Communications: directive radio wave systems and devices (e.g. – Determining velocity – Combined with determining distance
Patent
1993-02-12
1994-03-15
Hellner, Mark
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Combined with determining distance
342111, G01S 1358
Patent
active
052949320
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the simultaneous determination of the distance and the speed of a target in a radar system.
2. Background Information
In radar systems operating according to the (High Pulse Repetition Frequency) method, the speed can be determined unequivocally up to a maximum speed of approximately Mach nine. The higher the unambiguity range for the determination of the speed, however, the smaller is the unambiguity range in the distance direction for a determination of the distance of a target. Typically, this unambiguity range is presently limited to a maximum distance of approximately one kilometer.
SUMMARY OF THE INVENTION
It is the object of the invention to improve a method of this type in that, while maintaining an unambiguous speed range up to a maximum speed of at least Mach nine, it becomes possible to unambiguously determine the distance of a target in a distance range whose maximum distance limit is substantially greater than one kilometer.
This is accomplished by determining the group delay of the target spectrum in the Doppler domain and determining the distance of the target from the group delay.
One advantage of the invention is that even if a target travels at a maximum speed of Mach nine, its distance can still be unequivocally determined up to a maximum distance of approximately 400 km.
The invention is based on the fact that in an HPRF method the transmitted signals put out by the radar antenna and reflected by a moving target are evaluated in the Doppler domain. For this purpose, the group delay of the target spectrum associated with the moving target is initially determined for the received signal, which essentially corresponds to the reflected transmitted signal, and then the desired distance is determined from the group delay.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to one embodiment thereof in conjunction with the drawings in which:
FIG. 1 shows the real component of a transmitted signal versus time;
FIG. 2 shows a typical arrangement of an aircraft equipped with a radar system;
FIG. 3 shows a processing of radar signals;
FIG. 4 shows a phase ranging process; and
FIG. 5 shows a non-fluctuating received signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the example below it is assumed that a pulse modulated Doppler radar system is available in an airborne vehicle, for example an aircraft, and operates at a high pulse repetition rate, called the "HPRF mode" in the English-language literature. Such a radar system suitable for an airborne vehicle is also called "airborne radar". The HPRF mode is usually employed as a search mode in an airborne radar system.
The real component Re{s(t)} (ordinate) of the transmitted signal s(t) of such a search mode is plotted in FIG. 1 over the time t (abscissa). This transmitted signal s(t) is composed of pulses having a time duration .tau.. The pulses are repeated periodically in time after a pulse repetition time T. The pulses include an alternating voltage signal at a transmitting frequency f.sub.O. The points in FIG. 1 indicate that pulses are transmitted successively in time.
The transmitted signal s(t) can be described mathematically as follows: ##EQU1## where r.sub.r (t) is the normalized amplitude of the transmitted signal.
FIG. 2 shows a typical arrangement of an aircraft F equipped with a radar system operating in the HPRF mode and a target Z which, for the description below, is considered to be dot shaped.
From such a dot-shaped target Z, which moves from a distance r at a relative speed v.sub.r toward the antenna, the following reflected received signal s.sub.r (t) is obtained: ##EQU2##
In Equation (2) it is not considered that the antenna is directed toward target Z only for a finite time and that the amplitude a of the received signal may fluctuate for real targets. In Equation (2), t.sub.r is the delay of the signal and f.sub.D the Doppler shift. Taking c as the speed of light, the
REFERENCES:
patent: 4338604 (1982-07-01), Petitjean
patent: 4382258 (1983-05-01), Tabourier
patent: 4916452 (1990-04-01), Borchert et al.
patent: 4920347 (1990-04-01), Kurihara
Deutsche Aerospace AG
Hellner Mark
LandOfFree
Method for the simultaneous determination of the distance and th does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the simultaneous determination of the distance and th, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the simultaneous determination of the distance and th will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1538581