Synthetic aperture radar (SAR) transmits and receives pulses at a certain repetition frequency, and real antennas occupy a fictitious linear array antenna element position in turn. The received signals of equivalent synthetic aperture antennas are synthesized by superimposing the amplitudes of the received signals of these antenna elements with the phases of the related transmitted signals. If the signal vectors of each unit are added directly, the unfocused synthetic aperture antenna signal can be obtained. Phase correction is carried out before signal addition, so that the signals of each unit are added in phase, and the focused synthetic aperture antenna signal is obtained. The reflected waves of the ground objects are received by the synthetic linear array antenna, demodulated coherently with the transmitting carrier, recorded on the photos according to different distance units, and then focused and imaged by illuminating the photos with coherent light. This process is similar to holography, but the difference is that the synthetic linear array antenna is one-dimensional, and synthetic aperture radar is only similar to holography in orientation, so synthetic aperture radar can also be called quasi-microwave holographic equipment.
Synthetic Aperture Radar: Using the movement of the remote sensing platform, a small-aperture antenna is installed on the side of the platform to replace the large-aperture antenna to improve the azimuth resolution.
In aviation, the resolution of synthetic aperture radar can reach within 1 meter. Synthetic Aperture Radar (SAR) on spacecraft has a long range, so it is complicated to obtain high resolution. The Apollo spacecraft launched in 1972, the ocean satellite launched in 1978 and the space shuttle Columbia launched in 198 1 year are all equipped with synthetic aperture radar.
Synthetic aperture radar is mainly used in aerial survey, aerial remote sensing, satellite ocean observation, space reconnaissance, image matching guidance and so on. It can find hidden and disguised targets, such as identifying disguised missile underground silos and identifying ground targets in fog-shrouded areas. In missile image matching guidance, using synthetic aperture radar to shoot images can make missiles hit hidden and disguised targets. Synthetic aperture radar (SAR) is also used for deep space exploration, for example, to detect the geological structure of the moon and Venus.