How Things Work: Phased-Array Radar
It takes a big eye to see a missile coming.
- By Sam Goldberg
- Air & Space magazine, July 2006
(Page 3 of 3)
To point the SBX’s powerful main beam, computers command each of its radiating elements to slightly shift the initial phase of the radio waves they shoot.
Thus, each element emits a radio wave with crests and troughs that are slightly out of sync with the crests and troughs of the radio waves emitted by its neighbors. For example, a wave being radiated from element A may start at a crest, while the wave emanating from element B begins life as a trough.
The effect is that the beam swings from the center to the right or left (see diagram, opposite). With the new elements added, the beam can be pointed up or down as well. The direction of the beam can be changed in 20 microseconds or less.
The main advantage to this approach is that the radar can keep a constant eye on a target—it can shoot and watch for radio reflections thousands of times per second instead of going blind until the next rotation sweeps the main beam past the target again.
Since the main beam can be pointed almost instanteously, it can jump from object to object as they come into range.
Phased-array radars are not without disadvantages. Most are functional through a cone of just 120 degrees, because the width of the main beam diminishes the farther it gets from broadside. As an example, think of how narrow your wide-screen television looks when you’re in an adjacent room.
For this reason, at least four radars are needed to cover a hemisphere. To compensate for the narrow field of view, the SBX’s main array rotates and tilts; it’s one of the few phased arrays to do that.
Although the initial cost is 100,000 times more expensive than a conventional radar with the same beam width, a phased-array device may be cheaper long-term because the system will still function as needed even if many of its smallest components fail.