FIG.  12   ). The metal-to-metal contact created by the pinning mechanism between the contact portion  322  of pin member  330  and the laterally-extending fixing screw  360  (and/or the sidewalls of the opening  310 ) may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  330  to tune the resonant filter  250 . 
     That is, as the thread patterns of the threaded hole  362  and the fixing screw  360  are outside of the aperture  263  and are otherwise not vertically aligned with the internal cavity  274  of the resonator  270 , metal particles created by the rotational friction between the threading of the threaded hole  362  and the fixing screw  360  may be reduced or may not be introduced into the interior  274  of the resonator  270 . Accordingly, as with the embodiments of  FIGS.  6 - 10   , the embodiments of  FIGS.  11  and  12 A- 12 B  thus provide configurations that move the threading of the turret member  340  outside of or otherwise not adjacent to the interior of the filter cavity  274 , which may help reduce or prevent metal shavings or debris that may be cut from the threading on threaded hole  362  and the fixing screw  360  when the fixing screw  360  is loosened or tightened from falling into the interior  274  of the resonant cavity filter  250 . 
       FIG.  13 A  is a cross-sectional view of a tuning element  400  according to yet further embodiments of the present invention inserted into a top cover  262  of and extending into a resonator  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter.  FIG.  13 B  is an exploded view of the tuning element  400  of  FIG.  13 A . As shown in  FIGS.  13 A- 13 B , and as similarly shown in  FIGS.  9 ,  10 , and  12   , the resonant cavity filter  250  includes a housing  264  that has a top cover  262 . A resonator  270  is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  that define an open interior  274 . The top cover  262  includes an opening or aperture  263  that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 . 
     A tuning element  400  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . The tuning element  400  includes an elongated conductive pin member  430  having a contact portion  422  on an outer surface  431  thereof that is used to secure the pin member  430  in a desired position to adjust a frequency response of the filter  250 . At least the contact portion  422  on the outer surface  431  of the pin member  430  is free of threading, such that the pin member  430  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     As shown in greater detail in  FIGS.  13 A- 13 B , the elongated pin member  430  of the tuning element  400  includes a hollow opening  410  extending along a major axis of the pin member  430 . The hollow opening  410  extends within the conductive outer surface  431  of the pin member  430 , from an upper end or head portion  436  of the pin member  430  along the major axis. At least a portion of the upper end  436  of the pin member  430  is slotted  435  or otherwise configured such that sidewalls thereof define fingers  416  having sufficient flexibility or elasticity to expand or vary a diameter of the pin member  430  responsive to insertion of another member into the hollow opening  410 . 
     In the example of  FIGS.  13 A- 13 B , the hollow opening  410  is sized and otherwise configured to accept a screw-shaped member  460 . The hollow opening  410  includes an internal thread pattern that is configured to mate with a thread pattern of the screw-shaped member  460 . The hollow opening  410  is tapered (e.g., has a varying diameter such that an area of a transverse cross-section of one portion exceeds an area of a transverse cross-section of another portion) along the major axis of the elongated pin member  430  toward a lower end  437 , such that insertion of the screw-shaped member  460  into the hollow opening  410  causes expansion of the contact portion  422  at the fingers  416  of the conductive outer surface  431  to contact the sidewall of the aperture  263 , with sufficient expansion force and friction to secure the pin member  430  in the desired position. That is, the pin member  430  may be a slotted expansion pin in some embodiments, where the position of the screw-shaped member  460  in the hollow opening  410  will determine an expansion of the fingers  416  at the sidewalls, and thus the interference fit or blockage of the pin member  430  in the aperture  263 . 
