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: 1. Description -------------------------- The basic elements of a Stretch system are the heterodyne mixer and the dispersive delay device. Although dispersive elements have been used widely in pulse compression radar [1] and their operation in this and related applications is well understood, a brief summary of their basic principles will be given here, to set the framework for the analysis. We will define a dispersive element to include all devices in which phase shift varies in a nonlinear manner with frequency. As an example, let us consider a device that has a linear dispersive characteristic; that is, one in which the relationship between delay through a device and the frequency of the applied signal is linear and of frequency/ delay slope a. The response of this device to a short pulse (on a constant frequency carrier) of bandwidth B and time duration T-/B will be a longer pulse of length B/a. This response will, however, retain the bandwidth B by virtue of a frequency modulation of the carrier. The pulse power is reduced by the same proportion that the pulse width is increased to conserve the pulse energy. It has been shown [2] - [4] that the output signal can be represented quite well by a line in the frequency/time plane as long as the time-bandwidth product (the product of the time duration of the dispersed pulse and its bandwidth) is considerably greater than unity. This representation will be used extensively in the following sections. The compression process involves introducing the dispersed pulse into a device of slope a, obtaining a short pulse (length = 7). The two networks when connected in cascade have a constant total delay and constitute nothing more or less than a delay fine. The original pulse shape is therefore recovered. Notice that if a frequency shift of Af is applied to the dispersed signal prior to compression, a shift (zAt) in the time position of the output pulse is obtained [5] where At = Af//a. Thus the time of the output pulse is determined by the time at which the dispersed signal passes through any particular frequency and by the delay of the compressor at that frequency. The time of the output pulse is not influenced by the start and finish times of the dispersed signal. Dispersive devices have been used most extensively in pulse compression radar. They have been constructed to make use of acoustic [6], electrical [7], and electromagnetic [8] dispersion. The principles which give rise to dispersion and the construction techniques are outlined in the referenced papers. Fig. is a functional block diagram of one implementation of the Stretch technique. http://read.pudn.com/downloads153/doc/673057/A%20Time-Transformation%20Technique.pdf
milstar: M.Skolnik 3 -e izdanie ,opisanie strech processing s primerami glawa 8 Pulse compression Radar ,napisana specialistami Lockheed Martin ################################################# http://www.scribd.com/doc/49249408/0071485473/Radar-Handbook3rd str.427 Strech compression Radar Examples 1.Haystack -LRIR swept bandwitch 1000 mhz/pulsewidth 250 microsec / stretch processing bandwitch -3.2 mhz /range window = 120 metrow 2.MMW -swept bandwitch -100 mhz/pulsewidth 50 microsec/ strech processing bandwitch -5 mhz / range window -37.5 metra 3.Cobra Dane -8.36 str 428
milstar: Seg. ADC 1. Single core 12 bitnie e2v 1.5 gsps ,TI/NATIONAL 1.8 gsps dajut wozmoznost west spektr srazu bez strech processing IF /Pch = 1000 mhz ,polosa /bandwitch 500 mhz 750-1250 mhz no s SNR tolko 56 dbc i SFDR 65 dbFS Stoimost dannix ADC 1000 + $ za 1 stuku Postprocessing mozet prinesti do 10-12 db in SFDR Averaging 100 stuk +2ß db in SNR No eto malo Nuzno SNR i SFDR bolee 100 db Wixod strechprocessing dlja rezima dicriminazii s perexodom k 16 bit ADC tipa AD9467 w polose 210 -280 mhz (BW=70 mhz) SFDR = 95-96 dbfs ,SNR 73-75 dbc single core + averaging + postprocessing
milstar: Glawa 8 M.Skolnik 2008 goda . Pulse compression radar (awtori -Lockheed ) Mnogo o strech processing i primeri Strech processing w ynikalnix RLS Cobra Dane ( 1 megawatt srednej kak Don-2N), Haystack ,MMW 35 ghz http://www.scribd.com/doc/17534245/Chapter-8-Pulse-Compression-Radar smotri 8.31 ili str 30/na dannom linke/
milstar: http://www.mitre.org/work/best_papers/00/torres_efficient/index.html
