Patent Description:
The present invention generally relates to radio communications and, more particularly, to base station antennas that support communications in multiple frequency bands.

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 one or more base stations. A base station may include baseband equipment, radios and antennas that are configured to provide two-way radio frequency ("RF") communications with mobile subscribers that are geographically positioned within the cell. A common cellular communications system network plan involves a base station serving a cell using three base station antennas, wherein each base station antenna serves a <NUM> degree "sector" of the cell in the azimuth plane. 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 base station antenna directed outwardly to serve the respective sector. Typically, a base station antenna is implemented as a phase-controlled array of radiating elements, with the radiating elements arranged in one or more vertical columns. Herein, "vertical" refers to a direction that is perpendicular relative to the plane defined by the horizon.

As demand has grown for cellular communications systems to support increased capacity and provide enhanced capabilities, a variety of new cellular services have been introduced. These new services typically operate in different frequency bands from existing services to avoid interference. When new services are introduced, the existing "legacy" services typically must be maintained to support legacy mobile devices. Thus, as new services are introduced, either new cellular base stations must be deployed or existing cellular base stations must be upgraded to support the new services in the new frequency bands. In order to reduce cost and the total number of base station antennas deployed, base station antennas are now available that include at least two different arrays of radiating elements, where each array of radiating elements supports a different type of cellular service in a different frequency band. Such antennas are typically referred to as multi-band antennas. <CIT> and <CIT> disclose multi-band base station antennas.

According to the invention a base station antenna unit according to claim <NUM> is provided. Preferred embodiments are set forth in dependent claims. Pursuant to embodiments of the present invention, base station antenna units are provided that include a first base station antenna that has (<NUM>) a first housing, a first radome having a front surface that is positioned in front of the first housing, a first vertically-disposed linear array of low-band radiating elements mounted on a first backplane behind the front surface of the first radome and a second vertically-disposed linear array of mid-band radiating elements mounted on the first backplane behind the front surface of the first radome and (<NUM>) a second base station antenna that has a second housing that is separate from the first housing, a second radome having a front surface that is positioned in front of the second housing and a third array of high-band radiating elements mounted on a second backplane behind the front surface of the second radome, the second radome being separate from the first radome. The second base station antenna is mounted on top of the first base station antenna in a vertically stacked arrangement and the first and second base station antennas are configured to be mounted as a single structure.

Many state-of-the-art base station antennas now include multiple vertical columns ("arrays") of radiating elements in order to support several different types of cellular service. A very common base station antenna configuration includes a first vertical linear array of radiating elements that transmits and receives signals in a first frequency band (herein the "low-band") and one or more additional vertical linear arrays of radiating elements that transmit and receive signals in a second frequency band (herein the "mid-band") that is at higher frequencies than the first frequency band. These antennas are referred to as "dual-band" antennas as they support service in two different frequency bands using two different sets of radiating elements. Typically, the first frequency band includes one or more specific frequency bands that are below about <NUM>, and the second frequency band includes one or more specific frequency bands that are in the range of <NUM>-<NUM> (and typically between about <NUM>-<NUM>). The specific frequency bands may correspond to specific types of cellular service such as, for example, Global System for Mobile Communications ("GSM") service, Universal Mobile Telecommunications system ("UTMS") service, Long Term Evolution ("LTE") service, CDMA service, etc..

<FIG> illustrate a typical conventional multi-band base station antenna <NUM>. In particular, <FIG> is a perspective view of the conventional multi-band base station antenna <NUM> and <FIG> is a schematic front view of the multi-band base station antenna <NUM> with the radome removed therefrom to schematically illustrate the linear arrays of radiating elements included in the antenna <NUM>.

As shown in <FIG>, the conventional multi-band base station antenna <NUM> includes a housing <NUM> and a radome <NUM> that is mounted on a front portion of the housing <NUM>. The housing <NUM> may comprise a tray <NUM> that extends around the sides and back of the antenna <NUM> and bottom and top end caps <NUM>, <NUM>. The tray <NUM>, end caps <NUM>, <NUM> and radome <NUM> protect the antenna <NUM>. The radome <NUM> and tray <NUM> may be formed of, for example, extruded plastic, and may be multiple parts or implemented as a monolithic structure. In other embodiments, the tray <NUM> may be made from metal and may act as an additional reflector to improve the front-to-back ratio for the antenna <NUM>. Mounting brackets <NUM> may extend through the back of the tray <NUM> which may be used to mount the base station antenna <NUM> to another structure such as, for example, an antenna tower (not shown). A plurality of connectors <NUM> may extend through respective openings in the bottom end cap <NUM>. Cables (not shown) may be connected to the connectors <NUM> to pass signals between the base station antenna <NUM> and a plurality of radios (not shown).

