Communications: directive radio wave systems and devices (e.g. – With particular circuit – Complex signal
Reexamination Certificate
2000-03-31
2001-04-03
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
With particular circuit
Complex signal
C342S021000, C342S101000, C342S189000, C342S196000
Reexamination Certificate
active
06211815
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to radar systems and more particularly to target information extraction arrangements in radar systems.
1. Background of the Invention
In radar systems, energy from a pulse or other signal is radiated and a radio wave returned in response to the radiated signal is analyzed to determine location or other information of targets from which the radiation is reflected. Accordingly, radar detection equipment must provide accurate information of the returned radio wave.
A radar system may have a coherent or a non-coherent receiver. In a receiver using coherent detection, local oscillation is arranged to be synchronous with the signal produced by the transmitter that is radiated by the radar system antenna. Coherent radar detection utilizes both the magnitude and phase of the returned signal to extract target information. The phase is calculated with respect to an oscillator that is used to both generate the transmitted waveform and to down convert the received waveform for detection. The phase of the received signal is captured by performing a complex mixing operation on the incoming signal which results in real and imaginary components that can be expressed in polar coordinates as magnitude and phase. An example of a coherent detector is disclosed in U.S. Pat. No. 3,896,436 issued to G. F. Johnson Jul. 22, 1975. As is well known, coherent detection of radar returns provides a significant improvement in receiver sensitivity over non-coherent detection. The coherent detection also allows detection of Doppler shifts to estimate wind shear, etc. However, truly coherent receiver/transmitters for radar systems are complex and very expensive.
Non-coherent detectors for radar systems provide a less expensive alternative. In one radar system disclosed in U.S. Pat. No. 5, 589,833 issued to M. A. Randall Dec. 31, 1996, a return radio wave is down converted and processed in an analog pre-processor. The pre-processed signal is applied to a digital IF processor in which the signal corresponding to the return radio wave is A/D converted, split into in-phase and quadrature phase I and Q signals, converted to baseband through a low pass filter and then match filtered. The match filtering for each of the I and Q signals is performed in a digital signal processor programmed to optimally match available radar pulse widths transmitted by the radar system transmitter. The pulses from the radar system transmitter, however, change over time in shape and frequency so that the programmed matched filter for available radar pulse widths may not provide the needed detection accuracy or precision for the changes in transmitted pulses over time and under varying conditions.
2. Brief Summary of the Invention
The invention is directed to a radar system in which a transmitter produces a pulse to be radiated by an antenna. Radio waves returned in response to the radiated pulse are converted to a return signal in a receiver of the radar system. The return signal is complex demodulated and filtered through a filter to provide a signal for target information extraction.
According to the invention, the pulse produced by the transmitter is coupled to the receiver in which an attenuated waveform of the transmitter produced pulse is complex demodulated. A filter is formed in response to the complex demodulated pulse. The complex demodulated return signal is correlated with the filter formed in response to the complex demodulated waveform of the transmitter produced pulse.
According to one aspect of the invention, the filter formed in response to the complex demodulated pulse is a matched filter formed in response to the complex demodulated waveform of the transmitter produced pulse.
According to another aspect of the invention, the matched filter is a time reversed conjugate image of the waveform of the pulse produced by the transmitter.
According to yet another aspect of the invention, the complex demodulation waveform of the produced pulse is delayed for at least a time corresponding to its width.
According to still yet another aspect of the invention, the produced pulse coupled to the receiver is attenuated prior to its complex demodulation.
According to still another aspect of the invention, the produced pulse is coupled through a circulator and a receiver-transmitter-isolation switch and an attenuator between the transmitter and the receiver.
In an embodiment of the invention, the receiver is a non-coherent receiver and the signal from the receiver is processed in a digital signal processor which operates to down convert the signal applied thereto using a complex sinusoid IF signal to form baseband in-phase I and quadrature phase Q signals. The baseband I and Q signals corresponding to the transmitter pulse are processed in the digital signal processor to form a matched filter representative of a time reversed conjugate image of the transmitted pulse. The return signal from the receiver is complex demodulated in the digital signal processor using the complex sinusoid IF signal and the demodulated I and Q signals for the return signal are correlated with the matched filter in the digital signal processor to provide a signal for target information extraction.
REFERENCES:
patent: 3803598 (1974-04-01), Abernathy et al.
patent: 5793703 (1998-08-01), Shippey
patent: 6011505 (2000-01-01), Poehler et al.
patent: 6046695 (2000-04-01), Poehler et al.
Gibson Timothy
Richey Manuel
Honeywell International , Inc.
Sotomayor John B.
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