Patent Grant
11870134
The present invention generally relates to radio communications and, more particularly, to base station antennas for cellular communications systems.
Cellular communications systems are well known in the art. In a cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells.” Each cell may be served by a respective base station. Each base station may include one or more base station antennas that are configured to provide two-way radio frequency (“RF”) communications with fixed and mobile subscribers (or “users”) that are located within the cell served by the base station. In many cases, a base station may be divided into “sectors.” For example, in one common configuration, a hexagonally shaped cell is divided into three 120° sectors in the azimuth plane (i.e., the plane defined by the horizon) and each sector is served by one or more base station antennas to provide full 360° coverage in the azimuth plane.
Each base station antenna may include one or more vertically-oriented linear arrays of radiating elements. Each linear array of radiating elements may generate a radiation pattern (also referred to herein as an “antenna beam”) that is directed outwardly in the general direction of the horizon. In some cases two or more of the vertically-oriented linear arrays of radiating elements may be designed to work together to generate a single (narrower) antenna beam. Multiple linear arrays of radiating elements may be provided on a base station antenna to, for example, provide cellular service in multiple frequency bands and/or to reduce the azimuth beamwidth of the antenna beam. The number of radiating elements in each linear array is typically based on a desired beamwidth in the elevation plane, where the elevation beamwidth refers to the angular extent of the antenna beam along an axis that is perpendicular to the azimuth plane.
The radiating elements of each linear array are most typically implemented as dipole radiating elements, although other types of radiating elements such as patch radiating elements are sometimes used. Most base station antennas now use radiating elements that employ cross-dipole radiators that have first and second dipoles that are arranged to transmit/receive RF signals at orthogonal polarizations. The slant −45°/+45° cross-dipole radiator approach is most typically used, where one of the dipoles transmits and receives at a first linear polarization that is arranged at an angle of −45° with respect to the longitudinal axis of the linear array, while the other one of the dipoles transmits and receives at a second linear polarization that is arranged at an angle of +45° with respect to the longitudinal axis of the linear array. Both dipoles are typically mounted in front of and parallel to a ground plane such as metal reflector that is coupled to electrical ground. Typically, the dipoles are mounted at a distance of about 0.16κ to 0.25λ above the ground plane, where λ is the wavelength corresponding to a center frequency of the frequency band at which the radiating element is designed to operate.
Radiating elements are known in the art that have dipole radiators formed using metal rods, sheet metal, printed circuit boards, and a variety of other materials. As multi-band base station antennas have been introduced that include two or more linear arrays of radiating elements that operate in different frequency bands, the designs of the dipole radiators have tended to become more complicated, in an effort to decouple the radiating elements of different frequency bands as much as possible. The dipole radiators of these radiating elements are often implemented using printed circuit boards.
Embodiments of the present invention relate generally to radiating elements for base station antennas that include dipole radiators that are formed of pieces of sheet metal that are adhered to a dielectric mounting support. The pieces of sheet metal may form one or more dipoles. The sheet metal dipoles may be mounted onto the dielectric mounting support using an adhesive. The dielectric mounting support may physically support the sheet metal dipoles to reduce the tendency of the thin dipoles to move and/or bend during use. Herein, such dipole radiators may be referred to as “sheet metal-on-dielectric radiators.”
As noted above, base station antennas having printed circuit board-based dipole radiators are known in the art. Printed circuit boards, however, may be relatively expensive. Aluminum and/or copper sheet metal may be relatively inexpensive and can easily be stamped to form desired planar shapes. Consequently, the dipole radiators according to embodiments of the present invention may be cheaper than printed circuit board-based dipole radiators. Moreover, one potential difficulty with printed circuit board based-dipole radiators is that the thickness of the metal layers on standard printed circuit boards may be less than desirable to ensure low signal transmission loss and good impedance matching with the feeding RF transmission lines. While printed circuit boards can be fabricated to have thicker metal layers, these non-standard printed circuit boards may cost significantly more. Since state-of-the art multi-band base station antenna may have a large number of radiating elements (e.g., 25-40), the use of such specialized printed circuit boards can have measurable impact on the price of a base station antenna. The sheet metal-on-dielectric dipole radiators according to embodiments of the present invention may be formed to have any desired thickness, and hence may exhibit improved impedance matching and/or reduced signal transmission losses as compared to low-cost printed circuit board based dipole radiators.
