In radar receivers, which component is responsible for converting the received signal to the intermediate frequency?

• A. Local oscillator
• B. RF amplifier
• C. Mixer
• D. Detector

Answer: (C)

Converting to an intermediate frequency in radar receivers happens through mixing. The received RF signal from the antenna is combined with a locally generated oscillator signal inside a nonlinear mixer. The mixer produces new signals at the sum and difference of the two frequencies, and the intermediate frequency we want is the difference frequency (|f_RF − f_LO|). This fixed IF is easier to filter and amplify with high stability.

The local oscillator supplies the reference frequency used by the mixer but does not perform the conversion by itself. The RF amplifier's job is to boost the incoming signal before mixing, and after the IF stage, a detector recovers the modulated information from the IF signal. So the element that actually performs the downconversion to the intermediate frequency is the mixer.