Communications: radio wave antennas – Antennas – With support for antenna – reflector or director
Reexamination Certificate
1998-01-09
2001-04-24
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
With support for antenna, reflector or director
C343S878000, C343S7000MS
Reexamination Certificate
active
06222503
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to radio frequency antennas and related components, and more particularly, to aesthetically unobtrusive, base station antennas and antenna subsystems for use by commercial communications service providers to transmit and receive radio signals.
BACKGROUND OF THE INVENTION
It would be advantageous for providers of commercial of communications, data transfer services, and identification systems to have a system and method of deploying a plurality of aesthetically unobtrusive, base station antennas and antenna subsystems, thereby avoiding or complying with zoning ordinances or other restrictive covenants of urban, suburban, and rural communities. While increasing public acceptance and service, the invention would also reduce site location, acquisition, and maintenance costs for radio base stations. Many of the concealment features of the invention described herein are useful in cellular telephone systems as well as automatic-identification and data-collection systems such as toll collection, utility billing, security services, asset (vehicle, logistics) tracking and others.
Due to the conditions that are imposed by physics of the art, the size of any antenna device is related to the wavelength of the electromagnetic radiation that is being propagated and the effective aperture gain and pattern characteristics of the antenna that is needed to meet the requirements of the particular communications or other systems. Usually, particularly in the case of terrestrial communications systems, the antenna dimensions are large enough to be readily noticed. As antennas are typically protected behind radomes in rectangular or cylindrical packages (primarily to prevent them from being damaged by the environment or mishandling), the resulting objects often have the unsightly appearance of large, rectangular boxes hanging from towers or water heaters and other protrusions on rooftops. To compound the problem, a variety of antennas of varying sizes and shapes for several different systems are often found on a common tower that is often the most visually objectionable apparatus. Besides aesthetics, potential performance problems (i.e., interference due to noise or intermodulation signals that emanate from adjacent systems) can also result from such collocation of antennas.
From the prior art and as described herein, an antenna may be comprised of one or more radiating elements that may be arranged and combined in a variety of ways to achieve the desired, effective aperture and spatial radiation (or reception) characteristics or patterns. Attempts in the prior art to conceal antennas were directed toward mobile antennas, which were mounted on vehicles, or rooftop-mounted antennas that were directed primarily toward use by hobbyists. Application of these principles to antenna systems suitable for mass deployment in commercial communications systems has not been successful. In particular, harmonious integration of stationary antennas and related components that are found in base stations and repeaters into common objects has not been successful.
In addition to the physics of the art, many factors influence the size and configuration of an antenna that is used in a particular application. Top-level system requirements include the following: efficient use of the allotted electromagnetic spectrum, user coverage (range and area), use satisfaction (voice quality, data integrity, continuity of service, low call drop rate, etc.), minimal interference with other systems, and compliance with regulatory restrictions. In turn, these requirements ultimately translate to specifications for the subsystem hardware comprising the infrastructure of the communications systems. Of these, few are of greater importance than the location (or site) of the base station and placement of the antennas. Because the characteristics of site locations are varied and always less than ideal, the size, number and type of antenna to be used becomes increasingly critical to the ultimate performance of the system.
Securing a suitable site for locating the base stations or repeaters and the associated antennas is a difficult and expensive proposition. Site locations are a scarce commodity because, in general, the preferred locations are the highest available ground relative to the surrounding terrain within the intended coverage area. Preferably, the line of sight will also be free of obstructions that will reflect electromagnetic waves from the direction of the desired coverage. As such, the aesthetics problem is greatly exacerbated; the antennas are ideally mounted on towers atop the most prominent, visible locations within the surrounding landscape. For these reasons, site owners often incur significant expenses such as brokerage fees, land acquisition costs, permit fees, lobbying expenses for zoning rights, insurance premiums, costs for tower construction, etc. Therefore, site owners must lease tower ‘space’ to service providers at substantial premiums.
Once the site location is determined, commercial wireless communications systems typically use the same basic approach to system performance and reduce operating costs associated with base station or repeater (antenna) sites. First, they transmit at the maximum power that the Federal Communications Commission (FCC) allows. Second, they use the highest gain with the appropriate radiation pattern (i.e., the largest) antenna that the location permits to maximize range and coverage. Third, the antenna is mounted as high as the site will permit to further increase range. Fourth, they use multiple antenna arrangements and receiver channels for diversity, a common means of improving system performance, in each sector at a site to help mitigate fading due to multipath. Another common technique to enhance uplink sensitivity is to mount a low-noise preamplifier with filters below and external to the antenna on the tower which adds to the unsightly clutter at the site. However, shadowed or otherwise uncovered areas remain common and result in ‘dead spots’ or ‘drop-outs’ where service is interrupted.
Those who are skilled in the art are designing and deploying super or “smart” antenna in the form of multibeam, switched or steerable arrays that require many more antenna elements, and may form twelve or more sectors at a particular site. Unfortunately, these features translate to a larger, more obtrusive antenna structure. While promoting the ability to avoid interference, these super-antenna systems are capable of significant range and penetration. However, these clustered, collocated antenna systems do not overcome some fading, shadowing, and other propagation problems. Additionally, maintenance costs and down time are increased due to system complexity and the inability of these system to compensate for certain failures.
From a cost standpoint, designers of existing cellular systems to minimize the number of base station sites because of several economic factors. Obviously, the purchase cost of the base station as well as tower and shelter construction costs are considerable. In addition, the costs of maintenance, leasing of tower space, energy, and insurance constitute significant operational overhead. Because sites are hard to find, more complex and visually objectionable antenna arrangements are being deployed to maximize coverage at each location. In turn, the visual as well as electromagnetic pollution that the public finds objectionable increases their resistance to additional sites within their communities. In fact, site planning and acquisition costs are among the most significant obstacles in terms of money and time.
Deployment of the most modern and sophisticated cellular radio communications systems are being delayed and becoming increasingly expensive because of the difficulty and lengthy procedures involved in obtaining sites. Typically, these systems require a large number of sites as a result of technical limitations Additionally, new sites must continually be found as a result of technical problems with collocation as well a
Gietema William
Harlan Richard R.
Chen Shih-Chao
Ho Tan
Smith ,Danamraj & Youst, P.C.
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