Shunt and notch-fed HF aircraft antennas

In the hf range radiation from aircraft must be accomplished by exciting radiating currents on the airframe itself. One method of exciting such currents is by shunts or notches which electrically penetrate the airframe. The strength of coupling of such devices is analyzed and shown to be proportional to the square of the normal mode current which they interrupt. A theory is developed and substantiated by experimental data, which enables the prediction of the impedance characteristics of such antennas. It is shown that these antennas are most effective when located in a region of high current concentration, and that the current concentration which occurs in the fillet area of swept-wing aircraft makes this area particularly favorable for their installation. Shunt and notch antennas, when they can be used, have a number of structural advantages over cap-type antennas, and certain electrical advantages also. They require no special lightning protection and eliminate the need for special isolating devices. In general, they are capable of handling higher powers before encountering high-altitude voltage breakdown.