Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
2000-03-21
2002-09-17
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
C361S118000
Reexamination Certificate
active
06452773
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed generally to surge protectors, and, more particularly, relates to a broadband surge protector for use in high frequency communications systems.
BACKGROUND OF THE INVENTION
A surge protector is a device placed in an electrical circuit to prevent the passage of dangerous surges and spikes that could damage electronic equipment. One particularly useful application of surge protectors is in the antenna transmission and receiving systems of wireless communications systems. In such antenna systems, a surge protector is generally connected in line between a main feeder coaxial cable and a jumper coaxial cable. During normal operation of the antenna system, microwave and radio frequency signals pass through the surge protector without interruption. When a dangerous surge occurs in the antenna system, the surge protector prevents passage of the dangerous surge from one coaxial cable to the other coaxial cable by diverting the surge to ground.
One type of surge protector for antenna systems has a tee-shaped configuration including a coaxial through-section and a straight coaxial stub connected perpendicular to a middle portion of the coaxial through-section. One end of the coaxial through-section is adapted to interface with a mating connector at the end of the main feeder coaxial cable, while the other end of the coaxial through-section is adapted to interface with a mating connector at the end of the jumper coaxial cable. Both the coaxial through-section and the straight coaxial stub include inner and outer conductors. At the tee-shaped junction between the coaxial stub and the coaxial through-section, the inner and outer conductors of the coaxial stub are connected to the respective inner and outer conductors of the coaxial through-section. At the other end of the straight coaxial stub, the inner and outer conductors of the coaxial stub are connected together creating a short. The short is indirectly connected to a grounding device, such as a grounded buss bar, by some sort of clamp. The physical length from the junction at one end of the coaxial stub and the short at the other end of the coaxial stub is approximately equal to one-quarter of the center frequency wavelength for a desired narrow band of microwave or radio frequencies.
During normal “non-surge” operation, a surge protector permits signals within the frequency band to pass through the surge protector between the two cables connected thereto, in either direction. The direction of signal travel depends upon whether the surge protector is used on the transmission side or receiving side of an antenna system. Signals within the desired band of operating frequencies pass through one of the interfaces (depending on the direction of signal travel) to the surge protector. When passing through the surge protector, signals within the desired frequency band travel through the coaxial through-section of the surge protector. A portion of the desired signal, however, encounters the stub while passing through the coaxial through-section. The stub scatters this signal portion which causes this signal portion to travel down the stub. After reflecting off the short, the scattered signal portion returns along the stub. Because the physical length of the stub from the junction with the inner conductor of the coaxial through-section to the short is designed to be equal to one-quarter of the center frequency wavelength for the desired band of operating frequencies, the scattered signal portion adds in phase to the non-scattered signal portion and passes through to the other end of the coaxial through-section.
When a surge occurs in the antenna system (e.g. from a lightning strike), the physical length of the stub is much shorter than one-quarter of the center frequency wavelength because the surge is at a much lower frequency than the desired band of operating frequencies. In this situation, the surge travels along the inner conductor of the coaxial through-section to the stub, through the stub to the short, through the short to the grounding attachment, and through the grounding attachment to a grounding device attached thereto. Thus, the surge is diverted to ground by the surge protector.
A drawback of the above tee-shaped surge protectors is that these surge protectors have a limited operating bandwidth. Original equipment manufacturers (“OEM”) and wireless service providers are currently required to purchase a multitude of shorted stub surge protectors to address all of the various applications that operate at different frequencies. Since there is an increasing preference towards shorted stub surge protectors because of their multiple strike capabilities and superior passive intermodulation distortion performance, an OEM or service provider would have to stock and inventory a multitude of different shorted stub surge protectors for the common allocated operating bandwidths of today's systems (800-870 MHz, 824-896 MHz, 870-960 MHz, 1425-1535 MHz, 1700-1900 MHz, 1850-1990 MHz, 2110-2170 MHz, 2300-2485 MHz, etc.). A broadband shorted stub surge protector that can operate over this entire frequency range would allow an OEM or service provider to carry one product; obviously, simplifying inventory requirements and offering the cost advantages leveraged in higher volume purchases.
Additionally, there is a significant need for a broadband surge protector because there is an increasing amount of pressure from society to limit the number of cell sites associated with wireless communications systems. Towards this end, there is an increasing need for wireless service providers to co-locate their operating systems employing diplexing and triplexing techniques via the existing coaxial transmission lines. This trend of multiplexing various operating frequencies has made it essential for all traditional narrowband components, such as surge protectors, to be upgraded to broadband devices.
While other types of broadband surge protectors are available being manufactured today, many employ a technique of installing a gas discharge tube between the inner and outer conductors of the coaxial surge device. While these types of devices offer broadband performance, they suffer from several undesirable features including the need for regular scheduled maintenance, the inability to withstand multiple strikes, and poor passive intermodulation distortion performance.
Accordingly, there exists a need for a surge protector which has a broad operating bandwidth for use in wireless communications systems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a surge protector which has a broad operating bandwidth for use in wireless communications systems.
In one embodiment, the foregoing object is realized by providing a surge protector comprising a coaxial through-section having a first inner conductor, a first outer conductor, and a first dielectric disposed between the first inner and first outer conductors, and a coaxial shorting stub having a second inner conductor and a second outer conductor. The stub has a first end and a second end. The stub is coupled to the coaxial through-section wherein the second inner conductor is conductively coupled to the first inner conductor at the first end of the stub and the second outer conductor is conductively coupled to the first outer conductor at the first end of the stub. The second inner conductor is substantially hollow and has at least one helical aperture disposed therein. The at least one helical aperture is continuous for at least about one revolution around the second inner conductor. A shorting plate is conductively coupled to the second inner and second outer conductors at the second end of the stub.
The above summary of the present invention is not intended to represent each embodiment, or every aspect, of the present invention. Additional features and benefits of the present invention will become apparent from the detailed description, figures, and claims set forth below.
REFERENCES:
patent: 2774044 (1956-12-01), Silvey et al.
patent: 33
Aleksa Jonas V.
Gorecki James A.
Andrew Corporation
Jackson Stephen W.
Jenkens & Gilchrist
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