CN111509341B - Tuning element, device, filter assembly and method for tuning a filter - Google Patents

Abstract

The invention discloses a tuning element, a tuning device, a filter assembly and a method for tuning the filter. A tuning element implemented in an opening of a metal plate of a filter, the tuning element comprising: a coupling element; a first arm having a first end connected to a metal plate and a second end connected to the coupling element; and a second arm having a first end connected to the metal plate and a second end connected to the coupling element.

Description

Tuning element, device, filter assembly and method for tuning a filter

The divisional application is based on the Chinese patent application with patent application number 201610596975.4 entitled "Filter Assembly, tuning element and method for tuning Filter", 2016, 7, 26.

This application claims priority to chinese patent application No. 201511036066.7 filed 11, 13/2015.

Technical Field

The present invention relates generally to communication systems and, more particularly, to filters suitable for use in cellular communication systems.

Background

Wireless base stations are well known in the art and typically include baseband equipment, radios, and antennas, among other components. The antenna is typically mounted on top of a tower or other elevated structure such as a pole, roof, water tower, etc. Typically, multiple antennas are mounted on the tower, with a separate baseband unit and radio connected to each antenna. Each antenna provides cellular service to a defined coverage area or "sector".

Fig. 1 is a highly simplified schematic diagram illustrating 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 located at the bottom of the antenna tower 30. A plurality of baseband units 22 and radios 24 are located within the device housing 20. Each baseband unit 22 is connected to a respective one of the radios 24 and is also in communication with a backhaul communication system 44. Three sectorized antennas 32 (labeled as antennas 32-1, 32-2, 32-3) are located at the top of the antenna tower 30. Three coaxial cables 34 (shown bundled together as a single cable in fig. 1) connect the radios 24 to respective antennas 32. Each end of each coaxial cable 34 may be connected to a duplexer (not shown) so that transmit and receive signals for each radio 24 may be carried on a single coaxial cable 34. It should be understood that in many cases, the radio 24 is located at the top of the tower 30, rather than in the equipment enclosure 20, in order to reduce signal transmission losses.

Cellular base stations typically use directional antennas 32, such as phased array antennas, to provide enhanced antenna gain throughout a defined coverage area. A typical phased array antenna 32 may be implemented as a linear array of radiating elements mounted on a panel, each linear array may have 10 radiating elements. Typically, each radiating element is for: (1) transmit radio frequency ("RF") signals received from the transmit port of the associated radio 24 and (2) receive RF signals from the mobile user and feed such received signals to the receive port of the associated radio 24. A duplexer is typically used to connect the radio 24 to each respective radiating element of the antenna 32. "duplexer" refers to a three-port filter assembly of a well-known type for connecting both the transmit and receive ports of the radio 24 to the antenna 32 or to the radiating elements of the multi-element antenna 32. The duplexer serves to isolate the RF transmission paths to the transmit and receive ports of the radio 24 from each other and allows both RF transmission paths to access the radiating element of the antenna 32, and to do so even though the transmit and receive bands may be closely spaced together.

In order to transmit and receive RF signals to and from a defined coverage area, each directional antenna 32 is typically mounted facing a particular direction (referred to as "azimuth") relative to a reference direction, e.g., due north, tilted at a particular downward angle (referred to as "downtilt" or "elevation") relative to the horizontal direction of the azimuth plane, and aligned vertically to the horizontal direction (referred to as "roll"). Unintentional changes in azimuth, downtilt, and roll angles can adversely affect the coverage of directional antenna 32. Unfortunately, high winds, vibration, corrosiveness, or other various factors may cause the azimuth, downtilt, and/or roll angles of antenna 32 to change over time. Thus, the wireless service provider may monitor the antenna 32 at the cellular base station 10 to identify when the antenna 32 is no longer pointing in the desired direction.

In some cases, the antenna 32 may be mounted on a motorized gimbal ring, and thus, an operator may adjust the pointing direction of the antenna 32 from a remote location by sending a control signal to the motorized gimbal ring (motorized gimbal). In addition, some antennas 32 are designed such that the "electronic downtilt" of the antenna 32 can be adjusted from a remote location. With an antenna 32 that includes such electronic tilt capability, the physical orientation of the antenna 32 is fixed, but the effective angle of the antenna beam can still be adjusted electronically, for example by controlling phase shifters that adjust the phase of the signal provided to each radiating element of the antenna 32. The phase shifter and other associated circuitry are typically built into the antenna 32 and may be controlled from a remote location. Typically, the phase shifters are controlled using antenna interface standard group ("AISG") control signals, which is an industry-standardized set of control signals for controlling antennas used in cellular communication systems. Typically, electronic adjustment of the antenna beam is used to change the downward angle or "downtilt" of the antenna beam. An antenna 32 having a beam pattern whose downtilt angle is electronically adjustable from a remote location is commonly referred to as a remote electronic tilt ("RET") antenna.

With RET antennas, a first phase shifter is used for the transmit frequency band and a second phase shifter is used for the receive frequency band. Because of making

Separate transmit and receive phase shifters are used and a duplexer for allowing each radiating element to transmit and receive signals is necessarily located along the transmission path between the phase shifter and the radiating element. With RET antennas, phase shifters are typically mounted on the back side of the antenna panel, very close to the radiating elements. Accordingly, a duplexer is also generally mounted on the back side of the antenna panel. As the number of radiating elements increases (to provide better antenna gain patterns), this makes it more difficult to find space-mounted duplexers and other RF devices and associated electronics on each antenna panel.

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 a cover plate removed. Fig. 4 is a top perspective view of a portion of the housing of the duplexer 50.

Referring to fig. 2-4, a conventional duplexer 50 is implemented as a three-port resonator filter. The diplexer 50 includes a housing 60 having a bottom surface 62 and a plurality of sidewalls 64. An interior ledge 66 is formed around the perimeter of the housing 60. A plurality of 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 in the walls 68, and these windows 72 and the openings between the walls 68 allow communication between the cavities 70. A plurality of internally threaded cavities 74 are formed in the wall 68. A plurality of resonant elements 76 are mounted within the cavity 70. The resonating element 76 may comprise, for example, a dielectric resonator or a coaxial metal resonator, and may be mounted by screws 80 to selected ones of the internally threaded cavities 74 formed in the wall 68. The cover plate 78 serves as a top cover of the duplexer 50. A large number of additional screws 80 are used to hold the cover plate 78 tightly in place so that the cover plate 78 continuously contacts the interior ledge 66 and the top surface of the wall 68 to provide good performance against passive intermodulation ("PIM") distortion.

The input port 82 may be attached to an output port of a transmit path phase shifter (not shown) via a first cable connection 83. The output port 84 may be attached to an input port of the receive path phase shifter via a second cable connection 85. The common port 86 may connect the duplexer 50 to a radiating element (not shown) of the antenna via a third cable connection (not shown). A plurality of tuning screws 90 are also provided. Tuning screws 90 may be adjusted to tune various aspects of the frequency response of duplexer 50, such as the center frequency of the notch of the filter response. It should be noted that the device in fig. 2-4 includes two duplexers sharing a common housing, which is why the device includes more than three ports (the device includes a total of six ports, although not all ports are visible in the views of fig. 2-4).

The conventional duplexer 50 of fig. 2-4 may provide acceptable performance. However, the duplexers 50 may be relatively large, and thus it may be difficult to make room to mount a large number of these duplexers 50 (e.g., 10) on a single-plate phased array antenna. The duplexer 50 may also be relatively heavy, which increases the load on the antenna. The duplexer 50 also has a large number of components making it more expensive to manufacture and assemble.

Disclosure of Invention

In view of at least one of the above-mentioned technical problems, the present invention provides a filter assembly, a tuning element and a method of tuning a filter.

According to a first aspect of the invention, a filter assembly is provided. The filter assembly includes: a housing having a top cover, a bottom cover, and at least one sidewall, the top cover, the bottom cover, and the at least one sidewall defining an interior cavity, the housing configured to receive first through third Radio Frequency (RF) transmission lines; a top metal sheet mounted within the internal cavity and having a plurality of openings forming a first hole pattern; and a bottom metal sheet mounted within the internal cavity having a plurality of openings forming a second hole pattern, wherein the top metal sheet and the bottom metal sheet are vertically spaced from each other in a vertically stacked relationship within the internal cavity, and wherein each of the top metal sheet and the bottom metal sheet includes at least one resonator.

According to a second aspect of the invention, a filter assembly is provided. The filter assembly includes: a housing; a top resonator plate mounted within the housing; and a bottom resonator plate mounted within the housing in stacked relation to the top resonator plate, wherein the top resonator plate is welded to the housing via a first continuous weld extending around the entire interior perimeter of the housing.

According to a third aspect of the invention, a filter assembly is provided. The filter assembly includes: a housing defining an interior cavity; a first substantially planar metal resonator plate mounted within the internal cavity having a first aperture pattern formed therein; a second substantially planar metallic resonator plate mounted in stacked relation to the first substantially planar metallic resonator plate within the internal cavity having a second aperture pattern formed therein; wherein at least the first and second aperture patterns, the distance between the first and second substantially planar metallic resonator plates, and the size and shape of the internal cavity are configured to achieve a preselected filter response.

According to a fourth aspect of the invention, a filter assembly is provided. The filter assembly includes: a housing having a top cover, a bottom cover, and a first sidewall, the top cover, the bottom cover, and the first sidewall defining an interior cavity; a printed circuit board mounted at least partially within the housing, the printed circuit board including at least a first conductive layer and a second conductive layer, each conductive layer including a plurality of resonant elements forming part of a resonant cavity filter.

According to a fifth aspect of the invention, a tuning element is provided, which is realized in an opening in a metal plate of a filter. The tuning element comprises: a coupling element; a first arm having a first end connected to the metal plate and a second end connected to the coupling element; and a second arm having a first end connected to the metal plate and a second end connected to the coupling element.

According to a sixth aspect of the invention, a tuning element is provided. The tuning element comprises: a coupling element arranged in an opening in a wall of the filter housing, the coupling element being connected to the wall by respective first and second arms.

According to a seventh aspect of the invention, a method of tuning a filter is provided. The method comprises the following steps: the coupling plate is moved in a direction substantially perpendicular to a plane defined by the walls of the filter, the coupling plate being arranged in the opening of the wall.

Embodiments of any of the above aspects of the invention provide filter assemblies having the advantages of being small, light weight, low cost, easy to manufacture and assemble, which may be used as duplexers, diplexers, combiners and/or other filters for cellular communication systems and other applications.

