Key characteristics for an airplane to remain invisible on enemy radar include geometry designed to deflect radar signals away, the use of radar-absorbing materials (RAM) to reduce the radar return, and minimized heat signatures from jet engine exhaust. Stealth designs like the F-117 and F-22 feature acute angles and smooth surfaces to enhance radar evasion, avoiding protruding edges. The F-22 employs a passive radar system that detects enemy radar without emitting its own, allowing it to remain undetected until necessary. When engaging targets, it can upload guidance data to missiles using low-bandwidth signals, masking its radar signature. Overall, effective stealth technology combines advanced materials and design principles to significantly reduce visibility on enemy radar systems.