Theory of Long Wire Antennas

Date: 2026-01-12

• A long wire antenna is a straight conductor longer than about half a wavelength.
• As length increases, the current distribution forms multiple standing-wave lobes.
• The radiation pattern narrows in the plane of the wire and develops multiple main lobes.
• End effects increase the physical length compared to ideal free-space calculations.
• Height above ground and soil conductivity strongly affect impedance and pattern.
• End-fed long wires typically present high feed impedance at the end.
• Feed impedance varies substantially with frequency and wire length.
• Counterpoise or earth connection is required for end-fed systems.
• Balanced feed can be used with center-fed or off-center-fed long wires.
• For portable HF, random-length wires are common with tuners.
• Efficiency is driven by conductor loss and ground loss.
• Modeling is recommended because formulas are approximate.