The input impedance of an antenna is a physical parameter of the antenna. It can be defined as the ratio of the complex amplitude of the high-frequency voltage applied to the antenna to the complex amplitude of the current flowing through the antenna. Measurements are taken directly at the antenna terminals. As a rule, the input impedance of an antenna is a complex quantity. The input impedance consists of the sum of the antenna’s radiation resistance and loss resistance. The radiation resistance Rrad and the loss resistance Rloss, unlike the input impedance, are theoretically determinable values.
Most VHF antennas have an impedance of 50 Ohms.
Related articles:
Characteristic Impedance,
Characteristic Impedance of Coaxial Cable,
Standing Wave Ratio,
Traveling Wave Ratio,
Wavelength Shortening Factor in a Feeder Line, Antenna Matching Unit (AMU)