Synthetic Aperture Antennas and Imaging

• Published in: Smart Antennas and Electromagnetic Signal Processing for Advanced Wireless Technology pp. 167 - 193
• Main Authors: Hua, Tan Pek, Goh, Dennis, Hoole, P.R.P., Abeyratne, U.R.
• Format: Book Chapter
• Language: English
• Published: Denmark Routledge 2020; River Publishers
• Edition: 1
• Subjects: Aerospace & Radar Technology; Electronic Devices; Electronics & Semiconductors; Radar & Navigation Systems; Return Pulses; SAR; Range Image; Azimuth Positions; Point Scatterers; Synthetic Array; Azimuth Resolution; Transmitted Radar Pulse; Linear FM Signal; Azimuth Direction; Artech House; Data Collection Geometry; Seawater; Chirp Pulse; Radar Antenna; Linear FM Waveform; Range Resolution; Chirp Rate; Azimuth Beam Width; ISAR; Smart Antennas; Linear FM; Wave Energy; Stationary Antenna; Matched Filter
• ISBN: 9788770222068; 8770222061
• DOI: 10.1201/9781003339564-6

This chapter presents the basic technique for single dimension electromagnetic signal processing of radar signals to obtain two-dimensional images. The synthetic aperture radar (SAR) is a powerful technology for getting pictures whether in the day time or in the night time when a normal camera or the naked eye cannot be used to get a visual image of the scene, the SAR, where a moving radar antenna looking at an object (e.g. a spy plane radar flying over a military installation on ground) may be used with suitable electromagnetic signal processing of the reflected electromagnetic signals picked up the radar antennas. In the inverse synthetic aperture radar (ISAR), although the radar antenna itself is a stationary single element antenna, the moving target, such as an aircraft, is like a set of antenna elements as it moves and, from each point, reflects a signal back to the radar antenna. This set of signals makes the moving target a synthetic array antenna. The technique presented here, illustrated for three different points on the target, may be used to get a picture of the target (e.g. an aircraft). The same technique is used with an array of stationary antenna elements on earth pointing skyward to obtain images of galaxies. This chapter discusses the principles of synthetic aperture antennas by looking at its performance in a radar system. Hence, to improve azimuth resolution, we have to resort to synthetic array or aperture. As the object moves around the antenna, different views of it are presented to the antenna so that the return pulses carry back a complete range of information on the entire target. The case study considered is that of imaging an aircraft in flight by a stationary antenna. The reader would now realize that designing an antenna system to perform complex activity like imaging requires only a synthetic array or synthetic aperture antenna but also a waveform that is well shaped and suited for the particular application. Since the beam of the antenna is narrow and pointed in a known direction, the amount of wave energy reflected back from the target will depend on the direction and the reflectivity of the target in that direction.