The following is the Feb. 12, 2020 Congressional Research Service In Focus report, Department of Defense Counter-Unmanned Aircraft Systems.
From the report
Unmanned aircraft systems (UAS), commonly called drones, have proliferated rapidly and are available to nation-states and to nonstate actors and individuals. These systems could provide U.S. adversaries with a low-cost means of conducting intelligence, surveillance, and reconnaissance missions against—or attacking—U.S. forces. Furthermore, many smaller UASs cannot be detected by traditional air defense systems due to their size, construction material, and flight altitude. As a result, in FY2020, the Department of Defense (DOD) plans to spend at least $373 million on counter-UAS (C-UAS) research and development and at least $200 million on C-UAS procurement. As DOD continues to develop, procure, and deploy these systems, congressional oversight of their use may increase, and Congress may have to make decisions about future authorizations, appropriations, and other legislative actions.
C-UAS can employ a number of methods to detect the presence of hostile or unauthorized UAS. The first is using electro-optical, infrared, or acoustic sensors to detect a target by its visual, heat, or sound signatures, respectively. A second method is to use radar systems. However, these methods are not always capable of detecting small UAS due to the limited signatures and size of such UAS. A third method is identifying the wireless signals used to control the UAS, commonly using radio frequency sensors. These methods can be—and often are—combined to provide a more effective, layered detection capability. Once detected, the UAS may be engaged or disabled. Electronic warfare “jamming” can interfere with a UAS’s communications link to its operator. Jamming devices can be as light as 5 to 10 pounds and therefore man-portable, or as heavy as several hundred pounds and in fixed locations or mounted on vehicles. UAS can also be neutralized or destroyed using guns, nets, directed energy, traditional air defense systems, or even trained animals such as eagles. DOD is developing and procuring a number of different C-UAS technologies to try to ensure a robust defensive capability.
Download the document here.