Drawings

Fig. 1 is a highly 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 a cover plate removed therefrom.

Fig. 4 is a top perspective view of a portion of the housing of the conventional duplexer of fig. 2-3 with the top cover and resonating elements removed.

Fig. 5 is a perspective view of a filter assembly according to an embodiment of the invention.

Fig. 6 is an exploded perspective view of the filter assembly of fig. 5.

Fig. 7 is a cross-sectional perspective view of a portion of the filter assembly of fig. 5-6.

Fig. 8 is a back side view of an antenna panel including six of the filter assemblies of fig. 5-7.

Fig. 9 is a top view of a filter assembly according to other embodiments of the present invention with the top cover removed.

Fig. 10 is a bottom view of a portion of the filter assembly of fig. 9 with the bottom cover made transparent.

Fig. 11 is a graph showing the filter response of the filter assembly of fig. 9-10.

Fig. 12 is an exploded perspective view of a filter assembly according to further embodiments of the present invention.

Fig. 13 is an exploded perspective view of a modified version of the filter assembly of fig. 12.

Fig. 14 is an exploded perspective view of a filter assembly according to still further embodiments of the invention.

Fig. 15 is an exploded perspective view of the filter assembly of fig. 14.

Fig. 16 is a perspective view of a filter assembly according to further embodiments of the invention.

Fig. 17A is a schematic structural block diagram of an antenna including the filter component of fig. 16.

Fig. 17B is a schematic block diagram illustrating the RF communication path of the antenna of fig. 17A.

Fig. 18 is a perspective view of a filter assembly according to further embodiments of the invention.

Fig. 19 is a perspective view of a filter assembly according to further embodiments of the invention.

Figure 20 is a top view of a crimpable tuning element of a filter according to some embodiments of the present invention.

Fig. 21 is a bottom perspective view of the tuning element of fig. 20 after the tuning element has been moved downward to tune the filter.

Figure 22 is a top view of a top cover of a filter having a plurality of the crimpable tuning elements of figure 20 formed therein.

Fig. 23A-23D are perspective and plan views of a conventional filter tuning element.

Fig. 24A-C are schematic diagrams illustrating simulated current distributions in a single-stub tuning element, a double-stub tuning element, and a crimpable tuning element, respectively, according to an embodiment of the present invention.

Fig. 25A-25C are cross-sectional views of the tuning elements of fig. 24A-24C, respectively, illustrating electric fields along the respective cross-sections.

Fig. 26A-26C are perspective views of the electric field outside the filter housing and above the tuning element of fig. 24A-24C, respectively.

Fig. 27 is a graph comparing the resonant frequency tuning range of a crimpable tuning element according to an embodiment of the present invention with conventional tuning screws and with conventional single-bend and double-bend tuning stubs.

Figure 28 is a top view of a rollable tuning element for a filter according to a further embodiment of the present invention

Detailed Description

Embodiments of the present invention provide small, lightweight, low cost, easy to manufacture and assemble filter assemblies that can be used as duplexers, diplexers, combiners, and/or other filters for cellular communication systems and other applications. These filter components may be implemented as a plurality of resonator plates mounted within a housing to implement a resonant cavity RF filter. The resonator plates may be mounted in a stacked relationship. In an exemplary embodiment, two resonator plates, generally referred to herein as a "top" resonator plate and a "bottom" resonator plate, may be provided. However, it is understood that more than two resonator plates may be included in a filter assembly in other embodiments, and the orientation of the resonator plates may be varied (e.g., the resonator plates may be arranged side-by-side). The resonator plate may be secured to the housing by continuous weld points and/or may be integrally die cast with other components of the housing to provide very high levels of RF and PIM distortion performance.

For example, each resonator plate may comprise a substantially flat or "planar" metal plate having a plurality of resonators formed therein. These resonators may be formed by stamping or other means of cutting a plurality of holes in each resonator plate in a particular pattern. The resonator plate may include an organic solderability preservative ("OSP") as a protective coating on its metallic surfaces prior to soldering. Alternative coatings may be used to provide a solderable surface and will provide a mechanically reliable connection. Examples of such alternative plating are silver or tin. In other embodiments, the resonator plate may include a patterned conductive layer on one or more printed circuit boards. The shape and relative position of the resonators, the distance between the resonator plates, and the size and shape of the filter cavity may be designed to provide a resonator filter with a desired filter (frequency) response. For example, the housing may be implemented as a frame having a plurality of side walls and a pair of planar metal sheets that serve as a top cover and a bottom cover that are welded to the frame. For example, the frame may be manufactured by die casting or by using a computer numerical control ("CNC") machine. As mentioned above, a silver or tin surface coating may also be provided. The interior of the housing may comprise a single cavity and the resonator plate may be mounted within the cavity. In some embodiments, a continuous ledge may extend around the interior of the frame, and the top and bottom resonator plates may be welded to the respective top and bottom surfaces of the ledge. A bendable tuning stub (stub) or crimpable tuning element may be provided on the top cover, bottom cover and/or resonator plate for tuning the response of the filter.

In some embodiments, the filter component may include a three-port device, such as an RF duplexer or diplexer. In other embodiments, these filter components may include additional ports to implement multiplexers, triplexers, combiners, and so forth.

For example, a filter assembly according to an embodiment of the invention may include two or more ports for electrically connecting the filter assembly to other external devices. These ports may include "individual" ports, which refer to ports that are only used to carry signals having multiple specific ranges of frequencies, and "common" ports, which are used to carry signals having multiple specific ranges of frequencies. For example, when the filter assembly according to an embodiment of the invention is a duplexer, the filter assembly will comprise a first individual port connected to the transmit path phase shifter, a second individual port connected to the receive path phase shifter and a common port connected to a radiating element, such as a radiating element of a phased array antenna. In some embodiments, for example, the individual and common ports may be implemented as coaxial connector ports designed to mate with connectorized coaxial cables. In other embodiments, the individual and common ports may simply comprise respective openings in the housing that receive the connectorized cables. In such embodiments, the center conductor of each cable may be connected (e.g., soldered) to one of the resonator plates, and the outer conductor of each cable may be connected (e.g., soldered) to the housing. By using such a soldered connection, the size and cost of the filter assembly may be further reduced in some embodiments. In still other embodiments, the individual and/or common ports may be implemented as transmission lines on the printed circuit board that extend through openings of the filter housing. Such embodiments may reduce or eliminate the need for coaxial cables and/or soldered connections for the filter.

Filter assemblies according to embodiments of the invention can provide a high level of RF performance. Because the continuously soldered connections may be used to mount the resonator plate within the cavity and the top and bottom covers to the frame, the filter assembly may have a highly consistent metal-to-metal interface and may thus exhibit low insertion loss values and very low levels of passive intermodulation ("PIM") distortion. The top and bottom caps may be formed of thin sheet metal, and the absence of internally threaded posts (for receiving screws) may greatly reduce the amount of metal required to form the housing. Thus, both the size and weight of the filter assembly can be significantly reduced compared to prior art filter designs. The filter assembly is also formed using a very small number of parts, which reduces the material cost and assembly cost of the filter assembly. In some embodiments, one or both resonator plates may be die cast with the frame to provide a unitary structure, thereby eliminating the need for a welded connection between the resonator plates and the frame. This may improve the PIM distortion performance of the filter and/or simplify the manufacture of the filter.

In some embodiments, the filter may include a crimpable tuning element that may be cut or inscribed into a wall of the filter housing (e.g., top and bottom covers or sidewalls) or resonator plate. The crimpable tuning element may comprise a coupling element and two or more arms connecting the coupling element to a wall or plate. The coupling element may be axially displaceable into the filter cavity and may be movable along an axis substantially perpendicular to a plane defined by the wall or plate. In this way, the tuning element can be designed to remain centered on the underlying element (e.g., resonator plate) in the filter cavity regardless of the degree of movement of the tuning element as part of the tuning process. The tuning element may rotate or "curl" in a plane parallel to the wall or plate as it moves, which helps to maintain its position along the axis. As discussed herein, these crimpable tuning elements may be very inexpensive and easy to manufacture while exhibiting superior performance over more complex and expensive conventional tuning elements (e.g., tuning screws and tuning stubs).

Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, in which exemplary embodiments are depicted.

Fig. 5-7 illustrate a filter assembly 100 according to an embodiment of the invention. Specifically, fig. 5 is a perspective view of the filter assembly 100, fig. 6 is an exploded perspective view of the filter assembly 100, and fig. 7 is an enlarged side perspective view of a portion of the filter assembly 100.

As shown in fig. 5-7, the filter assembly 100 includes a housing 110 including a frame 120, a top cover 130, and a bottom cover 140. The first and second resonator plates 150, 160 are mounted within the housing 110. The filter assembly 100 also includes a pair of individual ports 170, 180 and a common port 190.

The housing 110 may include, for example, a rectangular housing 110 having a top 112, a bottom 114, and four sidewalls 116. The top cover 130 may form the top 112 of the housing 110, the bottom cover 140 may form the bottom 114 of the housing 110, and the frame 120 may form the four sidewalls 116 of the housing 110. The top 112, bottom 114 and side walls 116 define a cavity 118 in the interior of the housing 110. The frame 120 may have more or fewer than four sidewalls 116.

For example, the frame 120 may comprise a single piece of metal forming the four sidewalls 116. The ledge 122 may extend around the interior of the frame. The ledge 122 is a continuous ledge, but in other embodiments the ledge 122 may be discontinuous or may even be omitted entirely. The first and second resonator plates 150, 160 may be mounted on the ledge 122, and the ledge 122 may separate the first and second resonator plates 150, 160 by a predetermined distance such that the filter assembly 100 provides a desired frequency response. In some embodiments, the frame 120 may be made of aluminum or an aluminum alloy plated with copper, although other metals may be used, such as zinc, zinc alloys, copper alloys, and the like. Although the frame 120 is rectangular in the depicted embodiment, it should be understood that other shaped frames (e.g., circular, pentagonal, etc.) may also be used.

