Patent Application
20240283164
The present invention generally relates to radio communications and, more particularly, to base station antennas utilized in cellular and other communications systems
Cellular communications systems are well known in the art. In a typical cellular communications system, a geographic area is divided into a series of regions that are referred to as “cells,” and each cell is served by a base station. The base station may include baseband equipment, radios and base station antennas that are configured to provide two-way radio frequency (“RF”) communications with subscribers that are positioned throughout the cell. Most cells are divided into a plurality of “sectors,” and separate base station antennas provide coverage to each of the sectors. The base station antennas are often mounted on a tower or other raised structure, with the radiation pattern (“antenna beam”) that is generated by each antenna directed outwardly to serve a respective sector. Typically, a base station antenna includes one or more phase-controlled arrays of radiating elements, with the radiating elements arranged in one or more vertical columns when the antenna is mounted for use. Herein, “vertical” refers to a direction that is generally perpendicular relative to the plane defined by the horizon. Reference will also be made herein to the “azimuth” plane, which refers to a horizontal plane that bisects the base station antenna that is parallel to the plane defined by the horizon.
A common base station configuration is a “three sector” configuration in which a cell is divided into three 120° sectors in the azimuth plane, and the base station includes three base station antennas that provide coverage to the three respective sectors. In a three sector configuration, the antenna beams generated by each base station antenna typically have a half power beamwidth in the azimuth plane (“azimuth HPBW”) of about 65°. Such antenna beams may provide good coverage to a 120° sector in the azimuth plane.
Each individual radiating element in the above-discussed arrays will typically be designed to generate an individual antenna beam (i.e., the antenna beam that is generated if an RF signal is only transmitted through a single radiating element of the array, which is also referred to herein as an “element pattern”) having an azimuth HPBW of about 65°. The azimuth HPBW of an antenna beam generated by an array of radiating elements is a function of (among other things) the azimuth HPBW of the element pattern of the radiating elements in the array and the distance between the leftmost and rightmost radiating elements in the array (referred to as the “aperture” of the array in the azimuth plane). As noted above, for a three-sector base station, it is typically desired that the antenna beams generated by an array of radiating elements have an azimuth HPBW of about 65°. Since most radiating elements are designed to have an azimuth HPBW of about 65°, a single radiating element, or a vertically-extending column of radiating elements, will generate antenna beams having the desired 65° azimuth HPBW.
Cellular communications are primarily performed in three different frequency ranges, which are commonly referred to as the “low-band,” “mid-band” and “high-band” frequency ranges. The low-band frequency range is generally defined as the 696-960 MHz frequency range (or more recently as the 617-960 MHz frequency range). The mid-band frequency range is generally defined as the 1695-2690 MHz frequency range (or, more recently as the 1427-2690 MHz frequency range). The high-band frequency range is more variable in nature, but may include different ranges of frequencies in the 3.1-5.8 GHz frequency range. Cellular operators are licensed to use small sub-bands in each of these frequency ranges, where the sub-bands will vary with geographic location and cellular operator. Consequently, base station antennas typically include linear arrays that support service across the full low-band and mid-band frequency ranges so that the antennas can be used by any operator in any geographic location.
Most modern base station antennas include arrays that are formed using dual polarization radiating elements. A dual polarization radiating element refers to a radiating element that has first and second radiators that transmit/receive RF signals at orthogonal (i.e., non-interfering) polarizations. The use of dual polarization radiating elements allows the number of antenna beams generated by an antenna to be doubled as compared to an antenna that uses single polarization radiating elements, typically with only a minimal increase in the size of the antenna. For example, so-called slant +45°/−45° cross-dipole radiating elements are commonly used in base station antennas. These radiating elements include a first dipole radiator that is oriented at an angle of +45° (with respect to the horizon) and a second dipole radiator that is oriented at an angle of −45° so that together the two dipole radiators have a cross-shape. The first dipole radiator is fed a first RF signal through a first RF port to generate a first element pattern having a +45° linear polarization, and the second dipole radiator is fed a second RF signal through a second RF port to generate a second element pattern having a −45° linear polarization. The first and second RF ports may be coupled to respective first and second ports of a radio.
There is significant interest in base station antennas that include two linear arrays of low-band radiating elements, since such base station antennas can support 4×MIMO communications in the low-band. MIMO stands for “multi-input-multi-output,” and the term 4×MIMO refers to a communication technique where a baseband data stream is sub-divided into four sub-streams that are used to generate four RF signals that are transmitted through multiple different arrays of radiating elements. The different arrays are, for example, spatially separated from one another and/or at orthogonal polarizations so that the transmitted RF signals will be sufficiently decorrelated. The four RF signals are recovered at the receiver and demodulated and decoded to recover the original four data sub-streams, which are then recombined. The use of MIMO transmission techniques may help overcome the negative effects of multipath fading, and may be particularly effective in urban environments where reflections may increase the level of decorrelation between the RF signals. When dual-polarized radiating elements are used, two linear arrays of low-band radiating elements can be used to transmit four separate RF signals, and thus can support 4×MIMO communications.
The size of a radiating element is inversely correlated with its frequency of operation, and hence the low-band radiating elements are usually the largest radiating elements in a base station antenna. Consequently, it can be challenging to implement base station antennas that have two arrays of dual polarization low-band radiating elements where the base station antenna meets cellular operator expectations for the width of the base station antenna.
