Current distribution on wing-cap and tail-cap antennas

Surface current distributions on aircraft are examined for wing-cap and tail-cap antennas in the hf band using scale models. Current paths involved in structural resonances are investigated, and the effect of such resonances on antenna impedance is discussed. Measured results are also applied to the interpretation of radiation patterns. A technique is described for measuring the relative amplitude and phase of the surface current, and for determining the direction of current flow. In this method the detector is placed in the model and the probe is driven by an external source of rf power. This technique permits the frequency to be changed easily. The system is more sensitive than others described in the literature, since a higher power source can be used when it is not required to be enclosed in the aircraft model.