     As such, the pin member  430  may be inserted into the aperture  263  in the cover  262  and may be raised and lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (illustrated by the up-and-down arrows in  FIG.  13 A ) to a desired position to adjust the frequency response of the filter  250 , e.g., by sliding the pin member  430  within the aperture  263 . The pin member  430  may be secured in the desired position by rotating the screw-shaped member  460  (illustrated by the rotating arrow in  FIG.  13 A ) such that the screw-shaped member  460  moves toward the lower end of the pin member  430  (illustrated by the downward arrow in  FIG.  13 A ), which deforms the fingers  416  to expand the outer surface  431  of the pin member  430  such that the contact portion  422  contacts the sidewalls of the aperture  263  in the cover  262  (illustrated by left and right arrows pointing away from the pin member  430  in  FIG.  13 A ). The metal-to-metal contact created by the expansion mechanism  416 ,  460  between the contact portion  422  (which is free of a threading pattern) and the sidewall of the aperture  263  may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  430  to tune the resonant filter  250 . Also, an end  437  of the elongated pin member  430  opposite the hollow opening  410  is closed, such that any metal particles created by the rotational friction between the threading on the internal surface of the opening  410  and the external surfaces of the screw-shaped member  460  may not be introduced into the interior  274  of the resonator  270 . 
     In some embodiments, a head portion of the screw elements  360 ,  460  may include one or more slots, openings, protrusions or other mating structures  214  that are designed to cooperate with a tool for purposes of rotating the screws  360 ,  460 . For example, the head portion of the screw elements  360  and/or  460  may include a female mating structure such as a slot that is configured to receive the end of a regular screwdriver, a pair of crossed slots that are configured to receive the end of a Phillips screwdriver, a square or hexagonal aperture that is designed to receive an end of an Allen wrench, a star shaped cavity that is configured to receive an end of a Torx tool, etc. In contrast, a head portion of the elongated pin members  230 ,  330 ,  430  described herein may be free of slots or other mating structures. 
       FIG.  14 A  is a cross-sectional view of a tuning element according to further embodiments of the present invention inserted into a top cover  262  of and extending into a resonator  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter  250 .  FIG.  14 B  is a perspective view of the tuning element  500  of  FIG.  14 A . As shown in  FIG.  14   , and as similarly shown in  FIGS.  9 ,  10 ,  12 , and  13   , the resonant cavity filter  250  includes a housing  264  that has a cover  262 . A resonator  270  is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  that define an open interior  274 . The top cover  262  includes an opening or aperture  263 . 
     A tuning element  500  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . The tuning element  500  includes an elongated pin member  530  having a contact portion  522  that is used to secure the pin member  530  in a desired position to adjust a frequency response of the filter  250 . At least the contact portion  522  on the conductive outer surface  531  of the pin member  530  is free of threading, such that the pin member  530  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     As shown in greater detail in  FIGS.  14 A- 14 B , the elongated pin member  530  of the tuning element  500  includes an elastic inner portion  518  defining a hollow opening  510  and including the conductive outer surface  531  thereon. The outer surface  531  of the pin member  530  may be a metal or other layer having sufficient or desired conductivity, while the inner portion  518  of the pin member  530  may be plastic or other material having sufficient or desired elasticity. The hollow opening  510  extends within the elastic inner portion  518  of the pin member  530  from an upper end or head portion  536  of the pin member  530  along the major axis. The elastic inner portion  518  may comprise a tubular structure concentrically arranged within and surrounded by the conductive outer surface  531 . The lower end  537  of the tubular structure may or may not be open. 
     At least a portion of the upper end  536  of the pin member  530  is slotted  535  or otherwise configured to define fingers  516  having sufficient flexibility or elasticity to vary a diameter of the pin member  530  for insertion into the aperture  263 . More particularly, the elastic inner portion  518  has sufficient flexibility to be compressed during insertion of the pin member  530  into the aperture  263 , and to be expanded responsive to release of the compression to contact the sidewall of the aperture  263  to secure the pin member  530  in the desired position. 
