What is the purpose of placing an electrostatic shield around a small-loop direction-finding antenna?
It adds capacitive loading, increasing the bandwidth of the antenna
It eliminates unbalanced capacitive coupling to the antenna’s surroundings, improving the depth of its nulls✓Bonne réponse
It eliminates tracking errors caused by strong out-of-band signals
It increases signal strength by providing a better match to the feed line
Explication
A small direction-finding loop should respond only to the magnetic field; unbalanced capacitive coupling to nearby objects adds an electric-field response that fills in and shifts the nulls. A grounded shield around the loop, broken at one point so it does not act as a shorted turn, removes that coupling and restores deep, symmetrical nulls.