What type of antenna is used to receive 1030 MHz interrogation signals in an aircraft's Mode C transponder?

The correct answer is a L-band monopole blade-type omnidirectional antenna. This type of antenna is specifically designed to operate effectively in the L-band frequency range, which includes 1030 MHz, the frequency used for interrogation signals in aircraft Mode C transponders.

Monopole antennas are particularly suitable for applications that require omnidirectional radiation patterns, often used in aviation to ensure that the transponder can receive signals coming from any direction. The blade design further reduces aerodynamic drag and helps maintain the aircraft's overall performance.

In aviation, the use of this antenna type allows for reliable communication and transponder operation, ensuring that interrogations from ground radar systems are accurately received and processed by the aircraft's systems. This is crucial for air traffic control functions and collision avoidance. Other types of antennas listed, while useful in various applications, do not meet the specific requirements for receiving 1030 MHz signals in the context of aircraft transponders.