milstar: http://www.scribd.com/doc/17534245/22/RADAR-HANDBOOK Stretch Pulse Compression. 5760,62 Stretch pulse compression is a technique forperforming LFM pulse compression of wideband waveforms using a signal processorwith bandwidth that is much smaller than the waveform bandwidth, without loss of signal-to-noise ratio or range resolution. Stretch pulse compression is used for a singletarget or for multiple targets that are located within a relatively small range windowcentered at a selected range. Stretch Pulse Compression Radar Examples. This section describes threeexamples of radars that employ stretch pulse compression systems. Long Range Imaging Radar. 62,63 The Long Range Imaging Radar (LRIR) is anX-band radar with stretch processing bandwidths of 0.8, 1.6 MHz, and 3.2 MHz. Thewideband waveform has a swept bandwidth of 1000 MHz, to a pulsewidth of approxi-mately 250 s, and a LFM slope B / T ≈ 1000 MHz/(250 s) = 4 MHz/s. The rangewindow width for the 3.2 MHz processing bandwidth is ∆ r c B BT ms p ==×= 215032120(/). MHz4MHzsm Millimeter Wave Radar. The stretch processing implementation for the MillimeterWave radar (MMW) located at Kwajalein Atoll is described by Abouzahara andAvent. 64 The MMW radar operates at a carrier frequency of 35 GHz using waveformswith a maximum swept bandwidth of 1000 MHz and pulsewidth of 50 s. The LFMslope for the transmit waveform is α === BT 100020MHz50sMHz/s The stretch processing bandwidth is B p = 5 MHz. The width of the stretch processingtime window is ∆ t == 5025MHz20MHzss . The reference waveform pulsewidth is T R = 50 + 0.25 = 50.25 s to avoid a loss in SNRfor targets at the edges of the range window. The swept bandwidth of the referencewaveform and the range window width are B R =×= 20MHz/s50.25s1005MHz ∆∆ r ct ==×= 2150ms0.25s37.5m The 6-dB range resolution width with Hamming weighting applied over the 50-spulsewidth in the spectral analysis processing is ∆ Rc B 6 1812181150027 === ...ms1000MHzm Cobra Dane Wideband Pulse Compression System. 67 The characteristics of thewideband pulse compression system developed for the Cobra Dane radar are sum-marized in Table 8.9.
milstar: http://aess.cs.unh.edu/Radar%202010%20PDFs/Radar%202009%20A_11%20Waveforms%20and%20Pulse%20Compression.pdf
milstar: 7.3.2. Stretch Processor Stretch processing, also known as active correlation, is normally used to process extremely high bandwidth LFM waveforms. This processing technique consists of the following steps: First, the radar returns are mixed with a replica (reference signal) of the transmitted waveform. This is followed by Low Pass Filtering (LPF) and coherent detection. Next, Analog to Digital (A/D) conver- sion is performed; and finally, a bank of Narrow Band Filters (NBFs) is used in order to extract the tones that are proportional to target range, since stretch pro- cessing effectively converts time delay into frequency. All returns from the same range bin produce the same constant frequency. http://dsp-book.narod.ru/RSAD/C1828_PDF_C07.pdf
milstar: 7.3.2. Stretch Processor Stretch processing, also known as active correlation, is normally used to process extremely high bandwidth LFM waveforms. This processing technique consists of the following steps: First, the radar returns are mixed with a replica (reference signal) of the transmitted waveform. This is followed by Low Pass Filtering (LPF) and coherent detection. Next, Analog to Digital (A/D) conver- sion is performed; and finally, a bank of Narrow Band Filters (NBFs) is used in order to extract the tones that are proportional to target range, since stretch pro- cessing effectively converts time delay into frequency. All returns from the same range bin produce the same constant frequency. http://dsp-book.narod.ru/RSAD/C1828_PDF_C07.pdf
milstar: http://de.scribd.com/doc/17534245/22/RADAR-HANDBOOK Figure 8.1 shows a block diagram of a basic pulse compression radar. The codedpulse is generated at a low power level in the waveform generator and amplified to therequired peak transmit power using a power amplifier transmitter. The received signalis mixed to an intermediate frequency (IF) and amplified by the IF amplifier. The sig-nal is then processed using a pulse compression filter that consists of a matched filterto achieve maximum signal-to-noise ratio (SNR). As discussed below, the matchedfilter is followed by a weighting filter if required for reduction of time sidelobes. Theoutput of the pulse compression filter is applied to an envelope detector, amplified bythe video amplifier, and displayed to an operator
milstar: http://de.scribd.com/doc/17534245/22/RADAR-HANDBOOK Figure 8.1 shows a block diagram of a basic pulse compression radar. The codedpulse is generated at a low power level in the waveform generator and amplified to therequired peak transmit power using a power amplifier transmitter. The received signalis mixed to an intermediate frequency (IF) and amplified by the IF amplifier. The sig-nal is then processed using a pulse compression filter that consists of a matched filterto achieve maximum signal-to-noise ratio (SNR). As discussed below, the matchedfilter is followed by a weighting filter if required for reduction of time sidelobes. Theoutput of the pulse compression filter is applied to an envelope detector, amplified bythe video amplifier, and displayed to an operator
