Communications: directive radio wave systems and devices (e.g. – Return signal controls radar system – Receiver
Patent
1997-08-29
1999-01-26
Sotomayor, John B.
Communications: directive radio wave systems and devices (e.g.,
Return signal controls radar system
Receiver
342 99, 342 21, 342101, G01S 728
Patent
active
058643133
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a process for determining the intermediate-frequency deviation in a frequency-pulse radar system.
In frequency-pulse radar systems, as a result of frequency shift keying, the transmission oscillator is also used as a local oscillator (LO). The basic block diagram of such a radar system is illustrated in FIG. 1, which corresponds to the system described in German patent document DE 41 04 907. For generating transmission pulses, the voltage controlled oscillator (VCO) is switched to the transmission frequency f.sub.s during the transmission interval ,while in the remainder of the pulse repetition interval T.sub.p it remains on the LO-frequency f.sub.LO. For further details of the system illustrated in FIG. 1, reference is made to German Patent Document DE 41 04 907.
Illustration (a) of FIG. 2 shows the oscillator frequency as a function of time. The corresponding time sequence of the amplitude of the transmission signal and of the amplitude of the LO-signal (with the frequencies f.sub.s and f.sub.LO) is found in Illustrations (b) and (c) of FIG. 2. The difference between the transmission frequency and the LO-frequency (f.sub.s -f.sub.LO) is the intermediate frequency IF, which is determined by the frequency shift of the oscillator.
Illustration (d) of FIG. 2 shows the time sequence of the echo signal with the frequency f.sub.s +f.sub.Doppler. Since this echo signal is delayed corresponding to the target distance R by Tz=2R/c (c=speed of light), it can be mixed onto the intermediate frequency IF in the radar system with the transmission oscillator switched over in the interim to LO-frequency. The time sequence of the amplitude of the intermediate-frequency echo signal, which is displaced here by a Doppler frequency in the case of a moved target, is shown in Illustration (e) in FIG. 2.
As described in German patent document DE 41 04 907, the transmission signal f.sub.s and the LO-signal (f.sub.LO) are coherent because they are generated by the frequency shift keying of the same oscillator. The intermediate-frequency pulses, which are generated by the mixing of both signals, are therefore phase-stable from pulse to pulse (apart from a possible Doppler shift), as well as coherent with respect to the control signal (pulse repetition frequency PRF) which controls the frequency shift keying of the oscillator. As a result of the coherence of IF and PRF, by means of a reference signal f.sub.R coherent to the PRF, the IF-signal can be mixed coherently into the base band, where the sampling and the filtering of the Doppler signal is obtained from the phase differences between the IF signal and the reference signal (f.sub.R) (see also Merill I. Skolnik: "Introduction to Radar Systems", 2 nd Edition 1980, Page 117, Publishers McGraw-Hill, N.Y.).
The sampling takes place in range cells whose width (sampling time T.sub.A) normally corresponds to the pulse width .tau.The range cells are combined with respect to time, and each range cell reflects a certain distance range corresponding to its delay with respect to the transmission pulse. The range cell width is determined by the duration of the sampling (T.sub.A) and determines the range resolution (.increment. R) of the radar (.increment.R=c.circle-solid.T.sub.A /2, c= speed of light).
FIG. 3 shows the time sequences of the transmission signal, the echo signal and the arrangement of the range cells for an interval of the pulse repetition frequency. The transmission signal (a) has the pulse width. The center representation (b) is an example of an echo signal with 5 targets at different distances. (The difference in the distance must be larger than T.sub.A in order to be able to detect the individual targets as separate objects.) The range cells 1 to n, which cover the whole range measuring area, are illustrated in Representation (c). In the respective range cells, the sampled value (amount of the complex echo signal in the base band plane, .sqroot. (I.sup.2 +Q.sup.2)) corresponds to the amplitude of the echo s
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Flacke Joachim
Kaiser Bruno
Speck Ralph
Dornier GmbH
Sotomayor John B.
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