The radiating elements having sheet metal-on-dielectric dipole radiators according to embodiments of the present invention may also exhibit improved passive intermodulation (“PIM”) distortion performance as compared to printed circuit board based dipole radiators. In particular, metal layers on printed circuit boards generally have a relatively high degree of surface roughness, which may help reduce the possibility that layers of the printed circuit board delaminate. This surface roughness may, however, be a source for PIM distortion. Moreover, while printed circuit boards having reduced levels of surface roughness may be obtained, these printed circuit boards cost more and still have some degree of surface roughness. As a result, radiating elements formed using printed circuit board based dipole radiators may tend to exhibit higher levels of PIM distortion. Sheet metal may be readily obtained that has very low levels of surface roughness, and can also be readily and inexpensively polished to further reduce surface roughness. Accordingly, the radiating elements according to embodiments of the present invention may be cheaper than conventional radiating elements that use printed circuit board based dipole radiators and may also provide enhanced performance.
In some embodiments, the sheet metal-on-dielectric dipole radiators according to embodiments of the present invention may be formed as non-planar elements. This may allow the dipoles to have a desired electrical length while reducing the “footprint” of each dipole (i.e., the size of the dipole when viewed from the front of the antenna). By reducing the footprint, the physical spacing between the radiating elements of adjacent linear arrays may be increased, which may reduce the impact that adjacent radiating elements have on their respective radiation patterns. In other embodiments, the dielectric mounting substrate may include an integrated dipole support structure to reduce manufacturing costs and improve the physical stability of the radiating element.
Embodiments of the present invention will now be described in further detail with reference to the attached figures.
As shown in
Referring to
As shown in
Each feed stalk 310 may comprise a pair of printed circuit boards 312-1, 312-2 that have RF transmission lines 314 formed thereon. These RF transmission lines 314 carry RF signals between the printed circuit board 252 and the cross-dipole radiators 320. A first of the printed circuit boards 312-1 may include a lower vertical slit and the second of the printed circuit boards 312-2 includes an upper vertical slit. These vertical slits allow the printed circuit boards 312 to be assembled together to form a vertically-extending column that has generally x-shaped cross-section. Lower portions of each printed circuit board 312 may include plated projections 316. These plated projections 316 are inserted through slits in the printed circuit board 252. The plated projections 316 of printed circuit board 312 may be soldered to plated portions on printed circuit board 252 to electrically connect the printed circuit boards 312 to the printed circuit board 252. The RF transmission lines 314 on the respective feed stalks 310 may feed the RF signals to the cross-dipole radiators 320. Dipole supports 318 may also be provided to hold the cross-dipole radiators 320 in their proper positions.
The cross-dipole radiator 320 includes first and second metal dipoles 330-1, 320-2. The first metal dipole 330-1 includes first and second dipole arms 332-1, 332-2, and the second metal dipole 330-2 includes third and fourth dipole arms 332-3, 332-4. All four dipole arms 332 are mounted on the dielectric mounting substrate 340. Each metal dipole 330 may, for example, have two dipole arms 332 that are between 0.2 to 0.35 of an operating wavelength in length, where the “operating wavelength” refers to the wavelength corresponding to the center frequency of the operating frequency band of the radiating element 300. For example, if the low-band radiating elements 300 are designed as wideband radiating elements that are used to transmit and receive signals across the full 694-960 MHz frequency band, then the center frequency of the operating frequency band would be 827 MHz and the corresponding operating wavelength would be 36.25 cm.
As shown in
Each dipole arm 332 includes first and second spaced-apart conductive segments 334-1, 334-2 that together form a generally oval shape. In the depicted embodiment, all four dipole arms 332 lie in a common plane that is generally parallel to a plane defined by the underlying reflector 214. Each feed stalk 310 may extend in a direction that is generally perpendicular to the plane defined by the dipole arms 332. Each conductive segment 334-1, 334-2 may comprise a metal pattern that has a plurality of widened segments 336 and at least one narrowed trace section 338. The narrowed trace sections 338 may be implemented as non-linear conductive traces that follow a meandered path to increase the path length thereof. The first conductive segment 334-1 may form half of the generally oval shape and the second conductive segment 334-2 may form the other half of the generally oval shape. The dipole arms 330 may have shapes other than a generally oval shape, such as, for example, an elongated generally rectangular shape.
As shown in
When the high-band radiating elements 400 transmit and receive signals, the high-band RF signals may tend to induce currents on the dipole arms 332 of the low-band radiating elements 300. This can particularly be true when the low-band and high-band radiating elements 300, 400 are designed to operate in frequency bands having center frequencies that are separated by about a factor of two, as a low-band dipole arm 332 having a length that is about a quarter wavelength of the low-band operating frequency will, in that case, have a length of approximately a half wavelength of the high-band operating frequency. The greater the extent that high-band currents are induced on the low-band dipole arms 332, the greater the impact on the characteristics of the radiation pattern of the linear arrays 230 of high-band radiating elements 400.
