gsm microwave links
Things I would do, in order of importance:
1) If you have headroom, bump up the transmit power on both ends.
2) change to high gain antennas on both ends and point them AWAY from the military base as much as possible while maintaining proper link margin. The higher antenna gain will give more off-boresight attenuation drop off.
3) Hook a spectrum analyzer to the antenna and figure out just what frequencies are jamminng you at the site. (Only do this if you think you will not get shot for being a spy!!!). IF the jamming frequencies are out of band, you could add a band-reject or bandpass filter to pass your desired frequencies while rejecting the jamming frequencies. It might be possible to move to a channel within your 15 GHz band that is jammed a little less than the other channels.
4) if it is a critical application and the above do not work, you could go to a frequency diversity system with a hitless switch.
And I would also try swaping antenna polarization, as suggested above. It MIGHT help, although a lot of radars are circular polarization (where you would be out of luck).