Patent Description:
The present invention is directed to cellular communication systems and, more particularly, to a low-PIM stackable cable hanger used to reduce passive intermodulation interference (PIM) at cellular telephone base station antenna sites.

<CIT> is a document that discusses a clip for a snap-in cable hanger with a top from which at least two clip arm(s) extend and at least one of the clip arm(s) formed with a clip tab projecting proximate a distal end. <CIT> is a document that discusses an attachment device for one or a plurality of lines includes a reinforcement part and a synthetic layer which at least partially surrounds the reinforcement part. A respective retainer is provided for each line. The reinforcement part has a C-shaped section, as seen in cross-section, for each retainer. <CIT> is a document that discusses an adapter and hanger mounts an associated article to an associated anchor rail. The anchor rail is formed as a U-shaped channel having a pair of upstanding, opposing legs, each leg having an inwardly extending wall and terminating in a downwardly oriented lip. An essential element of modern mobile communications systems is the cellular telephone base station, also known as a "cell site. " The cell site includes one or more directional base station antennas aimed at a desired geographical area of coverage with coaxial cables connecting the antennas to base station radio equipment. The performance of a cell site is often limited by passive intermodulation (PIM) interference. PIM interference occurs when the high-power downlink signals transmitted by the base station antennas mix at passive, non-linear junctions in the RF path, creating new signals known as intermodulation products. When these intermodulation products fall in an operator's uplink band, they act as interference and reduce the SINR (signal to interference plus noise ratio). As the SINR is reduced, the geographic coverage and data capacity of the cell site is reduced.

It is well documented that loosely touching metal-to-metal surfaces can behave in a non-linear fashion and become sources of PIM interference when illuminated by high power RF (radio frequency) signals. Recently, it has been determined that loose metal-to-metal connections located behind base station antennas are also able to generate high levels of PIM interference. Even though this region is well outside the main beam of the antenna, enough RF energy is present in this region to excite non-linear objects and generate PIM interference. Based on field measurements it has been determined that loose metal-to-metal contacts located very close to base station antennas (within <NUM> wavelength of the carrier frequency) are more likely to generate high levels of PIM interference than loose metal-to-metal contacts located farther away (greater than <NUM> wavelength) from base station antennas.

A common source of loose metal-to-metal contact found in the region close to the base station antenna is metal brackets and associated hardware for supporting coaxial cables. Coaxial cables, typically <NUM>/<NUM>-inch in diameter, are used to transfer RF signals between tower mounted radio equipment and the base station antenna. These cables need to be mechanically supported periodically along their length to prevent movement of the cable in the wind. The metal antenna mounting pipe close to the back of the base station antenna provides a convenient rigid surface to mechanically secure these coaxial cables. At operating frequencies at or below <NUM>, this mounting pipe is typically located within <NUM> wavelength of the antenna within the zone of high PIM concern.

Two different methods for mechanically supporting coaxial cables are commonly found at cell sites. The first utilizes two plastic clamp blocks that fit around one or more coaxial cables. An example of this style cable support block is disclosed in <CIT>. A <NUM>/<NUM>-inch or <NUM> diameter stainless steel threaded fastener is inserted into the support block pairs and stainless-steel hardware is installed to clamp the plastic block halves together on the threaded fastener. A steel interface bracket is often attached to one end of the threaded fastener using nuts and lock washers. The interface bracket is then secured to the antenna mounting pipe or other nearby metal members using a stainless-steel hose clamp. The hose clamp provides a convenient method for securing interface brackets to metal members since the hose clamp conforms easily to different shapes and is adjustable in length allowing it to fit around a wide variety of metal member sizes.

