Radiation from Large Circular Loops

In this paper is calculated the radiation resistance of a circular loop of any radius and also its polar diagram of electric field at a large distance. It is shown that, according to the radius, the field can be zero in the equatorial plane or at any angle of elevation. It is shown that the ¿high-angle¿ radiation can be sensibly removed by using two concentric and coplanar loops having suitably chosen radii: but with this disposition the current must be supplied to both loops and it is impracticable to induce one current from the other. The ¿high-angle¿ radiation can also be much reduced by the use of two similar coaxial large loops in parallel planes, and this offers a disposition which may be useful in practice. The power gain of a stack of N similar small loops is shown to be equal numerically to the gain of an N-member in-line array of electric doublets; and it can be shown that this is true whatever the radius of the loop, but one or more side lobes can be sensibly obliterated by suitable choice of this radius. Having regard to the difficulties of ¿feeding,¿ inherent in the construction of all aerial systems, it would seem that a pair of parallel large loops is one of the simplest systems for obtaining a horizontal electric field concentrated mainly in a zone of about ± 30° from the equator. The choice between two such loops and a stack of small loops depends very much on the wavelength to be used.