Fig. 1: Beam path in an unwound Lewis scanner
A Lewis Scanner is an antenna in which the primary feed (horn radiator) is moved in front of a reflector using a motor to enable a continuous change of direction of the antenna pattern with this antenna. The invention by Willard D. Lewis of Bell Telephone Laboratories Inc. was patented in 1947.
Figure 2: The feed slot was rolled up into a truncated cone.
How it works
The Lewis scanner is built inside a waveguide with a 45° lying reflector. The general principle of operation is a movable horn feed in front of this reflector. Depending on the angle from which this reflector is illuminated, the radiation angle of the antenna shifts. The divergence caused by the horn radiator is corrected by a dielectric lens. The flat representation in Figure 1 would already work, but it would have a disadvantage in that the horn radiator would have to be moved back and forth. This movement would require very complicated mechanics with which no linearity of motion is possible. (Converting a rotary motion into a pendulum motion would always result in a sinusoidal velocity change.)
Therefore, in the first step, the slot for the feed is rolled up into a round construction. Now the motor can continuously rotate the horn radiator with constant speed in front of the feed slot. To make this antenna even more compact, the rest of the waveguide is also rolled up, leaving only a truncated cone-shaped antenna. This antenna is usually positioned in front of an additional single curved parabolic reflector to focus on the plane that is not electromechanically steered by the Lewis scanner.
- Patent U.S. 2,585,562 “Directive Antenna System”, eingereicht von Willard D. Lewis, Bell Telephone Laboratories Inc. (online)