In some embodiments, the frame 120 may be a die cast frame. In other embodiments, the frame 120 may be a stamped sheet metal formed into a rectangle and welded together at the ends. In such an embodiment, the ledge 122 may be one or more separate pieces of metal that are welded or otherwise secured to the interior of the frame 120. As best shown in fig. 7, the interior of the upper surface of the frame 120 includes a groove 124 such that a flange 125 extends upwardly along an exterior portion of the upper surface of the frame 120. The outer edge of the cap 130 may rest on the bottom surface of the groove 124, which provides a convenient surface for welding the cap 130 to the frame 120. Similarly, the interior of the lower surface of the frame 120 includes a groove 126 such that a flange 127 extends down an exterior portion of the lower surface of the frame 120. The outer edge of the bottom cover 140 may rest on the bottom surface of the groove 126, which provides a convenient surface for welding the bottom cover 140 to the frame 120. A plurality of flanges 128 may extend from an outer surface of the frame 120. Each flange 128 may have an aperture 129 therethrough. Screws (not shown) may be inserted through these holes to mount the filter assembly 100 to an underlying surface (e.g., the back of a panel antenna).

The top cover 130 and the bottom cover 140 may each include a metal plate. In some embodiments, the top and bottom covers 130, 140 may be formed of copper plated aluminum, although other materials may be used, including, for example, any of the exemplary metals listed above that may be used in some embodiments to form the frame 120. The top and bottom covers 130, 140 include OSP as a protective coating for these metal surfaces prior to soldering. Alternative coatings may be used to provide a solderable surface and will provide a mechanically reliable connection. Examples of such alternative plating are silver or tin. The top cover 130 may be placed on the frame such that the outer periphery of its bottom surface rests in the groove 124. The top cover 130 may be welded to the frame 120 by a continuous weld extending around the outer periphery of the bottom surface of the top cover 130.

A plurality of tuning stubs 132 may be formed in the top cover 130. For example, each tuning stub 132 may be formed by making a U-shaped cut in the top cover 130 to form a cantilevered tab 134. The cantilever tabs 134 may be bent inward to tune the filter assembly 100. This tuning of the filter assembly 100 may be performed during the final stages of manufacture to fine tune the filter response. As described below, a plurality of openings 136 may also be provided in the top cover 130, for example, to provide access to additional tuning stubs that may be formed on one or more of the resonator plates 150, 160.

The bottom cover 140 may be similar to the top cover 130 and may include a plurality of tuning stubs 142 in the form of cantilevered tabs 144. The cantilever tabs 144 may be bent inward to tune the filter assembly 100. A plurality of openings 146 may also be provided in the bottom cover 140, which may provide access to tuning stubs formed on one or more of the resonator plates 150, 160, for example. The bottom cover 140 may be placed on the frame 120 such that the outer periphery of its top surface rests in the groove 126. The bottom cover 140 may be welded to the frame 120 by a continuous weld extending around an outer periphery of a top surface of the bottom cover 140.

Although the housing 110 of the filter assembly 100 is constructed from the frame 120, the top cover 130, and the bottom cover 140, it should be understood that other housing designs may be used in other embodiments that may be shaped differently, formed differently, and/or have more or fewer components. As a simple example, in another embodiment, the bottom cover 140 and the frame 120 may comprise a single die-cast unit, and the ledge 122 may be discontinuous so as to allow the bottom resonator plate 160 to be inserted from above under the ledge 122 (which also necessitates a change of the bottom resonator plate) and welded to the underside of the ledge 122. Many other variations to the housing 110 are possible. Accordingly, it should be understood that the housing 110 is shown so that this disclosure is thorough and complete, and is not intended to limit the scope of the invention.

The resonator plates 150, 160 may each comprise, for example, a substantially flat metal plate. The resonator plates 150, 160 may be only "substantially" flat in that they may include, for example, non-flat features such as tuning stubs that may be bent up or down to tune the response of the filter assembly 100. Each resonator plate 150, 160 may be formed, for example, of copper or a copper alloy, although other metals may also be used. Each resonator plate 150, 160 includes one or more resonant elements. Openings 152, 162 are punched or otherwise formed in the respective resonator plates 150, 160 to create a "hole pattern" in each resonator plate 150, 160. The size and location of these openings 152, 162 and the distance between the two resonator plates 150, 160, the location of the resonator plates 150, 160 within the cavity 118, and the size and shape of the cavity 118 at least partially determine the frequency response of the filter assembly 100. The resonator plates 150, 160 may be in a closely spaced relationship such that they strongly couple to each other, which may provide a transmission zero (i.e., a null in the frequency response) for providing a steep filter response. Such a response is desirable to achieve high RF performance.

Dielectric spacers (not shown in fig. 5-7, but similar spacers are shown in the embodiments of fig. 8-9 discussed below) may be provided that are positioned between the resonator plates 150, 160 to ensure that a desired spacing distance can be maintained between the resonator plates 150, 160. Such spacers may also be provided between the resonator plate 150 and the top cover 130 and/or between the resonator plate 160 and the bottom cover 140. Tuning stubs may also be included on one or both of the resonator plates 150, 160. In the depicted embodiment, the tuning stub 164 is included on the bottom resonator plate 160.

As best shown in fig. 6 and 7, the resonator plate 150 may rest on an upper surface of the ledge 122 and the resonator plate 160 may rest on a lower surface of the ledge 122. In some embodiments, each resonator plate 150, 160 may be welded to the ledge 122.

As best shown in fig. 5, the filter assembly 100 also includes a pair of individual ports 170, 180 and a common port 190. In the depicted embodiment, each of the ports 170, 180, 190 may be realized as an opening in the sidewall 116 of the housing configured to receive a coaxial cable. Each port 170, 180, 190 may include one or more outwardly projecting flanges 172, 182, 192, respectively. Each of these flanges 172, 182, 192 may define a portion of a circle (or an entire circle), and the inner radius defined by the flange 172, 182, 192 of each port 170, 180, 190 may be sized to mate with the outer conductor of a coaxial cable inserted into the respective port 170, 180, 190. Each of these coaxial cables may be prepared for termination into filter assembly 100 by removing a portion of the dielectric layer and outer conductor of the cable such that the center conductor protrudes from the end of the cable. The jacket material may also be removed from the end of each cable to expose the end portions of the center and outer conductors. The coaxial cables may be inserted into the respective ports 170, 180, 190 such that the center conductor of each cable extends into the cavity 118. The center conductor of each cable may be physically and electrically connected to one of the resonator plates 150, 160, for example by soldering. In some embodiments, the center conductors of the coaxial cables may all be connected to the same resonator plate 150, 160, although embodiments of the invention are not limited thereto. The outer conductor of the coaxial cable may be physically and electrically connected to the housing 110, for example, by soldering the outer conductor to the respective flanges 172, l82, 192 of the respective ports 170, 180, 190.

In some embodiments, the resonator plates 150, 160 may be soldered to the frame 120 using a first type of solder, and the top and bottom covers 130, 140 may be soldered to the frame 120 using a second type of solder. For example, high temperature tin-silver-copper solder paste may be printed along the edge (i.e., outer perimeter) of the lower surface of the top resonator plate 150, and the top resonator plate 150 may be placed on the upper surface of the ledge 122 of the frame 120. High temperature tin-silver-copper solder paste may also be printed along the edges of the upper surface of the bottom resonator plate 160 and the bottom resonator plate 160 may be placed on the underside of the ledge 122 of the frame 120. As mentioned above, a dielectric spacer may also be provided between the resonator plates 150, 160. These spacers may be formed of a material that can withstand the temperature used to reflow the solder paste. The resonator plates 150, 160 may be held in place using suitable fixtures, and then the frame 120, resonator plates 150, 160, and any dielectric spacers may be heated, for example in a convection oven, to a temperature sufficient to reflow the solder paste to form a continuous solder joint between each resonator plate 150, 160 and the ledge 122. It should be noted that solder paste may additionally or alternatively be printed or otherwise applied to the ledge 122. It should also be understood that alternative solder materials may be used in place of solder paste, such as one or more pre-formed solder tabs.

A second welding process may be used to attach the top and bottom covers 130, 140 to the frame 120 and weld the coaxial cables to the filter assembly 100. A lower temperature solder may be used in this subsequent process so that the solder used to attach the resonator plates 150, 160 to the frame 120 does not reflow during the process steps for soldering the coaxial cables in place and soldering the covers 130, 140 to the frame 120. In some embodiments, a bismuth tin silver solder paste may be used in the second soldering operation. The center and outer conductors of the coaxial cable may be coated with solder paste and inserted through the respective ports 170, 180, 190 such that the solder on the outer conductor engages the respective flanges 172, 182, 192 and the center conductor (solder on) is attached to the appropriate resonator plate 150, 160. Alternative solder materials may also be used in place of solder paste, such as one or more pre-formed solder tabs. In some embodiments, solder paste may be used to solder the resonator plates 150, 160 and top and bottom covers 130, 140 to the frame 120, while preformed solder tabs are used to solder the cables to the respective ports 170, 180, 190 and/or flanges 172, 182, 192. Alternative soldering processes, such as induction soldering or manual soldering using a soldering iron, can be used to solder the cable to the filter assembly 100.

A bismuth tin silver solder paste stencil may then be printed onto the edges of the bottom surface of the top cover 130 and the edges of the top surface of the bottom cover 140, or alternatively (or additionally) a bismuth tin silver solder paste stencil may be printed onto the respective top and bottom surfaces of the recesses 124, 126, and the top and bottom covers 130, 140 may be attached to the frame 120 using additional fixtures and/or alternative pre-formed solder tab materials if necessary. The filter assembly 100 may then be placed again in a convection oven and heated to a temperature sufficient to reflow the bismuth silver solder paste, but lower than the melting temperature of the tin silver copper solder paste.

The filter assembly 100 can implement a filter that is conventional from an equivalent circuit point of view because it has resonators and cross-coupling of conventional nature and that provides a conventional frequency response. However, the mechanical design of the filter assembly 100 may be much simpler than conventional filter assemblies, such that the filter assembly 100 has much fewer components, smaller physical size, lighter weight than conventional filter assemblies, and is much easier to manufacture and assemble.

In some embodiments, the filter assembly 100 may be a duplexer for use on a phased array antenna with remote electronic tilt functionality. For example, a phased array antenna may have 10 radiating elements, 5 of which are used to transmit and receive signals having a first polarization and the other 5 of which are used to transmit and receive signals having a second, orthogonal polarization. To achieve remote electronic tilt, a total of 4 phase shifters are provided, which are typically mounted within the antenna (e.g., on the back of a planar array). In particular, one or more "transmit path" phase shifters are provided for adjusting the phase of signals in the transmit frequency band and one or more "receive path" phase shifters are provided for adjusting the phase of signals in the receive frequency band. A duplexer is provided at the input of each radiating element for connecting the transmit and receive transmission paths to the radiating elements. Since the phase shifter is mounted on the antenna, each duplexer is also typically mounted on the antenna. Therefore, the antenna must have room for a large number of duplexers (10 in the above example), which is why the size and weight of the duplexers may be an important consideration.

