DARPA is looking for radio-frequency (RF) seekers for smart shells.
The goal is sensors accurate and rugged enough for DARPA's Multi-Azimuth Defense-Fast Intercept Round Engagement System, or MAD FIRES, smart shell program. "Current projectile technologies have been demonstrated in flight maneuver, but only recently have advances in electronics and gun survivability opened the possibility of projectile-based seekers," explains the DARPA research solicitation.
RF seekers are a promising solution, but current seekers are too big for medium-caliber projectiles. "The antennas must reside within the outer mold line of a medium-caliber projectile and survive gun launch and ballistic fly out," DARPA said. "The antenna should provide sufficient gain in the forward direction to track targets during fly out and terminal engagement. The antennas must support accurate measurement of line of sight to target for terminal phase guidance."