Final answer:
The Monopulse Secondary Surveillance Radar receiver creates both Sum and Difference Signals when mixing the 1090 MHz replies with the local oscillator. These signals help accurately determine the angle of arrival of radar signals for improved target localization.
Step-by-step explanation:
When the Monopulse Secondary Surveillance Radar (MSSR) receiver mixes the 1090 MHz replies with the local oscillator (LO) from the receiver interface, a Sum and Difference Signal are created. This technique allows for accurately determining the angle of arrival of the signal, which is crucial for radar tracking. The sum signal is the result of the direct addition of the two frequencies, whereas the difference signal is the result of their subtraction. In practical MSSR systems, this process is used to enhance the accuracy of target localization.