Duplexer radio frequency assembly

Abstract

A duplexer includes a cavity resonator defining an opening covered by an RF plate. The RF plate defines an opening through which a pass-band tuning pipe extends and is secured thereto. A collar is attached to one end of the pipe, and at least one steel set screw extends into the interior of the collar, the at least one end having a soft (e.g., brass) tip. A tuning plunger is slidingly positioned within the pass-band tuning pipe. A rod is attached to a first end of the tuning plunger and extends through the collar, the rod being fabricated from a material harder than the tip of the at least one set screw. The at least one set screw is configured for tightening down on the rod to secure the rod and tuning plunger in place. A trimmer capacitor is positioned in the RF plate.

Claims

1. A radio frequency (RF) assembly configured for fitting over an opening defined in a cavity resonator of a duplexer, the RF assembly comprising: an RF plate; first and second RF connectors secured to the RF plate and configured for receiving first and second co-axial cables carrying RF signals; an RF junction bar connecting the first and second RF connectors; a trimmer capacitor positioned in the RF plate; a coupling loop coupling the RF junction bar to the trimmer capacitor positioned in the RF plate; a hole defined in the RF plate; a pass-band tuning pipe extending through the hole and secured to the RF plate, the pipe having a first end and a second end; a shaft-locking collar attached to the first end of the pipe, the collar defining an interior portion and at least one threaded hole for receiving at least one set screw having at least one end extending into the interior portion of the collar; a tuning plunger having a rod attached to one end of the tuning plunger, the plunger extending slidingly through the tuning pipe and collar, wherein the tip of the at least one set screw is fabricated from a material softer than the rod, the at least one set screw being configured for tightening on the rod to secure the rod and tuning plunger in place; and one or more fasteners for securing the RF plate over the opening of the cavity resonator.

2. The RF assembly of claim 1 wherein surfaces of the RF assembly in the interior of the cavity resonator are silver plated.

3. The RF assembly of claim 1 wherein the cavity resonator is manufactured from copper.

4. The RF assembly of claim 1 wherein the rod is manufactured from invar.

5. The RF assembly of claim 1 wherein the tip of the at least one set screw is fabricated from brass.

6. The RF assembly of claim 1 wherein the trimmer capacitor is a ceramic air variable capacitor.

7. The RF assembly of claim 1 wherein the trimmer capacitor is an air trimmer capacitor.

8. The RF assembly of claim 1 wherein the trimmer capacitor is a ceramic trimmer capacitor.

9. The RF assembly of claim 1 wherein the RF connectors are one of N-type connectors, BNC connectors, TNC connectors, and 4.3/10 connectors.

10. The RF assembly of claim 1 wherein the fasteners are screws.

11. The RF assembly of claim 1 further comprising a gasket interposed between the RF plate and the duplexer, wherein the gasket comprises a conductive elastomer.

12. A pass-band tuning plunger assembly configured for fitting in a duplexer pass-band tuning pipe, the assembly comprising: a shaft-locking collar attached to one end of the pipe, the collar defining an interior portion and at least one threaded hole for receiving at least one set screw having at least one end extending into the interior portion of the collar; a tuning plunger having a rod attached to one end of the tuning plunger, the plunger extending slidingly through the tuning pipe and collar, wherein the tip of the at least one set screw is fabricated from a material softer than the rod, the at least one set screw being configured for tightening on the rod to secure the rod and tuning plunger in place.

