Communications: directive radio wave systems and devices (e.g. – Determining velocity – Combined with determining distance
Reexamination Certificate
2002-11-25
2004-02-03
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Determining velocity
Combined with determining distance
C342S081000, C342S104000, C342S127000, C342S128000, C342S129000, C342S130000
Reexamination Certificate
active
06686871
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of 011 27 990.8, filed Nov. 24, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for High Pulse Repitition Frequency (HPRF) radar measurement of target range and Doppler frequency, such as may be used, for example, in an airborne radar system.
The use of a well known radar waveform with two slightly different transmit frequencies is often referred to in the literature as a frequency shift keying (FSK) technique. Using such a technique, target range and velocity can be measured unambiguously even in multi target situations.
FIG. 1
shows the two carrier frequencies f
1
and f
2
as a function of time. Each frequency represented by a horizontal line corresponds to a coherent processing interval (CPI), and includes a pulse sequence of N-2048 pulses each.
In each CPI of length T, a received pulsed signal is directly down converted with the individual instantaneous transmit frequency, and shows as a single information the Doppler frequencies of the observed targets. The two base band signals are Fourier transformed, and target line left out will be observed in two adjacent CPI's in the same Doppler bin, but with different phase information. For a simultaneous range measurement, these two phases &phgr;
1
, &phgr;
2
in the same Doppler bin are considered and the phase difference &Dgr;&phgr;=&phgr;
2
−&phgr;
1
is calculated. The latter is directly related to the target range R in accordance with the following equation:
Δ
φ
=
2
π
·
Δ
f
·
2
R
c
Eq
.
(
1
)
The range measurement is unambiguous if &Dgr;&phgr;<2&pgr;. In order to measure target ranges up to R
max
=150 km, the frequency shift in the FSK wave form must be:
Δ
f
≤
c
2
R
=
1
kHz
.
The basic idea is applicable to the extent that the assumptions of a purely stationary observation are fulfilled. But each target maneuver inside the measurement time 2T will have a large influence on the phase measurement in the adjacent CPI's, and will cause large range errors in the range estimation procedure in accordance with Eq. 1.
One object of the present invention is to provide a method for simultaneously and unambiguously measuring target range and target Doppler frequency for highly mobile targets, even in multiple target situations.
This and other objects and advantages are achieved by the present invention, in which a transmit oscillator generates a single unmodulated frequency. The HPRF pulse sequence is split into two interleaved parts, which are distinguished and modulated with a digital phase shift keying (PSK) modulation scheme as follows:
The pulses of the first pulse sequence have the same phase state or alternatively have a linearly increasing phase value with a fixed phase difference &phgr;
1n
from pulse to pulse; and
The pulses of the second pulse sequence have a linearly increasing phase value with a fixed phase difference &phgr;
2n
from pulse to pulse with &phgr;
1n
≠&phgr;
2n
and &phgr;
1n
>0.
The latter step is important because it renders the down conversion process simple. The PSK technique guarantees unambiguous range measurement and the interleaved pulse sequences make the measurement robust against target maneuver. Before this background all important requirements can be fulfilled with the PSK waveform according to the invention.
REFERENCES:
patent: 3889261 (1975-06-01), Sirven
patent: 4106017 (1978-08-01), Roeder et al.
patent: 5294932 (1994-03-01), Nagel
patent: 5311189 (1994-05-01), Nagel
patent: 5633643 (1997-05-01), Erhage
patent: 5646623 (1997-07-01), Walters et al.
patent: 6232912 (2001-05-01), Nagel
Guener Wilhelm
Hommel Hans
Nagel Dieter
Rohling Hermann
Crowell & Moring LLP
EADS Deutschland GmbH
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