6.5.1 Single-Beam Antennas

Electronically scanned arrays are made up of a number of components, most of which are not RF or microwave. Figure 6.28 shows a block diagram of a typical electronically scanned array. It consists of radiating elements, phase shifters, an RF distribution feed network, phase shifter drivers, array logic circuits, a beam-steering computer, power supply, cooling means, built in test and calibration, and miscellaneous sensors for temperature, arcing, failure detection, and so on. The beam-steering computer receives a look direction, the frequency of operation, and the operating mode of the data link or radar, which it uses in conjunction with the temperature of the array and calibration data to generate a set of phase commands to each phase shifter driver. An elaborate logic network distributes these commands to the phase shifter drivers as rapidly as possible. The phase shifter driver, in turn, generates a set of voltages (currents) that cause the phase shifter to produce the nearest phase shift to the commanded value. When the RF reaches the phase shifter through the feed distribution network, it is phase shifted by the appropriate amount and radiated. On receive, the process is similar. With very broadband arrays, the phase shifters must be spun both on transmit and receive to keep the beam pointed in the commanded direction. ^[25]

Figure 6.28: Electronically scanned array block diagram

The simplest electronically scanned array has two elements. A two-element scanned array is shown in Fig. 6.29. The elements can be...