Loop Antennas for Aircraft

While the theory of operation and the procedure for measurement are similar for all loop antennas, the electrical and mechanical design of aircraft loop antennas differs considerably from that of the other types. In this paper those characteristics, requirements, and design considerations which are associated uniquely with aircraft loop antennas operating in radio range or beacon band extending from 200 to 400 kilocycles will be discussed. In the case of aircraft loop antennas it is necessary to satisfy three important requirements. The first requirement is that a loop antenna form a highly efficient portable antenna; the second, and most important requirement, is that the loop be capable of being used as an accurate direction finder; and third, an electrostatically shielded loop antenna is an effective way of decreasing precipitation or snow static which is quite bothersome to radio reception on aircraft. The "low-impedance" and the "high-impedance" types of air-core aircraft loops are considered in detail. Both types are analyzed mathematically on the basis of their receiving efficiency and directive properties. Actual polar-characteristic curves are given for a number of loop antennas of both types. Iron-core loop antennas which have been used quite extensively abroad are considered separately and comparison is made with the more widely used air-core types.