Although the filter assembly 100 includes two resonator plates 150, 160, it should be understood that one or more additional resonator plates may be included in other embodiments. The use of additional resonator plates will generally provide the ability to fine tune the frequency response to more closely approximate the ideal frequency response, but adding additional resonator plates may involve a compromise of the filter assembly with respect to increased cost and/or complexity, and may also increase the insertion loss of the filter assembly.

Fig. 8 is a rear view of a portion of an antenna panel 200 including 5 cross-polarized radiating elements and 10 duplexers of fig. 5-7, of which 6 duplexers are visible in the portion of the antenna 200 shown in fig. 8. As shown in fig. 8, the duplexer 100 is small enough that two duplexers 100 can be mounted side by side within the width of the antenna panel 200 (typically 300 millimeters). Where the individual ports 170 of the 5 duplexers 100 may be connected through respective coaxial cables to one of the five outputs of the transmit path phase shifter for the first polarization. Likewise, the individual ports 180 of the 5 duplexers 100 may be connected to one of the five outputs of the receive path phase shifter by additional respective coaxial cables for the first polarization. The common port 190 of these 5 above duplexers 100 may be connected by additional coaxial cables to the printed circuit board associated with each radiating element having the first polarization. The remaining 5 duplexers may be connected in the same manner to the transmit and receive path duplexers and radiating elements having a second, orthogonal polarization.

Fig. 9 and 10 show a filter assembly 300 according to another embodiment of the invention. Specifically, fig. 9 is a top view of the filter assembly 300 with the top cover removed and set to one side, and fig. 10 is a bottom view of a portion of the filter assembly 200 with the bottom cover made transparent.

The filter assembly 300 is very similar to the filter assembly 100 described above, and therefore only a brief description of the filter assembly 300 is provided herein. The description of the filter assembly 300 will focus on various features described above but not necessarily clearly shown in the drawings, such as tuning stubs and dielectric spacers on the resonator plates.

Referring to fig. 9-10, filter assembly 300 includes a housing 310 including a frame 320, a top cover 330, and a bottom cover 340. The top and bottom resonator plates 350, 360 are mounted within the housing 310. The filter assembly 300 further includes ports 370, 380, 390.

As shown in fig. 9 and 10, a plurality of dielectric spacers 354 are provided for helping to maintain the spacing between the resonator plates 350, 360 at a desired distance. Each dielectric spacer 354 is shaped like a bolt having a head 356 and a distal end. A radially extending flange 358 is disposed at the distal end of each media spacer 354. Dielectric spacers 354 are inserted through holes or other openings in the top resonator plate 350 toward the bottom resonator plate 360. The distal end of each dielectric spacer 354 is inserted through a hole or other opening in the bottom resonator plate 360. The flanges 358 are bent as each dielectric spacer 354 is inserted through an opening in the resonator plate 360. In this manner, the spacers 354 may maintain the resonator plates 350, 360 at a consistent separation distance.

As shown in fig. 10, a plurality of tuning stubs 353 are included on the top resonator plate 350. These tuning stubs are accessible through holes 346 in the bottom cover 340. Because the design and operation of filter assembly 300 is otherwise very similar to the design and operation of filter assembly 100 as described in detail above, further description of filter assembly 300 will be omitted.

Given a cavity of selected size and dimension, the spacing between the resonator elements and the resonator plate in the resonator plate of the above-described filter assembly can be designed using conventional filter design techniques. As known to those skilled in the art, high performance RF filters/duplexers require high isolation close to the passband (i.e., the frequency range over which a signal should be allowed to pass with respect to at least one port of the device). This high isolation is typically achieved by cross-coupling or by additional resonant elements that provide transmission zeros (i.e., steep dips in the frequency response) near the passband. Each cross-coupling may need to be coupled to a non-adjacent resonator and thus may require a specific resonator configuration and/or additional coupling elements. Conventionally, at least three resonators are used to generate transmission zeros (nulls). However, in the filter assembly according to an embodiment of the present invention, a hybrid magnetoelectric coupling technique is used to realize transmission zeros above/below a pass band with only two resonators. A more detailed description of these techniques can be found, for example, in the following documents: H.Wang and Q.Chu, An Inline Coaxial quick-Electric Filter With Controllable Mixed Electric and Magnetic Coupling, IEEE Transactions on Microwave heating and technical, Vo.57, No.3, March 2009at 667 673 and Q.Chu and H.Wang, A Compact Open-Loop Filter With Mixed Electric and Magnetic Coupling, IEEE Transactions on Microwave heating and technical, Vo.56, No.2, February 2008at 439, each of which is incorporated herein by reference. By using a filter design comprising two stacked metal resonator plates it is possible to control the magneto-electric coupling without requiring additional elements and/or without requiring very narrow gaps, which may be important for the tolerance.

Given the desired frequency response, simulation software such as Microwave Office and/or CST may be used to design the parameters of the filter. The simulation software will, for example, specify the number of resonators required and their relative relationships, which can then be implemented in accordance with the techniques disclosed herein to provide a filter assembly in accordance with an embodiment of the invention. Fig. 11 is a graph showing the filter response of the filter assembly 300 of fig. 9-10. The view of the filter assembly 300 of fig. 9 is also included in fig. 11. In fig. 11, a curve 400 shows the attenuation with frequency occurring on the RF signal passing between the common port and the first individual port, and a curve 410 shows the attenuation with frequency occurring on the RF signal passing between the common port and the second individual port. As indicated by the arrows in fig. 11, the portion of the resonator plates 350, 360 within the boxes 402, 404 creates the null of the curve 400 and the portion of the resonator plates 350, 360 within the boxes 412, 414 creates the null of the curve 410. As shown in fig. 11, a steep null is generated very close to the corresponding pass band.

Filter assemblies according to embodiments of the invention may provide a number of advantages over conventional filter assemblies. As described above, most or even all of the components of a filter assembly according to embodiments of the invention (including the top and bottom covers, the resonator plates, and the coaxial cables attached to the individual and common ports) may be soldered together using continuous solder joints to provide a highly consistent metal-to-metal connection. As is known in the art, PIM distortion may occur when two or more RF signals encounter a non-linear electrical joint or material along an RF transmission path. This non-linearity can act like a mixer so that a new RF signal is generated with a mathematical combination of the original RF signals. If the newly generated RF signals fall within the bandwidth of the existing RF signals, the noise level experienced by those existing RF signals actually increases. As the noise level increases, it may be necessary to reduce the data rate and/or quality of service. PIM distortion may be an important interconnection quality characteristic of an RF communication system, as PIM distortion resulting from a single low quality interconnection may degrade the electrical performance of the overall RF communication system. Therefore, it would be desirable to ensure that components used in RF communication systems will produce acceptably low levels of PIM distortion.

As described above, one possible source of PIM distortion is inconsistent metal-to-metal contact along the RF transmission path. Referring again to fig. 2-4, it can be seen that the conventional filter assembly 50 includes a very large number of screws 80. Such a large number of screws 80 are used to ensure that relatively consistent metal-to-metal contact is maintained to ensure an acceptably low level of PIM distortion. A filter assembly according to some embodiments of the present invention may remove all of these screws, which may greatly simplify the structure of the filter assembly and greatly reduce the time required to assemble the filter. Furthermore, continuous solder connections may generally provide improved PIM distortion performance compared to the filter assemblies of fig. 2-4 assembled using screws.

Furthermore, if the filter assembly is assembled using screws, minute metal shavings may be torn off from the outer surface of the screw and/or from the inner surface of the internally threaded hole that receives the screw when the screw is tightened. Such swarf is another well-known source of PIM distortion in RF components and is particularly troublesome because swarf can move around within the filter components, not only causing increased PIM distortion, but also causing PIM distortion levels to change in an unpredictable manner over time. If an increased level of PIM distortion is determined during the PIM distortion test during a particular cell quantification, the filter components involved may be turned on and cleaned to remove metal particles. However, if the metal particles are not initially detected, it can become a serious problem because PIM distortion can occur after the filter assembly has been installed (e.g., when installed on the antenna of a cell tower), which requires very expensive replacement operations, down time of the cellular base station, and the like. It should be noted that the use of a bendable tuning stub in place of a tuning screw may avoid the creation of metal filings within the filter assembly, as the creation of metal filings may also be due to the adjustment of the tuning screw.

It should be noted that in addition to PIM distortion, inconsistent metal-to-metal connections may cause reflections in the RF communication system, which increases return loss along the RF transmission path. Devices with such inconsistent metal-to-metal connections may exhibit increased insertion loss values. By using a continuously welded connection, a filter assembly according to embodiments of the invention may exhibit improved insertion loss performance.

Filter assemblies according to embodiments of the present invention may be smaller and lighter in weight than conventional filters used in cellular communication systems. This may be important because, for example, filter assemblies may be mounted on planar antenna arrays that have limited space for electronic circuitry and because heavier antenna structures may increase the structural requirements of the antenna mounting structure.

Filter assemblies according to embodiments of the invention may also be cost-effective because they may require less material to implement and because the frame may be the only die-cast part, while many or even all of the remaining components of the filter may be formed from stamped metal. Furthermore, by reducing or even eliminating screws, and by substantially reducing the number of parts required to form each filter assembly, assembly costs (and time required for assembly) can be significantly reduced.

It should be understood that filter assemblies according to embodiments of the present invention may be used to implement a variety of different devices, including duplexers, diplexers, multiplexers, combiners, and the like. It should be understood that filter assemblies according to embodiments of the present invention may also be used in other applications than cellular communication systems.

According to a further embodiment of the invention, a filter assembly may be provided in which at least one of the resonator plates is die-cast as part of the frame. Fig. 12 is an exploded perspective view of the filter assembly 500 of such an embodiment of the present invention.

