Give the Secondary Radar systems

Secondary Radar systems are used primarily in aviation for aircraft identification and tracking. Unlike primary radar systems that rely on the reflection of radio waves from the aircraft, secondary radar systems involve the transmission of signals from both the ground-based radar system (interrogator) and the aircraft's transponder. Here are the key components and functions of secondary radar systems:

1. Interrogator: The ground-based radar system, known as the interrogator, transmits interrogation signals toward the aircraft. These signals typically operate in the microwave frequency range.

2. Transponder: Each aircraft equipped with secondary radar capabilities is fitted with a transponder. The transponder receives the interrogation signals from the ground-based radar and responds with a coded reply signal. The reply signal includes identification information such as the aircraft's unique identifier (squawk code) and altitude.

3. Mode A, C, and S: Secondary radar systems operate in different modes:

   • Mode A: Provides the aircraft's 4-digit squawk code (e.g., 1200 for Visual Flight Rules (VFR) flights in the United States).
   • Mode C: Adds altitude information to the squawk code, typically using pressure altitude.
   • Mode S: Provides selective addressing and additional data capacity, allowing for more detailed information exchange between aircraft and ground systems. Mode S is used extensively in Air Traffic Control (ATC) for surveillance and communication purposes.

4. Functionality:

   • Identification: Allows ATC to uniquely identify and track each aircraft within its coverage area based on the transponder reply.
   • Collision Avoidance: Enhances the safety of air traffic by enabling aircraft to exchange position and velocity information via secondary radar systems.
   • Surveillance: Provides continuous surveillance of aircraft, aiding in route planning, traffic separation, and management.

5. Integration with ATC: Secondary radar systems are integral to Air Traffic Control (ATC) operations, providing real-time aircraft identification and surveillance data to controllers for safe and efficient management of airspace.

6. Advantages: Compared to primary radar systems, secondary radar systems offer more accurate and reliable identification of aircraft, reduce the likelihood of radar clutter, and enable more effective traffic management in busy airspace.

Overall, secondary radar systems play a critical role in modern aviation, providing essential information for air traffic management, aircraft surveillance, and collision avoidance, thereby ensuring safe and efficient operations within controlled airspace.