What are your sources?
I'm pretty sure the antenna in the AGM-122 is practically useless at VHF/UHF frequencies. Here's a sectioned view of the AGM-122 seeker:
(borrowed from
)
The body diameter of an AIM-9 is approximately 5" / 127mm, so let's say the antenna diameter is approximately 110mm. By using a simple parabolic antenna gain calculator, with ideal conditions (100% efficiency), we get an approximation of how well the antenna works at different frequencies:
VHF/UHF:
100MHz: -18,8dB
200MHz: -12,7dB
300MHz: -9,2dB
Negative gain = a really terrible antenna at these frequencies.
J band:
10GHz: +21,2dB
15GHz: +24,7dB
20GHz: +27,2dB
So the antenna is about 4000 times (36dB) as effective at 15GHz than it is at 200MHz. This combined with the fact that it is pretty unlikely that the RF receiver is wideband enough to detect anything at these low frequencies leads me to conclude that it is unlikely that the AGM-122 can detect, track and intercept VHF/UHF EWR radars. But if anyone has actual technical data (no, wikipedia etc. is not a reliable source) that says otherwise, feel free to post it here.