If an antenna's beam is narrow in either the horizontal or vertical plane, what is it said to have?

When an antenna's beam is narrow in either the horizontal or vertical plane, it is recognized as having high directivity. High directivity refers to the ability of an antenna to focus energy in a particular direction more effectively than in others. This means that the antenna can transmit or receive signals primarily along a specific path, resulting in enhanced performance in that direction.

In practical terms, narrow beamwidth indicates that the antenna is adept at minimizing the reception of signals from other angles, thereby increasing the effectiveness and strength of the signal in the intended direction. This characteristic is beneficial in applications where precise targeting of signals is essential, such as in radar or communication systems.

Thinking about the other choices can clarify why they do not fit the description. Low frequency does not correlate with beamwidth; rather, it refers to the wavelength of the signals being transmitted. High power is related to the strength of the signal being transmitted but doesn't specify how well the signal is directed. Low gain suggests that the antenna would be less effective at focusing energy, which contradicts the concept of a narrow beam that typically signifies higher gain and directivity.