     That is, the tuning element  500  may include a pin member  530  with elastic, compressible fingers  516  that define a diameter that is larger than the aperture  263  in the cover  262  of the filter housing  264 . Compression of the fingers  516  (illustrated by left and right arrows pointing toward the opening  510  in  FIG.  14 A ) deforms the outer surface  531  of the pin member  530  to be smaller than a diameter of the aperture  263 , such that the pin member  530  can be moved into or out of the aperture  263  (illustrated by up-and-down arrows in  FIG.  14 A ), e.g., by sliding the pin member  530  within the aperture  263 . Releasing the compression of the fingers  516  expands the outer surface  531  of the pin member  530  to be greater than the diameter of the aperture  263 , such that the contact portion  522  contacts the sidewalls of the aperture  263  in the top cover  262 , and the pin member  530  may be fixed in a desired position by the expansion force and friction fit with the sidewalls of the aperture  263 . The metal-to-metal contact between the contact portion  522  (which is free of a threading pattern) and the sidewall of the aperture  263  created by the expansion mechanism  516  may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  530  to tune the resonant filter  250 . 
       FIG.  15 A  is a cross-sectional view of a tuning element  600  according to further embodiments of the present invention inserted into a top cover  262  of and extending into a resonator  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter  250 .  FIG.  15 B  is perspective view of the tuning element  600  of  FIG.  15 A .  FIG.  15 C  is an enlarged perspective view of the tuning element  600  of  FIG.  15 B . 
     As shown in  FIGS.  15 A- 15 C , the resonant cavity filter  250  includes a housing  264  that has a cover  262 . A resonator  270  is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  that define an open interior  274 . The top cover  262  includes an opening or aperture  263 . A tuning element  600  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . The tuning element  600  includes an elongated pin member  630  having a contact portion  622  that is used to secure the pin member  630  in a desired position to adjust a frequency response of the filter  250 . At least the contact portion  622  on the conductive outer surface  631  of the pin member  630  is free of threading, such that the pin member  630  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     The tuning element  600  further includes a turret member  640  having an opening  610  therein that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 , with a diameter that is sufficient or is otherwise is sized to accept the nut  660 . The nut  660  includes an opening therein that is sufficient or otherwise sized to accept and guide the pin member  630  into or out of the interior  274  of the resonator  270 . A base  616  of the turret member  640  is sized to fit in the aperture  263  for mounting on the cover  262 , and may be mounted on the cover  262  by screw fit, press fit, soldering, or other mounting technique, as similarly described above with reference to the turret member  240  of  FIGS.  6 - 9 A . 
     Still referring to  FIGS.  15 A- 15 C , the opening  610  in the turret member  640  has an internal thread pattern  617  and is tapered toward the interior  274  of the resonator  270 . The nut  660  includes a lower end that is sized to fit within the opening  610  and has an external thread pattern  667  that is configured to mate with the internal thread pattern  617 . The tuning element  600  also includes a compressible ring  665  having a diameter sized to fit within the opening  610  in the turret member  640 . The compressible ring  665  may include a slot or cut  661  therein, which may allow the diameter of the compressible ring  665  to vary responsive to force. The elongated pin member  630  extends through the compressible ring  665  and the nut  660  for insertion into the interior  274  of the resonator  270 . Tightening of the nut  660  advances the compressible ring  665  toward the interior  274  of the resonator  270 . As the compressible ring  665  is advanced toward the interior  274  of the resonator  270 , the tapered opening  610  in the turret member  640  causes contraction of the compressible ring  665  against the contact portion  622  of the pin member  630  to secure the pin member  630  in the desired position. 
     For example, in some embodiments the compressible ring  665  may be a conic shaped elastic ring. The turret member  640  may be a perforated and threaded bush or bushing that is mounted into the aperture  263  in the filter cover  262 , the nut  660  and the elastic ring  665  can be inserted on the pin  630 , and the pin member  630  (including the nut  660  and the ring  665  thereon) can be inserted into the opening  610  in the bush  640  and raised or lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (as shown by the up-and-down arrows in  FIG.  15 A ) to adjust the frequency response of the filter  250 . As the internal surface in the opening  610  of the bush  640  is tapered (for example, also conic shaped) toward the interior  274  of the resonator  270 , the nut  660  can be screwed into the opening  610  in the bush  640  thus pressing the elastic ring  665  in the conic seat at the base  616  of the bush  640 , forcing the elastic ring  665  against the contact surface  622  of the pin member  630 . Since the elastic ring  665  has the slot or cut  661  therein, its diameter can be reduced as it is compressed around the pin member  630 , and the pin member  630  may be fixed in a desired position by the compression force and friction fit. The metal-to-metal contact between the contact portion  622  (which is free of a threading pattern) and the ring  665  created by the compression or clamping mechanism  661 ,  610  may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  630  to tune the resonant filter  250 . Also, the compressible ring  665  and/or the tapered shape of the opening  610  in the turret member  640  may reduce and/or prevent any metal particles created from rotational friction between the thread patterns  617  and  667  from entering the interior  274  of the resonator. 