Another common system used for mechanically supporting coaxial cables uses metal "snap-in" style cable support hangers. The snap-in cable support hangers are made from thin "U" or "C" shaped stainless-steel members designed to wrap around individual coaxial cables. The hangers include locking features able to insert into round holes in supporting interface brackets. Once inserted, the locking features on the hanger expand outward to secure the cable to the interface bracket. A variation of this style cable hanger design includes a hole on one end of the hanger to accept an additional cable hanger. This enables multiple coaxial cables to be secured to a single interface bracket by stacking one hanger on top of another. Examples of this style cable hanger are disclosed in <CIT> and <CIT>.

A problem with these conventional designs is that PIM can be generated at the metal-to-metal contacting surfaces between stacked metal snap-in style cable hangers and at the metal-to-metal contacting surface between the interface bracket and the snap-in hanger. Manufacturers such as Commscope have introduced plastic versions of their stackable snap-in style cable support hangers that eliminate the metal-to-metal contacting surfaces that generate PIM. These all-plastic snap-in cable hangers, however, introduce new problems. First, the all-plastic snap-in hangers are not as strong as the all-metal snap-in hangers. This limits the number of cables that can be reliably stacked on top of each other for a given support spacing. The all-plastic snap-in hangers are also prone to breaking, for example during installation when the plastic locking features are over-stressed due to misalignment.

A second problem with all-plastic snap-in hangers is that the plastic material used to produce these hangers is not able to bite into the cable jacket as effectively as all-metal snap-in hangers. This reduces the all-plastic hanger's ability to prevent longitudinal movement of the cable due to wind forces or due to gravity when the cable is oriented vertically.

A third problem with the existing all-plastic snap-in hangers is that they are not able to rotate freely at the hanger-to-hanger interface. Due to geometry constraints, the all-plastic hangers are only able to connect to one another in a fixed orientation. This requires all supported cables to be parallel to each other at the point of support. Cables that are not perfectly parallel stress the plastic supports, leading to breakage. Mechanical stress is also imposed on the RF cable, leading to cable deformation and reduced RF performance.

An improved low PIM snap-in style cable hanger is therefore needed to overcome the limitations of the existing alternatives.

An embodiment of the present invention is a low-PIM, stackable cable hanger, comprising: a metallic cable block comprising a receptacle side defining a receptacle hole for stacking the cable block to an adjacent cable block, cable clasps for supporting a cable positioned to extend through the cable block, a pair of metal sides, each metal side positioned to extend away from the receptacle side and comprising a cable clasp for supporting a cable positioned to extend through the cable block; a pair of polymeric sides, each positioned adjacent to a corresponding one of the metal sides of the cable block; a pair of polymeric snap-in legs for fitting into an adjacent receptacle hole. The present invention meets the needs described above through a low-PIM stackable cable hanger used to reduce PIM (passive intermodulation) interference at cellular telephone base station antenna sites. The cable hanger includes a hybrid metal-and-polymeric construction including a metal cable block carrying a polymeric sleeve. The metal cable block forms the cable mounting section, while the polymeric sleeve insulates the metal sides of the cable block and provides non-metallic (low-PIM) snap-in legs for attaching the cable hanger to mounting structures and stacking the cable hangers together. The metal cable block supports the cable more securely than a polymeric mounting section, while the polymeric sleeve avoids loose metal-to-metal connections when the cable hangers are attached to metal mounting structures or stacked together. The metal cable block includes metal sides that form metal cable clasps, while the sleeve includes polymeric sides that cover the metal sides of the cable block to prevent metal-to-metal contact on the sides of the cable block.

It will be understood that specific embodiments may include a variety of features in different combinations, as desired by different users. The specific techniques and systems for implementing particular embodiments of the invention and accomplishing the associated advantages will become apparent from the following detailed description of the embodiments and the appended drawings and claims.

The numerous advantages of the embodiments of the invention may be better understood with reference to the accompanying figures.

Embodiments of the invention include a stackable, low-PIM cable hanger, and arrays of these cable hangers, used to reduce passive intermodulation interference at cellular telephone base station antenna sites. These embodiments may be utilized in concert with other techniques to reduce PIM at cellular base stations, such as the low-PIM cable bracket described in commonly owned <CIT>.

