The correct answer is B: It eliminates unbalanced capacitive coupling to the antenna's surroundings, improving the depth of its nulls. The purpose of placing an electrostatic shield around a small-loop direction-finding antenna is to eliminate unbalanced capacitive coupling to the antenna's surroundings, improving the depth of its nulls. The shield prevents the antenna from coupling capacitively to nearby objects. Small loop antennas for direction-finding rely on sharp nulls to determine direction. Without a shield, the loop can couple capacitively to nearby objects (ground, buildings, etc.), which distorts the pattern and makes the nulls less sharp. An electrostatic shield (typically a Faraday shield - conductive but not a complete electrical circuit) blocks electric field coupling while allowing magnetic field coupling. This eliminates the capacitive coupling, making the nulls deeper and sharper, which improves direction-finding accuracy. The shield is essential for good DF performance.