       FIG.  16 A  is a cross-sectional view of a tuning element  700  according to further embodiments of the present invention inserted into a top cover  262  of and extending into a resonator  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter  250 .  FIG.  16 B  is perspective view of the tuning element  700  of  FIG.  16 A .  FIG.  16 C  is an enlarged perspective view of the turret member  740  of  FIGS.  16 A- 16 B . 
     As shown in  FIG.  16 A , the resonant cavity filter  250  includes a housing  264  that has a cover  262 . A resonator  270  is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  that define an open interior  274 . The top cover  262  includes an opening or aperture  763 . A tuning element  700  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  763  and into the interior  274  of the resonator  270 . The tuning element  700  includes an elongated pin member  730  having a contact portion  722  that is used to secure the pin member  730  in a desired position to adjust a frequency response of the filter  250 , where at least the contact portion  722  on the conductive outer surface  731  of the pin member  730  is free of threading such that the pin member  730  can be inserted through the aperture  763  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     As shown in  FIGS.  16 A- 16 C , the aperture  763  in the top cover  262  is tapered in a direction away from the interior  274  of the resonator  270 . The tuning element  700  further includes a turret member  740  having an opening  710  therein that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 . The opening  710  extends completely through the turret member  740  and has a diameter that is sufficient or is otherwise is sized to accept and guide the pin member  730  into or out of the interior  274  of the resonator  270 , e.g., by sliding the pin member  730  within the opening  710 . The turret member  740  includes a plurality of petals or fingers  716  respectively positioned around a perimeter of the opening  710  therein. For example, a base of the turret member  740  may be tapered and slotted to define fingers  716  that are shaped to mate with the shape of the tapered aperture  763  in the top cover  262 . The fingers  716  are flexible and/or elastic to grip the contact portion  722  of the pin member  730  therebetween, in order to secure the pin member  730  in the desired position to adjust the frequency response of the filter  250 . 
     For example, in the embodiments of  FIGS.  16 A- 16 C , the tuning element  700  further includes a nut  760  having an internal thread pattern  767  that is shaped to mate with an external thread pattern  717  of the turret member  740 , which protrudes outside of the aperture  763  opposite the resonator  270 . The nut  760  can be loosened around the external thread pattern such that the pin member  730  may be freely raised and lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (illustrated by the up-and-down arrows in  FIG.  16 A ) to adjust the frequency response of the filter  250 . Tightening the nut  760  (illustrated by the rotating arrow in  FIG.  16 A ) on the external thread pattern  717  of the turret member  740  causes acceptance of the fingers  716  into the tapered aperture  763 , forcing the fingers  716  towards the pin member  730  to clamp the contact portion  722  of the outer surface  731  therebetween and secure the pin member  730  in a desired position. The metal-to-metal contact between the contact portion  722  (which is free of a threading pattern) and the turret member  740  created by the clamping mechanism  716 ,  760  may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  730  to tune the resonant filter  250 . Also, as the external thread pattern  717  of the turret member  740  is outside of the aperture  763 , any metal particles created by the rotational friction between the threading  767  on the internal surface of the nut  760  and the external surfaces of the turret member  740  may not be introduced into the interior  274  of the resonator  270 . A washer  765  may also be provided between the nut  760  and the top cover  262  to block the external thread pattern  717  from the interior of the filter  250 . 
