Antenna Arrays Questions and Answers

Answer: A

With no mechanical motion, the limit is how quickly the phase shifter settings can be computed and applied, which is typically microseconds. That is thousands of times faster than any mechanical mount. The array face has inertia but is never rotated, aperture transit time is a few nanoseconds and irrelevant, and frequency agility is a separate capability. It is this speed that allows one aperture to interleave several radar functions apparently simultaneously.

Answer: B

Because the beam is steered by phase alone, the aperture stays fixed and every connection to it can be permanent, removing a component that is a major source of wear, loss and failure in a mechanically scanned radar. Optical distribution is used in some designs but is not the reason, separate faces are a coverage arrangement rather than a substitute for a joint, and a flexible loop would still be a moving connection. Eliminating moving parts is one of the strongest practical arguments for the technology.

Answer: C

Once the element signals are digitised, each additional beam is another weighted sum in the processor, so the limit is computation rather than hardware. The element count sets the aperture and the degrees of freedom rather than the beam count, bandwidth affects the sampling rate, and a digital array may have no phase shifters at all. This is the fundamental advantage of digital over analogue beamforming and the reason it has spread as processing has become cheaper.

Answer: D

Tapering the aperture widens the beam and lowers the aperture efficiency, and the random error floor must be pushed below the design level, which raises the precision required of every component. Very low side lobe arrays are therefore expensive out of proportion to their size. Bandwidth and scan range are affected by other choices, and the cost per element rises rather than falls. Knowing what a specification will cost before committing to it is much of the art of system engineering.