As shown in fig. 12, the filter assembly 500 may be very similar to the filter assembly 100 previously discussed with reference to fig. 5-7. Specifically, filter assembly 500 includes a housing including a frame 520, a top cover 530, and a bottom cover 540. The first resonator plate 550 is mounted within the housing. The filter assembly 500 also includes a pair of individual ports 570, 580 and a common port 590. The top and bottom covers 530, 540 may be identical to the top and bottom covers 130, 140 of the filter assembly 100 and may be attached to the frame 520 in the same manner as the top and bottom covers 130, 140 are attached to the frame 120 of the filter assembly 100. Therefore, further description of the top and bottom covers 530 and 540 will be omitted. Similarly, the individual ports 570, 580 and the common port 590 may be identical to the individual ports 170, 180 and the common port 190 of the filter assembly 100, and therefore further description of these ports will also be omitted here.

The housing may be identical to housing 110 of filter assembly 100 and may include a top cover 530, a bottom cover 540, and four sidewalls 516 formed by frame 520. The top cover 530, bottom cover 540, and side walls 516 define a cavity inside the housing.

The frame 520 may comprise a single piece of metal, for example, and may be similar to the frame 120 of the filter assembly 100. The frame 520 may form four sidewalls 516 of the housing. The ledge 522 may extend around the interior of the frame 520. The ledge 522 may be continuous or discontinuous and may be omitted in some embodiments. The frame 520 may also include a second resonator plate 560 formed as an integral part of the frame 520. The frame 520 may be die cast, for example, to form the four sidewalls 516, the ledge 522, and the second resonator plate 560 as a single unitary structure.

The second resonator plate 560 may be in contact with the ledge 522 and/or may be separate from the ledge 122. Thus, while the illustrated embodiment shows the ledge 522 in direct contact with the second resonator plate 560 and extending upwardly from the second resonator plate 560, it will be appreciated that embodiments of the invention are not so limited. The first resonator plate 550 may be mounted on the ledge 522. The first and second resonator plates 550, 560 may be spaced apart a predetermined distance such that the filter assembly 500 provides a desired frequency response.

The frame 520 may be made of a suitable metal, such as aluminum or an aluminum alloy plated with copper. While the frame 520 is rectangular in the depicted embodiment, it should be understood that other shaped frames may be used. In some embodiments, the ledge 522 may be welded to the sidewall 516 or the second resonator plate 560 rather than being die cast with the sidewall 516 and the second resonator plate 560. The frame 520 may also include grooves and flanges that are identical to the corresponding grooves 124, 126 and flanges 125, 127 included on the frame 120 of the filter assembly 100 described above with reference to fig. 7. Frame 520 may also include a flange, which may be identical to flange 128 of frame 120, that may be used to mount filter assembly 500 to a mounting surface.

Although the top cover 530 and the bottom cover 540 are both separate from the frame 520 in the above-described embodiment, it is understood that in other embodiments, the bottom cover 540 may be die cast as part of the frame 520 rather than as a separate unit.

The first resonator plate 550 may be substantially identical to the resonator plate 150 described above. The second resonator plate 560 similarly may be substantially identical to the second resonator plate 160 described above, except that the second resonator plate 560 may be integrally formed with the frame 520 as a single die-cast integral unit. Therefore, further description of the resonator plates 550, 560 will be omitted. It will be appreciated that one or more additional resonator plates may also be included in other embodiments.

A dielectric spacer (not shown in fig. 12) may be provided which is positioned between the resonator plates 550, 560 in the same manner as the dielectric spacer is positioned between the resonator plates 150, 160 as described above. It will also be appreciated that the welding techniques, materials, etc. discussed above with respect to filter assembly 100 may be equally applied to filter assembly 500.

Filter assembly 500 may be simpler than filter assembly 100 discussed above because it requires at least one less manufacturing step, i.e., welding second resonator plate 560 to frame 520. In addition, omitting the soldering step also removes one possible source of PIM distortion, as poor solder connections are a possible source of PIM distortion. For example, the filter assembly 500 may be a duplexer for use on a phased array antenna with remote electronic tilt functionality.

While the second resonator plate 560 and, in some embodiments, the bottom cover 540 are formed integrally with the frame 520 in the filter assembly 500, it will be appreciated that the first resonator plate 550 and the top cover 530 (as desired) may alternatively be formed integrally with the frame 520 in other embodiments.

Fig. 13 is an exploded perspective view of a filter assembly 500' according to further embodiments of the present invention. As can be seen by comparing fig. 12 and 13, filter assembly 500' is nearly identical to filter assembly 500 described above. However, in filter assembly 500 ', both resonator plates 550, 560 are formed integrally with frame 520'. For example, the frame 520' and the first and second resonator plates 550, 560 may be die cast as a single unitary structure. In the embodiment of fig. 13, the ledge 522 included in the filter assembly 500 may be omitted. In some embodiments, one or both of the top and bottom covers 530, 540 may also be formed as one piece with the frame 520' and the first and second resonator plates 550, 560 in, for example, a die casting operation.

According to further embodiments of the present invention, filters may be provided that implement one or more resonator plates using a printed circuit board. Fig. 14 is an exploded perspective view of a filter assembly 600 implemented using a printed circuit board resonator plate according to an embodiment of the present invention. Herein, the term "printed circuit board" is used broadly to refer to any substrate having at least one patterned conductive layer thereon.

As shown in fig. 14, the filter assembly 600 is similar to the filter assembly 100 discussed above with reference to fig. 5-7. The filter assembly 600 includes a housing including a frame 620, a top cover 630, and a bottom cover 640. The filter assembly 600 also includes a pair of individual ports 670, 680 and a common port 690. The top cover 630, the bottom cover 640, and the ports 670, 680, 690 may be identical to the respective corresponding covers 130, 140 and ports 170, 180, 190 of the filter assembly 100, and thus further description thereof will be omitted. The frame 620 may be identical to the frame 120 of the filter assembly 100. While the frame 620 includes the ledge 622, it is understood that the ledge 622 may be omitted or may be located lower or higher along the side wall 616 in some embodiments.

The filter assembly 600 also includes a printed circuit board 652. The printed circuit board 652 may be mounted to the ledge 622 (if present) by, for example, soldering. In such an embodiment, the face of the printed circuit board 652 in contact with the ledge 622 may have a copper (or other metal) rim in direct contact with the ledge 622 to facilitate soldering the printed circuit board 652 to the ledge 622. Other mechanisms for mounting the printed circuit board 652 within the housing may be used in other embodiments.

The printed circuit board 652 in the illustrated embodiment comprises a double-sided printed circuit board having patterned conductive layers on both the top and bottom surfaces of a dielectric substrate 654. The patterned conductive layer on the top side of the dielectric substrate 654 may comprise a first resonator plate 650 and the patterned conductive layer on the bottom side of the dielectric substrate 654 may comprise a second resonator plate 660. The patterned conductive layers comprising the respective first and second resonator plates 650, 660 may be formed by etching a hole pattern in respective conductive strips (e.g., copper sheets) formed on respective top and bottom surfaces of the dielectric substrate 654. The aperture pattern may for example be the same as the aperture pattern comprised in the resonator plates 150, 160. In some embodiments, portions of the dielectric substrate 654 may also be removed, such as between the regions where both the respective top and bottom conductive strips are etched. Removing these portions of the dielectric substrate 654 may improve coupling between the resonator plates 650, 660, but is not required.

While in the above described embodiment both the top cover 630 and the bottom cover 640 are separate from the frame 620, it is understood that in other embodiments either the top cover 630 or the bottom cover 640 may be die cast as part of the frame 620.

Fig. 15 is an exploded perspective view of a filter assembly 600' according to further embodiments of the invention. The filter assembly 600 ' is similar to the filter assembly 600 except that the filter assembly 600 ' includes a single-sided printed circuit board 652 ' having a patterned conductive layer formed on only one side thereof as one of the first and second resonator plates 650, 660. An engraved metal sheet (or a metal sheet integral with the frame 620) may be used as the other of the first and second resonator plates 650, 660. In the embodiment shown, a patterned conductive layer on the printed circuit board 652 is used to realize the first resonator plate 650, and a separate second resonator plate 660 formed of sheet metal is provided. In other embodiments, the configuration may be reversed, with a printed circuit board used to implement the second resonator plate 660 and an engraved metal sheet used to implement the first resonator plate 650. It should also be understood that in each of the above embodiments, the patterned conductive layer may be formed on the top or bottom side of the printed circuit board 652'. The height of the ledge 622 (if any) may be adjusted (i.e., on top or bottom) based on the position of the patterned conductive layer on the printed circuit board 652' to ensure proper spacing between the resonator plates 650, 660 to achieve a desired filter response.

In embodiments of the invention using a printed circuit board based resonator plate, the tuning stub is not typically provided on the printed circuit board. However, tuning may still be performed, for example by etching away additional portions of the conductive pattern to reduce coupling and/or by soldering or otherwise attaching metal to the printed circuit board to improve coupling (e.g., soldering a small foil).

Fig. 16 is a perspective view of a filter assembly 700 according to still further embodiments of the invention. The filter assembly 700 may be similar to the filter assembly 600 described above using the printed circuit board 652 to implement the resonator plates 650, 660. However, in filter assembly 700, a much larger printed circuit board 752 is used, and frame 720 includes a slot 724 along a sidewall thereof, slot 724 allowing first portion 754 of printed circuit board 752 to be inserted within housing 710. The first portion 754 of the printed circuit board 720, which is received within the housing 710, may include conductive patterns that form the first and second resonator plates 750, 760. Because a larger printed circuit board 752 is used that extends into the housing 710, it is possible to implement other components, such as an antenna, on the second portion 756 of the printed circuit board 752 that extends out of the housing 710.

Because the printed circuit board 752 extends into the housing 710, the individual ports 670, 680 included in the filter assembly 600 may be omitted and replaced with traces or other transmission line structures on the printed circuit board 752 that extend from the second portion 756 of the printed circuit board 752 to the first portion 754 of the printed circuit board 752 that is located within the housing 710. The common port 690 of the filter assembly 600 may alternatively and/or additionally be omitted and replaced with traces or other transmission line structures on the printed circuit board 752 that extend from the second portion 756 of the printed circuit board 752 to the first portion 754 of the printed circuit board 752 located within the housing 710. Replacing one or more of the ports 670, 680, 690 of the filter assembly 600 with printed circuit board transmission lines as implemented in the filter assembly 700 of fig. 16 may advantageously reduce the number of solder joints required, simplify antenna manufacture and remove various potential PIM distortion points. This will be explained in more detail with reference to fig. 17A and 17B.

