Wave transmission lines and networks – Long lines – Leaky lines
Patent
1987-12-01
1991-01-22
LaRoche, Eugene R.
Wave transmission lines and networks
Long lines
Leaky lines
333243, 174 36, H01Q 1320, H01P 302
Patent
active
049873946
ABSTRACT:
A leaky cable useful antenna or as an intruder detector sensor either buried in a single trench or above ground substantially reducing sensitivity variations due to the environment. Egression of the electric field from the cable is blocked but magnetic fields escape. The velocity of the externally propagating electromagnetic field is slowed and attenuated. In one embodiment, the leaky coaxial cable is comprised of an inner conductor, a dielectric surrounding the inner conductor, a first external shield having low series impedance at VHF frequencies surrounding the dielectric, means for coupling a magnetic field through the first external shield, a second external shield surrounding the first external shield having high series impedance relative to series impedance of the first external shield and means for limiting VHF conduction current between the shields, which effectively causes separation of the internal and external propagation fields of the cables. The external shields are arranged so that the first external low series impedance shield does not short circuit the second external high series impedance shield, thus separating the internal and external propagating fields of the cable. A thin semiconductor or insulating sheath can be placed between the two shields. Alternatively, the skin depths at VHF in the two shields are made adequate to effectively separate the two signals. The external signal, propagating on the outside of the second external shield and the internal signal propagating on the first external shield are effectively separated thereby.
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Harman R. Keith
Smith Kenneth L.
LaRoche Eugene R.
Lee Benny T.
Senstar Corporation
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