The threat is recognized:
It began as a cheap, off-the-shelf tactic.
Buy a commercially available drone, strap a bomb to it and let it fly.
It didn’t take long for the tactic to catch on, spreading across the battlefields of Iraq and Syria as the Islamic State group tried to hold onto its territory against advancing U.S.-backed Iraqi forces.
The homemade flying bombs were not the terrorists’ most effective tool—truck bombs were still far deadlier—but they achieved their intended purpose and drove the U.S. Army and other services to rush to find effective ways to counter this new threat.
“It’s the first time any military has ever had to look up since the Korean War, especially when the U.S. military’s involved, because we’ve had air superiority,” said retired Maj. John W. Spencer, chair of urban warfare studies with the Modern War Institute at the U.S. Military Academy at West Point, New York.
But what the article doesn't mention is what I mentioned in an older article in Army magazine--air defense drones to free the forward Army ground forces from the need to lug around and operate ground-based drone defenses.
My point was to free the infantry from needing to look up into what I called "the brown skies" just above the ground where drones operate, rather than make them more effective at looking up.
Although a bubble of electronic warfare that moves with the infantry to nullify drones that way would be acceptable for that aspect of keeping the infantry focus on the enemy in front of them.
UPDATE: Strategypage looks at anti-UAV defense (AUD).