As shown in
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Base station antennas having the design of base station antenna 1 will typically have a width that exceeds 400 mm and often more than 450 mm. Antennas having such large widths are heavy, have high wind loading, and may exceed local ordinances governing the permissible sizes for base station antennas. Several techniques, however, are known in the art for reducing the width of a base station antenna. For example, U.S. Pat. No. 10,879,605 discloses several antenna designs that include arrays of radiating elements that comprise a column of radiating elements plus an additional radiating element that is horizontally offset from the column of radiating elements. The additional horizontally offset radiating element increases the “aperture” of the array in the azimuth plane, which acts to narrow the azimuth beamwidth of the antenna beams generated by the array. However, since only a single horizontally offset radiating element is added to the array, the overall impact on the azimuth beamwidth tends to be small. As another example, the width of the antenna may be reduced by decreasing the lateral spacing between the linear arrays 20-1, 20-2. However, this results in increased coupling between the linear arrays 20-1, 20-2 and this “parasitic” coupling can itself lead to an undesired increase in the azimuth HPBW of the generated antenna beams. It is also possible to reduce the size of each low-band radiating element 22 to decrease the width of the base station antenna, but the smaller low-band radiating elements 22 have larger azimuth HPBWs and thus the generated antenna beams will tend to have reduced gain and/or spill over into neighboring sectors. Consequently, it may be difficult to provide base station antennas that have two or more arrays of dual polarization low-band radiating elements in a commercially acceptable manner.
Another complication that is present in multiband antennas (i.e., an antenna that includes linear arrays that operate in different frequency bands) is that coupling between the radiating elements of the different arrays may occur. This coupling may cause “scattering” of the RF signals emitted by a second frequency band linear array by the radiating elements of a first frequency band linear array. Scattering is undesirable as it may change the shape of the antenna beams generated by the second frequency band linear array, and the changes in the shape of the antenna beam may vary significantly with frequency. This may make it difficult to compensate for the effects of scattering using other techniques. For example, scattering tends to negatively impact the beamwidth, beam shape, pointing angle, gain and front-to-back ratio of the antenna beams in the azimuth plane.
Scattering primarily occurs when a conductive structure of a first frequency band radiating element has an electrical length that makes the structure resonant in the operating frequency band of a nearby radiating element that operates in the second (different) frequency band. As discussed above, most modern base station antennas include low-band radiating elements that operate in the 617-960 MHz frequency band or a portion thereof and mid-band radiating elements that operate in the 1427-2690 MHz frequency band or a portion thereof. If cross-dipole radiating elements are used, each low-band dipole radiator typically is implemented as a pair of dipole arms that each have an electrical length that is approximately ¼ a wavelength (herein “the center wavelength”) that corresponds to the center frequency of the operating frequency band for the low-band radiating element. Thus, each dipole radiator has an electrical length that is approximately ½ the “center” wavelength.
Since the mid-band frequency range encompasses frequencies that are twice the frequencies in the low-band frequency range, the electrical length of each low-band dipole arm may be approximately ½ a wavelength of RF signals transmitted in the lower portion of the mid-band operating frequency band. As such, RF energy transmitted by the mid-band radiating elements (particularly when the mid-band radiating elements operate in the lower portion of the mid-band operating frequency band) may couple to the dipole arms of nearby low-band radiating elements, where such RF energy is then re-radiated from the low-band dipole arms, often in undesired directions. Such coupling and re-radiating of the mid-band RF energy by the low-band dipole arms acts to distort the antenna beams generated by the array of mid-band radiating elements.
Radiating elements that are designed to suppress such scattering are known in the art, and are commonly referred to as “cloaking” radiating elements. For example, U.S. Pat. No. 10,439,285 and U.S. Pat. No. 10,770,803 each disclose low-band radiating elements that include dipole arms that are formed as a series of widened metal segments that are coupled by narrow inductive metal segments, which may be implemented as small, meandered trace segments on a printed circuit board. The entire content of U.S. Pat. Nos. 10,439,285 and 10,770,803 is incorporated herein by reference. In each case, the narrow inductive metal segments act as high impedance elements for RF energy in the mid-band frequency range, rendering the low-band radiating elements substantially transparent to RF energy in that frequency range. These cloaking radiating elements are designed so that the RF energy emitted by the mid-band radiating element tends to not form mid-band currents on the dipole arms of the low-band radiating elements.
Pursuant to embodiments of the present invention, base station antennas are provided that comprise a reflector, a first radiating element that extends forwardly from the reflector and that is configured to operate in a first frequency band and a second radiating element that extends forwardly from the reflector and that is configured to operate in a second frequency band that is different from the first frequency band. The first radiating element comprises a first dipole radiator that has first and second dipole arms, a second dipole radiator that has third and fourth dipole arms, a first dielectric block positioned adjacent the first dipole arm, and a first metal pattern positioned between the first dielectric block and the reflector.
In some embodiments, the first metal pattern is configured to attenuate RF energy emitted by the second radiating element that is incident on the first metal pattern. In some embodiments, the metal pattern is unitary with the dielectric block. In some embodiments, the first metal pattern comprises a metamaterial.
In some embodiments, the first radiating element further comprises a second dielectric block positioned adjacent the second dipole arm, a second metal pattern positioned between the second dielectric block and the reflector, a third dielectric block positioned adjacent the third dipole arm, a third metal pattern positioned between the third dielectric block and the reflector, a fourth dielectric block positioned adjacent the fourth dipole arm, and a fourth metal pattern positioned between the fourth dielectric block and the reflector.
