Theory of Loop Antennas

Date: 2026-01-12

• Loop antennas are closed conductors; full-wave loops are efficient radiators.
• Large loops (circumference ~1 lambda) have low-angle radiation and gain.
• Small loops (<< 0.1 lambda) are magnetic loops with high Q and narrow bandwidth.
• Current is distributed around the loop; voltage peaks at the feed point.
• Feed impedance depends on size, height, and loop shape.
• Loops are often quieter on receive due to reduced E-field pickup.
• Coupling can be direct feed or via a coupling loop.
• Nearby conductive objects detune the loop and reduce efficiency.