The Probe Excited Airframe as a High Frequency Antenna

An electrically isolated probe mounted on an airframe extremity has been investigated as a means of exciting the airframe as a high-frequency antenna. The probe maintains most of the advantages of isolated structure or ``cap'' type antennas over fixed wires, and it does not require a break in basic airframe structure. Measurements have been made of radiation patterns and impedance of such a probe mounted at a number of positions on a B-47 airplane. Impedance characteristics at low frequencies depend strongly on the length of the probe and its location on the airframe, but not to any great degree on the shape of the airframe itself. At higher frequencies, however, the impedance indicates clearly the effects of various resonant modes of the airframe. Radiation pattern characteristics of these antennas are due primarily to excitation of the airframe and are modified by the probe itself only to the extent that the probe location influences the airframe modes which are excited.