13. The assembly of claim 12 wherein the rod is manufactured from invar.

14. The assembly of claim 12 wherein the tip of the at least one set screw is fabricated from brass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 exemplifies a perspective view of a duplexer embodying features of the invention;

(3) FIG. 2 exemplifies an opening in the duplexer of FIG. 1;

(4) FIG. 3 exemplifies details of an RF assembly configured to fit in the opening of the duplexer of FIG. 2;

(5) FIG. 4 is a cross-section taken along the line 4-4 of FIG. 3;

(6) FIG. 5 is a cross-section taken along the line 5-5 of FIG. 4;

(7) FIG. 6 exemplifies a tuning plunger and rod positioned within a cavity resonator with one wall removed;

(8) FIGS. 7-8 exemplify an assembly of the tuning plunger, rod and shaft locking collar of the duplexer of FIGS. 1-4;

(9) FIG. 9 exemplifies a gasket configured for placement between the RF plate and duplexer;

(10) FIG. 10 exemplifies a perspective view of a set screw for engaging the plunger rod and securing the plunger in place;

(11) FIG. 11 is a side view of the set screw of FIG. 10; and

(12) FIG. 12 is an end view of the set screw of FIG. 11 taken along the line 12-12 of FIG. 11.

DETAILED DESCRIPTION

(13) In the discussion of the FIGURES, the same reference numerals will be used throughout to refer to the same or similar components. In the interest of conciseness, various other components known to the art have not been shown or discussed. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. Additionally, as used herein, the term substantially is to be construed as a term of approximation.

(14) Referring to FIG. 1 of the drawings, the reference numeral 100 generally designates a duplexer embodying features of the present invention. The duplexer 100 preferably includes a number of resonator cavities (also referred to herein simply as cavities) exemplified as six cavities 104a, 104b, 104c, 104d, 104e, and 104f and referred to herein collectively as cavities 104. Co-axial cable 108 carries transmit signals to, and receive signals from, an antenna (not shown). The transmit signals are carried by co-axial cable 110 and the receive signals are carried by co-axial cable 112. The duplexer 100 includes a plunger/rod assembly 118 for each cavity, and an end plate 102. Duplexers are considered to be well-known and so will not be described in further detail herein except insofar as necessary to describe the invention.

(15) Referring to FIG. 2 of the drawings, there is generally exemplified a duplexer showing cavities 104a and 104b. Cavity 104a is open to show an opening 130, and cavity 104b is covered with a radio frequency (RF) assembly 160 having an RF plate 162. Fasteners 126, such as screws, received by threaded holes 125, secure RF plate 162, and hence RF assembly 160, to duplexer 100. RF plate 162 includes first and second RF connectors 120 and 122, respectively, secured to the RF plate and configured for receiving respective first and second co-axial cables (not shown) carrying respective transmit and receive RF signals. A gasket 170 (described in further detail below) is preferably interposed between RF plate 162 and duplexer 100.

(16) As depicted more clearly in FIGS. 3 and 6, an RF junction bar 132 connects first and second RF connectors 120 and 122, and a coupling loop 128 couples RF junction bar 132 to a trimmer capacitor 124 positioned in RF plate 162. Trimmer capacitor 124 is preferably a Knowles-Johanson or similar type trimmer capacitor, and is preferably an air trimmer capacitor or a ceramic trimmer capacitor.

(17) A hole, not shown, but circumscribed preferably by solder 164, is defined in RF plate 162, and a pass-band tuning pipe 146 extends through the hole and is preferably secured to RF plate 162 by means of solder 164 or the like. Tuning pipe 146 includes fingers 148 to guide tuning plunger 144 (described below) as the plunger is slid linearly through the pipe. With reference also to FIG. 4, shaft-locking collar 150 is attached to an end of pipe 146 that is outside of a respective cavity, such as cavities 104a and 104b. At least one threaded hole is formed in collar 150 for receiving at least one set screw 152 having at least one end extending into the interior portion of the collar. With reference to FIGS. 4 and 5, in a preferred embodiment, two threaded holes are formed in collar 150 for receiving two set screws 152 spaced apart by 90? and having two ends extending into the interior portion of collar 150. As shown most clearly in FIGS. 10-12, set screw 152 includes a threaded portion 182 and a tip portion 184. Threaded portion 182 is preferably fabricated from a relatively hard material such as 18-8 stainless steel, and tip portion 184 is preferably fabricated from a softer material such as brass or the like. An end 186 of set screw 152, opposite tip portion 184, includes means for engaging a tool, such as an Allen key/wrench or the like, so set screw 152 may be tightened or loosened as described in further detail below. Referring back to FIGS. 4 and 5, pipe 146 preferably also defines at least one hole and collar 150 also defines at least one corresponding hole for receiving at least one screw 154 for securing collar 150 to tuning pipe 146. In a preferred embodiment, pipe 146 defines three holes spaced apart by 120? and collar 150 also defines three corresponding threaded holes for receiving three screws 154 for securing collar 150 to tuning pipe 146.

