Beamformers - General Information
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An added advantage of this approach is that passive networks can be built to be very rugged, reliable and electrically stable under the harshest environmental conditions. Elements commonly used to make beamformers are quadrature couplers, hybrid junctions, phase shifters and power dividers.
Figure 1 illustrates a simple beamformer comprising a simple antenna array connected to a quadrature coupler. In the quadrature coupler, "in-phase" input signals combine in output A and cancel in output B. Signals separated by 90º will combine in output B and cancel in output A. Therefore, a wavefront arriving from the left arrives at the left antenna prior.
Figure 1: Simple Beamformer Using Quadrature Coupler
to arriving at the right antenna. The difference is 90º. When the energy captured by the two antennas is combined in the quadrature coupler, it is routed to just one output of the quadrature coupler. This is referred to as a beam left signal. The converse situation can be seen for a wavefront arriving from the right. Both examples of course depend on proper antenna element spacing for the frequency of interest.
If a 180º hybrid junction had been used in Figure 1 in place of the quadrature coupler, the two-element array would respond to arriving wavefronts arriving along a line between the two antenna elements and would comprise an end-fire beam.
A simple example of a beamformer is a quadrapole which divides a single signal input into four outputs of equal amplitude but differing in phase by, 0º ,90º, 180º and 270º. This basic network is shown in Figure 2. Figure 3 shows an actual quadrapole unit.
Figure 2: Quadrapole Network Schematic
When used in conjunction with specialized receivers, beamformer networks can identify the location of an RF energy source. Moreover, when interfaced with suitable transducers, beamformers can be used in acoustic source location devices related to sonar. Thus, beamformers are employed in an assortment of direction finding systems.
Figure 3: Quadrapole Network In Submarine Periscope Antenna Application
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