Patent Application
20050057429
This invention relates generally to microwave systems, and, more particularly, to feed networks between electronics and antennas located proximate the bottom and top of a support structure, respectively.
In wireless or cellular communications systems, a network of cells may be defined by spaced towers having antennas directed in particular directions. Usually, several antennas are mounted at or near the tops of the towers, while associated electronics, such as radio frequency (RF) power amplifiers, radios, and/or low noise amplifiers (LNAs), etc., are contained within small housings, or huts, located near the bases of the towers. Such an arrangement of a tower, antennas, and associated electronics are often referred to as a “base terminal station” (BTS) or “cell site”. Moreover, some cell sites employ the same tower structure for a plurality of operators, such as AT&T, Sprint, Verizon, etc., utilizing multiple frequencies and/or applications.
Predominantly, cell sites utilize multiple coaxial cables that traverse the tower, connecting the electronics to the antennas. Unfortunately, such coaxial cables are typically very lossy, a significant amount of the power in signals being conducted by cables being dissipated or “lost” between the electronics and the antennas. For example, for transmitting a signal, a RF power amplifier may be located at the base of the tower, while the associated antenna is at the top of the tower, a coaxial cable coupling the two. Consequently, for a given amount of power delivered to the antenna, the RF power amplifier must have the additional gain necessary to overcome any losses inherent in the coaxial cable. Often, a RF power amplifier having the additional output power necessary is not realizable or is more expensive, thereby increasing the costs of the cell site, or, at a minimum, the performance of an existing amplifier may be reduced.
Conversely, in receiving a signal, the power incident on an antenna at the top of the tower is coupled, via a coaxial cable, to a radio or LNA at the base of the tower. Typically, received signals are relatively low in power, and are further reduced in power by conducting through the coaxial cable. Moreover, noise, received by such coaxial cables, may reduce in the signal-to-noise ratio (S/N). One approach to improving the S/N is to locate amplifiers, typically LNAs, at the tops of the towers to overcome the noise problems associated with the coaxial cables. However, the implementation and/or maintenance of tower top LNAs can be expensive, and the mounting and installation of LNAs somewhat difficult.
There is a need to provide a method and apparatus for coupling antennas located proximate the top of a support structure with electronics located proximate the base of the support structure to overcome losses typically associated with coaxial cables.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the detailed description given below, serve to explain the principles of the invention.
With reference to
Referring initially to
Electronics 24 may be housed in a building or hut 26, or some other suitable structure, at or adjacent tower 14, or some distance away from tower 14. In the antenna system 10 depicted in
Wireless feeder 12 comprises a waveguide 28 and a multiplexing waveguide network 30 located at each end of waveguide 28. Waveguide networks 30 couple different signals into waveguide 28 for transmission. Waveguide networks 30 are configured to combine frequencies and applications. A discussion of a “Multi-Port, Multi-Frequency Microwave Combiner with Overmoded Square Waveguide Section” may be found in U.S. Pat. No. 4,491,810, the disclosure of which is fully incorporated herein by reference. Those skilled in the art will appreciate that other combining networks, such as circular combining networks, may be used without departing from the spirit and scope of the invention.
For example, a first portion 32a of electronics 24 may be associated with a first service provider and/or application, while a second portion 32b of electronics 24 may be associated with a second service provider and/or application. Moreover, each portion 32a, 32b of electronics 24 may include one or more radio frequency (RF) power amplifiers 34a, 34b and one or more radios or low noise amplifiers (LNAs) 36a, 36b. Thus, feeder 12 may combine or multiplex frequencies, i.e., transmit and receive, in a manner that reduces the number of feeders required.
Further, as configured in
Those skilled in the art will appreciate that additional feeders may, along with any necessary associated antennas or electronics, be used as required for additional applications and/or service providers.
Referring now to
An advantage of an elliptical waveguide is manufacturing and/or installation convenience. An elliptical waveguide is often comprised of a strip of copper that is corrugated, folded over, welded and jacketed. Further, elliptical waveguides are typically available in continuous lengths up to practical shipping limits of approximately 3,000 feet, the only joints being connectors at each end. The connectors of elliptical waveguide 28′ are indicated a reference numeral 38. Portions 40 of connectors 38 form a transition between the elliptical cross-sections 2A-2A and a rectangular coupling (not shown), as will be appreciated by those skilled in the art.
Another advantage of an elliptical waveguide is ease of installation. Thus, unlike a rigid or rectangular waveguide, an elliptical waveguide may be bent or curved without damage, and more importantly, without electrical degradation. This curving eases installation of the elliptical waveguide, such as transitioning from tower 14 to hut 26, shown in
Referring still to
Those skilled in the art will appreciate that the physical dimensions of elliptical waveguide 28′ and waveguide networks 30′ determine, in part, the usable frequency range of wireless feeder 28′. The further specifics of constructing such an elliptical waveguide and waveguide networks, and the tuning of the same, are well known to those skilled in the art.
For example, a 3G wireless system covering 1,920 to 2,170 Megahertz (MHz), as assigned to 3G services throughout most of the world, may utilize antenna 22a having a single polarization and electronics 32a, shown in
Referring now to
A circular waveguide may be preferred to a rectangular or elliptical waveguide in installations where longer lengths are required since circular waveguides generally have less attenuation than either rectangular or elliptical wavegides. As will be appreciate by those skilled in the art, a principle difference between a circular waveguide and rectangular or elliptical waveguide is the manner in which energy is fed and removed from the waveguide. Further, due to symmetrical construction, a circular waveguide is configured to support circular, horizontal, and vertical polarizations, or dual polarizations. Thus, one advantage of a circular waveguide may be the ability to support dual or multiple polarizations.
Referring still to
Those skilled in the art will appreciate that the physical dimensions of circular waveguide 28″ and waveguide networks 30″ determine, in part, the usable frequency range of wireless feeder 28″. The further specifics of constructing such a circular waveguide and waveguide networks, and the tuning of the same, are well known to those skilled in the art.
Wireless feeder 12″ comprises a multiplexing waveguide network 30″ located at each end of circular waveguide 28″ to combine frequencies, i.e., transmit and receive, and applications, e.g., a third generation (3G) wireless system and a personal communications services (PCS) system. To this end, waveguide networks 30″ comprise ports 44a-b and 46a-b.
For example, a 3G wireless system may utilize antenna 22a having a dual polarization and electronics 32a, shown in
While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. For example, it will be understood that an antenna may have one or more, e.g., dual, polarizations. Moreover, a waveguide may be elliptical, circular, or even rectangle or rigid, each having their own particular advantages depending on the installation. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicants' general inventive concept.
