Oh! I didn't see the bandwidth was so wide. You are correct. Wouldn't the resolution still be decent with a narrower bandwidth (i.e. the 10s of MHz that a yagi could manage)?
Also, as an alternative to a horn antenna, a parabolic reflector should work well in this band without being too large, right?
The range resolution would go from 8.5" to five yards if you changed the bandwidth to 30 MHz. Currently the radar could figure out the direction a person is facing to about 45 degrees. 5 yards would be good to find the orientation of a house.
Parabolic antennas are just horns with lenses. The bigger the parabola, the better the focus and the wider the bandwidth. A horn would be a few inches across, but a 700 MHz reflector would be a couple feet.
Also, as an alternative to a horn antenna, a parabolic reflector should work well in this band without being too large, right?