I'm sure the OP has already read his Skolnik given his comment but for those following along that's usually the best place to start.
https://www.amazon.com/Radar-Handbook-Third-Merrill-Skolnik/...
https://www.amazon.com/Radar-Handbook-Third-Merrill-Skolnik/...
Which builds up from first principles a ballistic missile defence system. Always useful to have.