1. Faceted shaping
The F-117 approach: flat panels at angles that bounce radar energy away from any plausible threat direction. Crude looking but mathematically clean — only required 1970s computing power.
2. Continuous curvature
B-2, F-22, F-35: smooth curves designed to scatter energy in non-threat directions. Required modern Method-of-Moments and FDTD simulation. Aerodynamically much better than facets.
3. Edge alignment
Wings, intakes, control surfaces, weapons-bay doors — all aligned to a small number of azimuth angles. Look at a top-down photo of an F-22 and count the parallel lines: that's RCS engineering, not styling.
4. Radar-absorbent materials (RAM)
Iron-ball paint, carbon-loaded ferrite tiles, structural composites tuned to absorb specific frequencies. Maintenance-heavy — RAM degrades with weather, exhaust and physical contact.
5. Cavity management
Engine intakes and exhausts are giant radar reflectors. Stealth aircraft hide them with S-shaped ducts, screened inlets, and serrated trailing edges. Every cavity is engineered as carefully as the airframe.
6. Active cancellation (the future)
Detect the incoming radar pulse and emit an out-of-phase response that cancels the reflection. Hard to do across a band, hard to do at multiple angles — but lab demonstrations exist and operational systems are rumoured.