This chapter forms the technical core of the course. The main points:
- Principle: the radar transmits, the target reflects, the radar measures travel time (→ range, R = c·Δt/2), direction (→ azimuth/elevation) and Doppler shift (→ radial velocity).
- The enemies of detection are noise (random, always present) and clutter (real but unwanted echoes); the weapons against them are SNR, Doppler filtering, CFAR and integration.
- The radar equation punishes distance with 1/R⁴: range is expensive, stealth "only" has to beat the fourth root, and jammers have the 1/R² advantage.
- Pulse radar parameters — PRF, PRI, PW, duty cycle, peak/average power — determine the minimum range (c·PW/2) and the maximum unambiguous range (c·PRI/2), and together form the electronic fingerprint of every radar.
- Doppler processing (MTI, pulse-Doppler) separates moving targets from stationary clutter; blind speeds are countered with staggered PRI.
- CW measures velocity only, FMCW also range with low, hard-to-detect power; passive radar transmits nothing itself and relies on broadcast transmitters.
- The antenna determines gain, beam shape and side lobes — and with them both the performance and the vulnerabilities (side-lobe jamming) of the system.
- Resolution has three dimensions: angle (∝ λ/D, deteriorates with range), range (∝ PW or 1/B, independent of range) and velocity (∝ 1/dwell time).
- Ambiguity: a measurement is unambiguous if one interpretation is possible, ambiguous if there are several. The PRF determines both windows — range wants a low PRF, Doppler a high one — and the low/medium/high-PRF regimes are the three ways of dealing with that conflict.
With this knowledge you can take apart any radar system you come across into its choices and compromises — and understand where it is vulnerable. The following chapters cover the passive counterparts: infrared and visible light, and then laser.