Ground-based Air Surveillance Radars for the military play a key role in air defense at the strategic and operational levels. These radars detect and track airborne targets. This lets air defense personnel ascertain which of these targets are friendly, neutral or hostile.
Ground-based air surveillance radars help protect national airspace, or the airspace of several countries. They may also protect expeditionary deployments in an operational theater, or specific areas where large events like sporting occasions are taking place. In a nutshell, a ground-based air surveillance radar provides an umbrella of coverage over the airspace across a particular area.
Integrated Air Defense Systems
Military surveillance radars are typically tied into a larger Integrated Air Defense System (IADS). An IADS is a networked collection of air defense assets protecting a defined area. This could include part, or all, of an operational theater, a country or a group of nations. The IADS comprises kinetic capabilities like fighters, Surface-to-Air Missiles (SAMs) and Anti-Aircraft Artillery (AAA). Ground-based air surveillance radars work closely with Fire Control/Ground-Controlled Interception (FC/GCI) radars. Their role is to help manage the interception of an airborne target by a SAM, fighter or AAA.
Ground-based air surveillance radars feed their radar picture into operations centers. At these centers, air defense personnel determine which of these targets are hostile. Using the data from these radars, they then task the IADS’ kinetic elements to engage the targets. Communications links like conventional telecommunications and radio connect these components which may be separated by vast distances.
Coverage & Early Warning
Air surveillance radars typically cover a wide area. For example, a radar with a range of 216 nautical miles (400 kilometers) could monitor 146,534 square nautical miles (502,600 square kilometers). However, this may be insufficient to monitor a country’s entire airspace, depending on its size. As such, several radars may be needed to provide adequate coverage. An IADS may merge imagery provided by each of these radars into a Recognised Air Picture (RAP) of the area it controls. It is important to note these radars are not only tasked with watching the airspace above a specific area. They may also need to watch air approaches stretching several hundreds of nautical miles beyond it. This provides early warning of potential threats heading towards the protected airspace.
Airspace Surveillance Design Considerations
Ground-based air surveillance radar design differs according to the task the radar performs. For example, some radars transmit in comparatively low frequencies of three megahertz to three gigahertz. Such radars can be capable of detecting targets with ‘stealth’ characteristics designed to reduce their radar visibility. However, these radars may be physically large as their signals’ long wavelengths need large antennas. This may mean they can only be used in a fixed configuration and are hence less practical to deploy. While these radars can detect targets with a low Radar Cross Section (RCS), their wavelengths can deprive them of target precision. For example, they may be able to indicate the general area where such a target may be. Therefore, they may be unable to provide the requisite precision to help manage a SAM or AAA engagement.
Higher frequencies from three to six gigahertz are also used by military airspace radars. These may use comparatively smaller antennas and hence be more deployable. Nonetheless, they may have poorer performance regarding low RCS targets. That said, they may detect targets in more detail and have more utility to help direct interceptions.
As with all elements of radar engineering there is no perfect design. Instead, this depends on the radar’s intended tasks and the specific requirements of the user.