The present invention relates generally to wireless communications systems and, more particularly, to a monopole-mounted antenna system in which constituent antennas are arranged circumferentially about a monopole tower such that the visual impact is reduced and in which the individual antennas have a remote electrically-adjustable main beam direction.
Antenna towers have long been used for supporting antennas used in wireless communication networks, such as cellular communications systems. One common type of antenna tower is constructed of an interconnected lattice framework of steel beams. Another common type of antenna tower is a monopole tower consisting of a single tubular mast or pole extending upwardly from ground level. Monopole towers have grown in popularity because the visual impact of monopole towers is less than that of lattice-type towers and because of the relatively low cost as compared with lattice-type towers.
Wireless communication networks are divided into cells each arranged to communicate with mobile stations with minimal interference and that, in the aggregate, define a coverage area. A mobile station traversing the coverage area has its communications handed-off between adjacent cells. Each cell includes one or more individual antennas arranged and combined in a manner to communicate with a mobile station. Each antenna consists of multiple radiating elements that are housed within an outer housing, which may have a rectangular, box-like shape, that is affixed to a triangular support platform mounted to the monopole tower.
Changes in wireless coverage are accomplished by changing a main beam direction of the antenna. In most wireless communication networks, the main beam direction may be changed by an elevational or azimuthal adjustment after the antennas have been installed on the antenna tower. The main beam direction may be adjusted for varying the coverage area of each cell as the number of customers increases and additional cells are added to accommodate increasing numbers of mobile stations. The main beam direction may also be adjusted to compensate for new adjacent construction, vegetation growth, or other changes in the surrounding environment of the monopole tower.
One method for altering the main beam direction of the radiation pattern is to physically relocate the antennas and/or direction or to replace the antennas with certain fixed radiation characteristics with antennas having different fixed radiation characteristics. However, such physical relocation or replacement is difficult. Another method for altering the coverage is to mount the antennas to the antenna tower with brackets that allow mechanical adjustment of the downtilt of the individual antennas. However, service personnel must adjust the main beam direction of the antennas by climbing the tower to a service platform near the antennas or by being supported from an elevated lifting device such as a cherry picker. Not only is this costly, but wireless communications service is interrupted while the manual adjustment of the downtilt is being performed.
Operators of wireless communication networks typically need to obtain permission from residential and zoning boards to erect antenna towers. Antenna towers are by their very nature prominent structures. The preferred locations for antenna towers are the most visible locations relative to the surrounding landscape within the intended coverage area. Conventional monopole towers with triangular support platforms have an appearance that, while less objectionable than lattice-type towers, is not aesthetically pleasing. As a result, permission to erect an unsightly monopole tower may be difficult to obtain in urban and suburban venues. One approach for overcoming zoning opposition is to disguise or otherwise conceal the antennas and supporting platforms of the monopole tower to lessen the visual impact. For example, the monopole tower may be adorned with structures emulating foliage such that, to a casual observer, the tower resembles a tree or other vegetation. However, such camouflaging structures are impractical, difficult and expensive to construct, and costly to maintain.
Each wireless telephony provider in a geographical area requires their own dedicated cells to provide coverage. As a result, each provider will position their own set of towers in suitable sites within the geographic area. Because suitable sites are increasingly difficult to secure, more complex and visually objectionable antenna arrangements are being deployed to maximize coverage in the geographic area. In particular, the usage of the monopole tower may be increased by permitting multiple operators to share a single monopole tower. To that end, multiple operators may be accommodated by attaching additional triangular support platforms to the monopole tower and providing each platform with an additional set of antennas.
The number of antennas required to service multiple providers may be further reduced by diplexing individual providers on the same antennas. However, combining providers on a single antenna increases the likelihood of intermodulation distortion. In addition, the installation process for diplexed systems becomes more critical as, for example, a poorly-made jumper, a dirty connector or an improperly torqued connector may degrade performance. As the number of antennas servicing each antenna is limited, the ability to correct an antenna failure by simply changing to a spare antenna is limited. Furthermore, the duplexer adds losses that reduce coverage. Moreover, the coverage area for diplexed providers is identical and, as a result, variations in the main beam direction must be mutually agreed upon. Specifically, the main beam directions for two providers sharing antennas are not independently adjustable. Finally, the diplexing equipment is expensive and adds significantly to the system cost.
Therefore, it would be desirable to construct a monopole tower having antennas arranged to accommodate multiple carriers or providers, and yet which presents a reduced visual impact and affords independent control of the respective coverage areas.
The invention is directed to an antenna system for wireless communications systems and, more particularly, to a monopole-mounted antenna system having an electrically-adjustable main beam direction and constituent antennas arranged side-by-side about a monopole tower so as to reduce the visual impact of the composite structure. Although the invention will be described next in connection with certain embodiments, it will be understood that the invention is not limited to those particular embodiments. On the contrary, the description of the invention is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.
With reference to
Each of the antennas 10 is attached at one end by conventional fasteners to a lower mounting flange 20. Similarly, each of the antennas 25 is attached at one end by conventional fasteners to a lower mounting flange 22. Additional mounting flanges (not shown) may be provided for securing the antennas 10 in group 12 and the antennas 25 in group 27 to the outer surface 15a of monopole tower 15.