In particular, fig. 17A is a block diagram schematically illustrating an antenna 800 including multiple filter components 830 implemented using a single common printed circuit board. Each filter assembly 830 may have the design of filter assembly 700 of fig. 16. Fig. 17B is a schematic block diagram illustrating connections between phase shifters, filter components, and radiating elements included in the antenna 800. The antenna 800 is simpler to manufacture and generates less PIM distortion than conventional antennas.

Referring first to fig. 17A and 17B, an antenna 800 includes a transmit path phase shifter 810, a receive path phase shifter 820, a plurality of filter components 830-1 through 830-7, and a plurality of radiating elements 840-1 through 840-7. These components are mounted on a common printed circuit board 850. In the illustrated embodiment, the phase shifters 810, 820 and filter assemblies 830-1 through 830-7 are implemented on one side of the printed circuit board 850, and the radiating elements 840-1 through 840-7 are mounted to extend from the other side of the printed circuit board 850, and are thus shown using dashed lines. The radiating elements 840 may be aligned to form a linear array 842. The antenna 800 may include many other elements known to those skilled in the art, such as a remote electronic tilt down unit, an input connector, a processing unit, and the like. These additional elements are not shown in fig. 17A and 17B to simplify the drawing.

As shown in fig. 17B, the transmit path phase shifter 810 may comprise, for example, a 1x7 phase shifter having a single input port and 7 output ports. Each output port of the transmit path phase shifter 810 may be connected to a respective one of the filter assemblies 830. Similarly, the receive path phase shifter 820 may comprise, for example, a 1x7 phase shifter having 7 input ports and a single output port. Each input port of the receive path phase shifter 810 may also be connected to a respective one of the filter assemblies 830. Transmit phase shifter 820 may subdivide the RF signal received from the radio into 7 sub-components and may apply a linear phase taper on these 7 sub-components to electrically change the elevation angle of the antenna beam formed by radiating element 840, in a manner known to those skilled in the art. The receive phase shifter 820 may similarly subdivide the received RF signal into 7 sub-components and apply a linear phase taper on the 7 sub-components to electrically change the elevation of the receive antenna beam formed by the linear array 842. The transmit and receive phase shifters 810, 820 may be adjustable and may be adjustable from a remote location.

Each filter component 830 may include a duplexer and may be used to separate/combine RF signals of a transmit band from RF signals of a receive band. Each duplexer may have a transmit port 832, a receive port 834, and a common port 836. The common port 836 of each duplexer may be connected to a respective radiating element 840. The common port 836 may be configured to pass signals of transmit and receive frequency bands of the linear array 842. The transmit port 832 of each duplexer may be connected to a respective output of the transmit path phase shifter 810 and may be configured to pass signals of the transmit frequency band of the linear array 842 and not pass signals of the receive frequency band of the linear array 842. The receive port 834 of each duplexer may be configured to pass signals of a receive band of the linear array 842 but not a transmit band of the linear array 842.

Each radiating element 840 may comprise, for example, a dipole radiating element. A standard dipole radiating element is shown in fig. 17A and 17B to simplify the example, although more typically an orthogonal dipole or other orthogonally polarized radiating element is used that includes two radiators radiating in orthogonal polarizations. It will be appreciated that if orthogonal dipole radiating elements are used, the phase shifters 810, 820 and the filter assembly 830 will be repeated for orthogonal polarizations. It will also be appreciated that any suitable radiating element may be used, including, for example, a patch radiating element, a horn radiating element, and other radiating elements known to those skilled in the art. The radiating elements 840 may be arranged to form a linear array as shown. More than one linear array 842 of radiating elements 840 may be provided on antenna 800. The circuit shown in fig. 17A-17B may be repeated for each linear array.

Each duplexer may, for example, have the design of filter assembly 700 discussed above. As shown in fig. 17A and 17B, all 7 duplexers may be implemented on a common printed circuit board 850. The printed circuit board may include a plurality of fingers 852. Each finger 852 may be housed within the housing of a respective one of the duplexers, allowing all 7 duplexers to be formed on the common printed circuit board 850.

The phase shifters 810 and 820 and the radiating element 840 are also formed on and/or mounted on a common printed circuit board 850. As a result, the communication path between the phase shifters 810, 820 and the input/output ports of the duplexer can be a printed circuit board transmission path, such as conductive traces on the printed circuit board 850. The communication path between the duplexer and the corresponding radiating element 840 may also be implemented as a printed circuit board transmission path. As a result, soldered coaxial cable connections used to connect the phase shifter and the radiating element to the duplexer in conventional antennas can be omitted. This may reduce antenna cost, simplify its manufacture, and remove many possible sources of PIM distortion degradation.

Fig. 18 is a perspective view of a filter assembly 700' according to further embodiments of the present invention. Filter assembly 700 ' may be similar to filter assembly 700 described above, except that housing 720 ' of filter assembly 700 ' includes ledges 722 on two opposing sides thereof, and printed circuit board 752 ' extends through two ledges 722 such that printed circuit board 752 has a second central portion 756 within housing 710 and first and third end portions 754, 758 extending outside of housing 720 '.

Fig. 19 is a perspective view of an assembly 900 according to further embodiments of the invention. The assembly 900 includes a plurality of filter assemblies 910 formed on a common printed circuit board 930. Each filter assembly 910 may be similar to filter assemblies 700 and 700' discussed above in that filter assembly 910 implements a resonator plate using conductive patterns on the top and bottom surfaces of a portion of printed circuit board 930 that includes other components. However, in the filter assembly 910, its housing 920 includes first and second open boxes 922, 924 that are soldered to respective top and bottom surfaces of a printed circuit board 930 to cover respective first and second resonator plates (not visible in fig. 19). The first and second resonator plates are implemented as conductive patterns on portions of the printed circuit board 930 that are located within the respective housing 920. Each open box 922, 924 may comprise, for example, a metal box having four sidewalls and a cover on one end. Metal boxes 922, 924 may be welded in place over the respective first and second resonator plates to form filter assembly 910. In all other respects, filter component 910 may be, for example, the same as filter component 700 or filter component 700' discussed above. A plurality of filters 910 may be included on a printed circuit board 930, as schematically shown in fig. 19. Other elements of the antenna, such as phase shifter 940, may also be implemented on printed circuit board 930. This may advantageously allow for a reduction in the number of coaxial cables and/or soldered connections, as discussed above with reference to fig. 17A and 17B. It will be appreciated that additional phase shifters, radiating elements, etc. may also be mounted on the printed circuit board in the same manner as discussed above with reference to fig. 17A-17B.

According to a further embodiment of the invention, a filter having a tuning element exhibiting enhanced performance may be provided. In some embodiments, the tuning elements may be formed in an outer wall of the filter housing, such as in a top cover, a bottom cover, or in a side wall of the filter. Furthermore, the tuning element may be easier to adjust than conventional tuning stubs, less expensive to manufacture, mechanically robust, and/or perform better than various conventional tuning elements (e.g., tuning stubs or tuning screws).

Figure 20 is a top view of a tuning element 1000 of a filter according to some embodiments of the invention. Fig. 21 is a bottom perspective view of the tuning element 1000 of fig. 20 after the tuning element 1000 has been moved downward to tune the filter. Figure 22 is a top view of a top cover of a filter having a plurality of the tuning elements of figure 20 formed therein. In fig. 22, some tuning elements 1000 are in their original positions at the time of manufacture, while other tuning elements 1000 have been moved downward to tune the filter.

As shown in fig. 20-22, the tuning element 1000 is provided in an opening 1062 in the cover 1060 of the housing of the filter 1050. In fig. 22, the cover 1060 is the top cover 1060 of the filter housing, but it is understood that the tuning element 1000 may be formed in the bottom cover, frame and/or resonator plate of the filter.

Tuning element 1000 includes a coupling element 1010 and first and second arms 1020, 1030. First arm 1020 connects first side 1012 of coupling element 1010 to top cap 1060, while second arm 1030 connects second side 1014 of coupling element 1010 to top cap 1060. In the illustrated embodiment, coupling element 1010 comprises a generally annular sheet of metal having a hole 1016 therethrough. The first and second arms 1020, 1030 are each implemented as curved arms. The first end 1022 of the first arm 1020 is connected to the sidewall of the opening 1062, and the second end 1024 of the first arm 1020 is connected to the coupling element 1010. Similarly, a first end 1032 of second arm 1030 is connected to a sidewall of opening 1062, and a second end 1034 of second arm 1030 is connected to coupling element 1010. Second ends 1024, 1034 of the first and second arms 1020, 1030 are connected to opposite ends of the coupling element 1010. Further, each of the first and second arms 1020, 1030 is bent over more than one-third of the circumference of the circular coupling element 1010 such that the first and second ends 1022, 1032, 1024, 1034 of each arm 1020, 1030 are located approximately on opposite sides of the circular coupling element 1010. As explained in detail below, this design of the tuning element 1000 allows the tuning element 1000 to curl when moved along an axis extending through the center of the opening 1062, where the axis is perpendicular to the plane defined by the top cover 1060 of the filter housing.

The tuning element 1000 may be formed by cutting a generally arcuate portion from a metal sheet such as the top cover 1060. As shown in fig. 20 and 22, two arcuate cut-outs, each having a relatively constant diameter and each extending through approximately 330 degrees, may be formed, for example, by laser cutting or any other suitable cutting or punching technique. However, it will be appreciated that in other embodiments, the arcuate cut-out portions may have a non-constant diameter and/or may extend for different lengths. For example, if circular coupling element 1010 is replaced with an elliptical or rectangular coupling element, the arcuate cut-out portion will have a non-constant diameter. It should also be appreciated that in other embodiments more than two arms may be used, which would reduce the length of each arcuate cut-out. For example, in an alternative exemplary embodiment, three arms may be provided. It should also be understood that in all embodiments, the arms 1020, 1030 need not be curved.

The tuning elements 1000 shown in fig. 20-22 may be used to tune an associated filter as follows. A force may be applied to the circular coupling element 1010 in a direction generally perpendicular to a plane defined by a wall 1060 of the housing of the filter 1050, wherein the wall 1060 has the tuning element 1000 formed therein. This force may cause coupling element 1010 to displace downward into the internal cavity of the filter. Since the arms 1020, 1030 have a fixed length, as the coupling element 1010 moves downward, it curls such that the distal end 1024, 1034 of each arm 1020, 1030 curls in the direction of the base 1022, 1032 of the respective arm 1020, 1030. As a result, coupling element 1010 may move downward without significant axial movement (i.e., the center of coupling element 1010 may remain substantially vertically aligned with the center of opening 1062 of cover 1060). Further, as the coupling element 1010 moves downward, the coupling element 1010 may remain substantially parallel to the plane defined by the lid 1060. As a result, the coupling element 1010 may remain substantially parallel to a resonator plate or other structure disposed in the cavity below the tuning element 1000, and may thus exhibit enhanced capacitive coupling due to the parallel arrangement. This can be seen in fig. 21 and 22, which show several tuning elements 1010 after they are displaced within the cavity of the filter to tune the filter 1010.