       FIG.  17 A  is a cross-sectional view of a tuning element  800  according to further embodiments of the present invention inserted into a top cover  262  of and extending into a resonator  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter  250 .  FIG.  17 B  is an enlarged view of a portion of the tuning element  800  of  FIG.  17 A . 
     As shown in  FIGS.  17 A- 17 B  the resonant cavity filter  250  includes a housing  264  that has a cover  262 . A resonator  270  is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  that define an open interior  274 . The top cover  262  includes an opening or aperture  263 . A tuning element  800  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . The tuning element  800  includes an elongated pin member  830  having a contact portion  822  that is used to secure the pin member  830  in a desired position to adjust a frequency response of the filter  250 , where at least the contact portion  822  on a conductive outer surface  831  of the pin member  830  is free of threading such that the pin member  830  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     The tuning element  800  also includes a turret member  840  having an opening therein that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 . The opening in the turret member  840  and has a diameter that is sufficient or is otherwise is sized to accept and guide the pin member  830  into or out of the interior  274  of the resonator  270 , e.g., by sliding the pin member  830  within the opening. The turret member  840  may include an external thread pattern  817  protruding outside of the aperture  263  in the top cover  262  opposite the resonator  270 . A nut  860  having an opening that is sized to accept the protruding portion of the turret member  840  includes an internal thread pattern  867  that is configured to mate with the external thread pattern  817  of the turret member  840 . Loosening or tightening of the nut  860  may be used in precise positioning of the pin member  830 . 
     The pin member  830  further includes an elongated bar member  832  extending along a major axis of a hollow opening  810  in the conductive outer surface  831 . The hollow opening  810  has a varying width (e.g., a non-constant diameter) along its major axis. The varying width of the opening  810  is illustrated by way of example with respective widths W 1  and W 2 , but it will be understood that the opening  810  may gradually and/or continuously vary as well. As shown in  FIG.  17 B , the bar member  832  has a wider portion at an end thereof (illustrated as a bulb-shaped end portion  833 ) proximate the interior  274  of the resonator  270 . Retraction of the bar member  832  into the hollow opening  810  along the major axis (illustrated by upward arrow in  FIG.  17 B ) causes expansion of the contact portion  822  (illustrated by left and right arrows pointing away from the pin member  830  in  FIG.  17 B ), deforming the conductive outer surface  831  to secure the pin member  830  in the desired position by interference fit with the sidewall of the turret member  840  (e.g., at base portion  865 ). In some embodiments, the interference fit with the sidewall of the turret member  840  by retraction of the bar member  832  may also be used for positioning the pin member  830 , and in such embodiments the nut  860  may be omitted. 
     As similarly mentioned above, the metal-to-metal contact between the contact portion  822  (which is free of a threading pattern) and the turret member  840  created by the expansion mechanism  831 ,  832  may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  830  to tune the resonant filter  250 . Also, as the external thread pattern  817  of the turret member  840  is outside of the aperture  263 , any metal particles created by the rotational friction between the threading  867  on the internal surface of the nut  860  and the external surfaces of the turret member  840  may not be introduced into the interior  274  of the resonator  270 . 
       FIG.  18 A  is a cross-sectional view of a tuning element  900  according to further embodiments of the present invention inserted into a top cover  262  of and extending into one of a plurality of resonators  270  of a resonant cavity filter  250  in order to tune the frequency response of the filter  250 .  FIG.  18 B  is an enlarged perspective view of the turret member  940  of  FIG.  18 A . 
     Referring now to  FIG.  18 A , the resonant cavity filter  250  includes a housing  264  that has a top cover  262 . A resonator  270 , for example, a metallic coaxial resonator, is disposed within a cavity  268  of the filter  250  and has one or more sidewalls  272  (for example, a generally cylindrical shaped sidewall) that define an open interior  274 . The top cover  262  includes an opening or aperture  263  that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 . 
