Communications: radio wave antennas – Antennas – High frequency type loops
Patent
1987-11-18
1989-09-12
Davie, James W.
Communications: radio wave antennas
Antennas
High frequency type loops
343867, H01Q 1112
Patent
active
048664553
ABSTRACT:
For use in an electronic security system, an antenna system which provides a magnetic field which is substantially zero at distances large compared to the dimensions of the antenna, and has magnetic coupling between transmitting and receiving antennas which can be readily predetermined by varying the relative sizes of the antenna loops. The size and shape of the detection pattern can also be readily predetermined by varying the relative sizes of the antenna loops. Preferably, the transmitting and receiving antennas each comprise three magnetic loops lying in a single plane, the center loop having a magnetic phase which is in phase opposition to that of the upper and lower loops. The sum of the three magnetic dipoles is equal to zero to provide a net magnetic field as seen from distances large compared to the antenna dimension, which is substantially zero. Each antenna is substantially symmetrical about a centerline through the middle loop, and the antenna is driven at the geometric center of the loop such that the magnetic field caused by the opposite symmetrical sections of the antenna are in phase opposition and cause substantial cancellation of the magnetic field at distances large compared to the dimensions of the antenna. The antenna system can thereby be easily tailored to suit specific installations to permit intended coupling of carrier signal from the transmitting to the receiving antenna and to provide an intended spacing between the transmitting and receiving antennas.
REFERENCES:
patent: 4243980 (1981-01-01), Lichtblau
patent: 4260990 (1981-04-01), Lichtblau
Davie James W.
Wise Robert E.
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