Referring now to <FIG>, it can be seen that the base station antenna includes a first vertical array <NUM> of low-band radiating elements <NUM>, a second vertical array <NUM>-<NUM> of mid-band radiating elements <NUM> and a third vertical array <NUM>-<NUM> of mid-band radiating elements <NUM>. Note that herein when multiple of the same component are provided the components may be assigned two-part reference numerals and the components may be referred to individually by their full reference numeral (e.g., vertical array <NUM>-<NUM>) and collectively by the first part of their reference numerals (e.g., the vertical arrays <NUM>). Each of the three vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM> may be mounted on a reflector <NUM>. The radiating elements <NUM> in the first vertical array <NUM> may be fed by a first corporate feed network (not shown) that divides a low-band RF signal to be transmitted into a plurality of sub-components. Each sub-component may be fed to one of the radiating elements <NUM> or to a sub-array that includes multiple of the radiating elements <NUM>. One or more phase shifters (not shown) may be included in the corporate feed network. The phase shifters may apply different phase shifts to respective ones of the sub-components of the low-band RF signal to apply a phase taper to the sub-components that may be used to control the elevation beamwidth of an antenna beam formed by the first vertical array <NUM> and/or to adjust the elevation angle of the antenna beam formed by the first vertical array <NUM>. The antenna beam formed by the first vertical array <NUM> may have an azimuth beamwidth of, for example, about <NUM> degrees and an elevation beamwidth of about <NUM>-<NUM> degrees in example embodiments. The phase shifters and the corporate feed network may be mounted within the housing <NUM>.

In some embodiments, the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM> may be fed by a second corporate feed network (not shown) that divides a mid-band RF signal to be transmitted into a plurality of sub-components. Each sub-component may be fed to one of the radiating elements <NUM> or to a sub-array that includes multiple of the radiating elements <NUM>. One or more phase shifters (not shown) may be included in the corporate feed network. The phase shifters may apply different phase shifts to respective ones of the sub-components of the mid-band RF signal to apply a phase taper to the sub-components that may be used to control the elevation beamwidth of an antenna beam formed by the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM> and/or to adjust the elevation angle of the antenna beam formed by the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM>. The antenna beam formed by the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM> may have an azimuth beamwidth of, for example, about <NUM> degrees and an elevation beamwidth of about <NUM>-<NUM> degrees. In other embodiments, the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM> may be fed by respective second and third corporate feed networks (not shown). For example, the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM> may be connected to respective radios that communicate in different sub-bands of the second frequency range. In such embodiments, the second and third vertical arrays <NUM>-<NUM>, <NUM>-<NUM> may generate independent antenna beams that overlap in coverage area but are separated in frequency.

Many mobile operators are considering deploying new services in a third frequency band that is at higher frequencies than the first and second frequency bands discussed above. For example, a number of mobile operators, particularly in Europe and/or the United States, are considering supporting new services using a frequency band at about <NUM>. Service could also be supported, for example, in the unlicensed <NUM> spectrum. These frequency bands could be used to support, for example, Long Term Evolution ("LTE") time division duplexing ("TDD") service or other <NUM> technologies. In order to avoid increasing the antenna count at cellular base stations, it may be desirable to support services in a third frequency band in the same antenna structure used to support services in the first and second frequency bands. Reducing the number of antennas may have a number of advantages including reduced installation costs, a reduction in the number of mounting supports required on the antenna tower, a reduction in the overall weight of the antennas and a more aesthetic appearance, and may also be required in some cases to comply with local ordinances and/or zoning regulations.

Unfortunately, increasing the number of frequency bands supported by a base station antenna may tend to require larger and more complex antenna structures. Moreover, the more frequency bands that are supported by a base station antenna, the more likely it is that interference will arise between signals transmitted in the different frequency bands. For example, it is expected that integrating radiating elements for a <NUM> or <NUM> frequency band into a conventional dual-band base station antenna such as base station antenna <NUM> that supports services in the above-described first and second frequency bands will require compromising some of the performance metrics for the lower frequency bands. As such, many operators are considering supporting the <NUM> or <NUM> frequency band using separate antenna structures, despite the above described disadvantages of using separate units.

Base station antennas typically come in several vertical lengths. In particular, the elevation beamwidth of a vertical array of radiating elements included on a base station antenna is a function of (<NUM>) the frequency band and (<NUM>) the spacing between the uppermost and lowermost radiating elements in the vertical array. Depending upon the size and geography of the cell and various other parameters, an operator may require base station antennas with different elevation beamwidths. For example, in some cases, it may be desirable to have a small elevation beamwidth (e.g., <NUM>-<NUM> degrees) in order to increase the antenna gain and/or to reduce spillover of the antenna beam into adjacent cells (as such spillover appears as interference in the adjacent cells). This requires relatively long base station antennas that have a large spacing between the uppermost and lowermost radiating elements in order to narrow the elevation beamwidth of the antenna beam. In other cases, larger elevation beamwidths are acceptable, allowing the use of shorter base station antennas that have fewer radiating elements in the vertical arrays. Typical heights for base station antenna are <NUM> meters (or <NUM> feet), <NUM> meters (or <NUM> feet) and <NUM> meters (or <NUM> feet). While the number of base station antennas deployed at a base station is an important parameter (e.g., to comply with local zoning ordinances and/or because installation fees are typically charged on a per antenna basis), less attention is typically paid to the height of each base station antenna.