In some embodiments, the first dipole arm is implemented using a first printed circuit board, and the first dielectric block is mounted rearwardly of the first printed circuit board.
In some embodiments, the first metal pattern is printed on the first dielectric block.
In some embodiments, the first metal pattern has a negative refractive index. In some embodiments, the first metal pattern has at least one of a negative permittivity and a negative permeability within at least a portion of the second frequency band.
In some embodiments, the first dielectric block has a dielectric constant that is greater than 4.0.
In some embodiments, the first metal pattern comprises a plurality of unit cell structures. In some embodiments, each unit cell includes a plurality of sub-unit cells, and wherein at least some of the sub-cells in a first of the unit cells are oriented differently from other of the sub-cells in the first of the unit cells.
In some embodiments, a thickness of the first dielectric block in the forward direction is at least ten times a thickness of the first dipole arm.
In some embodiments, each of the first through fourth dipole arms has an end-to-end physical length that is less than 0.2 of a wavelength that corresponds to a center frequency of the first frequency band.
In some embodiments, the first dielectric block is configured to dielectrically load the first dipole arm.
In some embodiments, the first dipole arm is implemented as a sheet metal dipole arm.
In some embodiments, the first dipole arm is configured to be substantially transparent to RF energy emitted by the second radiating element.
Pursuant to further embodiments of the present invention, base station antennas are provided that comprise a second radiating element that that is configured to operate in a second frequency band, a first radiating element that is configured to operate in a first frequency band that is different from the second frequency band, the first radiating element comprising a first radiator and a first dielectric loading element for the first radiator, the first dielectric loading element including a first metal pattern that is not part of the first radiator and that is configured to reduce the impact of the first dielectric loading element on RF energy emitted by the second radiating element.
In some embodiments, a first dipole radiator has first and second dipole arms, the first radiating element further comprising a second dipole radiator that has third and fourth dipole arms, and the first dielectric loading element is positioned adjacent the first dipole arm.
In some embodiments, the first dipole arm is implemented using a first printed circuit board, and the first dielectric loading element is mounted rearwardly of the first printed circuit board.
In some embodiments, the first dipole arm is implemented as a sheet metal dipole arm.
In some embodiments, the first metal pattern is unitary with the first dielectric loading element.
In some embodiments, the first radiating element further comprises a second dielectric loading element positioned adjacent the second dipole arm, a second metal pattern positioned between the second dielectric block and the reflector, a third dielectric loading element positioned adjacent the third dipole arm, a third metal pattern positioned between the third dielectric block and the reflector, a fourth dielectric loading element positioned adjacent the fourth dipole arm, and a fourth metal pattern positioned between the fourth dielectric block and the reflector.
In some embodiments, the first metal pattern comprises a metamaterial.
In some embodiments, the first metal pattern is printed on the first dielectric loading element.
In some embodiments, the first metal pattern has a negative refractive index. In some embodiments, the first metal pattern has at least one of a negative permittivity and a negative permeability within at least a portion of the second frequency band.
In some embodiments, each of the first through fourth dielectric loading elements has a dielectric constant that is greater than 4.0.
In some embodiments, the first metal pattern comprises a plurality of unit cell structures.
In some embodiments, each of the first through fourth dipole arms has an end-to-end physical length that is less than 0.2 of a wavelength that corresponds to a center frequency of the first frequency band.
Pursuant to still further embodiments of the present invention, radiating elements that are configured to operate in a first frequency band are provided that comprise a first dipole radiator that has a first dipole arm and a second dipole arm and a second dipole radiator that has a third dipole arm and a fourth dipole arm, wherein one or more dielectric blocks having dielectric constants of at least 4.0 are positioned adjacent the first through fourth dipole arms to dielectrically load the first through fourth dipole arms, and the dielectric blocks are cloaked with respect to RF energy in a second frequency band that is different from the first frequency band.
In some embodiments, the first dipole arm is implemented using a first printed circuit board, and the first dielectric block is mounted rearwardly of the first printed circuit board.
In some embodiments, the first dipole arm is implemented as a sheet metal dipole arm.
In some embodiments, the one or more dielectric blocks each include a respective associated metal pattern that is configured to act as a partially reflective surface in the second frequency band.
In some embodiments, each associated metal pattern is unitary with a respective one of the one or more dielectric blocks.
In some embodiments, each associated metal pattern comprises a metamaterial.
In some embodiments, each associated metal pattern comprises a plurality of unit cell structures. In some embodiments, each unit cell includes a plurality of sub-unit cells, and wherein at least some of the sub-cells in a first of the unit cells are oriented differently from other of the sub-cells in the first of the unit cells.
Pursuant to yet additional embodiments of the present invention, radiating elements that are configured to operate in a first frequency band are provided that comprise a feed stalk, a first dipole radiator that has a first dipole arm and a second dipole arm, the first dipole radiator mounted adjacent a forward end of the feed stalk, a second dipole radiator that has a third dipole arm and a fourth dipole arm, the second dipole radiator mounted adjacent the forward end of the feed stalk, a dielectric block positioned immediately behind the first dipole arm, and a metal pattern that includes a plurality of unit cell structures positioned immediately behind the dielectric block.
In some embodiments, the metal pattern is unitary with the dielectric block.
In some embodiments, the radiating element further comprises a second dielectric block positioned immediately behind the second dipole arm, a second metal pattern positioned between the second dielectric block and the reflector, a third dielectric block positioned immediately behind the third dipole arm, a third metal pattern positioned between the third dielectric block and the reflector, a fourth dielectric block positioned immediately behind the fourth dipole arm, and a fourth metal pattern positioned between the fourth dielectric block and the reflector.
