The use of spherical reflectors as microwave scanning aerials

The paraboloid, fed by a source at its focus, is an ideal reflector for producing narrow beams of radiation at very short wavelengths, but it is, in general, unsuitable for an aerial which must radiate a beam capable of rapid scanning, since the radiation pattern deteriorates seriously as the source is moved sideways in the focal plane. The sphere, on the other hand, cannot produce so good a radiation pattern as the paraboloid at its best, but is free from extra aberrations when the source is moved along the correct arc. The conditions which govern the use of spherical reflectors are discussed in the main text, and experiments are described which confirm the theoretical predictions. A detailed description is given of a large spherical reflector designed to produce a beam less than 1° wide at half-power, which can be scanned through 6° at a frequency of 4 c/s. An Appendix describes a method of computation which is especially applicable to sphericalreflectors.