An illustrative embodiment of the stackable, low-PIM cable hanger includes a hybrid metal-and-polymeric construction including a metal cable block carrying a polymeric sleeve. The metal cable block forms the cable mounting section, while the polymeric sleeve insulates the metal sides of the cable block and provides non-metallic (low-PIM) snap-in legs for attaching the cable hanger to mounting structures and stacking the cable hangers together. The metal cable block supports the cable more securely than a polymeric mounting section, while the polymeric sleeve avoids loose metal-to-metal connections when the cable hangers are attached to metal mounting structures or stacked together.

The metal cable block includes a receptacle side with a receptacle flange defining a receptacle hole. The receptacle side is referred to as the "top" side as a matter of descriptive convenience, although it will be appreciated that the receptacle can be placed in any orientation. Additional opposing sides of the cable block extending away from the receptacle side have portions that are punched-out on three sides forming a pair of opposing cable clasps that extend into the cable block to securely grasp a cable passing through the cable block. The cable block also includes a pair of metal block clips that help to secure the cable block to the polymeric sleeve. The metal cable block may be stainless steel, as used in conventional stackable cable hangers, or any other suitable material. The geometry of the cable block is very similar to existing all-metal designs where metal barbs on one hanger engage with a hole on the top of the next hanger. The barbs prevent the hangers from separating from each other but do not prevent rotation between hangers. This allows cables at different angles to be attached without generating high stress on the cable or the mating hangers.

The polymeric sleeve includes polymeric sides that cover associated metal sides of the cable block. This prevents the metal sides of adjacent cable blocks from rubbing or banging into each other, for example in the wind, which could generate PIM. The polymeric sleeve also includes a pair of polymeric sleeve clips that, along with the metal block clips, secure the cable block to the polymeric sleeve. The polymeric sleeve also includes a pair of snap-in legs with barb heads that are configured to snap into the receptacle hole of an adjacent cable block. The snap-in legs are deflected toward each other as they are pressed into a receptacle hole, such as a receptacle hole on a mounting surface or another cable hanger. The snap-in legs then spring away from each after the barb heads clear the receptacle flange to capture the snap-in legs in the receptacle hole. The polymeric sleeve may be made from a UV stable plastic material, such as glass-filled Nylon.

It should be noted that the metal cable block includes a metal receptacle flange that forms a component of the locking system used to stack the hangers together. This locking system is stronger than the locking system of comparably sized all-plastic hangers, while the polymeric snap-in legs of the adjacent cable hanger avoid metal-to-metal contact in the locking section to eliminate PIM. This allows the metal cable block to support the mechanical loads acting on the hanger by wind or gravity, while the mechanical stress level on the polymeric snap-in legs remains relatively low due to large surface areas of polymeric barb heads. A variety of techniques can be used to attach the metal cable block to the polymeric sleeve. The illustrative embodiment uses a pair of metal block clips and a pair of opposing sleeve clips. Other approaches may be used, such as molding the polymeric material in the locking section around metal legs of the cable block, or mechanically attaching the polymeric sleeve to the metal cable block using a heat staking or adhesive bonding process.

<FIG> and <FIG> show perspective views of the stackable, low-PIM hanger <NUM>. This hybrid metal-and-polymeric cable hanger includes a metal cable block <NUM> attached to a polymeric sleeve <NUM>. The metal cable block <NUM> forms the cable mounting section, while the polymeric sleeve <NUM> insulates the metal sides of the cable block and provides non-metallic (low-PIM) snap-in legs for attaching the cable hanger to mounting structures and stacking the cable hangers together. The metal cable block <NUM> supports the cable more securely than a polymeric mounting section, while the polymeric sleeve <NUM> avoids loose metal-to-metal connections when the cable hangers are attached to metal mounting structures or stacked together.