In some embodiments, the first through fourth dielectric blocks each have a dielectric constant that is greater than 4.0.
In some embodiments, the first metal pattern has at least one of a negative permittivity and a negative permeability within at least a portion of the second frequency band.
In some embodiments, each unit cell includes a plurality of sub-unit cells, and wherein at least some of the sub-cells in a first of the unit cells are oriented differently from other of the sub-cells in the first of the unit cells.
In some embodiments, a thickness of the first dielectric block in the forward direction is at least ten times a thickness of the first dipole arm.
In some embodiments, each of the first through fourth dipole arms has an end-to-end physical length that is less than 0.2 of a wavelength that corresponds to a center frequency of the first frequency band.
Pursuant to yet additional embodiments of the present invention, base station antennas are provided that comprise a first RF port, a first power divider, a first array of radiating elements, first polarization radiators of each of the radiating elements in the first array coupled to the first RF port through the first power divider, a second RF port, a second power divider, a second array of radiating elements, first polarization radiators of each of the radiating elements in the second array coupled to the second RF port through the second power divider, and a coupler having a first input port coupled to a first output of the first power divider, a first output port coupled to the first polarization radiator of a first radiating element in the first array of radiating elements, a second input port coupled to a first output of the second power divider, a second output port coupled to the first polarization radiator of a first radiating element in the second array of radiating elements, a first coupling transmission line and a second coupling transmission line. A first end of the first coupling transmission line is connected to a first end of the second coupling transmission line port via an RF transmission line.
In some embodiments, a second end of the first coupling transmission line is connected to a first terminated load. In some embodiments, a second end of the second coupling transmission line is connected to a second terminated load. In other embodiments, a second end of the second coupling transmission line is connected to the first terminated load.
In some embodiments, an electrical length of the RF transmission line is set so that RF energy that passes from the first RF port to the first polarization radiator of the first radiating element in the second array of radiating elements is approximately 180° out-of-phase with respect to RG energy that directly couples from the first polarization radiator of the first radiating element in the first array of radiating elements to the first polarization radiator of the first radiating element in the second array of radiating elements.
In some embodiments, the coupler is a hybrid coupler.
Another known technique for reducing the width of a base station antenna is to use dielectrically-loaded radiating elements. Dielectrically-loaded radiating elements include blocks of high dielectric constant dielectric materials that are placed adjacent one or more sides of the radiators of the radiating element. Since the electrical length of a radiator, such as a dipole radiator, is a function of the dielectric constant of the surrounding medium, the blocks of higher dielectric constant dielectric materials allow the physical length of the dipole radiators to be reduced while the dipole radiators still maintain the electrical length necessary to be resonant in a desired operating frequency band. Radiating elements having such dielectrically-loaded dipole arms are disclosed, for example, in U.S. Patent Publication No. 2022/0006182, filed May 10, 2021, the entire content of which is incorporated herein by reference. Thus, if the dipole arms of the low-band radiating elements 22 in the base station antenna 1 are dielectrically loaded, the size of each low-band radiating element 22 may be reduced, allowing the width of base station antenna 1 to be reduced.
While the dielectric loading of the dipole arms may help reduce the width of the base station antenna 1, the blocks of higher dielectric constant dielectric material can adversely impact the shape of the antenna beams generated by the mid-band linear arrays 30-1, 30-2. As described above, the mid-band radiating elements 32 are mounted behind the low-band radiating elements 22, and hence emit RF radiating through the low-band radiating elements 22. The blocks of higher dielectric constant dielectric material can act like an RF lens focusing RF energy incident thereon, which acts to change the shape of the mid-band antenna beams, typically in undesirable ways. Moreover, since the mechanism (focusing) by which the blocks of higher dielectric constant dielectric material impact the mid-band antenna beams differs from the mechanism (scattering) by which the low-band dipole arms impact the mid-band antenna beams, the techniques used to cloak the low-band dipole arms cannot be used to reduce the impact that the blocks of higher dielectric constant dielectric material have on the mid-band antenna beams.
Pursuant to embodiments of the present invention, multiband base station antennas are provided that include at least two arrays of low-band radiating elements (and hence can support 4×MIMO operations in the low-band frequency range) while having a much smaller size than conventional base station antennas that include multiple low-band arrays. The base station antennas according to embodiments of the present invention may employ dielectrically-loaded low-band radiating elements, since dielectrically loading the low-band radiators may significantly reduce the size of the low-band radiating elements. For example, dielectrically loading the dipole arms may reduce the footprint of each radiating element (i.e., the area defined by the smallest rectangle that encloses the radiating element when viewed from the front) by, for example, more than 20%, more than 30%, more than 40%, more than 50%, or even more than 60% in example embodiments. The amount of the reduction may be a factor of the amount of dielectric loading material and the dielectric constant thereof.
The dielectrically-loaded low-band radiating elements may also include metamaterial metal patterns or other structures that are used to reduce the impact that the dielectric loading material has on RF energy emitted by other radiating elements included in the multiband antenna, such as mid-band radiating elements that are located in close proximity to the low-band radiating elements. If the low-band radiating elements do not include such structures, the dielectric loading material mounted on or adjacent the radiators of the low-band radiating elements may distort the shape of the antenna beams formed by the mid-band radiating elements.