In the event that coupling element 1010 is displaced too far downward during the tuning process (at which point the enhanced capacitive coupling will cease to help improve the performance of the filter and instead begin to degrade its performance), the short end of the L-shaped probe may be inserted within aperture 1016 of coupling element 1010 and an upward force may be applied to pull coupling element 1010 upward to reduce coupling. The filter 1050 may be tested with the coupling element 1010 in various positions to tune the filter 1050 until a minimum performance level is achieved or exceeded. Once the filter 1050 is tuned, a sticker can be placed over the opening 1062 to prevent debris from falling into the filter 1050.

Fig. 23A-23D are perspective and plan views of a conventional filter tuning element. Referring to fig. 23A, a top cover 1110 of a filter housing is shown to include a plurality of conventional tuning screws 1100 mounted therein. Cap 1110 has a plurality of holes 1112 extending therethrough (one tuning screw 1110 has been removed to reveal holes 1112). A threaded bushing 1114 may be welded to each bore 1112. The tuning screws 1100 are threaded through respective threaded bushings 1114 to extend into respective holes 1112. The tuning screw 1100 can be easily threaded further into and out of the threaded bushing 1114 and thus into and out of the cavity of the filter, thus facilitating very precise tuning of the filter. The tuning screw 1100 can be adjusted multiple times without performance degradation. Since the tuning screw 1100 is inserted within the threaded bushing, there is no opening to allow electromagnetic radiation to leak out. In addition, the tuning screw 1100 is capable of accepting auto-tuning. Auto-tuning refers to the process in which a device is used to displace a tuning element on a filter and measure the response of the filter during or after such displacement. The tuning screw 1100 can be easily adapted to auto-tuning because the automated equipment available to tighten and loosen the screw is readily available. Although not shown, in other embodiments, a thicker cap 1110 having a tapped hole formed therein may be used, and the threaded bushing 1114 may not be required.

However, the tuning screw 1100 and threaded bushing 1114 increase the material cost of the filter and the need to weld the bushing 1114 over the hole 112 increases the manufacturing cost. Furthermore, soldered connections are a potential source of PIM distortion. In an alternative embodiment where the holes 1112 and threaded bushings 1114 are replaced with threaded holes, a thicker cap 1110 may increase the weight and material cost of the filter, as well as the cost of the tuning screw 1100. The tuning screw 1100 also becomes a source of potential PIM distortion due to potential inconsistent metal-to-metal contact and/or because small metal shavings may be removed from the tuning screw 1100 or the threaded bushing 1114 (or tapped hole) as the tuning screw 1100 is threaded into the corresponding bushing 1114 and may fall into the filter. Tuning screw 1100 may also be susceptible to movement in response to vibrations that may adversely affect tuning. Thus, while the tuning screws 1100 may provide very precise tuning, they are expensive to implement and have potential performance drawbacks.

Referring to fig. 23B, the cover 1130 of the filter housing is shown to include a plurality of self-locking tuning screws mounted therein. Self-locking tuning screws are mounted in corresponding tapped holes 1132 in the cover 1130. The self-locking tuning screw may also provide very precise filter tuning and may be adjusted relatively many times without performance degradation. Self-locking tuning screws are very easy to auto-tune and do not include any openings that allow electromagnetic radiation to leak out. However, self-locking tuning screws have each of the drawbacks of the conventional tuning screw 1100 discussed above, namely, increased cost, the need for a thicker cover, and the source of PIM distortion that is possible with tuning screws due to metal chipping, loosening of the screw, and/or inconsistent metal-to-metal contact.

Fig. 23C is a plan view of a conventional single bend tuning stub 1140 formed in a top cover 1150 of a filter housing. As shown in fig. 23C, the single bend tuning stub 1140 includes a cantilevered finger having a bottom 1142 and a distal end 1144 opposite the bottom 1142, the bottom 1142 being attached to the top cap 1150. A hole 1146 may be formed in the distal end 1144 of the single bend tuning stub 1140. The single bend tuning stub 1140 may be simply formed by cutting a U-shaped region from the top cover 1150. The bottom 1142 of the single bend tuning stub 1140 may be narrower than the rest of the single bend tuning stub 1140 so that it is easier to bend the single bend tuning stub 1140. The single bend tuning stub 1140 may be mechanically very robust and its formation may be very simple and inexpensive.

To tune the filter, the single bend tuning stub 1140 may be bent downward such that the distal end 1144 of the tuning stub 1140 is received in a cavity of the filter. The single bend tuning stub 1140 tunes the filter by changing the amount of coupling between an element of the filter, here the top cover 1150, that includes the tuning stub 1140 and another element of the filter, such as a resonator plate. Since only the distal end of the single curved tuning stub 1140 is moved significantly closer to another element of the filter, the tuning effect of the single curved tuning stub 1140 may be very low because it cannot significantly increase the amount of capacitive coupling. As a result, a greater number of single-bend tuning stubs 1140 may be required, which increases manufacturing costs. Furthermore, since single-bend tuning stub 1140 is bent downward, a large opening appears in top cover 1150, which may allow electromagnetic radiation to escape. This effect may be exacerbated by the need for a relatively large number of single-turn tuning stubs 1140, meaning that a large number of such openings may occur when tuning stubs 1140 are adjusted to provide a significant increase in coupling. Further, whenever the single-bend tuning stub 1140 is used, microcracks may occur when the single-bend tuning stub 1140 is bent to affect tuning. Such microcracks may develop further, for example, if a particular single-bend tuning stub 1140 is bent multiple times. These microcracks may be a source of PIM distortion. Thus, while the single-bend tuning stub 1140 has the advantage of simplicity, the use of such a single-bend tuning stub 1140 may degrade the performance of the filter.

Fig. 23D is a plan view of a conventional double-bent tuning stub 1160 formed in the top cap 1170 of the filter housing. As shown in fig. 23D, double-bent tuning stub 1160 is similar to single-bent tuning stub 1140 in that tuning stub 1160 includes a bottom 1162 and a distal end 1164, and may be formed by cutting an opening having the shape shown in fig. 23D from a top cap 1170. However, double-bent tuning stub 1160 has a narrower finger 1168 (i.e., the portion between bottom 1162 and distal end 1164) and the distal end 1164 of double-bent tuning stub 1160 is widened. In the illustrated embodiment, the distal end 1164 has a rectangular shape, but any shape may be used. An aperture 1166 may be formed in the distal end 1164 of double-bent tuning stub 1160. The finger 1168 of the double-bent tuning stub 1160 may be bent at two locations, i.e., at the bottom 1162 and at the end of the finger 1168 (i.e., before the widened distal end 1164). A first bend in the tuning stub 1160 adjacent to the bottom 1162 may be used to change the distance between the distal end 1164 of the double-bent tuning stub 1160 and the underlying structure, and a second bend in the double-bent tuning stub 1160 adjacent to the distal end 1164 may be used to keep the widened distal end 1164 substantially parallel to the underlying structure, regardless of the extent of the first bend. This may increase the capacitive coupling between the double-bent tuning stub 1160 and the underlying structure compared to the single-bent tuning stub 1140 of fig. 23C.

Double-bent tuning stub 1160 has a simple shape and may provide significant tuning capabilities similar to tuning screws since double-bent tuning stub 1160 may produce significant capacitive coupling. However, the use of double-bend tuning stub 1160 is cumbersome because it requires multiple bends and it is mechanically less stiff and therefore easier to detune in response to vibration and the like. Double-bent tuning stub 1160 also leaves a relatively large opening due to the downward bending of double-bent tuning stub 1160, which allows electromagnetic radiation to leak out.

Referring again to fig. 22, the crimpable tuning element 1000 may present a number of significant advantages over the conventional tuning elements 1100, 1140, 1160 described above. For example, the crimpable tuning element 1000 may be much less expensive to implement than the tuning screw 1100 described above, because the crimpable tuning element 1000 does not require additional components and may be formed by simply cutting or punching a sheet of metal. The crimpable tuning element 1000 is less likely to act as a source of PIM distortion and may be implemented on thinner covers than some tuning screw embodiments. The crimpable tuning element 1000 may also have good mechanical rigidity and may exhibit comparable performance to tuning screws.

In contrast to tuning stubs 1140, 1160, the crimpable tuning element 1000 may exhibit only axial movement (i.e., movement along an axis perpendicular to a plane defined by a wall in which the tuning element 1000 is formed), which may simplify the tuning process. Furthermore, crimpable tuning element 1000 may exhibit a lower level of electromagnetic radiation leakage and provide a more pronounced tuning effect than bendable tuning stubs 1140, 1160. The use of crimpable tuning element 1000 may be simpler (i.e., easier to bend) and more suitable for auto-tuning since crimpable tuning element 1000 moves in only one direction. The substantially improved performance compared to single-bend and double- bend tuning stubs 1140, 1160 is illustrated in fig. 24A through 26C, which are cross-sectional and perspective views of various simulated performance parameters for these three different types of tuning elements.

In particular, turning first to fig. 24A-24C, a schematic diagram is provided of a single curved tuning stub 1200, a double curved tuning stub 1220 and a crimpable tuning element 1240 in accordance with an embodiment of the present invention used in the simulation. As shown in fig. 24A, the single-bend tuning stub 1200 includes a cantilevered finger 1202 (see fig. 25A) formed by making a U-shaped cut in the wall 1212 of the filter 1210. Cantilevered fingers 1202 curve downward into cavity 1214 of filter 1210 as seen in fig. 25A. Referring to fig. 24B and 25B, the double-bent tuning stub 1220 includes a cantilevered finger 1222 formed by making a U-shaped cut in the wall 1232 of the filter 1230. The cantilevered fingers 1222 may be longer than the cantilevered fingers 1202. The cantilevered fingers 1222 are bent downward into the cavity 1234 of the filter 1230 and another bend may be added near the distal ends 1224 of the cantilevered fingers 1222 so that the distal ends of the double-bent tuning stub 1220 extend substantially parallel to the plane defined by the walls 1232. Referring to fig. 24C and 25C, crimpable tuning element 1240 has the design of crimpable tuning element 1000 described above.