The metal cable block <NUM> includes a receptacle side <NUM> (shown as the top side in <FIG> and <FIG>) with a receptacle flange <NUM> defining a receptacle hole at the top of block. Additional opposing sides <NUM>, <NUM> of the cable block <NUM> have portions that are punched-out on three sides forming a pair of opposing cable clasps <NUM>, <NUM> that extend into the cable block <NUM> to securely grasp a cable passing through the cable block. The cable block <NUM> also includes a pair of metal block clips <NUM>, <NUM> that help to secure the cable block to the polymeric sleeve <NUM>. The metal cable block <NUM> may be stainless steel, as used in conventional stackable cable hangers, or any other suitable material. The geometry of the cable block <NUM> is very similar to existing all-metal designs where metal barbs on one hanger engage with a hole on the top of the next hanger. The barbs prevent the hangers from separating from each other but do not prevent rotation between hangers. This allows cables at different angles to be attached without generating high stress on the cable or the mating hangers.

The polymeric sleeve <NUM> includes polymeric sides <NUM>, <NUM> that cover the metal sides <NUM>, <NUM>, respectively, of the cable block <NUM>. This prevents the metal sides of adjacent cable blocks from rubbing or banging into each other, for example in the wind, which could generate PIM. The polymeric sleeve <NUM> also includes a pair of polymeric sleeve clips <NUM>, <NUM> that that help to secure the cable block <NUM> to the polymeric sleeve <NUM>. The polymeric sleeve <NUM> also includes a pair of snap-in legs <NUM>, <NUM> with barb heads <NUM>, <NUM>, respectively, that are configured to snap into the receptacle hole of an adjacent cable block. The snap-in legs <NUM>, <NUM> are deflected toward each other as they are pressed into a receptacle hole, such as a receptacle hole on a mounting surface or another cable hanger. The snap-in legs then spring away from each after the barb heads clear the receptacle flange to capture the snap-in legs in the receptacle hole. The polymeric sleeve <NUM> may be made from a UV stable plastic material, such as glass-filled Nylon.

<FIG> is a perspective view of a stacked pair <NUM> of the stackable, low-PIM cable hangers 10a, 10b. The snap-in legs of the upper cable hanger 10a extend through the receptacle hole of the lower cable hanger 10b, with the barb heads 27a, 28a of the upper cable hanger 10a captured by the receptacle flange 14b of the lower cable hanger 10b. The barb heads 27a, 28a of the upper cable hanger 10a slide with respect to the flange receptacle flange 14b of the lower cable hanger 10b allowing the upper cable hanger 10a to rotate with respect to the lower cable hanger 10b. This arrangement keeps the cable hangers 10a, 10b attached to each other, while allowing them to rotate with respect to each other to accommodate different cable support directions. The locking system allows two or more cable hangers to be attached to each other into an array cable hangers. In addition to allowing attachment to each other, the cable hangers may also be attached to other structures, such as mounting plates, in the same manner.

<FIG> is a perspective view of a portion <NUM> of a cellular base station antenna site using a lateral array <NUM> of the stackable, low-PIM cable hangers 10a-10d. In this embodiment, cable hanger 10a supports an associated cable 42a, the cable hanger 10b supports an associated cable 42b, the cable hanger 10c supports an associated cable 42c, and the cable hanger 10d supports an associated cable 42d. Each cable hanger 10a-10d is supported by a common mounting plate <NUM> which, in turn, is connected to an upright support pole <NUM>. In this particular example, the mounting plate <NUM> is connected to the support pole <NUM> using a low-PIM cable bracket <NUM> described in commonly owned <CIT>.