(18) With reference to FIGS. 3, 4, and 6-8, tuning plunger 144 has a tuning rod 142 attached to one end of the plunger, and the plunger extends slidingly through the tuning pipe 146 and collar 150. Alternatively, as shown in FIG. 8, collar 150 may be positioned on rod 142 prior to insertion in pipe 146. As discussed above, the tip 184 of the at least one set screw 152 is fabricated from a material, such as brass, that is softer than the rod, so that the at least one set screw can be urged against the rod and secure the rod and tuning plunger in place with respect to a cavity, such as cavities 104a and 104b. Trimmer capacitor 124 is positioned in RF plate 162 to facilitate coupling to the coupling loop 128, discussed above. One or more fasteners, such as screws, rivets, or the like, secure RF plate 162 over opening 130 of the cavity resonator 104. Tuning rod 142 preferably includes a knob 140 secured at one end of the rod with a fastener, such as screw 141, to facilitate sliding tuning plunger 144 linearly in tuning pipe 146.

(19) In one preferred embodiment, duplexer 100 comprises a body formed of a metallic material, the body comprising two or more compartments or cavities 104, commonly six cavities. RF connectors (preferably N-type connectors) and coax cables act as a waveguide to carry transmit and receive signals to and from each of the cavities.

(20) The thermal stability of duplexer 100 is preferably enhanced by using thicker metallic walls for the body, which not only promotes thermal stability, but also provides mechanical rigidity as well, the latter being important because tuning a duplexer can be affected by deformities in the body or housing.

(21) Regarding mechanical functionality, RF connectors 120 and 122 are provided for each cavity 104, each of which cavities must be tuned. The RF connectors, though, are too close together, making repair and other manipulations of the device for tuning purposes difficult and time-consuming. Thus, increasing the space between the RF connectors is paramount to a useful design, while also allowing for the use of torque wrenches and similar tools on the RF connectors.

(22) There are several elements that may influence and improve the tuning of the duplexer. First, a tightly fit and well-machined pass-band tuning plunger, such as designated by reference numeral 144, is important to easy and accurate tuning. Additionally, a trimmer capacitor, such as designated by reference numeral 124, is a key element to the duplexer tuning process. A resonance circuit in each cavity must be tuned, and thus, optimizing the capacitor for the tuning function results in improved performance of the duplexer. In this instance, use of an air (or alternatively, ceramic) trimmer capacitor (e.g., by Knowles-Johanson) results in vastly improved tuning when compared to the original 526 series of duplexer design. Second, the ability to lock a tuning rod, such as designated by reference numeral 142, into place once the device or the individual cavities in the device are tuned can be enhanced by using multiple set screws, such as designated by reference numeral 152, with tips made from brass, a metal alloy, or similar soft metal that is softer than the rod 142 material that the screws tightly engage, so as not to mark up or scratch the tuning rod and deform it such that it will not fit into a retainer disk, also known as a shaft-locking collar, such as designated by reference numeral 150, that serves to secure the tuning plunger in place.

