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Displaced Phase Center Antenna (DPCA)

Figure 1: Principle of the DCPA: the proper motion of the platform is compensated by shifting the phase center.

Figure 1: Principle of the DCPA: the proper motion of the platform is compensated by shifting the phase center.

Displaced phase centre antenna (DPCA) processing is a concept in radar space–time processing. It is used to improve the detection performance of airborne or space-borne MTI radars that are subject to clutter. The origins of this technology comes from General Electric where it was applied to airborne early warning (AEW) radars in the early 1950s. DPCA is a technique for countering the platform motion induced clutter spectrum spreading. The basic concept of is to make the antenna appear stationary even though the platform is moving forward by electronically shifting the receive aperture backwards during the operation.

In a moving target indication (MTI) radar, phase shifts between then echo signals of two or more pulse perods are used to distinguish between moving targets and fixed clutter. In airborne radar systems (e.g. SLAR) this technology is complicated by the proper motion of the radar platform. Here, the fixed targets also get a Doppler frequency. A way to mitigate the effects of clutter returns in such a system is to implement this displaced phase center antenna technique.

The displaced phase center antenna is a principle technique for ground moving target detection using a large phased array. In DPCA technique from an airborne phased array are used only a part of its radiators principally, so that e.g. the front-side half of the array forms a beam in a given pulse period. The rearmost half of the array forms the next beam in the next pulse period. During this pulse period, the aircraft continues to fly a short distance. If the aircraft motion is exactly compensated by the movement of the phase center of the antenna beam, then the second transmitting pulse is transmitted at the exact same location as the previous one. This has the advantage, that the aircraft motion produces no Doppler frequencies at fixed targets. The fixed clutter can be easy cancelled with a two pulse canceller now.

The condition is that platform velocity, Pulse Repetition Frequency (PRF) and phase centre distance of the antenna parts should be satisfied. The errant of platform velocity over the ground can destroy the condition usually. During the corresponding receiving times the advantages of digital beam forming technique can be used, by which multiple phase centers for receive beam can be formed.