Pursuant to embodiments of the present invention, composite base station antenna units are provided in which first and second base station antennas are mounted together in a vertically stacked arrangement so that the composite base station antenna unit has the appearance of a single base station antenna. The first base station antenna may comprise a conventional dual-band base station antenna that includes one or more low-band vertical arrays of radiating elements that communicate in a first frequency band (e.g., some or all of the <NUM>-<NUM> band) and one or more mid-band vertical arrays of radiating elements that communicate in a second frequency band (e.g., the <NUM>-<NUM> band). The height of the first base station antenna (i.e., the length of the antenna in the vertical direction that is perpendicular to the plane defined by the horizon when the antenna is mounted for use) may be, for example, in the range of about <NUM> meters to about <NUM> meters. The second base station antenna may comprise, for example, a planar array of radiating elements that communicate in a third frequency band (e.g., the <NUM> or <NUM> bands). The height of the second base station antenna may be for example, in the range of about <NUM> meters or less in some embodiments. As a result, the base station antenna units according to embodiments of the present invention may be no longer than conventional <NUM> meter base station antennas.

The first and second base station antennas may be mounted as a single unit and may appear, at least from a distance, as a single base station antenna. For example, the first and second base station antennas may be vertically aligned and may have substantially the same width. In some embodiments, the two antennas may be in direct contact, or nearly so, such that they appear as a single antenna when viewed from the front. The two antennas may be fixed to each other or fixed to a common mounting structure that connects the two antennas to form the single base station antenna unit. The single base station antenna unit including the two base station antennas may be mounted to an antenna tower or other raised structure using conventional base station antenna mounting hardware in some embodiments. By combining the two base station antennas into a single base station antenna unit it will appear as if there are fewer base station antennas mounted on a cell tower, which may be more aesthetically pleasing. The base station antenna units according to embodiments of the present invention may also be cheaper and easier to mount on a cell tower and require less mounting hardware as compared to two separate base station antennas that provide comparable functionality.

In some embodiments, the first base station antenna may include a first vertical array of low-band radiating elements and second and third vertical arrays of mid-band radiating elements. The first vertical array may be positioned between the second and third vertical arrays. The second base station antenna may include a fourth array of high-band radiating elements. The fourth array may include multiple columns of high-band radiating elements which may be arranged in a planar array. In some embodiments, the fourth array may include at least three vertical columns of high-band radiating elements and at least three rows of high-band radiating elements.

In some embodiments, the first and second base station antennas may share a common radome. The use of such a common radome may enhance the appearance that the two base station antennas are a single antenna. In further embodiments, the first and second base station antennas may be replaced with a single base station antenna that includes all four of the above-described first, second, third and fourth arrays of radiating elements. The fourth array may be mounted above the first, second and third vertical arrays. The first vertical array may be mounted between the second and third vertical arrays.

Embodiments of the present invention will now be discussed in further detail with reference to the figures, in which example embodiments of the invention are shown.

<FIG> and 3A-3D illustrate a base station antenna unit <NUM> according to certain embodiments of the present invention that includes two co-mounted base station antennas <NUM>, <NUM>. In particular, <FIG> is a schematic side view of a multi-band base station antenna unit <NUM>, <FIG> is a schematic front view of the multi-band base station antenna unit <NUM> with the radomes of each base station antenna <NUM>, <NUM> removed, and <FIG> is a front view of the multi-band base station antenna unit <NUM> with the radomes of each base station antenna <NUM>, <NUM> in place. <FIG> are a side view and a front view, respectively, of two of the low-band radiating elements included in the base station antenna <NUM>. <FIG> are a front view and a side view, respectively, of two of the mid-band radiating elements included in the base station antenna unit <NUM>.

Referring to <FIG> and <FIG>, the base station antenna unit <NUM> includes a first base station antenna <NUM> and a second base station antenna <NUM>. The second base station antenna <NUM> is mounted on top of the first base station antenna <NUM>. The first and second base station antennas <NUM>, <NUM> may appear to be a single base station antenna. The second base station antenna <NUM> may be referred to herein as a "high-band box top" as the second base station antenna <NUM> may be configured to communicate in a high frequency band and may be mounted atop the first base station antenna <NUM>.

Referring to <FIG>, the first base station antenna <NUM> includes three vertically-oriented linear arrays of radiating elements, namely a low-band array <NUM> that includes a plurality of low-band radiating elements <NUM> and first and second mid-band arrays <NUM>-<NUM>, <NUM>-<NUM> that each include a plurality of mid-band radiating elements <NUM>. The vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM> may be identical to the vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM> of the base station antenna <NUM> discussed above. It will be appreciated that any appropriate number of radiating elements <NUM>, <NUM> may be included in the vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM>. The radiating elements <NUM>, <NUM> are mounted on a backplane <NUM>. The backplane <NUM> may comprise a unitary structure or may comprise a plurality of structures that are attached together. The backplane <NUM> may comprise, for example, a reflector that serves as a ground plane for the radiating elements <NUM>, <NUM>.

Referring now to <FIG>, it can be seen that each low-band radiating element <NUM> may comprise a stalk <NUM> and a radiator <NUM>. Each stalk <NUM> may comprise one or more printed circuit boards. The radiator <NUM> may comprise, for example, a dipole radiator. In the depicted embodiment, the base station antenna <NUM> is a dual-polarized antenna, and hence each radiator <NUM> comprises a cross-dipole structure. Each radiator <NUM> may be disposed in a plane that is substantially perpendicular to a longitudinal axis of the corresponding stalk <NUM> of the radiating element <NUM>. In the depicted embodiment, the low-band radiating elements <NUM> are mounted in pairs on respective feed boards <NUM> that provide the sub-components of an RF signal that is to be transmitted to the respective radiating elements <NUM>. Supports <NUM> may facilitate holding the radiators <NUM> in place. It will be appreciated that while <FIG> illustrate one example low-band radiating element <NUM> that may be used in the base station antenna units according to embodiments of the present invention, any appropriate low-band radiating elements may be used.

