Final answer:
IFF/SIF returns can be received from a target without receiving a radar return because the target may be emitting an identification signal without reflecting the radar beams back to the radar receiver.
Step-by-step explanation:
In radar systems, an identification, friend or foe (IFF)/selective identification feature (SIF) return refers to a signal received from a target that indicates its identity or classification. On the other hand, a radar return is a signal received from a target that indicates its presence. It is possible to receive an IFF/SIF return from a target without receiving a radar return because the target may be emitting an identification signal without reflecting the radar beams back to the radar receiver.
For example, in military applications, aircraft are equipped with IFF/SIF systems that transmit signals to identify themselves as friendly aircraft. These signals are only intended to be received by other friendly aircraft or radar systems. They are not reflected back to the radar receiver, so a radar return may not be detected from the target, but an IFF/SIF return can still be received.