     A tuning element  900  is mounted on the top cover  262  for insertion (e.g., coaxial insertion) through the aperture  263  and into the interior  274  of the resonator  270 . Although described and illustrated herein primarily with reference to coaxial insertion of the tuning element  900  into the resonator  270 , it will be understood that the tuning element  900  can be out of concentricity or even beside the resonator  270  and still provide desired tuning effects described herein. The tuning element  900  includes an elongated pin member  930 . The pin member  930  includes a conductive material and has a contact portion  922  on its outer surface  931  that is used to secure the elongated pin member  930  in a desired position to adjust a frequency response of the filter  250 . At least the contact portion  922  on the outer surface  931  of the pin member  930  is free of threading, such that the pin member  930  can be inserted through the aperture  263  and can be moved into and out of the interior  274  of the resonator  270  to adjust the frequency response of the filter  250  without creating metal particles due to friction between threaded elements. 
     As shown in  FIG.  18 A , the tuning element  900  further includes a turret member  940  having an opening  910  therein that is aligned (e.g., coaxially aligned) with the interior  274  of the resonator  270 , with a diameter that is sufficient or is otherwise is sized to accept the pin member  930  and guide the pin member  930  into or out of the interior  274  of the resonator  270 , e.g., by sliding the pin member  930  within the opening  910 . A base  965  of the turret member  940  is sized to fit in the aperture  263  for mounting on the cover  262 , and may be mounted on the cover  262  by screw fit, press fit, soldering, or other mounting technique, as similarly described above with reference to the turret members  240  and  240 ′ of  FIGS.  9 A and  9 B . 
     As shown in greater detail in  FIG.  18 B , the turret member  940  includes a plurality of fingers  916  respectively positioned around a perimeter of the opening  910  therein. Although illustrated with reference to four fingers  916  by way of example, it will be understood that fewer or more fingers  916  may be included in some embodiments. The fingers  916  are flexible and/or elastic to grip the contact portion  922  of the pin member  930  therebetween, in order to secure the pin member  930  in the desired position to adjust the frequency response of the filter  250 . The outer surfaces of upper portions of the fingers  916  (defining an upper or top part of the turret member  940 ) respectively include an external thread pattern  917 . The outer surfaces of lower portions of the fingers  916  (defining a lower part of the turret member  940 , above the base  965 ) may have a tapered shape. That is, the fingers  916  include both a tapered portion  918  and a threaded portion  917 . The tapered portion  918  of the fingers  916  may define a width or diameter of the turret member  940  that is greater than that of the threaded portions  917 . 
     The tuning element  900  further includes a ring-shaped member (illustrated as an internally-threaded nut  960 ) having an inner surface  961  that is shaped to mate with outer surfaces of the fingers  916 . In particular, the nut  960  includes an internal thread pattern  967  on the inner surface  961  thereof that mates with the external thread pattern  917  of the fingers  916 . The inner surface  961  of the nut  960  defines an inner diameter, and the tapered portions  918  of the fingers  916  define dimensions of the turret member  940  that increase from a dimension similar to the inner diameter of the nut  960  to a dimension greater than the inner diameter of the nut  960 . In some embodiments, the tapered portions  918  and the threaded portions  917  of the fingers  916  may be combined, that is, the tapered portions of the fingers  916  may include the thread pattern  917 , and the inner surface  961  of the nut  960  may include a complementary tapered and threaded portion  967  for mating with the thread pattern  917 . 
     The pin member  930  may be secured in the desired position by tightening the nut  960  around the fingers  916  of the turret member  940  (illustrated by the rotating arrow in  FIG.  18 A ). When the nut  960  reaches the tapered portions  918  defining dimensions that are greater than the inner diameter of the nut  960 , the fingers  916  are deformed and forced towards the pin member  930  (illustrated by left and right arrows pointing toward the pin member  930  in  FIG.  18 A ) to clamp the contact portion  922  of the outer surface  931  therebetween and secure the pin member  930  in a desired position. Likewise, the nut  960  can be loosened around the external thread pattern  917  of the fingers  916  (by rotating the nut  960  opposite to the rotating arrow in  FIG.  18 A , so as to move the nut  960  away from the tapered portions  918 ) such that the pin member  930  may be freely raised and lowered to extend different distances (or not at all) into the open interior  274  of the resonator  270  (illustrated by the up-and-down arrows in  FIG.  18 A ). 