As shown in <FIG>, each mid-band radiating element <NUM> may comprise a stalk <NUM> and a radiator <NUM>. Each stalk <NUM> may comprise one or more printed circuit boards. The radiator <NUM> may comprise, for example, a dipole or patch radiator. In the depicted embodiment, each mid-band radiator <NUM> comprises a cross-dipole radiator <NUM> that is formed on a printed circuit board. Each radiator <NUM> may be disposed in a plane that is substantially perpendicular to a longitudinal axis of the corresponding stalk <NUM> of the radiating element <NUM>. In the depicted embodiment, the mid-band radiating elements <NUM> are mounted in pairs on respective feed boards <NUM> that provide the sub-components of an RF signal that is to be transmitted to the respective radiating elements <NUM>. Directors <NUM> may be mounted above the radiating elements <NUM> to help narrow the beamwidth of the radiating elements <NUM>.

Referring again to <FIG>, the first base station antenna <NUM> further includes a housing <NUM> and a radome <NUM>. The housing <NUM> may comprise a tray <NUM> that extends around the sides and back of the antenna <NUM> and bottom and top end caps <NUM>, <NUM>. The tray <NUM>, end caps <NUM>, <NUM> and radome <NUM> protect the antenna <NUM>. The radome <NUM> and tray <NUM> may be formed of, for example, extruded plastic, and may be multiple parts or implemented as a monolithic structure. In other embodiments, the tray <NUM> may be made from metal. Mounting brackets <NUM> may extend through the back of the tray <NUM>.

The backplane <NUM> may be mounted on or in the housing <NUM>. The radiating elements <NUM>, <NUM> of the first through third vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM> may extend forwardly from the backplane <NUM>. The radome <NUM> may be attached to the tray <NUM> and may extend forwardly therefrom to cover and protect the radiating elements <NUM>, <NUM>.

A plurality of connectors <NUM> may be mounted within openings in the bottom end cap <NUM>. Each connector <NUM> may have a longitudinal axis. The longitudinal axes of at least some of the connectors <NUM> may extend substantially in the vertical direction when the base station antenna <NUM> is mounted for use.

A plurality of circuit elements and other structures may be mounted within the housing <NUM>. These circuit elements and other structures may include, for example, phase shifters for one or more of the first through third vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM>, remote electronic tilt (RET) actuators for mechanically adjusting the phase shifters, one or more controllers, filters such as duplexers and/or diplexers, cabling connections, RF transmission lines and the like.

The second base station antenna <NUM> includes a two-dimensional planar array <NUM> of high-band radiating elements <NUM>. The planar array <NUM> may include at least two columns and two rows of high-band radiating elements <NUM>. In the depicted embodiment, the planar array <NUM> includes four columns and six rows of high-band radiating elements <NUM> for a total of twenty-four high-band radiating elements <NUM>. The high-band radiating elements <NUM> are mounted on a backplane <NUM>. The backplane <NUM> may comprise a unitary structure or may comprise a plurality of structures that are attached together. The backplane <NUM> may comprise, for example, a reflector that serves as a ground plane for the high-band radiating elements <NUM>.

In some embodiments, each high-band radiating element <NUM> may comprise a dipole or patch radiator. If the base station antenna <NUM> is a dual-polarized antenna, each high-band radiating element <NUM> may comprise, for example, a cross-dipole structure.

The second base station antenna <NUM> further includes a housing <NUM> and a radome <NUM>. The backplane <NUM> may be mounted on or in the housing <NUM>. The high-band radiating elements <NUM> of the fourth planar array <NUM> may extend forwardly from the backplane <NUM>. The radome <NUM> may be attached to the housing <NUM> and may extend forwardly therefrom to cover and protect the high-band radiating elements <NUM>.

The housing <NUM> may comprise a tray <NUM> that extends around the sides and back of the antenna <NUM> and bottom and top end caps <NUM>, <NUM>. The radome <NUM> and tray <NUM> may be formed of, for example, extruded plastic, and may be formed of multiple parts or implemented as a monolithic structure. In other embodiments, the tray <NUM> may be made from metal. An upper portion of the housing <NUM> may extend farther rearwardly than a lower portion of the housing <NUM> to define a lip <NUM>. A base plate <NUM> may form a bottom surface of the lip <NUM>. A plurality of connectors <NUM> may be mounted within openings in the base plate <NUM>. Each connector <NUM> may have a longitudinal axis. The longitudinal axes of at least some of the connectors <NUM> may extend substantially in the vertical direction. Since the bottom end cap <NUM> may not be accessible when the second base station antenna <NUM> is mounted on the first base station antenna <NUM>, the lip <NUM> and base plate <NUM> provide a convenient means for mounting the connectors <NUM> of the second base station antenna <NUM> in a readily accessible location.

In some embodiments, the high-band radiating elements <NUM> may be configured to operate in the <NUM> frequency band or the <NUM> frequency band, although embodiments of the present invention are not limited thereto. The planar array <NUM> of high-band radiating elements <NUM> may be configured to perform time division duplexing beamforming operations in which different antenna beams may be formed in different time slots to provide communications to different users or sets of users during each different time slot. The planar array <NUM> of high-band radiating elements <NUM> may be configured to generate multiple different antenna beams during any given time slot in order to provide high directivity coverage to selected portions of a coverage area during a given time slot.