milstar: Stretch Pulse Compression. 5760,62 Stretch pulse compression is a technique forperforming LFM pulse compression of wideband waveforms using a signal processorwith bandwidth that is much smaller than the waveform bandwidth, without loss of signal-to-noise ratio or range resolution. Stretch pulse compression is used for a singletarget or for multiple targets that are located within a relatively small range windowcentered at a selected range. http://de.scribd.com/doc/17534245/22/RADAR-HANDBOOK
milstar: http://guap.ru/guap/kaf25/aeu_4.pdf
milstar: http://www.ece.uah.edu/courses/material/EE710-Merv/Stretch_11.pdf 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 uncompressed pulse width. ------------------------------------------------------------- Thus, we couldnt use stretch processing for search because search requires 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 tracking ------------------------------------------------ One of the most common uses of wide bandwidth waveforms, and stretch processing, is in discrimination, where we need to distinguish individual scatterers on a target. ------------------------------------------------------ Another use we will look at is in SAR (synthetic aperture radar). Here we only try to map a small range extent of the ground but want very good range resolution to distinguish the individual scatterers that constitute the scene.
milstar: http://de.scribd.com/doc/17534054/Chapter-6-Radar-Receivers 6.10 RADAR HANDBOOK Stretch Processing. Stretch processing is a technique frequently used to pro-cess wide bandwidth linear FM waveforms. The advantage of this technique is that itallows the effective IF signal bandwidth to be substantially reduced, allowing digitiza-tion and subsequent digital signal processing, at more readily achievable sample rates.By applying a suitably matched chirp waveform to the receiver first LO, coincidentwith the expected time of arrival of the radar return, the resultant IF waveform hasa significantly reduced bandwidth for targets over a limited range-window of inter-est. Provided that the limited-range window can be tolerated, a substantially reducedprocessing bandwidth allows more economical A/D conversion and subsequent digitalsignal processing. It also allows a greater dynamic range to be achieved with lower-rate A/D converters than would be achievable if digitization of the entire RF signalbandwidth were performed.If the LO chirp rate is set equal to the received signal chirp rate of a point target,the resultant output is a constant frequency tone at the output of the stretch processorreceiver, with frequency ∆ tB / T , where ∆ t is the difference in time between the receivedsignal and the LO chirp signal, and B / T is the waveform chirp slope (chirp bandwidth/ pulse width). Target doppler is maintained through the stretch processing, producingan output frequency offset equal to the doppler frequency, though the wide percentagebandwidth often used means that the doppler frequency can change significantly overthe duration of the pulse.Ignoring the effect of target doppler, the required RF signal bandwidth is equal tothe transmitted waveform bandwidth. Given the RF signal bandwidth
milstar: 1.0 STRETCH PROCESSING 1.1 INTRODUCTION AND BACKGROUND Stretch processing is a way of processing large bandwidth waveforms using narrow band techniques. For our present purposes we want to look at stretch processing as applied to LFM waveforms. It turns out that the concepts of stretch processing appear in other applications such as FMCW radar and, as we will see later, SAR processing. http://www.ece.uah.edu/courses/material/EE710-Merv/Stretch_11.pdf According to the Skolnik Radar Handbook1 (page 10.11) one can build SAW compressors for bandwidths up to 1 GHz. However, I have not heard of hardware implementations with such devices. I would expect that the upper limit on bandwidth for practical SAW LFM compressors is in the 10s, or possibly low 100s, of MHz. The bandwidth of digital signal processors is usually limited by the sample rate of the analog-to-digital converters (ADCs) needed to convert the analog signal to a digital signal. I think that the current limit on ADC rates is 300 MHz or so. If an upper limit on ADC sample rate is 300 MHz, then the maximum bandwidth of a LFM signal processor would also be 300 MHz (assuming complex signals and processors). 