Strech processing
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 ALCORfs 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 3.44 during the Doppler-processing interval. The wideband waveform is 256 sec 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 sec (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 sec to 50 msec. The wideband window is then designated to the target. Antenna beamwidth is 0.05. (posle poslednej modifikazii 0.005 grad w diapazone 92-100ghz)
milstar: https://ieeexplore.ieee.org/document/6330617
milstar: https://www.ll.mit.edu/sites/default/files/page/doc/2018-05/21_1_7_Eshbaugh.pdf
milstar: https://arrc.ou.edu/~goodman/pubs/SAM_12_structured_lfm_dechirp.pdf
milstar: http://www.ittc.ku.edu/~sdblunt/papers/SEE-IntlRC19%20FMCW-PARC-MMF.pdf http://www.eng.auburn.edu/~daifa01/Top/PubPapers/2013/A%20650%20MHz%20DDFS%20for%20stretch%20processing%20radar%20in%20130nm%20BiCMOS%20process.pdf
milstar: Target Discrimination Target discrimination is a critical capability for the ASM seeker, especially in the presence of jamming and other EA (Electronic Attack). For this analysis, it is only indicated that the coherent seeker presents more information at, perhaps higher resolution, to the postprocessor for discrimination purposes https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.928.3912&rep=rep1&type=pdf
milstar: Stretch processing multiplies or mixes a returnLFM with a reference LFM. The process can be implemented in the analog domain witha mixer that can support the bandwidth of the LFM waveforms. To understand how thisworks, recall the following two mathematical relations: 1,10 https://etd.auburn.edu/bitstream/handle/10415/3021/ThesisHubbard416.pdf?sequence=4 Stretch processing multiplies or mixes a returnLFM with a reference LFM. The process can be implemented in the analog domain witha mixer that can support the bandwidth of the LFM waveforms. To understand how thisworks, recall the following two mathematical relations:
milstar: Stretch processing relieves the signal processor bandwidth problem by giving up all-range processing to obtain a narrow-band signal processor. If we were to use a matched filter we could look for targets over the entire waveform pulse repetition interval (PRI). With stretch processing we are limited to a range extent that is usually smaller than an uncompressedpulse width. Thus, we couldnt use stretch processing for search because searchrequires looking for targets over a large range extent, usually many pulse widths long. We could use stretch processing for track because we already know range fairly well but want a more accurate measurement of it. We must point out that, in general, wide bandwidth waveforms, and thus the need for stretch processing, is overkill for tracking. Generally speaking, bandwidths of 1s to 10s of MHz are sufficient for trackingOne of the most common usesof wide bandwidth waveforms, and stretch processing, is in discrimination,where we need to distinguish individual scatterers on atarget. Another use we will look at is in SAR (synthetic aperture radar). Here we only try to map a small range extent of theground but want very good range resolution to distinguish the individual scatterers that constitute the scene http://www.ece.uah.edu/courses/material/EE710-Merv/Stretch_11.pdf
milstar: The basic idea of stretch processing is that two LFM signals having the same frequency modulation slope are mixed together and filtered, the output will be a narrowband sinusoidal signal. The frequency of the sinusoidal signal is proportional to the time-offset between the two LFM signals. Therefore, a high range resolution can be achieved by analyzing the frequency component. By the way, the time-offset is determined by the difference between actual distance and estimated distance of the target. If the target is multi-point, the output of mixer is a group of narrow-band sinusoidal signals. Figure.2 shows stretch processing block diagram for a single channel. After transmitting http://wseas.us/e-library/transactions/signal/2009/32-582.pdf
milstar: Figure.2 shows stretch processing block diagram for a single channel. After transmitting a wideband LFM pulse ( )x t, radar will receive a delayed version of the transmitted pulse 0( )x t t−as the target echo, and 0tis unknown two-way propagation delay determined by the targets range . At the same time, the transmitted signal was delayed to the estimated target range as the deramping oscillator'0( )x t t−. The echo is demodulated in the mixer using the local oscillation signal. The following lowpass filter converts the target range difference into frequency difference, and the bandwidth of the filter limits the range region. Then, the information of the target can be obtained by taking FFT. http://wseas.us/e-library/transactions/signal/2009/32-582.pdf
milstar: quation (42) also demonstrates another reason why stretch processing should not be used in a search function: it would be too lossy http://www.ece.uah.edu/courses/material/EE710-Merv/Stretch_11.pdf
milstar: A Wideband digital Beamforming Method Based on Stretch Processing http://wseas.us/e-library/transactions/signal/2009/32-582.pdf he basic idea of stretch processing is that two LFM signals having the same frequency modulation slope are mixed together and filtered, the output will be a narrowband sinusoidal signal. The frequency of the sinusoidal signal is proportional to the time-offset between the two LFM signals. Therefore, a high range resolution can be achieved by analyzing the frequency component. By the way, the time-offset is determined by the difference between actual distance and estimated distance of the target. If the target is multi-point, the output of mixer is a group of narrow-band sinusoidal signals. Figure.2 shows stretch processing block diagram for a single channel.