Directional aerial for surveillance of rooms or spaces - has cylindrical parabolic reflector and strip radiator for optimum sensitivity

摘要

In surveillance systems for rooms or open spaces intended to detect intruders the area close to the aerial is difficult to cover. If the sensitivity is too great spurious alarms may be generated, e.g. by vegetation moving in the wind. If too low, intruders may pass undetected if close to the aerial. This defect is overcome by using a parabolic reflector (R) which is part of a long cylinder (L). The strip radiator (E) is placed on the line forming the focal line of the reflector. The length of the reflector (L) is chosen to be at least approximately equal to the square root of ZXW, where Z is the distance between sondes or aerials and W the wavelength of the electromagnetic emission.