Форум » Дискуссии » Strech processing » Ответить
Strech processing
milstar: Stretch: A Time-Transformation Technique WILLIAM J. CAPUTI, JR., Member, IEEE Institute of Science and Technology University of Michigan Ann Arbor, Mich. 48107 http://read.pudn.com/downloads153/doc/673057/A%20Time-Transformation%20Technique.pdf Stretch is a passive, linear, time-variant technique for performing temporal operations on many classes of signals. The technique employs three dispersive networks and a mixer. Signal slowdown, speedup, or time reversal can be attained by choice of network slopes. These temporal operations are performed within a signal "window," and the duration of the window is determined by the network time-bandwidth products. Both heuristic argumentation and rigorous analysis are presented, as are the results of a simple laboratory experiment. ALCOR operates at C-band (5672 MHz) with a signal bandwidth of 512 MHz that yields a range resolution of 0.5 m. (The ALCOR signal was heavily weighted to produce low range sidelobes with the concurrent broadening of the resolution.) Its widebandwidth waveform is a 10-„}sec pulse linearly swept over the 512-MHz frequency range. High signal-tonoise ratio of 23 dB per pulse on a one-square-meter target at a range of a thousand kilometers is achieved with a high-power transmitter (3 MW peak and 6 kW average) and a forty-foot-diameter antenna. Processing 500-MHz-bandwidth signals in some conventional pulse-compression scheme was not feasible with the technology available at the time of ALCORЃfs inception. Consequently, it was necessary to greatly reduce signal bandwidth while preserving range resolution. This is accomplished in a timebandwidth exchange technique (originated at the Airborne Instrument Laboratory, in Mineola, New York) called stretch processing [4], ------------------------------------- which retains range resolution but restricts range coverage to a narrow thirtymeter window. In order to acquire and track targets and designate desired targets to the thirty-meter(30 metr) wideband window, ------------------------------- ALCOR has a narrowband waveform with a duration of 10.2 „}sec and bandwidth of 6 MHz. This narrowband waveform has a much larger 2.5-km range data window. ---------------------------------------- http://www.ll.mit.edu/publications/journal/pdf/vol12_no2/12_2widebandradar.pdf ALCOR, shown in Figure 2, was the first highpower, long-range, wideband field radar system. Lincoln Laboratory was the prime contractor for ALCOR;It became operational at Kwajalein Atoll in 1970, and was probably the first wideband radar in the world to reach that status --------------------------------------------------- The LRIR, which was completed in 1978, is capable of detecting, tracking, and imaging satellites out to synchronous-orbit altitudes, approximately 40,000 km. The range resolution of 0.25 m is matched by a cross-range resolution of 0.25 m for targets that rotate at least 3.44Ѓ‹ during the Doppler-processing interval. The wideband waveform is 256 ѓКsec long and the bandwidth of 1024 MHz is generated by linear frequency modulation. The pulse-repetition frequency is 1200 pulses per second. The LRIR employs a time-bandwidth exchange process similar to that of ALCOR to reduce signal bandwidth from 1024 MHz to a maximum of 4 MHz, corresponding to a range window of 120 m, while preserving the range resolution of 0.25 m. To place a target in the wideband window, we first acquire the target with a continuous-wave acquisition pulse that is variable in length from 256 ѓКsec (for short-range targets) to 50 msec (for long-range targets). An acquired target is then placed in active tracking by using 10-MHzbandwidth chirped pulses, again of variable length, from 256 ѓКsec to 50 msec. The wideband window is then designated to the target. Antenna beamwidth is 0.05Ѓ‹. (posle poslednej modifikazii 0.005 grad w diapazone 92-100ghz)
Ответов - 31, стр:
1 2 All
полная версия страницы