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 uncompressed pulse width. Thus, we couldnt use stretch processing for search because search requires 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 tracking One of the most common uses of wide bandwidth waveforms, and stretch processing, is in discrimination, where we need to distinguish individual scatterers on a target. Another use we will look at is in SAR (synthetic aperture radar). Here we only try to map a small range extent of the ground but want very good range resolution to distinguish the individual scatterers that constitute the scene. In the above discussion, we have focused on the signal processor and have argued, without proof at this point, that we can use stretch processing to ease the bandwidth requirements on a signal processor used to compress wide bandwidth waveforms. Stretch processing does not relieve the bandwidth requirements on the rest of the radar. Specifically, the transmitter must be capable of generating and amplifying the wide bandwidth signal, the antenna must be capable of radiating the transmit signal and capturing the return signal, and the receiver must be capable of heterodyning and amplifying the wide bandwidth signal. This places stringent requirements on the transmitter, antenna and receiver, but current technology has advanced to be point of being able to cope with the requirements. Thus, the stretch processor encounters a SNR loss of h T relative to the matched filter. This means that we should be careful about using stretch processing for range extents that are significantly longer of the transmit pulse width. ########################## At first inspection it appears as if stretch processing could offer better SNR than a matched filter, which would contradict the fact that the matched filter maximizes SNR. The most obvious method of implementing the spectrum analyzer is to use an FFT. To do so, we need to determine the required ADC (analog-to-digital converter) sample rate and the number of points to use in the FFT.
milstar: ALCOR was a key tool in developing discrimination techniques for ballistic missile defense. The wide bandwidth yielded a range resolution that could resolve individual scatterers on reentering warhead-like objects. This waveform was normally processed with the STRETCH technique, which is a clever time-bandwidth exchange process developed by the Airborne Instrument Laboratory [21, 22]. The return signal is mixed with a linear-FM chirp and the low-frequency sideband is Fourier transformed to yield range information. For a variety of reasons, the output bandwidth and consequently the range window were limited. For example, the ALCOR STRETCH processor yielded only a thirty-meter data window. Therefore, examination of a number of reentry objects, or the long ionized trails or wakes behind some objects, required a sequence of transmissions http://www.ll.mit.edu/publications/journal/pdf/vol12_no2/12_2radarsignalprocessing.pdf analog device technology. During 1972 and 1973, Lincoln Laboratory developed a 512-MHz-bandwidth (on a 1-GHz intermediate frequency [IF]) 10-sec RAC linear-FM pulse compressor [23].
milstar: We can now use commercial parts for A-D converters that enable us to do direct digital sampling, says Douglas Reep, vice president and chief engineer of the Lockheed Martin Corp. radar systems segment in Syracuse, N.Y. We are seeing a trend where we remove analog components from systems. Now we can almost digitize microwave signals without the down-convert, says Jerald Nespor, Lockheed Martin senior fellow for radar development at the companys facility in Moorestown, N.J. We need A-D converters with sufficient sampling rates to do that. Everyone wants higher efficiency and more dynamic range, and we can do that with COTS technologies and innovative architectures. ------------- typical levels of target echo returns are in the range of -90 to - 120 dbm http://www.scienpress.com/Upload/JCM/Vol%204_1_11.pdf
milstar: Resolution 0.1 to 3.0m https://www.sandia.gov/RADAR/files/spie_lynx.pdf The Analog-to-Digital Conversion (ADC) is also accomplished by a custom VME board that operates at 125 MHz and provides 8-bit data. This data can be presummed and otherwise pre-processed before being sent across a RACE way bus to the signal processor http://read.pudn.com/downloads153/doc/673057/A%20Time-Transformation%20Technique.pdf Stretch:ATime-Transfor-mationTechnique Consider an experiment in which the rise timeassociated with a nonrepetitive nanosecond transientis to be mea-sured. If the signal is applied directly to the input of an oscilloscope,inefficient performance and cost results.This due to the factthatan expensive wide-band oscilloscope is required,despite the fact that the duration of the transient is short and the total information content is small.If we had aconvenientway of reducing the bandwidth of the signal by slowing down the waveform before the signal is displayed,we could use an inexpensive instrument.The purpose of this paper is to describe a technique that can be used to provide this function for a wide variety of applications. http://read.pudn.com/downloads153/doc/673057/A%20Time-Transformation%20Technique.pdf
milstar: https://www.its.bldrdoc.gov/media/31078/DavisRadar_waveforms.pdf