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The chirp pulse compression process transforms a long duration frequency-coded pulse into a narrow pulse of greatly increased amplitude. It is a technique used in radar and sonar systems because it is a method whereby a narrow pulse with high peak power can be derived from a long duration pulse with low peak power. Furthermore, the process offers good range resolution because the half-power beam width of the compressed pulse is consistent with the system bandwidth. The basics of the method for radar applications were developed in the late 1940s and early 1950s,〔Dicke R.H.,"Object Detection System", U.S. Patent 2,624,876, submitted Sept. 1945〕〔Darlington S.,"Pulse Transmission", U.S. Patent 2,678,997, submitted Sept. 1945〕〔Sproule D.O. and Hughes A.J., "Improvements in and Relating to System Operation by Means of Wave Trains", U.K. Patent 604,429, submitted June 1945〕 but it was not until 1960, following declassification of the subject matter, that a detailed article on the topic appeared the public domain.〔Klauder J.R., Price A.C., Darlington S. and Albersheim W.J., "The Theory and Design of Chirp Radars", BSTJ Vol.39, July 1960, (pp.745-808)〕 Thereafter, the number of published articles grew quickly, as demonstrated by the comprehensive selection of papers to be found in a compilation by Barton.〔Barton D.K. (ed), "Radars, Volume 3, Pulse Compression", Artech House 1975, 1978〕 Briefly, the basic pulse compression properties can be related as follows. For a chirp waveform that sweeps over a frequency range F1 to F2 in a time period T, the nominal bandwidth of the pulse is B, where B = F2 – F1, and the pulse has a time-bandwidth product of T×B . Following pulse compression, a narrow pulse of duration τ is obtained, where τ ≈ 1/B, together with a peak voltage amplification of √(T×B). == The Chirp Compression Process – in Outline == In order to compress a chirp pulse of duration T seconds, which sweeps linearly in frequency from F1 Hz to F2 Hz, a device with the characteristics of a dispersive delay line is required. This provides most delay for the frequency F1, the first to be generated, but with a delay which reduces linearly with frequency, to be T second less at the end frequency F2. Such a delay characteristic ensures that all frequency components of the chirp pass through the device, to arrive at the detector at the same time instant and so augment one another, to produce a narrow high amplitude pulse, as shown in the figure: centre An expression describing the required delay characteristic is : This has a phase component (f), where :, and the instantaneous delay is given by : which has a linear slope with frequency, as required. In this expression, the delay characteristic has been normalized (for convenience), so as to give zero delay when the frequency f equals the carrier frequency f0. Consequently, when the instantaneous frequency is (f0 - B/2) or (f0 + B/2), the required delay is +T/2 or -T/2, respectively, so k = B/T. The required dispersive characteristic may be obtained from a lumped element delay network,〔Bernfeld M., Cook C.E., Paolillo J., and Palmieri C.A., "Matched Filtering, Pulse Compression and Waveform Design", Microwave Journal, Oct 1964 - Jan 1965, (34 pp.)〕〔Farnett E.C. & Stevens G.H., "Pulse Compression Radar", Chapter 10 of "Radar Handbook, 2nd Ed.", ed Skolnik M., McGraw Hill 1990〕〔Millett R.E., "A Matched-Filter Pulse-Compression System Using a Non-linear F.M. Waveform", IEEE Trans. Aerospace and Electronic Systems, Vol. AES-6, No. 1, Jan 1970, (pp. 73-78)〕〔Cook C.E., "Pulse Compression - Key to More Efficient Radar Transmission", Proc. IRE, Vol.48, March 1960 (pp. 310-316)〕 a SAW device,〔Jones W.S., Kempf R.A. and Hartman C.S., "Practical Surface Wave Chirp Filters for Modern Radar Systems", Microwave Journal, May 1972 (pp. 43-50〕〔Butler M.B. "Radar applications of s.a.w. dispersive filters", Proc IEE, Vol.27, Pt. F, April 1980 (pp.118-124)〕〔Arthur J.W., Modern SAW-based pulse compression systems for radar applications. Part 1: SAW matched filters, Part 2: Practical systems", Electronics & Communication Engineering Journal, Dec 1995 (pp.236-246) and April 1996 (pp.57-79)〕〔Andersen Laboratories, " Handbook of Acoustic Signal Processing, Vols. 2 & 3, SAW Filters and Pulse Expansion/Compression IF Subsystems for Radar"〕〔MESL Microwave, "SAW Pulse Compression" (technical brochure), www.meslmicrowave/saw-pulse-compression/technical-notes/〕 or by means of digital signal processing 〔Halpern H.M. and Perry R.P., "Digital Matched Filters Using Fast Fourier Transforms", IEEE EASTCON '71 Record, (pp.222-230)〕〔Arthur J.W., "Digital Waveform Generation for SAW Compression Systems", Tech. Note, Racal MESL, Newbridge, Midlothian〕〔Alter J.J. and Coleman J.O., "Digital Signal Processing", Chapter 25 of "Radar Handbook, 3rd edition" ed. Skolnik M.I., McGraw Hill 2008〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chirp compression」の詳細全文を読む スポンサード リンク
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