What type of antenna is used to extract the RADAR signal from the waveguide?

The correct choice mentions a J-hook antenna, which is designed specifically for coupling with waveguides to extract radar signals. This type of antenna has a design that allows it to efficiently pick up microwave signals within the waveguide, making it effective for radar applications where precise and effective signal retrieval is critical.

In radar systems, the propagation of signals often occurs through waveguides, and a J-hook antenna complements this by providing a low-loss method for transitioning from the guided wave in the waveguide to an open-air transmission line. Its physical structure enables it to be compact while still maintaining efficiency in signal extraction, which is why it is commonly utilized in radar technology.

Other types of antennas, while they may serve various purposes in telecommunications, aren't specifically optimized for the tasks involved with radar and waveguide interaction in the same way the J-hook antenna is. For example, dipole antennas and loop antennas might not effectively extract signals in the same manner or may not be suited for the high-frequency applications typical of radar systems.