Special Aspects of Balanced Shielded Loops

The theory of operation of the balanced shielded loop antenna is reviewed. A method of analysis of this type of antenna is described, wherein transmission-line principles are utilized to account for the distributed nature of the loop constants for loops whose perimeters are of the order of one-quarter wavelength. It is shown that the loop conductor within the shield may be treated as a coaxial transmission line having uniformly distributed constants, and that the outer surface of the shield may be treated as a balanced two-conductor transmission line having nonuniform constants. A method is described whereby the relatively cumbersome equations of the latter type of transmission line may be avoided by the use of an "equivalent" line having uniform characteristic impedance. A sample calculation is included to illustrate the utility of this method of analysis.