What is the difference between a pulsed radar and a continuous wave radar at millimeter wave frequencies?

Pulsed radar and continuous-wave (CW) radar are the two fundamental radar architectures, with distinct operating principles and performance tradeoffs at mmWave: (1) Pulsed radar: transmits short pulses (nanoseconds to microseconds) and listens for echoes during the silent period between pulses. Range is measured from the pulse round-trip time: R = c × t_delay / 2. The transmitter and receiver are time-multiplexed (TX is off during RX, and vice versa). This provides inherent TX-RX isolation (no self-interference during receive). Range resolution: determined by the pulse width: Δr = c × tau_pulse / 2. For a 1 ns pulse: Δr = 15 cm. For a 10 ns pulse: Δr = 1.5 m. At mmWave: generating very short pulses (< 1 ns for cm-level resolution) is challenging. Pulsed compression (chirped pulse) can improve resolution without reducing pulse width. Peak power: a pulsed radar must transmit all its energy in the short pulse duration. For the same average power: the peak power is much higher than CW. Peak power = P_avg / duty_cycle. For 10% duty cycle: peak power is 10× the average. At mmWave: achieving high peak power (> 1 W) is expensive (requires large GaN PAs). (2) Continuous-wave (CW/FMCW) radar: transmits continuously (no pulses). The transmitter and receiver operate simultaneously. Range is measured from the frequency difference between the TX and RX signals (for FMCW). TX-RX isolation is a challenge: the TX signal leaks directly into the RX (since both operate simultaneously). CW leakage: -20 to -40 dB of the TX power reaches the RX. This sets the noise floor and limits the dynamic range. At mmWave: TX-RX isolation is achieved through: separate TX and RX antennas (physical separation), circulators (limited effectiveness at mmWave due to loss and bandwidth), and signal processing (subtracting the known TX leakage from the RX signal). Power: CW radar transmits at low, constant power (typically +10 to +20 dBm total). No high peak power requirement. This makes the PA design simpler and cheaper. (3) FMCW (the dominant mmWave CW variant): combines CW operation with frequency modulation for range measurement. The frequency sweep bandwidth determines the range resolution (Δr = c/(2×BW)). A 4 GHz sweep provides 3.75 cm resolution without requiring picosecond pulse widths.