The base station antennas according to embodiments of the present invention may also employ additional techniques for reducing the size of the antenna. These additional techniques may include, for example, using L-shaped or Y-shaped low-band arrays (or other array shapes that widen the aperture of the array in the azimuth plane), which may allow shrinking the size of the low-band radiating elements further. The antennas may also include couplers that are used to increase co-polarization isolation between the two low-band arrays. This may allow positioning the two low-band arrays closer to each other while still having adequate isolation therebetween.
In some embodiments, the above-described multiband base station antennas may include a reflector, a first radiating element that extends forwardly from the reflector and that is configured to operate in a first frequency band, and a second radiating element that extends forwardly from the reflector and that is configured to operate in a second frequency band that is different from the first frequency band. The first radiating element comprises a first dipole radiator that has first and second dipole arms, a second dipole radiator that has third and fourth dipole arms, a dielectric block positioned adjacent the first dipole arm, and a metal pattern positioned between the dielectric block and the reflector.
In other embodiments, these multiband base station antennas may include a first radiating element that is configured to operate in a first frequency band and a second radiating element that is configured to operate in a second frequency band that is different from the first frequency band. The first radiating element includes a first radiator and a dielectric loading element (such as a dielectric block) for the first radiator, where the dielectric loading element includes a metal pattern that is not part of the first radiator and that is configured to reduce the impact of the dielectric loading element on RF energy emitted by the second radiating element.
In still other embodiments, the first radiating elements may include a first dipole radiator that has a first dipole arm and a second dipole arm and a second dipole radiator that has a third dipole arm and a fourth dipole arm. In addition, the first radiating element may further include one or more dielectric blocks that have dielectric constants of at least 4.0 that are positioned adjacent the first through fourth dipole arms to dielectrically load the first through fourth dipole arms. Additionally, the dielectric blocks are cloaked with respect to RF energy in the second frequency band.
In still further embodiments, the first radiating elements may include a feed stalk, a first dipole radiator that has a first dipole arm and a second dipole arm, a second dipole radiator that has a third dipole arm and a fourth dipole arm, a dielectric block positioned immediately behind the first dipole arm, and a metal pattern that includes a plurality of unit cell structures positioned immediately behind the dielectric block.
In any or all of the above embodiments, the first dipole arm may be implemented using a first printed circuit board, and the dielectric block associated with the first dipole arm may be mounted rearwardly of the first printed circuit board. Alternatively, the first dipole arm may be implemented as a sheet metal dipole arm. In some embodiments, the metal pattern may be unitary with the dielectric block. For example, the metal pattern may be printed on the first dielectric block. In some embodiments, the metal pattern may comprise a metamaterial, have a negative refractive index and/or may have at least one of a negative permittivity and a negative permeability within at least a portion of the second frequency band. The metal pattern may comprise a plurality of unit cell structures. In some embodiments, each unit cell may include a plurality of sub-unit cells, and at least some of the sub-cells in a first of the unit cells may be oriented differently from other of the sub-cells in the first of the unit cells. The metal pattern may be configured to attenuate radio RF energy emitted by the second radiating element that is incident on the first metal pattern.
In any or all of the above embodiments, the dielectric block may have a dielectric constant that is greater than 4.0, greater than 5.0, greater than 6.0, greater than 7.0, greater than 8.0, or greater than 9.0. In some embodiments, the first radiating element may further include a second dielectric block positioned adjacent the second dipole arm, a second metal pattern positioned between the second dielectric block and the reflector, a third dielectric block positioned adjacent the third dipole arm, a third metal pattern positioned between the third dielectric block and the reflector, a fourth dielectric block positioned adjacent the fourth dipole arm, and a fourth metal pattern positioned between the fourth dielectric block and the reflector. Each dielectric block may be configured to dielectrically load a respective one of the dipole arms.
The base station antennas according to embodiments of the present invention may be much smaller than conventional base station antennas having the same number and types of arrays. For example, in one embodiment, a circular multiband base station antenna is provided that includes two arrays of low-band radiating elements that are designed to operate in the 718-960 MHz frequency band and two arrays of mid-band radiating elements that are designed to operate in the 1428-2170 MHz frequency band. All four arrays are enclosed within a radome having a diameter of 305 mm. A typical conventional base station antenna having the same arrays would have a width of at least 400 mm.
Embodiments of the present invention will now be discussed in more detail with reference to
Referring to
Referring to
Still referring to
Each low-band radiating element 122 is a center-fed slant −45°/+45° polarization cross-dipole radiating element that has a first dipole radiator 124-1 that is configured to transmit and receive slant +45° polarization RF radiation and a second dipole radiator 124-2 that is configured to transmit and receive slant −45° polarization RF radiation. Each low-band radiating element 122 may be configured to operate in some or all of the 617-960 MHz low-band frequency range. Each mid-band radiating element 132 is also a center-fed slant −45°/+45° polarization cross-dipole radiating element that has a first dipole radiator 134-1 that is configured to transmit and receive slant +45° polarization RF radiation and a second dipole radiator 134-2 that is configured to transmit and receive slant −45° polarization RF radiation. Each mid-band radiating element 132 may be configured to operate in some or all of the 1427-2690 MHz mid-band frequency range. Each radiating element 122, 132 is mounted to extend forwardly from the reflector 110.
Referring again to
In other embodiments, the base station antenna 100 may further include additional arrays of radiating elements. The number of radiating elements in each array may be varied from what is shown.
