Prematching of wire antennas by resistive loading

Most wire antennas for tactical HF (1.6-30 MHz) applications are narrowband and therefore require some means of adjustable impedance matching (using the so-called antenna tuning unit, ATU) in order to function effectively across that bandwidth or at least a reasonable portion of it. The author presents a method of modifying the driving-point impedance of the antenna by feedpoint resistive loading such that an acceptable VSWR can be obtained while not reducing the radiation efficiency excessively. A design technique based on the Smith chart is used and particular attention is paid to the effects of ground losses on antenna performance at the low height at which such antennas are frequently erected. The resistive loading can be used on its own or as a method of prematching, thereby reducing the complexity of any additional ATU which may be necessary