Showing papers on "Chirp published in 1968"

Matched-Filter Responses of the Linear FM Waveform

Abstract: Although the properties of the linear FM signal have been studied previously in considerable detail, such studies have involved rather narrow aspects of the theory. This paper extends the work in several respects. By presenting three-dimensional projections of the conventional ambiguity function of the linear FM signal in more detail than was available before, we can study the sidelobe behavior off as well as on the axes, without weighting, with unilateral weighting in the receiver, and with bilateral weighting. These plots reveal interesting properties related to the signal symmetry in time and frequency. The matched-filter response is then extended to include Doppler distortions of the modulation function. The results show that Woodward's ambiguity function is valid only for signals with relatively modest sophistication, even though in most practical situations one is interested only in those undistorted parts of the matched-filter response in the vicinity of the delay axis. Plots of the response are presented for various degrees of distortion, for signals with and without weighting. Lastly, we consider the effects of a mismatch in range acceleration, again for the various cases of interest. The results convey a thorough insight into the properties of chirp radar under a broad range of operational conditions.

Optical chirp pulse generator

Abstract: Pulses of light are generated by a laser oscillator, and the pulses are swept in frequency or chirped by rotating one of the resonator mirrors in such a way as to change the oscillator frequency continuously during the generation of the pulse.

FM "Chirp" Communications: Multiple Access to Dispersive Channels

Abstract: The white Gaussian noise-limited channel so often assumed by system designers is encountered less and less in practice as the density and sophistication of modem communications increase. Long-range radio communications in particular tend to be limited by interference rather than by receiver noise; for that reason, the design of the signal waveform has great impact on system performance. A waveform that shows particular promise for channels such as satellite relay and HF radio is swept FM or "chirp" modulation. The chirp waveform is characterized in Fig. 1. A carrier is swept in frequency over a band W during a sweep interval T. The sweeps shown are linear and assume a square amplitude envelope of unity value, although nonlinear sweeps and shaped envelopes may be used. The sweep slope W/T may be used to convey information in a variety of ways, the simplest being +W/T for binary 1 and -W/T for binary 0 (slope-shift keying SSK). Higher order alphabets can be represented by different slopes, and amplitude can be added if desired. SSK will usually be most efficient, reserving the distinguishability of different slopes for the purpose of defining channels or addresses in multiple-access applications. The value of chirp modulation derives from its efficient use of available bandwidth and transmitter power in combating multipath and other forms of interference, including the "clutter" of other transmissions in multiple-access systems.

Generation of chirped pulses at 10.6 microns wavelength

Abstract: Pulses in which the carrier frequency is swept through about 60 MHz have been generated with a CO 2 laser. The technique uses an offset rotating mirror. The pulse energy is about 2 × 10-4joule.