Fig. 25A-25C are cross-sectional views of the tuning elements of fig. 24A-24C, respectively, illustrating electric fields along the respective cross-sections. As shown in fig. 25, the single curved tuning stub 1200 is only capacitively coupled to the underlying resonator plate 1216 to a relatively small degree because only the distal end of the single curved tuning stub 1200 element is in close proximity to the resonator plate 1216. Double-bent tuning stub 1220 exhibits improved capacitive coupling. However, because the degree of axial alignment depends on how far down the double-bent tuning stub 1220 bends into the cavity 1234, the double-bent tuning screw 1220 may not be axially aligned with the opening 1238 in the cap 1232. In contrast, as shown in fig. 25C, the crimpable tuning element 1240 exhibits a high degree of axial alignment with the opening in the filter wall and a high degree of capacitive coupling.

Resonant cavity filterAnother measure of the performance of the tuning element of (a) is the amount of electromagnetic radiation that escapes through the tuning element structure. Fig. 26A-26C are perspective views of the electric field outside the filter housing and above the tuning element of fig. 24A-24C, respectively, showing this performance parameter. As shown in fig. 26A, single-bend tuning stub 1200 exhibited a substantial amount of leakage, with the electric field reaching a peak strength of 7.88x10⁶V/m. As shown in fig. 26B, double-bent tuning stub 1220 exhibited more leakage, and the electric field reached a peak strength of 1.24x10⁷V/m. As shown in fig. 26C, crimpable tuning element 1240 exhibits the least amount of leakage, with an electric field reaching a peak strength of 6.36x10⁶V/m. This leakage is only about half of the leakage of double-bent tuning stub 1220.

Fig. 27 is a graph comparing the resonant frequency tuning range of a crimpable tuning element according to an embodiment of the present invention with conventional tuning screws and with conventional single-bend and double-bend tuning stubs. The results in fig. 27 were obtained by simulation. As shown in fig. 27, the resonance frequency of the filter is tuned by an amount depending on the minimum distance between the tuning element concerned and the base resonator plate. In this example, the resonator plate is located 8.25mm below the top cover comprising the individual tuning elements. For the simulations, each tuning element was displaced downwards towards the resonator plate by a distance ranging from no displacement (corresponding to a horizontal axis value of 8.25 mm) to a distance of 7.75mm (corresponding to a horizontal axis value of 0.5 mm).

As can be seen from the graph of fig. 27, the double-bent tuning stub 1220 and the crimpable tuning element 1240 exhibit a maximum amount of tuning range, each capable of tuning the resonant frequency beyond 35 MHz. The resonant frequency tuning performance of both types of tuning elements is substantially the same, as shown in fig. 27, but as discussed above, the rollable tuning element 1240 has several advantages over the double-bent tuning stub 1220 in terms of ease of use, suitability for auto-tuning, electromagnetic radiation leakage performance, and PIM distortion performance. The tuning screw also provides a relatively large resonant frequency tuning range, but is still not as good as the crimpable tuning element 1240 and has a number of other disadvantages, as discussed above. The single bend tuning element 1200 provides only a limited resonant frequency tuning range (less than half the tuning range of the crimpable tuning element 1240) and has a number of other disadvantages as described above.

Figure 28 is a top view of a plurality of crimpable tuning elements 1300 for a filter according to a further embodiment of the present invention. As shown in fig. 28, each crimpable tuning element 1300 includes a coupling element 1310 and three arms 1320, 1330, 1340. Crimpable tuning element 1300 may be formed by cutting three substantially V-shaped cuts in a metal plate. Arms 1320, 1330, 1340 are formed between the legs of adjacent V-shaped cutouts. The coupling element 1310 may include a hole 1316 therein. In the illustrated embodiment, the coupling element 1310 has a generally triangular shape, although other shapes may be used. The crimpable tuning element 1300 operates in the same manner as crimpable tuning element 1000 described above, except that crimpable tuning element 1300 is supported by three arms instead of two arms.

The above-described tuning element according to an embodiment of the present invention may be formed by punching or cutting a metal sheet used to form a housing of the filter, and thus does not require any additional components. Furthermore, while the tuning elements described above are well suited for filters having sheet metal housings and/or covers, it will be appreciated that the tuning elements described herein may be used in other applications, including filters having housings/covers formed from materials other than sheet metal, and/or as internal tuning elements.

A crimpable tuning element according to embodiments of the present invention is much less expensive than a conventional tuning screw and will not produce metal shavings or chips or exhibit poor metal-to-metal contact (which, like filters using tuning screws, can produce passive intermodulation distortion). The crimpable tuning elements according to embodiments of the present invention are also advantageous over conventional bendable tuning stubs in that they are easier to move for tuning, exhibit low levels of electromagnetic radiation, are mechanically rigid and vibration resistant, have a high tuning range, and can be designed to provide tuning capacitance where it is just needed.

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 defined otherwise, 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 the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification 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 also 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.

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.

Claims (21)

1. A tuning element disposed in an opening of a metal plate of a filter, the tuning element comprising:

a coupling element;

a first arm having a first end connected to a metal plate and a second end connected to the coupling element; and

a second arm having a first end connected to the metal plate and a second end connected to the coupling element, wherein the coupling element is configured to rotate and remain parallel to a plane defined by the metal plate as the coupling element is displaced away from the plane defined by the metal plate.

2. The tuning element of claim 1, wherein the first arm is a curved arm and the coupling element comprises a flat piece of metal.

3. The tuning element of claim 1, wherein the width of the coupling element is greater than the width of the first arm.

4. The tuning element of claim 1, wherein a vertical axis perpendicular to a plane defined by the metal plate extends through a center of the opening, and the coupling element rotates about the vertical axis when the coupling element is displaced from the plane defined by the metal plate.

5. The tuning element of claim 1, wherein the metal plate is a top cover, a bottom cover, or a sidewall of a resonator cavity filter, or a resonator plate of a resonator cavity filter.

6. A tuning element, comprising:

a coupling element disposed in an opening in a wall of the filter housing; the coupling element is connected to the wall by respective first and second arms and is configured to rotate and remain parallel to a plane defined by the wall as the coupling element is displaced away from the plane defined by the wall.

7. The tuning element of claim 6, wherein the coupling element comprises a flat piece of metal.

8. A method of tuning a filter, the method comprising:

moving a coupling plate arranged in an opening of a wall of a filter in a direction perpendicular to a plane defined by the wall;

wherein the coupling plate is attached to the wall by a first arm and a second arm, the coupling plate rotating and remaining parallel to a plane defined by the wall when the coupling plate moves in a direction perpendicular to the plane defined by the wall.

9. The method of claim 8, wherein a vertical axis perpendicular to a plane defined by the wall extends through a center of the opening, and the coupling plate travels along the vertical axis as the coupling plate moves in a direction perpendicular to the plane defined by the wall.

10. A filter, comprising:

an outer housing comprising a metal sheet comprising at least a first and a second slot defining a tuning element within a surrounding portion of the metal sheet surrounding the tuning element, the tuning element comprising a coupling element, a first arm and a second arm,

wherein the tuning element and the surrounding portion of the metal sheet are a unitary structure;

wherein the coupling element is configured to rotate and remain parallel to a plane defined by the sheet metal as the coupling element is displaced away from the plane defined by the sheet metal.

11. A method of tuning a filter, the method comprising:

forming first and second slots in an outer wall of a housing for a filter, the first and second slots defining first and second arms and a coupling plate in the outer wall of the housing; and is

Moving the coupling plate in a direction perpendicular to a plane defined by the outer wall;

wherein as the coupling plate moves into the housing, the first and second arms move inward into the housing, and

wherein the coupling plate rotates and remains parallel to the plane defined by the outer wall when the coupling plate moves in a direction perpendicular to the plane defined by the outer wall.

12. A filter assembly comprising:

a housing having a top cover, a bottom cover, an interior ledge, and a frame having at least one sidewall, wherein the top cover, the bottom cover, and the at least one sidewall define an interior cavity, the interior ledge extending into the interior cavity from the at least one sidewall, wherein the housing is configured to receive a first radio frequency transmission line to a third radio frequency transmission line;

a top metal sheet mounted within said interior cavity on said interior ledge, the top metal sheet having a plurality of openings forming a first hole pattern;

a crimpable tuning element integral with said cap, said crimpable tuning element configured to rotate and remain parallel to a plane defined by said cap; and

a bottom metal sheet mounted within the interior cavity, the bottom metal sheet having a plurality of openings forming a second hole pattern,

wherein the top and bottom metal sheets are vertically spaced from one another in a vertically stacked relationship within the internal cavity, and

wherein the top metal sheet and the bottom metal sheet each comprise at least one resonator.

13. The filter assembly of claim 12, wherein the top and bottom metal sheets and the top and bottom covers define a set of mutually parallel planes, wherein the top metal sheet is secured to the top surface of the interior ledge via a first continuous weld and the bottom metal sheet is secured to the bottom surface of the interior ledge via a second continuous weld.

14. The filter assembly of claim 12, wherein the top metal sheet comprises a conductive layer of a printed circuit board, the conductive layer including the plurality of openings forming a first hole pattern.

15. A filter assembly comprising:

a housing having a top cover, a bottom cover, and at least one side wall, wherein the top cover, the bottom cover, and the at least one side wall define an interior cavity;

a plurality of resonators within the internal cavity; and

a crimpable tuning element integral with the cap, the crimpable tuning element configured to rotate and remain parallel to a plane defined by the cap.

16. The filter assembly of claim 15, wherein at least some of the resonators include narrow bases and wide distal ends.

17. The filter assembly of claim 16, wherein the resonators are integral with the frame and aligned with the plane.

18. The filter assembly of claim 17, wherein the bottom cover is integral with the frame.

19. The filter assembly of claim 15, wherein the top cover is welded to the frame by a continuous weld extending around a perimeter of the frame.

20. The filter assembly of claim 15, wherein the crimpable tuning element comprises a first arm, a second arm, and a coupling element, and the coupling element is configured to rotate as the coupling element is displaced into the internal cavity.

21. The filter assembly of claim 20, wherein the crimpable tuning element comprises a total of two or three arms.

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