As shown in <FIG>, the second base station antenna <NUM> is mounted on top of the first base station antenna <NUM> to form the base station antenna unit <NUM>. A lowermost portion of the second base station antenna <NUM> may be located, for example, within six inches, or within four inches, or within two inches of an uppermost portion of the first base station antenna <NUM> in example embodiments. The front surface <NUM> of the radome <NUM> of the second base station antenna <NUM> may be substantially vertically aligned with the front surface <NUM> of the radome <NUM> of the first base station antenna <NUM>. As shown in <FIG>, the width W1 of the radome <NUM> may be substantially the same as the width W2 of the second radome <NUM>. The front surfaces <NUM>, <NUM> of the respective first and second radomes <NUM>, <NUM> may be curved front surfaces. The front surfaces <NUM>, <NUM> may have substantially the same curvature in some embodiments.

An attachment mechanism <NUM> may be provided that attaches the first base station antenna <NUM> to the second base station antenna <NUM>. In some embodiments, the attachment mechanism <NUM> may be one or more supports that extend upwardly from the first base station antenna <NUM> that are attached to, surround and/or otherwise support the second base station antenna <NUM>. In other embodiments, the attachment mechanism <NUM> may be one or more supports that extend downwardly from the second base station antenna <NUM> that are attached to the first base station antenna <NUM>. In still other embodiments, the attachment mechanism <NUM> may comprise a separate structure that is attached to both of the first and second base station antennas <NUM>, <NUM>. A wide variety of other attachment mechanisms <NUM> will be apparent to those of skill in the art in light of the teachings of the present disclosure, and it will be appreciated that any appropriate attachment mechanism <NUM> may be used.

The attachment mechanism <NUM> allows the first and second base station antennas <NUM>, <NUM> to be mounted as a single structure (namely as the base station antenna unit <NUM>). In some embodiments, the first base station antenna <NUM> may include mounting brackets <NUM> or other attachment points/structures that are used to mount the base station antenna unit <NUM> on, for example, an antenna tower. Thus, both base station antennas <NUM>, <NUM> may be mounted in a single mounting location, saving room on the antenna tower. Additionally, since both base station antennas <NUM>, <NUM> may be mounted as a single unit using a single set of mounting brackets <NUM> or the like, it is possible to mount both base station antennas <NUM>, <NUM> with approximately the same amount of effort required to mount a single conventional base station antenna.

Another advantage of the high-band box top design of base station antenna unit <NUM> is that coupling between the radiating elements of different frequency bands in a multi-band base station antenna tends to be more problematic when the radiating elements are close to each other in the azimuth (horizontal) plane as opposed to the elevation (vertical) plane. Here, the first base station antenna <NUM> may comprise a conventional base station antenna that includes, for example, a vertical array of low-band radiating elements that is disposed between a pair of vertical arrays of mid-band radiating elements. Sufficient isolation may be readily achieved between the low-band radiating elements and the mid-band radiating elements using conventional techniques in a base station antenna having a suitably narrow width (e.g., a width of <NUM> or less). If the columns of high-band radiating elements <NUM> were interspersed between the low-band and mid-band vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM> it may be very difficult to minimize the impact of the high-band radiating elements <NUM> on the low-band and/or mid-band radiating elements <NUM>, <NUM>, even if decoupling structures are used. However, by mounting the high-band radiating elements <NUM> above the low-band and mid-band vertical arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM>, it is believed that the amount of coupling between the high-band radiating elements <NUM> and the low-band and/or mid-band radiating elements <NUM>, <NUM> may be kept low such that all of the low-band, mid-band and high-band arrays <NUM>, <NUM>, <NUM> may exhibit good performance.

Typical RVV type base station antenna which include one low-band (R-band) linear array and two mid-band (V-band) linear arrays have a width of <NUM> or less. This width may accommodate a high-band array <NUM> having at least four columns or high-band radiating elements <NUM> and possibly as many as six columns or high-band radiating elements <NUM> in the <NUM> frequency band (i.e., a wavelength of <NUM>) assuming a <NUM>. 65λ spacing between adjacent high-band radiating elements <NUM>. It will be appreciated that high-band box top antennas may also be provided that are configured to be mounted on top of RRVV base station antenna that include two low-band (R-band) linear array and two mid-band (V-band) linear arrays. High-band box top antennas that are designed to be mounted on top of RRVV base station antenna may include an even larger number of columns in the high-band array.

At least from a distance, the base station antenna unit <NUM> that includes two separate base station antennas <NUM>, <NUM> will appear as a single base station antenna. This is possible because the first and second base station antennas <NUM>, <NUM> may have similar or even identical front profiles and may be mounted in close proximity to each other. In fact, in some embodiments, a bottom of the second base station antenna <NUM> may directly contact a top of the first base station antenna <NUM>. In some embodiments, the second base station antenna <NUM> may have the rearwardly-extending lip or "cowling" <NUM> and hence a maximum depth of the second base station antenna <NUM> may exceed the maximum depth of the first base station antenna <NUM>. As described above, this may facilitate vertically mounting the connectors <NUM> for the second base station antenna <NUM> in the base plate <NUM> so that the cables feeding the second base station antenna <NUM> may connect to a lower surface of the antenna <NUM>, which helps protect against water/moisture ingress. However, as the cowling <NUM> is rearwardly-facing it should not substantially disrupt the appearance that the two base station antennas <NUM>, <NUM> are a single antenna.