Other arrangements may be used to connect the mounting plate to a support pole or other structure. To provide an additional example, <FIG> is a perspective view of another portion <NUM> of a cellular base station antenna site using a similar lateral array <NUM> of the stackable, low-PIM cable hangers 10a-10d. The cable hanger 10a supports an associated cable 52a, the cable hanger 10b supports an associated cable 52b, the cable hanger 10c supports an associated cable 52c, and the cable hanger 10d supports an associated cable 52d. Each cable hanger 10a-10d is supported by a common mounting plate <NUM> which, in turn, is connected to a lateral support bar <NUM>. In this particular example, the mounting plate <NUM> is connected to the support bar <NUM> using a hanger <NUM> that supports the mounting plate under the lateral support bar <NUM>.

<FIG> is a perspective view of a portion <NUM> of a cellular base station antenna site using multiple stacked arrays <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> of the stackable low-PIM cable hangers. Only one stacked array <NUM>-<NUM> is labeled with element numbers to avoid cluttering the figure. The stacked arrays <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> are similar to the labeled stacked array <NUM>-<NUM>. In addition, the arrangement shown in <FIG> is similar to the arrangement shown in <FIG>, except that each cable hanger 10a, 10b, 10C and 10d shown in <FIG> has, in <FIG>, been replaced with a stacked array of cable hangers <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>, respectively. In this particular example, the mounting plate <NUM> directly supports the cable hanger 10a-<NUM>, which supports cable hanger 10a-<NUM> (i.e., the snap-in legs of the cable hanger 10a-<NUM> are snapped into the receptacle hole of cable hanger 10a-<NUM>), which supports cable hanger 10a-<NUM> (i.e., the snap-in legs of the cable hanger 10a-<NUM> are snapped into the receptacle hole of cable hanger 10a-<NUM>). The mounting plate <NUM>, which is connected to the support pole <NUM> using the low-PIM cable bracket <NUM>, thus supports twelve low-PIM, stackable cable hangers. In this configuration, the stacked arrays <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> are positioned close enough to each other to raise the possibility that the outer sides of a cable block may make contact with a cable block of an adjacent stacked array. The polymeric sleeve sides cover and thus prevent the metal sides of the cable blocks from contacting each other to avoid metal-to-metal contact and the resulting PIM generation.

<FIG> is a perspective view of a first alternative stackable low-PIM cable hanger <NUM> not according to the claimed invention. This alternative is similar to the previously described cable hanger <NUM> except that the polymeric sleeve <NUM> has been replaced by polymeric feet 71a-b molded over or adhered to the feet or bases of the cable block <NUM>. The polymeric feet 71a-b include lateral plates 71a-b for separating adjacent cable blocks from each other (or from another support surface) and orthogonal legs 72a-b for attaching one cable block to an adjacent cable block (or another support surface). <FIG> also shows the flange <NUM> defining the receptacle hole of the cable block <NUM> and the cable clasps <NUM>, <NUM>.

<FIG> is a front view and <FIG> is a side view of two of the first alternative stackable low-PIM cable hangers 70a-b stacked together. The orthogonal legs 72a-b of the upper cable hanger 70a are received within the receptacle hole of the lower cable hanger 70b with their barbs captured against the flange 14b of the lower cable hanger. The plates 72a-b of the upper cable hanger 70a are disposed between the metal cable blocks 11a-b of the upper and lower cable hangers 70a-b to prevent lose metal-to-metal contact between the cable blocks.

Claim 1:
A low passive intermodulation, PIM, stackable cable hanger (<NUM>), comprising:
a metallic cable block (<NUM>) comprising a receptacle side (<NUM>) defining a receptacle hole for stacking the cable block to an adjacent cable block, cable clasps (<NUM>, <NUM>) for supporting a cable (52a) positioned to extend through the cable block, a pair of opposing metal sides (<NUM>, <NUM>), each metal side extending away from the receptacle side;
a pair of opposing polymeric sides (<NUM>, <NUM>), each covering a corresponding one of the metal sides (<NUM>, <NUM>) of the cable block;
a pair of polymeric snap-in legs (<NUM>, <NUM>) for fitting into an adjacent receptacle hole.