Each of the antennas 10 in group 12 includes a backplane 160, an array of, for example, ten radiating elements 110 disposed along a vertical dimension of backplane 160, and a radome 45. Similarly, each antenna 25 in group 27 includes a backplane 161, an array of, for example, five radiating elements 111 disposed along a vertical dimension of backplane 161, and a radome 50. Each of the antennas 10 may include a pair of electrical connectors 30 for electrically coupling radiating elements 110 via respective transmission cables (not shown) with a radio 55. Similarly, each of the antennas 25 is equipped with a pair of electrical connectors 40 configured to electrically couple with one end of respective transmission cables (not shown) for linking the radiating elements 111 of each antenna 25 with another radio (not shown). The individual radiating elements 110 and 111 may be any type of radiating element suitable for use in a wireless communication network configured for personal communication systems (PCS), personal communication networks (PCN), cellular voice communications, specialized mobile radio (SMR) service, enhanced SMR service, wireless local loop and rural telephony, and paging. For example, the individual radiating elements 110 and 111 may be monopole elements, dipole elements, loops, slots, spirals or helices, horns, or microstrip patches. The radiating elements 110 in each antenna 10 may be of the same or different type as radiating elements 111 in each antenna 25. In addition, the type of radiating elements 110 may differ among different antennas 10 or, similarly, the type of radiating elements 111 may differ among antennas 25. It is contemplated by the invention that additional groups of circumferentially-arranged antennas may be mounted to the monopole tower 15 in the same or similar manner to groups 12, 27 or that only one of group 12 or group 27 may be mounted to monopole tower 15.
With continued reference to
Radome 45 and backplane 160 collectively define an outer housing that encloses the radiating elements 110 of each antenna 10. Typically, a radially-outermost surface 45a of each radome 45 and a radially-outermost surface 50a of each radome 50 has a convex curvature.
With reference to
With reference to
With renewed reference to
Radiating elements 110 and radiating elements 111 are arranged spatially for producing a directional radiation pattern. The main beam direction of the radiation pattern emanating from each of the antennas 10 in group 12 may be varied by altering the phase angle of the constituent radiating elements 110. Similarly, the main beam direction of the radiation pattern emanating from each antenna 25 in group 27 may be varied by altering the phase angle of the constituent radiating elements 111. The elevation or the azimuthal direction of the main beam may be controlled without the use of mechanical mechanisms to vary the physical orientation of the antennas 10, 25. The main beam direction of radiation pattern emanating from antennas 10 may be varied independently of the main beam direction of the radiation pattern emanating from antennas 25. Similarly, the main beam direction of radiation pattern emanating from a set of antennas 10 may be varied independently of the main beam direction of the radiation pattern emanating from a different set of antennas 10. Similarly, the main beam direction of radiation pattern emanating from a set of antennas 25 may be varied independently of the main beam direction of the radiation pattern emanating from a different set of antennas 25. The sets of antennas 10 or antennas 25 constitute a number of antennas smaller than the full complement of antennas. Each set of antennas 10 or set of antennas 25 services a single wireless telephony provider so that multiple providers may share a single group 12 or 27, respectively.
With reference to
The phase shifters 65 may be actuated either electronically or mechanically. Electronic phase shifters may be based upon semiconductor diodes, monolithic microwave integrated circuits (MMIC), ferroelectric circuits, microelectromechanical systems (MEMS), and the like. Mechanical phase shifters may be based on coaxial transmission lines, stripline transmission lines, microstrip transmission lines, waveguide transmission lines, and the like and may be motor driven. Exemplary antenna systems featuring an adjustable main beam direction are disclosed in U.S. Pat. Nos. 6,346,924 and 6,198,458, the disclosure of each of which is hereby incorporated by reference herein in its entirety.
With reference to FIG. 4 and in accordance with one embodiment of the invention, each set of, for example, three antennas 10 may be coupled by corresponding feed networks 60 with a different operator's set of radios 55. As a result, each operator may vary their cell coverage by adjusting the phase shifters 65 of their associated feed networks 60 without impacting the operation of other operators sharing the group 12 of antennas 10. Antennas 25 may be coupled with one or more radios (not shown) in a similar manner and each operator using a set of antennas 25 may vary their individual cell coverage without impacting the operation of other providers using a different set of antennas 25 in group 27. In either case, each operator operates independently of other operators sharing the monopole tower 15 (
Because the main beam direction is varied without physically moving the corresponding antennas 10, 25, the visual appearance of each group 12, 27 is unchanged since the radomes 45, 50 have a fixed position relative to the monopole tower 15. It is contemplated by the invention that the radome 45 for group 12 and the radomes 50 for group 27 may each consist of one-piece or integral structures since the antennas 10, 25 remain static in position as the sector/cell coverage is varied by varying the phase angles of the individual radiating elements 110, 111.
According to another aspect of the invention and with reference to
With reference to
An antenna system constructed according to the principles of the invention has an aesthetically-pleasing appearance that increases public acceptance. As a result, the antenna system of the invention avoids or complies with zoning ordinances or other restrictive covenants of urban, suburban, and rural communities. In addition, the antenna system of the invention significantly reduces tower and site costs.
Moreover and in accordance with the principles of the invention, multiple providers may position antennas atop a single monopole tower and yet retain the ability to independently adjust the direction of the main radiation beam to change coverage by adjusting elevation and/or azimuth. The antenna system of the invention eliminates or, at the least, minimizes the problems of intermodulation that arise when more than one provider shares one set of antennas via diplexing and eliminates the additional losses incurred due to the use of a diplexer for combining or separating individual signals while optimizing the number of providers that may position antennas on a single monopole tower. The absolute number of monopole towers required to provide overlapping coverage areas for multiple providers may be reduced by the capability of sharing space on a monopole tower.
While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in considerable detail in order to describe the best mode of practicing the invention, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the spirit and scope of the invention will readily appear to those skilled in the art.
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Number | Date | Country | |
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20040174317 A1 | Sep 2004 | US |