A wide variety of attachment structures may be used to attach the first and second base station antennas <NUM>, <NUM> to each other to form the base station antenna unit <NUM>. For example, as shown in <FIG>, in some embodiments, a plurality of upwardly-extending support arms <NUM> could be mounted on the upper portion of the housing <NUM> of the first base station antenna <NUM> via screws, bolts, rivets or various other attachment mechanisms. The upper portions of these support arms <NUM> could be attached to the housing <NUM> of the second base station antenna <NUM> to attach the two base station antennas <NUM>, <NUM> together to form the base station antenna unit <NUM>. As shown in <FIG>, in another embodiment, an external housing <NUM> that has a front surface that does not block RF energy may be provided and both the first and second base station antennas <NUM>, <NUM> could be mounted within this housing <NUM>. The housing <NUM> may include openings (not visible in the drawing) along the back surface thereof that allow the mounting brackets <NUM> of the first base station antenna <NUM> to extend outside of the housing <NUM> so that the mounting brackets <NUM> may be used to mount the base station antenna unit <NUM> on an antenna tower or other structure. As shown in <FIG>, in yet other embodiments a composite radome <NUM> may be provided that acts as the radome for both the first and second base station antennas <NUM>, <NUM> (eliminating the need for radomes <NUM>, <NUM>), and the composite radome <NUM> may serve as at least part of the structural mechanism that attaches the first and second base station antennas <NUM>, <NUM> to each other. In such embodiments, additional structural mechanisms such as the above-described support arms <NUM> may also be provided.

It will be appreciated that numerous other attachment structures may be used. The attachment structure should provide mechanical integrity and ensure directional stability for the second base station antenna <NUM> (assuming that mounting brackets <NUM> on the first base station antenna <NUM> are used to mount the base station antenna unit <NUM> to a tower or other structure). The attachment structure also should not have a significant impact on the RF performance of either the first or second base station antennas <NUM>, <NUM>, with the caveat that in some cases an attachment structure may be provided that is designed to improve the RF performance of one or both base station antennas <NUM>, <NUM> by, for example, attenuating unwanted sidelobes or the like in the antenna patterns thereof.

The base station antenna unit <NUM> may be field deployable in that the second base station antenna <NUM> may be designed to be attached to conventional base station antenna in order to form the base station antenna unit <NUM>.

In some embodiments, the high-band array <NUM> may be designed to have a different coverage area than the low-band and mid-band arrays <NUM>, <NUM>-<NUM>, <NUM>-<NUM>. For example, in some cases the high-band array <NUM> may be designed to only cover a portion of the cell that is closer to a mounting structure (e.g., antenna tower) on which the base station antenna unit <NUM> is mounted. The base station antenna unit <NUM> may have such a design because the free-space loss at <NUM> or <NUM>, for example, will be higher than the free-space loss at the frequencies of the low-band and the mid-band, making it potentially more difficult to achieve coverage of the entire cell.

Since the high-band array <NUM> may have a reduced coverage area, it may be advantageous to "pre-set" the high-band array <NUM> to have some amount of downtilt (i.e., a tilt at an angle below the horizon in the elevation plane). This downtilt may either be a mechanical downtilt or an electrical downtilt. As known to those of skill in the art, a mechanical downtilt refers to physically pointing the radiating elements of an array downwardly from a plane parallel to the plane defined by the horizon. Such a downtilt is often used so that the main lobe of an antenna beam formed by an array will be pointed at the ground at some distance from the base station antenna. This technique may be used to increase the antenna gain within a coverage area for the base station antenna and/or to reduce the extent to which the antenna beam extends into adjacent cells.

An electrical downtilt refers to a downtilt that is implemented by adjusting the phases and/or amplitudes of the sub-components of an RF signal that is transmitted or received by the radiating elements of an array. Electrically downtilting a phased array antenna is often preferable to using a mechanical downtilt, both because the antenna pattern achieved using electrical downtilt is different from, and often preferable to, the antenna pattern formed by a mechanically downtilted phased array antenna, and because the electrical downtilt is typically implemented from a remote location using "remote electrical downtilt" capabilities by sending control signals that adjust settings on phase shifters included along the RF path in the antenna in order to implement the electronic downtilt.

In some embodiments, each high-band radiating element <NUM> may have a mechanical downtilt such as, for example, a mechanical downtilt of <NUM>-<NUM> degrees. Since the total height of the second base station antenna <NUM> may be fairly small (e.g., <NUM> meters or less), it may be possible to achieve this mechanical downtilt by physically tilting the backplane <NUM> away from the vertical plane within the radome <NUM>. In taller antennas (e.g., <NUM> to <NUM> meter antennas) this may not be possible because the mechanical downtilt may necessitate an increased depth for the antenna. Additionally, the high-band radiating elements <NUM> may be significantly shorter than the low-band and mid-band radiating elements <NUM>, <NUM>, and hence there may be room for tilting the backplane <NUM> in the second base station antenna <NUM>.

