Communications: directive radio wave systems and devices (e.g. – Return signal controls radar system – Transmitter
Reexamination Certificate
2000-06-15
2001-11-13
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls radar system
Transmitter
C342S083000, C342S128000, C342S200000
Reexamination Certificate
active
06317074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of electronic radar, and more particularly to apparatus for reducing the operating requirements on a linearizer by accounting for non-linearities in the transmitted waveform via processing in the radar receiver.
2. Description of the Related Art
A frequency modulated continuous wave (FMCW) radar system often uses linear frequency modulation to provide accurate range information. The resolution of the ranging information is directly dependent on the linearity of the transmit signal. A great deal of prior art exists related to linearizers. For example, applicant owns U.S. Pat. Nos. 5,642,081 and 5,379,001, both directed to closed loop linearizers. The entire contents of U.S. Pat. Nos. 5,642,081 and 5,379,001 are hereby incorporated by reference. Applicant also owns U.S. Pat. Nos. 5,172,123 and 4,692,766, which are directed to linearizers for FMCW radar transmitters, and the entire contents of U.S. Pat. Nos. 5,172,123 and 4,692,766 are hereby incorporated by reference.
Other prior art related to linearizers are found in U.S. Pat. Nos. 4,539,565, 4,593,287 and 4,754,277, all assigned to The Boeing Company. U.S. Pat. No. 5,189,427 assigned to U.S. Philips Corporation also relates to FMCW radar linearizers.
The prior art corrects for non-linearities in the transmitted waveform via further processing in the transmitter, which makes the transmitter circuitry unduly complicated. What is needed is a circuit which can correct for non-linearities in the transmitted waveform without unduly increasing the operating requirements on the transmitter circuitry.
SUMMARY OF THE INVENTION
Applicant has overcome the problems of the prior art by inventing a FMCW radar system which reduces the operating requirements on the linearizer portion of the transmitter circuitry by taking account of the non-linearities in the transmitted waveform via processing in the radar receiver.
This is accomplished by replacing the fixed frequency sample clock used to digitize the IF signal in the prior art FMCW radar system with a sample clock which is derived from the transmitted waveform itself. Rather than sample uniformly spaced in time using the fixed frequency sample clock, the inventive FMCW radar system shows small deviations from linearity as nonuniform time sampling, but uniform phase sampling in the receiver analog/digital (A/D) converter.
The output of the linearizer delay and mixing circuitry portion of the transmitter circuitry is multiplied in frequency, if necessary, by a fixed factor N, to achieve at least the Nyquist sampling rate, to directly become the A/D sample clock. As is well known in the art, the Nyquist sampling rate is the sample rate above which no aliasing or spectral overlap occurs.
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Alliant Techsystems Inc.
Sotomayor John B.
Vidas Arrett & Steinkraus P.A.
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