Scanning Techniques at www.japanese-home-gardens.com

It is possible to build arrays that can be mounted in a fixed position and scanned electronically in two dimensions. Either frequency scanning or phase Scanning techniques may be used for both dimensions, or frequency Scanning techniques may be used for one and phase Scanning techniques for the other. In general, the choice between frequency Scanning techniques and phase Scanning techniques depends on such considerations as the output power of the radar, the power consumption and temperature stability of the available phase shifting devices, the required range resolution, and the speed of beam programing.

Frequency-Scanning techniques and Phase-Scanning techniques rray Antennas.—The direction of the beam >f the conventional radar antenna is moved (scanned) by rotating the antenna structure ihysically. In contrast, the beam of the fre-luency-Scanning techniques or phase-Scanning techniques array antenna s moved by varying the radio frequency phases >f the signals emitted by the individual radiators. s a result, the speed and abruptness with which he direction of the beam can be changed are not imited by the inertia of the antenna structure.

Mechanical Scanning techniques, phase Scanning techniques, and frequency Scanning techniques may be employed individually or in combination to meet varied requirements. Let us assume, for example, that a radar is required to search the hemispherical air space above a ship. To accomplish this, a cylindrical reflector may be added to a simple linear array in such a way as to produce a pencil beam. This antenna is then oriented so that the beam can-be frequency scanned in a vertical plane, and a drive is provided which mechanically rotates the entire structure in azimuth.