Army air forces' portable instrument landing system

Describes transmitting equipment, mounted in trucks, providing an equi-signal glide path with marker beacons for aircraft landing. Six frequencies of operation are provided from 108.3 to 110.3 Mc/s. Broad-band aerials cover this range without adjustment. An array of 5 horizontal loops is used for the localizer. A mechanical modulator produces two overlapping radiation patterns having 90 and 150 c/s modulation respectively. A local monitor receiver automatically stops the transmitter if the set course varies. The aircraft comes in on the equi-signal path of the localizer and lands by means of an equi-signal glide path provided by two V-aerials fed by another mechanical modulator. The aircraft receivers operate a crossed pointer indicator. Three 75 Mc/s marker beacons are used. The theoretical polar diagrams of the aerials are derived and compared with the measured results.