feedpoint

A feedpoint is the electrical connection where a feedline attaches to a radiating element in an antenna system. It is the interface through which RF energy is delivered from the transmitter or receiver to the antenna, and from which the antenna’s input impedance is defined.

In RF practice, the feedpoint impedance is the impedance seen looking into the antenna from the feedline. This impedance determines how well the transmitter can deliver power into the antenna and how the reflected power is managed. For a center-fed half-wave dipole in free space, the characteristic impedance at the feedpoint is typically around 73 ohms (real) with a small reactive component; real-world installations can shift this value substantially due to height, ground effects, and nearby structures.

Impedance at the feedpoint varies with mounting position, environment, and frequency. Height above ground, nearby objects, and soil conductivity can alter both the resistance and reactance, affecting bandwidth and the standing-wave ratio. Accurate knowledge of the feedpoint impedance is essential for impedance matching and minimizing return loss.

To connect antennas to transmission lines, matching networks are commonly used. Baluns or transformers can convert between balanced antennas and unbalanced coaxial lines, while other networks achieve impedance transformation (for example, gamma matches or Ruthroff transformers). End-fed configurations frequently require matching networks to present a practical feedpoint impedance to the line.

Common feedpoint configurations include center-fed dipoles, folded dipoles, and end-fed antennas. The feedpoint position influences the radiation pattern and input impedance, so engineers select the feedpoint and matching approach to achieve the desired impedance, efficiency, and bandwidth for a given installation.