Measuring the shape of large reflectors by a simple radio method

Preliminary laboratory tests on a method for directly recording fluctuations in position of points on a reflecting surface are described. The surface is illuminated at 10 Gc/s by a horn aerial, and a small auxiliary reflecting device (which is amplitude-modulated at an audio frequency for identification purposes) is placed at a point on the surface whose movement is to be investigated. Detecting the position of the small standing wave produced by the device on the waveguide feeding the illuminating horn enables changes in position as small as 0.1 mm to be measured directly. The extension of the method for measuring the movement of a number of points simultaneously and for measuring absolute distance is discussed.