This memorandum describes in general terms a system by which early warning can be given of approaching aircraft. The advantages of the system are: long range, especially over water, detection of low-flying planes, and economy and simplicity of the installations which are suited to remote control. The main disadvantage is the complexity of interpreting the data that would result from several different flight groups. In principle the system gives the position (except altitude) and velocity of the planes in its range, working on the Doppler frequency shift of the reflected radiation.
Electronic design is not attempted, but the requirements, in terms of information theory considerations are indicated.
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