The PAC-3 is optimized for the anti-ballistic missile mission.
The initial dismal failure of the patriot system in the Gulf War was due to a software glitch that wasn't detectable within its original mission of shooting down aircraft. It utilized a "smart radar" system to maintain contact to tenths of a second. However, you can't accurately keep track of time in a binary system without updates.For example, trying to represent 1/3 to precision is impossible. .33333333333.... After 100 hours of continuous operation the system lost time and the missiles they were tracking. The fact the scuds didn't maintain a consistent trajectory because they "wobbled" due to modifications for longer range didn't help.
The Aegis Ballistic Missile Defense system can intercept missiles post boost phase and prior to re-entry.
THAAD is set to be deployed in 2009 and utilizes Pac3 kill technology (100% kinetic energy hit to kill), it was originally scheduled for deployment in 2012. I guess it was moved up before Obama could get elected and slash the military budget by 1/4. However, he has also promised to cut all ABM technology development.