How does an inverse synthetic aperture radar (ISAR) function?

An inverse synthetic aperture radar (ISAR) functions by utilizing the motion of a target and the radar signals it emits to produce high-resolution images. In contrast to synthetic aperture radar (SAR), which generally involves a moving radar platform to gather data, ISAR effectively exploits the movement of the target itself—such as a ship or aircraft—and combines this with radar signals to achieve detailed imaging. Through the processing of the received radar echoes as the target moves, ISAR can distinguish features of the target with precision. This capability is particularly valuable in applications like maritime surveillance and reconnaissance, where the relative motion provides the necessary data for imaging.

The other options do not correctly represent the mechanics of ISAR. The reliance on a stationary radar platform is characteristic of traditional radar systems, not a dynamic imaging system like ISAR. The notion of requiring multiple radar units does not align with how ISAR operates, as it efficiently uses a single radar unit with the target's movement for imaging. Lastly, ISAR is not limited to a fixed frequency band; it can operate over a range of frequencies to enhance its versatility and adaptability to different scenarios.