The narrowed trace sections 338 may act as high impedance sections that interrupt currents in the high-band frequency range that could otherwise be induced on the low-band dipole arms 332. The narrowed trace sections 338 may create this high impedance for high-band currents without significantly impacting the flow of the low-band currents on the dipole arms 332. As such, the narrowed trace sections 338 may reduce induced high-band currents on the low-band radiating elements 300 and consequent disturbance to the antenna pattern of the high-band linear arrays 230. In some embodiments, the narrowed trace sections 338 may make the low-band radiating elements 300 almost invisible to the high-band radiating elements 400, and thus the low-band radiating elements 300 may not distort the high-band antenna patterns.
As can further be seen in
By forming each dipole arm 332 as first and second spaced-apart conductive segments 334-1, 334-2, the currents that flow on the dipole arm 332 may be forced along two relatively narrow paths that are spaced apart from each other. This approach may provide better control over the radiation pattern. Additionally, by using the loop structure, the overall length of the dipole arms 332 may be reduced, allowing greater separation between each dipole arm 332 and other radiating elements 300, 400.
In some embodiments, the first and second metal dipoles 330-1, 330-2 may have “unbalanced” dipole arms 332 that have different shapes or sizes. The use of unbalanced dipole arms 332 may help correct for unbalanced current flow that may otherwise occur in radiating elements 300 that are located along the outer edges of a reflector 214. Such unbalanced current flow may occur because the inner dipole arms 332 on radiating elements 300 that are positioned close to the side edges of the reflector may “see” more of the ground plane 214 than the outer dipole arms 332. This may cause an imbalance in current flow, which may negatively affect the patterns of the low-band antenna beams. This imbalance may be reduced, for example, by including more metal along the distal edges of the outer dipole arms 332 that are adjacent the edge of the ground plane 214.
In some embodiments, capacitors may be formed between adjacent dipole arms 332 of different metal dipoles 330. For example, a first capacitor may be formed between dipole arms 332-1 and 332-3 and a second capacitor may be formed between dipole arms 332-2 and 332-4. These capacitors may be used to tune (improve) the return loss performance and/or antenna pattern for the low-band metal dipoles 330-1, 330-2. In some embodiments, the capacitors may be formed on the feed stalks 310.
As discussed above, pursuant to embodiments of the present invention, the dipole radiators 320 may be implemented by forming sheet metal in the desired shape for each dipole arm 332 and then adhering the dipole arms 332 to a dielectric mounting substrate 340.
Turning first to
The sheet metal that is used to from the dipole arms 332 may have very smooth major surfaces, either as manufactured or because a polishing or another smoothing operation is performed thereon. It is believed that roughness in the metal surface may be a source of PIM distortion. As know to those of skill in the art, PIM distortion is a form of electrical interference that may occur when two or more RF signals encounter non-linear electrical junctions or materials along an RF transmission path. Rough metal surfaces along an RF transmission path are one potential source for PIM distortion, particularly when such rough surfaces are in high current density regions of the RF transmission path. The non-linearities that arise may act like a mixer causing new RF signals to be generated at mathematical combinations of the original RF signals. If the newly generated RF signals fall within the bandwidth of the radio receiver, the noise level experienced by the receiver is effectively increased. When the noise level is increased, it may be necessary reduce the data rate and/or the quality of service. By using sheet metal having very smooth surfaces to form the dipole arms 332, the risk of PIM distortion arising in the dipole arms 332 may be significantly reduced.
As is further shown in
Referring to
The dielectric mounting substrate 340 may include four central openings 344 that receive respective ones of extensions 313 (see
Referring to
The dielectric mounting substrate 340 may be formed by any appropriate process including, for example, injection molding, other forms of molding, cutting, stamping or the like. Injection molding may be preferred in embodiments that include lips 346 and/or ribs 347. The dielectric mounting substrate 340 may typically comprise a single piece of dielectric material that all four dipole arms 332 are adhered to, although multi-piece dielectric mounting substrates may be used in some embodiments.
While
Pursuant to further embodiments of the present invention, radiating elements are provided which include both a dielectric mounting substrate and a dipole support that are integrated as a single monolithic dielectric mounting substrate and dipole support structure.