As discussed above, it can be difficult to provide base station antennas that include two linear arrays of low-band radiating elements that have widths of less than 400 mm. The base station antenna 100, in contrast, may have a width of less than 350 mm and even as small as 305 mm.
Referring to
The feed stalk 210 may be of any conventional design, and may be used to transfer RF signals between the first and second dipole radiators 220 and first and second feed networks of a base station antenna that includes the low-band radiating element 200 (e.g., a pair of feed networks of base station antenna 100). In the depicted embodiment, the feed stalk 210 comprises a pair of feed stalk printed circuit boards 212-1, 212-2. Feed stalk printed circuit board 212-1 passes RF signals between the first feed network (not shown) and dipole radiator 220-1, and feed stalk printed circuit board 212-2 passes RF signals between the second feed network (not shown) and dipole radiator 220-2. In some embodiments, the feed stalk printed circuit boards 212-1, 212-2 may comprise cloaked feed stalks that are configured to be substantially transparent to RF energy in some or all of the mid-band operating frequency range. For example, any of the cloaked feed stalks disclosed in U.S. Provisional Patent Application Ser. No. 63/437,146, filed Jan. 5, 2023 or in PCT Application Serial No. PCT/CN2023/070056, filed Jan. 3, 2023 may be used to implement the feed stalk printed circuit boards 212-1, 212-2. The entire content of U.S. Provisional Patent Application Ser. No. 63/437,146 and PCT Application Serial No. PCT/CN2023/070056 are incorporated herein by reference. It will be appreciated that non-cloaked feed stalk printed circuit boards may alternatively be used.
The first dipole radiator 220-1 includes a first dipole arm 224-1 and a second dipole arm 224-2. The first and second dipole arms 224-1, 224-2 extend along a first axis. The second dipole radiator 220-2 includes a third dipole arm 224-3 and a fourth dipole arm 224-4. The third and fourth dipole arms 224-3, 224-4 extend along a second axis that is perpendicular to the first axis. In the depicted embodiment, the dipole radiators 220-1, 220-2 are implemented on respective dipole radiator printed circuit boards 230-1, 230-2. Each dipole arm 224 comprises a metal pattern that is printed on the front side of one of the dipole radiator printed circuit boards 230-1, 230-2. In other embodiments, the dipole arms 224 may comprise respective metal patterns that are printed on the rear side of the dipole radiator printed circuit boards 230-1, 230-2. Such an embodiment may advantageously increase the amount of dielectric loading of the dipole arms 224 as a non-air dielectric is then disposed on both sides of each dipole arm 224.
Each dipole radiator printed circuit board 230 includes first and second slot-like openings 232 therein. Each feed stalk printed circuit boards 212-1, 212-2 includes a pair of forwardly-extending tabs 214. Each tab 214 extends through a respective one of the slot-like openings 232, which acts to mount the dipole radiator printed circuit boards 230-1, 230-2 on the feed stalk 210. Each tab 214 includes a metal pattern thereon that may be galvanically or capacitively coupled to a respective one of the dipole arms 224. RF signals that are input at the base (rear) of the feed stalk printed circuit boards 212-1, 212-2 couple to the respective dipole arms 224 through the metal patterns on the respective tabs 214. Thus, the dipole radiators 220-1, 220-2 are each implemented as center fed dipole radiators 220.
While each dipole arm 224 is implemented to have a specific “cloaking” pattern, it will be understood that a wide variety of cloaking radiating elements are known in the art, and any appropriate cloaking dipole arm may be used. Moreover, while the dipole arms 224 are implemented as printed circuit board based dipole arms, it will be appreciated that in other embodiments other implementations may be used. For example, sheet metal dipole arms could alternatively be used.
Dipole radiators typically have an electrical length of about one-half of a wavelength that corresponds to a center frequency of the operating frequency band of the radiating element. If the dipole arm is relatively narrow and surrounded by air, the electrical length will typically correspond to the physical length. In many cases, dipole arms are formed as loops or are widened (e.g., have leaf shapes) which allows the physical length of the dipole arm (as measured from the base of the arm to the distal end thereof) to be reduced while maintaining an electrical length of about one-half of the center wavelength.
Low-band radiating elements are typically designed to operate in the 617-960 MHz frequency band or in the 696-960 MHz frequency range. Thus, a dipole radiator having a physical end-to-end length that is half a wavelength of the 788.5 MHz center frequency of the 696-960 MHz frequency band has a length of about 180 mm. A cross-dipole low-band radiating element having dipole radiators that each have a length of 180 mm will have a footprint that is a square having sides that are about 127 mm (i.e., the width of each such radiating element is 127 mm). Thus, a base station antenna having two linear arrays of such low-band radiating elements will be relatively wide, as the arrays consume 254 mm in the width direction of the antenna and additional room is required so that the two arrays can be spaced apart from each other and also spaced apart from the outer edges of the antenna (so that the reflector extends farther in the width direction than the radiating elements). As a result, base station antennas that include two linear arrays of low-band radiating elements typically have a width that exceeds 400 mm.
As noted above, one known technique for reducing the physical size of a dipole arm while maintaining a desired electrical length is to “dielectrically load” the dipole arm. A dipole arm may be dielectrically loaded by placing blocks of relatively high dielectric constant dielectric materials on one or more sides of the dipole arm. The higher the dielectric constant, the thicker the dielectric blocks and the more sides of the dipole arm on which the dielectric blocks are placed the more the physical size of the dipole arm may be reduced while maintaining a desired electrical length.
