Coaxial cable ESD bleed

Details Coaxial cable ESD bleed Coaxial cable ESD bleed

2000-01-20

2001-04-17

Sircus, Brian (Department: 2839)

Electrical connectors

Including or for use with coaxial cable

C439S181000, C439S675000

Reexamination Certificate

active

06217382

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a ?,(SMA) connector for a coaxial cable and more particularly to providing an electrostatic discharge (ESD) bleed path for a floating center conductor of the coaxial cable.
BACKGROUND ART
Coaxial cables and radio frequency switches that are used to leave a communications port open circuited are located inside the payload of a communications satellite and are usually well shielded. The center conductor of a coaxial cable connected to an RF switch may be electrically floating when it is not being used as a path for a RF signal.
The energy of electrons in a space environment is capable of causing the floating center conductor to charge to a high potential. When the cable is switched into a RF path, it is possible to induce a transient pulse from the floating center conductor onto a circuit in the RF path. The problem is that the induced pulse may cause damage to the electronics and in particular to sensitive monolithic microwave integrated circuits (MMIC) in the RF path.
To avoid this potentially serious problem, it is possible to insert coaxial attenuators having a low attenuation value into the paths that are susceptible to the transient pulse. However, this technique takes up valuable space due to the need for more cable roughing space, thereby adding unwanted weight to the spacecraft. In addition, the technique adds insertion loss, which is also undesirable.
It is also possible to continuously monitor space weather in order to determine optimum conditions for switching RF switches. RF switches are temperature dependent and simply waiting for the center conductor current potential to drop to a satisfactory level may be enough to prevent transients from entering the RF circuit. However, the monitoring method is extremely costly in that continuous, real-time space weather monitoring is required. Furthermore, scheduling problems arise because, say at 20° C., it could take up to four days for the center conductor potential to drop to a satisfactory level. The scheduling problems adversely affect customer revenues due to the fact that the switches may be out of commission for an extended period of time.
According to flight data the probability of damage to sensitive electronic circuits during the switching process is low. However, should it occur, the effects could be extremely costly. Therefore, what is needed is a low cost method for preventing potential damage to sensitive electronic components without adversely affecting weight, and without occupying very limited, and very valuable, space onboard a spacecraft.
SUMMARY OF THE INVENTION
The present invention provides an electrostatic discharge bleed path for the center conductor of a coaxial cable. The present invention prevents spacecraft hardware damage by preventing the center conductor from charging in an enhanced electron environment, such as in a space environment, when no other bleed paths are available. Additionally, the present invention has minimal impact on the RF performance characteristics of the SMA connection.
In order to accomplish the above advantages, the present invention is realized in a disk fitted over the center pin, or contact, of a SMA male connector to bleed electrostatic charge. Preferably the disk is made of a polamide material, such as Kapton® which is a registered trademark of DuPont Corporation loaded with carbon. The disk is compressed between the male and female portions of the SMA connector, thereby providing an electrical connection among the connector, the inner conductor and the outer conductor of the coaxial cable.
The center conductor of a coaxial cable connected to an RF switch may be electrically floating when it is not being used as a path for a RF signal. In operation, the floating center conductor has a bleed path to ground through the electrical connection of the disk and coaxial cable outer conductor. Therefore, when switching occurs, the center conductor potential is well within satisfactory limits and the risk of damage to MMIC components is eliminated.
It is an object of the present invention to provide an electrostatic discharge bleed path when no other bleed paths are available. It is another object of the present invention to avoid potential damage to sensitive hardware by preventing charge build-up on a center conductor of a coaxial cable. It is yet another object of the present invention to prevent an unwanted transient pulse from being introduced into a circuit in a RF path when a coaxial cable is switched into the RF path.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.


REFERENCES:
patent: 4664467 (1987-05-01), Tengler et al.
patent: 4718864 (1988-01-01), Flanagan
patent: 5529522 (1996-06-01), Huang
patent: 5802710 (1998-09-01), Bufanda et al.

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