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.  In the figure 1 (right), the signal is emitted by the lower radiating element with a phase shift of 10 degrees earlier than of the upper radiating element. Because of this the main direction of the emitted sum-signal is moved upwards.

Figure 1: left: two antenna elements, fed with the same phase, right: two antenna elements, fed with different phase shift

(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 electronic phase shifter giving a continuous phase shift now, 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 phased array antenna is 120° (60° left and 60° right). With the sine theorem the necessary phase moving can 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 a Digital Beamforming architecture.

Figure 2: electronic beam-deflection,
left: Boresight, right: Deflected