Understanding Antenna Reactance
Reactance (X) is the part of impedance caused by energy being stored in the antenna’s electric and magnetic fields. It is also measured in ohms and can be either positive or negative. A positive reactance value means the antenna system is inductive, while a negative value means it is capacitive. The ideal reactance at resonance is approximately 0 ohms. For many common antennas, reactance is strongly related to electrical length. An antenna that is electrically too short will often show positive reactance, while one that is electrically too long will often show negative reactance, although loading coils and more complex antenna designs can alter this relationship. As the antenna is adjusted toward resonance, the reactance should move closer to zero.
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