What is a Phased Array Antenna?

Phased Array Antenna

A phased array antenna is composed of lots of radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction.
In the figure 1 (left) both radiating elements are fed with the same phase. The signal is amplified by constructive interference in the main direction. The beam sharpness is improved by the destructive interference.

(click to enlarge: 591·723px = 468 kByte)Figure 2: Animation of the electronic beam-deflection

In the figure 1 (right), the signal is emitted by the upper radiating element with a phase shift of 22 degrees later than of the lower radiating element. Because of this the main direction of the emitted sum-signal is moved slightly upwards.

(Note: Radiating elements have been used without reflector in the figure. Therefore the back lobe of the shown antenna diagrams is just as large as the main lobe.)

The main beam always points in the direction of the increasing phase shift. Well, if the signal to be radiated is delivered through an electronicphase shifter giving a continuous phase shift then the beam direction will be electronically adjustable. However, this cannot be extended unlimitedly. The highest value, which can be achieved for the Field of View (FOV) of a olanar phased array antenna is 120° (60° left and 60° right). With the sine theorem the necessary phase movingcan be calculated.

The following figure graphically shows the matrix of radiating elements. Arbitrary antenna constructions can be used as a spotlight in an antenna field. For a phased array antenna is decisive that the single radiating elements are steered for with a regular phase moving and the main direction of the beam therefore is changed. E.g. the antenna of the RRP 117 consists of 1584 radiating elements arranged in an analogue beamforming architecture. More sophsticated radar sets use the benefits of aDigital Beamforming architecture.

Advantages Disadvantages
  • high gain width los side lobes
  • Ability to permit the beam to jump from one target to the next in a few microseconds
  • Ability to provide an agile beam under computer control
  • arbitrarily modes of surveillance and tracking
  • free eligible Dwell Time
  • multifunction operation by emitting several beams simultaneously
  • Fault of single components reduces the capability and beam sharpness, but the system remains operational
  • the coverage is limited to a 120 degree sector in azimuth and elevation
  • deformation of the beam while the deflection
  • low frequency agility
  • very complex structure (processor, phase shifters)
  • still high costs

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