Pursuant to still further embodiments of the present invention, radiating elements are provided that have three-dimensional cross-dipole radiators 620. Such three-dimensional cross-dipole radiators 620 may readily be formed by bending the stamped metal dipole arms 332 (to form dipole arms 632) and by forming three-dimensional dielectric mounting substrates 640 via, for example, injection molding. The use of such three-dimensional cross-dipole radiators 620 may be advantageous for reducing the overall footprint of the cross-dipole radiator 620 when viewed from the front of the base station antenna, which may increase the distance between adjacent radiating elements (thereby improving isolation), allow for a reduction in the size of the base station antenna, and/or provide room for additional radiating elements.
Forming the dipole arms 632 and the dielectric mounting substrate 640 to include the undulations 638, 648 acts to reduce the physical “footprint” of the cross-dipole radiator 620. Herein, the footprint of a dipole (or cross-dipole) radiator refers to the area of the reflector that the dipole radiator “covers” when the dipole radiator is viewed from the front along a central axis of the feed stalk that the dipole radiator is mounted on. Typically, the length of each metal dipole (and hence the lengths of the dipole arms that may form the metal dipole) is set based on desired RF radiating characteristics for the radiating element. By bending the dipole arms 632 of cross-dipole radiator 620 to include one or more undulations 638, the footprint of cross-dipole radiator 620 may be reduced without effecting the length of the metal dipoles 630 thereof. Such three-dimensional cross-dipole radiators cannot readily be formed using printed circuit board technology, since conventional printed circuit board are planar structures. Moreover, while flexible printed circuit boards are known in the art, the metal layers on such flexible printed circuit boards typically are very thin and generally unsuitable for use as a dipole radiator of a base station antenna.
In the embodiment of
The feed stalks 410 may each comprise a pair of printed circuit boards that have RF transmission line feeds formed thereon. The feed stalks 410 may be assembled together to form a vertically-extending column that has generally x-shaped cross-sections. Each cross-dipole radiator 420 may also be implemented as a sheet metal-on-dielectric dipole radiator. In particular, cross-dipole radiator 420 may include four dipole arms 432 that together form first and second cross-polarized center fed metal dipoles 430-1, 430-2. The dipole arms 432 may be adhered to an underlying dielectric mounting substrate 440. As the cross-dipole radiator 420 may be identical to the cross-dipole radiator 320 discussed above except that the size thereof and the shape of the dipole arms 432 are modified for operation at the higher frequency band, further description of the cross-dipole radiators 420 will be omitted.
As shown in
While embodiments of the present invention have primarily been discussed above with respect to cross-dipole radiators, it will be appreciated that all of the above-described aspects of the present invention may be applied to single-polarization radiating elements that have a single dipole radiator as opposed to cross-polarized dipole radiators. It will likewise be appreciated that the techniques described herein may be used with any type of dual-polarized radiating element and not just with slant −45°/+45° dipole radiating elements.
The radiating elements according to embodiments of the present invention may provide a number of advantages over conventional radiating elements. As discussed above, the dipole radiators according to embodiments of the present invention may be significantly cheaper to manufacture as compared to printed circuit board dipole radiators. Additionally, because the thickness of the metal dipole arms may be, for example, five to forty-five times the thickness of low-cost printed circuit board dipole radiators, the dipole radiators according to embodiments of the present invention may exhibit reduced signal transmission loss and may have better impedance match with the RF transmission lines on the feed stalks, resulting in improved return loss performance.
Additionally, since the metal dipoles may be very smooth (i.e., almost no surface roughness), the dipole radiators according to embodiments of the present invention may exhibit improved PIM performance as compared to printed circuit board based dipole radiators, and the relatively large batch-to-batch variation that is present with printed circuit board based dipole radiators may be significantly reduced, providing more consistent RF performance. Moreover, since the dielectric mounting substrate may be injection molded to include desired cutouts, the fabrication step of cutting openings into printed circuit board based dipole radiators may be eliminated, further reducing manufacturing costs. Additionally, in some embodiments, the dipole radiators may include undulations that reduce the footprint thereof, and/or may include integrated dipole supports that provide increased stability.
Embodiments of the present invention have been described above with reference to the accompanying drawings, in which 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. Like numbers refer to like elements throughout.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (i.e., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.).
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, operations, elements, components, and/or groups thereof.
Aspects and elements of all of the embodiments disclosed above can be combined in any way and/or combination with aspects or elements of other embodiments to provide a plurality of additional embodiments.
The present application is a 35 U.S.C. § 371 national stage application of PCT Application No. PCT/US2018/030606, filed on May 2, 2018, which itself claims priority to U.S. Provisional Patent Application Ser. No. 62/528,611, filed Jul. 5, 2017, the entire contents of both of which are incorporated herein by reference as if set forth in their entireties. The above-referenced PCT Application was published in the English language as International Publication No. WO 2019/009951 A1 on Jan. 10, 2019.
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