Theory of End-Fed Quarter-Wave Antennas

Date: 2026-01-12

• An end-fed quarter-wave antenna is one quarter wavelength long and fed at the end.
• It uses a counterpoise or ground system to complete the return path.
• Feed impedance is low at a current maximum near the end, typically 20-40 ohms.
• Radiation is similar to a vertical monopole with omnidirectional azimuth pattern.
• Height and ground quality affect take-off angle and efficiency.
• Shortening requires loading coils or capacitive hats.
• Common-mode currents can appear on the feed line without a choke.