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US 5,473,336 AGranted
Cable for use as a distributed antenna
AssigneeAuratek Security Inc.
InventorsRobert K. Harman, Andre Gagnon
Life of this patent
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AssigneeAuratek Security Inc.
InventorsRobert K. Harman, Andre Gagnon
Estimating the term…
A cable for use as a distributed antenna in intrusion detection systems comprises an internal open transmission line in parallel with a periodically loaded structure which supports an external transmission line mode of operation, specifically a surface wave, and is "driven" by the open transmission line. The periodically loaded structure may comprise transmission line segments for example cylindrical conductor elements intercoupled by serial inductive coupling. There are no fewer than three and no more than fifteen conductor elements in one wavelength (.lambda..sub.S) of the external transmission line modes. Preferably the length of each transmission line segment is about one quarter of the wavelength (.lambda..sub.S) of the external transmission line modes. The inductive coupling may be provided by resistance wires extending alongside the conductor elements. The open transmission line may comprise a two-wire line and the transmission line segments two arrays of conductor elements, associated with respective ones of the two wire. Alternatively, the open transmission line may be an open coaxial cable and the transmission line segments a series of cylinders surrounding the coaxial cable.
A cable, suitable for use as a distributed antenna, comprising an internal open transmission line and a plurality of identical transmission line segments spaced apart along the length of the cable to form a periodically structure surrounding the open transmission line, the periodically loaded structure and the line being coupled electromagnetically for distributed coupling of radio frequency signals from one to the other, the cable further comprising coupling means interconnecting adjacent transmission line segments resistively and inductively such that the periodically loaded structure supports external transmission line modes having a velocity of propagation less than that of free space, and attenuation of external modes is greater than that of signals propagating along the internal open transmission line.
Dependencies are inferred from the claim text.