Multipath and interference effects in secondary surveillance radar systems

Secondary surveillance radar (SSR) offers many advantages for air traffic control (ATC) compared to normal (or primary) radar including substantially lower cost and improved performance. Because of the increasing reliance being placed on SSR by ATC a number of the system problems associated with SSR are becoming less easily tolerated. The paper discusses these problems, which mainly arise from multipath and mutual interference effects, and proposes solutions.