There are reams of doctrine about how to approach a SAM site from the air. Look up Suppression of Enemy Air Defense (SEAD) or Destruction of Enemy Air Defense

There are reams of doctrine about how to approach a SAM site from the air. Look up Suppression of Enemy Air Defense (SEAD) or Destruction of Enemy Air Defense (DEAD). Jammers (think emit a huge amount of energy on the frequency the radars use) and anti-radiation missiles (think radar homing) are a big part of it.