@AliYusuf
Below is the complete cycle of action
1. Launch - Missile is deployed to fire
2. Separate - Missile leaves the hard point and gets airborne
3. Initiate - SEMI ACTIVE Mode -Missile starts to get guidance from Aircraft's radar and then it sets on course towards the target (Boost + mid course Guidance)
4. Initiate - ACTIVE MODE - Missile is using own seeker as its got active.
This is the last part - the Active mode
The missile has a blue envelope pointing towards the aircraft (in orange). This blue envelope is the beamwidth (field of view) of the missile seeker. This could be 30 degrees or more. If the plane makes a 90 degrees and gets out the of the missile seeker envelope (beamwidth or FOV), the aircraft can evade the missile.