Referring again to
As shown in
In the depicted embodiment, dielectric blocks 240 are only provided behind each dipole arm 224. It will be appreciated that in other embodiments each dipole arm 224 may be sandwiched between a pair of dielectric blocks 240A, 240B as is schematically shown in
As noted above, the radiating element 200 may further include a dielectric support structure 250. In the depicted embodiment, the dielectric support structure 250 comprises a feed stalk support 252 and a dielectric block support 260. The feed stalk support 252 may include legs 254 that are used to mount the feed stalk support 252 on a reflector (or feed board) of a base station antenna that includes the radiating element 200 and a frame 256 that includes channels 258 that receive outer edges of the feed stalk printed circuit boards 212 to hold the feed stalk printed circuit boards 212 in their proper positions. The dielectric block support 260 is positioned forwardly of the feed stalk support 252 and is mounted on shoulders 216 that are formed in the feed stalk printed circuit boards 212. The dielectric block support 260 includes a central section 262 that has an opening. The feed stalk printed circuit boards 212 extend through the opening. The dielectric block support 260 further includes four arms 264 that extend radially outwardly from the central section 262. Each dielectric block 240 may be mounted on a respective one of the arms 264.
The dielectrically loaded dipole radiators 220-1, 220-2 may have a significantly reduced physical length. In example embodiments, each dielectrically loaded dipole radiator 220 may have a length of about 113 mm, which means that the dipole arms 224 in the radiating element 200 are reduced by more than 35% as compared to a conventional dipole radiator.
While implementing the low-band radiating elements 122 in the base station antenna 100 to have dielectrically loaded dipole arms 224 may significantly reduce the size of each low-band radiating element 122/200, the dielectric blocks 240 may negatively affect the performance of mid-band radiating elements 132 that are mounted rearwardly of the low-band radiating elements 122/200. This is particularly true when the low-band radiating elements 122/200 “overlap” the mid-band radiating elements 132 (i.e., an axis that is perpendicular to the main surface of the reflector 110 extends through both the low-band and the mid-band radiating elements 122/200, 132), as is the case in the base station antenna 100. The performance degradation arises because the dielectric blocks 240 act to focus the mid-band radiation incident thereon, which distorts the element patterns of the mid-band radiating elements 132. While the type and degree of this distortion will vary depending on the relative locations of the low-band and mid-band radiating elements 122/200, 132, it will in most cases degrade the shape of the mid-band antenna beams.
As discussed above, pursuant to embodiments of the present invention, metal patterns may be provided that are used to reduce the impact that the dielectric blocks 240 may have on the radiation patterns of mid-band radiating elements 132 that are mounted in close proximity to the low-band radiating element 122/200. The metal patterns may be metamaterial metal patterns in some embodiments.
As shown in
A metamaterial refers to a material that is engineered to have a property that is not found in naturally occurring materials. Metamaterials typically have a unit cell structure and are primarily designed to influence electromagnetic waves. Each unit cell of a metamaterial structure may have a size that is a small fraction (e.g., 1/10th or less) of a wavelength of the electromagnetic waves that are to be influenced by the metamaterial structure. Example structures that may be used to implement the unit cells of a metamaterial structure are split ring resonators and complementary split ring resonators.
A split ring resonator consists of a pair of concentric metallic rings (also called loops), which are usually formed by etching a metal layer on a dielectric substrate (e.g., using printed circuit board fabrication techniques). Slits are provided in each ring. The rings may be square, circular, oval, rectangular or any other appropriate shape. A small gap is provided between the inner and outer rings. Magnetic flux that is incident on the split ring resonator induces rotating currents in the rings, and in response to the currents, the rings produce their own flux to enhance or oppose the incident electromagnetic field (depending on the resonant properties of the split ring resonator). The small gap between the rings produce large capacitance values which lower the resonating frequency, which allows split ring resonators to act as if they are electrically smaller (as compared to their physical size) when responding to RF energy.
As shown in
As shown in
The metamaterial metal patterns 270 are positioned behind the dielectric blocks 240 so that the metamaterial metal patterns 270 may reflect/absorb RF energy emitted by nearby mid-band radiating elements 132 that would otherwise impinge on the dielectric blocks 240. The metamaterial metal patterns 270 may also help improve the cloaking performance of the dipole arms 224, since the metamaterial metal patterns 270 may prevent some of the mid-band radiation from impinging on the dipole arms 224 of the low-band radiating element 122/200.
As described above, by adjusting the parameters a, Li and Lo the location of the null in the transmission curve (S21) shown in
One way to reduce the width of a base station antenna that includes two arrays of low-band radiating elements is to use so-called L-arrays, Y-arrays or other arrays that have increased array apertures in the azimuth plane. For example, U.S. Pat. No. 11,031,678 (“the '678 patent”), issued Jun. 8, 2021, illustrates at FIG. 2A a known base station antenna that includes two arrays of radiating elements that are each implemented as L-arrays. In this base station antenna, two columns of radiating elements are provided that are connected to feed networks to provide two arrays of dual-polarization radiating elements. The first array comprises the top radiating element in the left column plus all but the bottom radiating element in the right column. The second array comprises the bottom radiating element in the right column plus all but the top radiating element in the left column. With this arrangement, each array includes a plurality of radiating elements that are all in a first column plus one radiating element from a second column, and each array has an L-shape (which may be a rotated and/or inverted L-shape). By off-setting one of the radiating elements in each array in the horizontal direction, the aperture of each array is increased in the azimuth plane, which, with proper phasing of the radiating elements, acts to reduce the azimuth HPBW of the antenna beams generated by each array. One disadvantage, however, of this design is that it requires adding an additional radiating element to each column (to allow one row of each array to include two radiating elements), which increases the length and cost of the antenna.
