I'm not sure I understand your question, but for regular radar applications, several circuit types are used. The transmitter uses a tube like your microwave oven to send out pulses of RF energy through the antenna structure, and the receiver is a low-noise, high-gain RF radio receiver. Then there is the electronic timing circuitry that times the echo return time to determine the distance. For Doppler-capable (speed sensing) radar, the receiver and timing circuitry work together more closely to calculate the speed of the reflecting object.
But some radar structures can be completely passive. Like the wind-driven hidden cube corner things that will blank out police doppler radar detectors... (but don't help against LIDAR obviously).
Since radar uses microwaves, from the output device until the antenna you have a system that uses electromagnetism and not circuits. Instead of the laws of Kirchoff you use the laws of Maxwell.
But most of the low power portion of the radar system uses circuits.