     As such, the turret member  940  may be secured or otherwise mounted to the top cover  262  above the aperture  263  such that the opening  910  in the turret member  940  is aligned with the interior  274  of the resonator  270 , and the pin member  930  may be inserted into the opening  910  in the turret member  940  and may be raised and lowered into the open interior  274  of the resonator  270  to a desired position to adjust the frequency response of the filter  250 . The metal-to-metal contact created by the clamping mechanism  916 ,  960 , which is free of internal threading aligned with the interior  274  of the resonator  270 , may be advantageous in that deposition of metal particles into the interior  274  of the resonator  270  may be reduced and/or avoided when adjusting the position of the pin member  930  to tune the resonant filter  250 . 
     Also, as the external thread pattern  917  of the fingers  916  is outside of the aperture  263  and is otherwise not vertically aligned with the internal cavity  274  of the resonator  270 , any metal particles created by the rotational friction between the threading  967  on the internal surface  961  of the nut  960  and the external surfaces of the fingers  916  may not be introduced into the interior  274  of the resonator  270 . That is, similar to the embodiments of  FIGS.  9  and  10   , the tuning element  900  may include an externally-threaded perforated turret member  940  with elastic fingers  916  that define a tapered shape around an opening or bore  910  therein, which can be used to mechanically fix a pin member  930  at a desired position by contact between the fingers  916  and a non-threaded contact portion  922  of the pin member  930 . 
     In some embodiments, the change in depth (or travel distance) of the pin member  230 ,  330 ,  430 ,  530 ,  630 ,  730 ,  830 ,  930  between its fully extracted and fully inserted positions with respect to the interior  274  of the resonator  270  may be up to about 30 millimeters or more (also be referred to herein as the “stroke” of the pin member). In some embodiments, the pin members  230 ,  330 ,  430 ,  530 ,  630 ,  730 ,  830 ,  930  may be used to tune the resonant frequency of resonant cavity filters as described herein between about 1720-1920 MHz. However, it will be appreciated that the filters may be designed to operate in any appropriate frequency band or bands. 
     Resonant cavity filters and associated tuning elements according to embodiments of the present invention may provide a number of advantages over conventional filters and tuning screws. For example, by fixing or securing the tuning pin member in its desired position to tune the frequency response of the filter via interference fit, interfaces between threaded components may be eliminated or provided to be remote from the opening in the filter housing. This may reduce or eliminate the possibility that metal shavings, which may be created by rotational friction of such elements, can fall into the interior of the filter. Thus, filters and associated tuning elements according to embodiments of the present invention may exhibit improved PIM distortion. 
     It will be appreciated that the filters according to embodiments of the present invention may be used to implement a wide variety of different devices including duplexers, diplexers, multiplexers, combiners and the like. It will be appreciated that the filters according to embodiments of the present invention may also be used in applications other than cellular communications systems. 
     While various embodiments of the present invention have been described above, it will be appreciated that these embodiments may be changed in many ways without departing from the scope of the present invention, which is detailed in the appended claims. It will also be appreciated that the various embodiments disclosed herein may be combined in any way to create additional embodiments, all of which are within the scope of the present invention. For example, the expansion-based pin members  430  and/or  530  of  FIGS.  13  and  14    may be sized and configured to fit in the openings  210  and/or  310  of the turret members  240  and/or  340  of  FIGS.  6 - 10  and  11 - 12   , to provide an interference fit with the turret members  240  and/or  340  rather than directly with the sidewalls of the aperture  263  in the top cover  262 . 
     The present invention has been described above with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that when an element (e.g., a device, circuit, etc.) is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” or “front” or “back” or “top” or “bottom” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. 
     Aspects and elements of all of the embodiments disclosed above can be combined in any way and/or combination with aspects or elements of other embodiments to provide a plurality of additional embodiments. 
     In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.