FIG. 2B of the '678 patent illustrates another known base station antenna that provides an increased horizontal aperture without the need for adding an extra radiating element in each column. The base station antenna shown in FIG. 2B of the '678 patent includes two columns of low-band radiating elements that form first and second so-called “Y-shaped” arrays (note that each array is one radiating element short of having a true “Y-shape”). With this design, each array includes the bottom radiating element in a first of the two columns of radiating elements plus all but the bottom radiating element of the radiating elements in the other column. Since each array includes a radiating element that is in the opposite column, the horizontal aperture of each array is increased, with a commensurate reduction in the azimuth beamwidth. Moreover, since the base station antenna of FIG. 2B does not include two radiating elements in any row, it does not suffer from the cost and size disadvantages associated with base station antenna of FIG. 2A of the '678 patent. FIG. 2C of the '678 patent illustrates yet another base station antenna that has an increased aperture in the azimuth plane.
The base station antennas according to embodiments of the present invention may employ the techniques shown in FIGS. 2A-2C of the '678 patent, or similar arrangements of radiating elements that increase the horizontal apertures of the arrays, in order to further reduce the size of the base station antenna. When these techniques are used, the size of the low-band radiating elements may be reduced to a degree while still achieving a desired azimuth HPBW. When the size of the low-band radiating elements are reduced, the overall width of the base station antenna may likewise be reduced.
One way to further reduce the width of a base station antenna that includes two arrays of low-band radiating elements is to space the two columns of radiating elements closer together. While such a technique reduces the width of the antenna, it also increases the coupling between the radiating elements of the two different low-band arrays. As discussed above, such increased coupling is undesirable as it degrades the shapes of the antenna beams formed by both arrays, and also may degrade other performance parameters such as return loss, insertion loss, etc.
Pursuant to further embodiments of the present invention, base station antennas are provided that employ one or more couplers that are used to at least partially cancel RF energy that couples from a first low-band array to a second low-band array that are provided in the antenna.
As shown in
The coupler 500 further includes a first coupling transmission line 514-1 that couples with the first RF transmission line segment 512-1 to tap off a small amount of the RF energy that is passed over the first RF transmission line segment 512-1 from the first RF port 140-1 to the one or more radiating elements 122 of the first low-band array 120-1. Similarly, the coupler 500 also includes a second coupling transmission line 514-2 that couples with the second RF transmission line segment 512-2 to tap off a small amount of the RF energy that is passed over the second RF transmission line segment 512-2 from the second RF port 140-3 to the one or more radiating elements 122 of the second low-band array 120-2. A first end of the first coupling transmission line 514-1 is coupled to a first end of the second coupling transmission line 514-2 via an RF transmission line 530, such as a coaxial cable, that forms a coupling path. As described above, an electrical length of the RF transmission line 530 may be set so that the phase of the RF energy coupled from the one or more radiating elements 122 of the first low-band array 120-1 to the one or more radiating elements 122 of the second low-band array 120-2 over the RF transmission line 530 may have a phase that is approximately 180° out-of-phase with respect to the RF energy that directly couples from the one or more radiating elements 122 of the first low-band array 120-1 to the one or more radiating elements 122 of the second low-band array 120-2. Second ends of the first coupling transmission line 514-1 and the second coupling transmission line 514-1 are coupled to a terminated load 540 such as, for example, a 50 ohm resistor. The first and second RF transmission lines 512-1, 512-2 may overlap with the respective first and second coupling transmission lines 514-1, 514-2 such that the amount of RF energy that couples therebetween is approximately equal to the amount of RF energy that directly couples from the one or more radiating elements 122 of the first low-band array 120-1 to the one or more radiating elements 122 of the second low-band array 120-2 (and vice versa).
In some cases, the couplers may be designed to cancel substantially all of the RF energy that directly couples between a pair of horizontally aligned radiating elements 122 from the first and second low-band linear arrays 120-1, 120-2. In other cases, this may result in too much power loss. In such situations, the couplers 500 may be designed to only cancel a portion of the coupled RF energy. This results in a compromise between the gain of the antenna beams and the shape thereof.
It will be appreciated that many modifications may be made to the above example embodiments without departing from the scope of the present invention. For example, the number of radiating elements in each column of the base station antennas may be varied from what is shown in the example embodiments above. Typical numbers of radiating elements per column may range from about four to twenty radiating elements, with six to ten radiating elements per column being common. As another example, while the above-described embodiments employ dipole radiating elements, it will be appreciated that other types of radiating elements may be used such as, for example, single polarization and dual polarization patch radiating elements.
While the example embodiments of the present invention discussed above are formed using low-band radiating elements, it will be appreciated that the techniques disclosed herein are equally applicable to radiating elements that operate in other frequency bands, such as the mid-band and high-band operating frequency ranges. Thus, each of the designs discussed above could alternatively be implemented using all mid-band or all high-band radiating elements.
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.
Herein, the term “substantially” refers to variation of less than 10%.
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.).
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 claims priority to U.S. Provisional Patent Application Ser. No. 63/446,413, filed Feb. 17, 2023, the entire content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63446413 | Feb 2023 | US |