Pursuant to embodiments of the present invention, the base station antenna units and base station antennas described herein may be designed so that phase shifters that are included in the antenna are pre-set to apply a pre-determined amount of electrical downtilt to the high-band array. For example, the phase shifters may be set so that the high-band array has a pre-set downtilt of between two and six degrees in some embodiments. As is known to those of skill in the art, when an electronic downtilt is applied to a phased array antenna, some distortion may occur to the antenna pattern thereof, and the amount of distortion tends to increase with the amount of the downtilt. For example, grating lobes may appear when an electrical downtilt exceeds a certain amount. A pre-set downtilt means that the phase shifters are set so that the highest elevation angle that the high-band array <NUM> may be set to is below the horizon (e.g., two to six degrees). The amount of downtilt can then be increased some additional amount using the phase shifters included in the corporate feed network for the high-band array <NUM>. In other embodiments, the radiating elements <NUM> of the high-band array <NUM> may have a pre-set amount of mechanical downtilt (e.g., <NUM>-<NUM> degrees) and electrical downtilt may then be used to further adjust the elevation pointing angle of the high-band array <NUM>.

In some embodiments, the high-band array <NUM> may be configured to have a greater amount of pre-set electrical downtilt than does the low-band array <NUM> and/or mid-band arrays <NUM>.

While the base station antenna unit <NUM> includes two completely separate base station antennas <NUM>, <NUM> that are mounted together as a single antenna, it will be appreciated that in other examples that do not form part of the main invention but are nonetheless useful for the understanding of the invention some components may be shared across both antennas. For example, <FIG> is a perspective view of a base station antenna unit <NUM> that includes first and second base station antennas that share a common radome <NUM>. The use of the common radome may enhance the appearance that the first and second base station antenna are a single antenna.

While the above-described embodiments of the present invention are directed to base station antenna units that include first and second base station antenna, it will be appreciated in light of the teachings of the present disclosure that in other examples that do not form part of the main invention but are nonetheless useful for the understanding of the invention a single tri-band base station antenna may be provided that includes arrays of radiating elements that support all three of the low-band, mid-band and high-band frequency bands in a single housing. Such base station antennas can have the arrays arranged in the same manner as the base station antenna unit <NUM> that is described above, although it may also be possible to further optimize the locations of the arrays to reduce interference.

<FIG> schematically illustrate several example tri-band base station antenna <NUM>, <NUM>, <NUM> according to examples that do not form part of the main invention but are nonetheless useful for the understanding of the invention that have such a design. In particular, <FIG> is a schematic perspective view of the tri-band base station antenna <NUM>, and <FIG> is a schematic front view of the base station antenna <NUM> with the radome thereof removed. <FIG> are schematic front views of tri-band base station antennas <NUM>, <NUM> (with the radomes removed) that are modified versions of the tri-band base station antenna <NUM>.

As can be seen in <FIG>, the tri-band base station antenna <NUM> includes three vertically-oriented linear arrays of radiating elements, namely a low-band array <NUM> that includes a plurality of low-band radiating elements <NUM> and first and second mid-band arrays <NUM>-<NUM>, <NUM>-<NUM> that each include a plurality of mid-band radiating elements <NUM>. The low-band radiating elements <NUM> and the mid-band radiating elements <NUM> may be identical to the respective low-band radiating elements <NUM> and the mid-band radiating elements <NUM> that are described above, and hence further description thereof will be omitted.

The tri-band base station antenna <NUM> further includes a two-dimensional planar array <NUM> of high-band radiating elements <NUM>. The planar array <NUM> may include at least two columns and two rows of high-band radiating elements <NUM>, and may be identical to the planar array <NUM> that is described above. The high-band radiating elements <NUM> may be identical to the high-band radiating elements <NUM> that are described above, and hence further description thereof will be omitted.

The radiating elements <NUM>, <NUM>, <NUM> may be mounted on a common backplane <NUM>. The backplane <NUM> may comprise a unitary structure or may comprise a plurality of structures that are attached together. The backplane <NUM> may comprise, for example, a reflector that serves as a ground plane for the radiating elements <NUM>, <NUM>, <NUM>. As shown in <FIG>, the tri-band base station antenna <NUM> may further include a housing <NUM> and a radome <NUM>. The backplane <NUM> may be mounted on or in the housing <NUM>. The radiating elements <NUM>, <NUM>, <NUM> may extend forwardly from the backplane <NUM>. The radome <NUM> may be attached to the housing <NUM> and may extend forwardly therefrom to cover and protect the radiating elements <NUM>, <NUM>, <NUM>. The housing <NUM> may include a tray <NUM>, a bottom end cap <NUM> and a top end cap <NUM>. The radome <NUM> may attach to the tray <NUM>. A plurality of connectors <NUM> may be mounted within openings in the bottom end cap <NUM>. Notably, the cowling <NUM> that is included in the second base station antenna <NUM> discussed above is unnecessary in the antennas <NUM>, <NUM>, <NUM> since the connectors <NUM> for the high-band array <NUM> may be mounted in the bottom end cap <NUM> and cables or transmission lines may be run through the housing <NUM> to the corporate feed network for the high-band array <NUM>. The base station antennas <NUM> and <NUM> may have the same housing and radome design as base station antenna <NUM> and hence may appear identical in perspective view to the base station antenna <NUM> illustrated in <FIG>.