(23) Further, surfaces of RF assembly 160 in the interior of cavity resonator 104 are plated with a conductive material, preferably silver. Cavity resonator 104 is preferably manufactured from copper. Tuning rod 142 is preferably manufactured from Invar?. Tip 184 of the at least one set screw 152 is preferably fabricated from a relatively soft material, such as brass. Trimmer capacitor 124 is preferably a Knowles-Johanson trimmer capacitor. Trimmer capacitor 124 is preferably one of an air trimmer capacitor or a ceramic trimmer capacitor. RF connectors 120, 122 are preferably one of N-type connectors, BNC connectors, TNC connectors, and 4.3/10 connectors.

(24) In operation, duplexer housing 100 would first need to have a hole and bolt pattern that matches the footprint of RF plate 162. If not there, then such hole and bolt pattern would need to be cut. Then duplexer 100 is preferably connected to a spectrum analyzer/tracking generator (not shown), or more typically to a vector network analyzer (not shown), and tuning plunger 144 is raised and lowered until the insertion loss at the pass-band is minimized, and the return loss at the same pass-band is also maximized. Once the pass-band is adjusted, tuning plunger 144 is secured in place using set screws 152 on collar 150 that engage rod 142 on tuning plunger 144. Trimmer capacitor 124 is then adjusted such that the insertion loss at the reject-band is maximized and the return loss at the reject-band is minimized.

(25) By implementing the key elements of duplexer 100 into RF assembly 160, thermal stability and resistance to vibration and deformation is improved. Tuning plunger 144 may be re-used many times. Moreover, the key elements of duplexer 100 which are subject to wear and damage can be easily removed, replaced, and serviced by the end user. The RF assembly concept further promotes periodic visual inspections of interior components. For example, duplexers that are struck by lightning may be quickly disassembled and visually inspected without the need of borescopes and special tools. Damaged capacitors, RF connectors, or elements which have become dirty and less conductive may easily be cleaned. Because tuning plunger 144 may be adjusted by being slid linearly in tuning pipe 146, i.e., without being rotated, it avoids being scratched from fingers 148, resulting in diminished performance.

(26) It will be readily apparent to those skilled in the art that the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. For example, pass-band tuning plunger 144 and tuning rod 142 in combination with locking collar 150 having at least one set screw 152 with a soft tip (i.e., softer than the rod, as discussed above) may be readily used in a model 526 duplexer without any modification to the duplexer. The plunger may then extend slidingly through the tuning pipe. Then the pass-band tuning plunger can slide up and down without getting scratched by brushes/contact fingers.

(27) In another example, with respect to FIG. 9, a gasket 170 is preferably provided having a shape, including cut-out 172 and holes 174, that mimics the shape of RF plate 162, including opening 130 and holes 125, respectively. As shown in FIG. 2, gasket 170 is seated between the flat surfaces of RF plate 162 and duplexer 100. Gasket 170 preferably comprises an elastomeric material, such as rubber, a rubber mix, or neoprene type material with sharp pieces of metal mixed therein. The sharp pieces of metal preferably contact the metal of RF plate 162 and facilitate conductivity between RF plate 162 and duplexer 100. Alternatively, gasket 170 may be fabricated from a conductive elastomer, such as conductive rubber, neoprene, or the like, such as manufactured by Da/Pro Rubber, Inc. The elastomeric material will be spread out and inhibit entry into the duplexer cavities of air and other gases that can corrode and tarnish the duplexer and ultimately diminish the functionality and conductivity of duplexers over time. This is important because duplexer sites have doors that are opened and closed and air otherwise gets in which will, over time, corrode the metal in the duplexer. In addition, duplexer sites typically have batteries in them, or coupled to them, and those batteries emit corrosive gases that will also cause tarnishing and corrosion of duplexers, potentially destroying the electrical contacts on the duplexers and diminishing their functionality. Gasket 170 reduces the leakage of RF energy from between duplexer cavity 104. The gasket also makes the unit more serviceable and reduces the need for the cavity housing to be perfectly flat.

(28) In a still further example, RF assembly 160 could also be modified into different shapes for other cavity designs. For example, some cavities are round. The RF assembly could then be made round rather than rectangular to match such a configuration.

(29) Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.