Explanation: A phased array antenna system precisely controls the phase of the radio frequency (RF) signal delivered to each of its multiple individual radiating elements. By varying these phase relationships, the electromagnetic waves from each element combine constructively in desired directions and destructively in others. This active phase control allows the system to electronically steer, shape, or focus its overall radiation pattern, creating a highly directional beam that can be pointed without physically moving the antenna. Therefore, option C correctly describes this process: "RF from multiple antennas is varied to produce a desired radiation pattern." Options A and B are incorrect because a phased array fundamentally consists of *multiple* antenna elements, not a single one. Option D is incorrect because phased arrays are designed to achieve significant *directional gain* by concentrating RF energy in specific directions, far exceeding unity gain (which implies an isotropic radiator with no directivity).