The base station antennas <NUM>, <NUM>, <NUM> differ from each other in the relative locations of the radiating elements <NUM>, <NUM>, <NUM>. For example, as shown in <FIG>, the base station antenna <NUM> is designed to locate the radiating elements <NUM>, <NUM>, <NUM> in the same positions in which the corresponding radiating elements <NUM>, <NUM>, <NUM> of base station antenna unit <NUM> are mounted. Thus, the primary difference between base station antenna unit <NUM> and base station antenna <NUM> is that base station antenna <NUM> includes a single housing <NUM> and a single radome <NUM>, whereas base station antenna unit <NUM> includes two housings <NUM>, <NUM> and two radomes <NUM>, <NUM>. As is also shown in <FIG>, since the base station antenna <NUM> integrates the arrays for all three of the low, mid and high frequency bands into a single antenna, the connectors that are used to transmit RF signals in each of the low, mid and high frequency bands may all be integrated into the bottom end cap <NUM> of the housing <NUM>, eliminating any need for the cowling <NUM> that is provided in the base station antenna unit <NUM> that is described above. The same is true with respect to base station antennas <NUM> and <NUM>, as can be seen from <FIG> and <FIG>. The support arms <NUM> (or other attachment structures) included in base station antenna unit <NUM> may also be omitted in base station antenna <NUM>.

Turning next to <FIG>, it can be seen that the base station antenna <NUM> is similar to the base station antenna <NUM>, except that the mid-band linear arrays <NUM>-<NUM>, <NUM>-<NUM> are moved downwardly on the backplane <NUM>. Typically, a height in the vertical direction of the mid-band linear arrays <NUM>-<NUM>, <NUM>-<NUM> is less than a height in the vertical direction of the low-band linear array <NUM>. Moreover, in some cases, the radiating elements <NUM> of the mid-band linear arrays <NUM>-<NUM>, <NUM>-<NUM> may be more prone to interact with the radiating elements <NUM> of the high-band array <NUM>. Consequently, by mounting the linear arrays <NUM>-<NUM>, <NUM>-<NUM> farther downwardly on the backplane <NUM> the isolation between the mid-band and high-band radiating elements <NUM>, <NUM> may be improved.

As shown in <FIG>, in some cases, the low-band radiating elements <NUM> and the high-band radiating elements <NUM> may tend to have very limited coupling therebetween. In such cases, it may be possibly to locate one or more of the low-band radiating elements <NUM> in openings within the high-band array <NUM>. The base station antenna <NUM> of <FIG> uses cross-polarized low-band radiating elements <NUM> that have horizontal and vertical polarizations as opposed to slant +<NUM>°/-<NUM>° polarizations, which is why "+" signs are used to represent the low-band radiating elements <NUM> in <FIG> instead of the "X" that is used to represent slant +<NUM>°/-<NUM>° cross-polarized low-band radiating elements in other of the figures. The design of base station antenna <NUM> where one or more of the low-band radiating elements <NUM> are interleaved between the high-band radiating elements <NUM> may reduce the overall length of the antenna, which may be advantageous in terms of aesthetics and cost. Such a design may also make it possible to include the array <NUM> of high-band radiating elements <NUM> in an antenna that includes a relatively large number of low-band and mid-band radiating elements <NUM>, <NUM>.

It will be appreciated that the embodiments of the invention described above are merely examples. For example, while antennas having specific numbers of arrays and radiating elements are shown in the figures, more or fewer of each type of array and more or fewer radiating elements may be included in other embodiments. Thus, it will be appreciated that the techniques disclosed herein may be used on a wide range of different base station antenna. As another example, the radomes for the base station antenna described above are mounted on the front portion of the antenna. In other embodiments, the radomes may extend all of the way around the antenna. Many other variations are possible.

It will be appreciated that the low-band radiating elements may be "wide-band" radiating elements that support multiple different types of cellular service that are within the low-band frequency range. Likewise, the mid-band radiating elements may be "wide-band" radiating elements that support multiple different types of cellular service that are within the mid-band frequency range. Thus, the multi-band antennas according to embodiments of the present invention may support multiple different types of cellular service within one or more of the frequency bands by using such wide-band radiating elements and using diplexers to split the signals in the two different cellular services that are received by the wide-band radiating elements and to combine the signals in the two different cellular services that are fed to the wide-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. 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.

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. 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.

It will be further understood that the terms "comprises" "comprising," "includes" and/or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Claim 1:
A base station antenna unit, comprising:
a first base station antenna that includes:
a first housing;
a first radome having a front surface that is positioned in front of the first housing;
a first vertically-disposed linear array of first frequency low-band radiating elements mounted on a first backplane behind the front surface of the first radome; and
a second vertically-disposed linear array of second frequency mid-band radiating elements mounted on the first backplane behind the front surface of the first radome; and
a second base station antenna that includes:
a second housing that is separate from the first housing;
a second radome having a front surface that is positioned in front of the second housing; and
a third array of third frequency high-band radiating elements mounted on a second backplane behind the front surface of the second radome, the second radome being separate from the first radome,
wherein the second base station antenna is mounted on top of the first base station antenna in a vertically stacked arrangement and the first and second base station antennas are configured to be mounted as a single structure.