RFI suppression circuit and method
First Claim
1. In a system for transmitting and receiving pulsed RF signals, comprising a transmitter for radiating pulsed RF signals, a directional antenna, and a broad band receiver coupled to said directional antenna for receiving and processing pulsed RF signals of a given frequency in the possible presence of narrow band RFI signals created by a plurality of extraneous narrow band RFI sources, said narrow band RFI being distinct in frequency from one another and from said given frequency, whereby said receiver incidentally detects said RFI signals in addition to detecting pulsed wide band RF signals of said given frequency, the improvement for reducing the effect of said RFI signals, comprising:
- separator means for parsing received signals amongst a plurality of separate and distinct frequency channels in dependence on the frequency of said signals and separately outputting each said channel, whereby a plurality of received RFI signals of different frequencies is produced at the respective channel outputs associated with such frequencies and wherein a received pulsed RF signal is divided into constituent spectral components and said constituent spectral components are individually output from respective channels associated with respective constituent spectral components;
counter signal generating means for producing a counter signal for each said channel;
each said counter signal corresponding to at least a respective RFI signal in a respective one of said plurality of channels, each respective counter signal being of essentially the same amplitude as and phase with said associated respective RFI signal;
first combiner means, responsive to said separator means and to said counter signal generating means, for subtractively combining signals from each of said plurality of channels with the respective ones of said plurality of counter signals from said counter signal generating means to produce a corresponding plurality of difference signals, wherein each said RFI is effectively minimized and wherein the constituent components of a received pulsed RF signal are presented; and
second combiner means, coupled to said first combiner means, for summing said plurality of difference signals to provide a composite output signal reproducing said pulsed RF signal.
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Abstract
Improvement of radar sign-to-noise ratio and detection sensitivity in radar systems is achieved by methods employing the subtraction of the unwanted radio frequency interference, RFI, or "clone" signals thereof, from the total received signal. The Clone signals are appropriately adjusted in phase and amplitude, and are obtained from an auxilliary broad beam antenna or from a delayed sample from the system'"'"'s principal antenna. When multiple RFI signals at different frequencies are present, the entire receive band is subdivided into a plurality of frequency sub-ranges.
48 Citations
26 Claims
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1. In a system for transmitting and receiving pulsed RF signals, comprising a transmitter for radiating pulsed RF signals, a directional antenna, and a broad band receiver coupled to said directional antenna for receiving and processing pulsed RF signals of a given frequency in the possible presence of narrow band RFI signals created by a plurality of extraneous narrow band RFI sources, said narrow band RFI being distinct in frequency from one another and from said given frequency, whereby said receiver incidentally detects said RFI signals in addition to detecting pulsed wide band RF signals of said given frequency, the improvement for reducing the effect of said RFI signals, comprising:
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separator means for parsing received signals amongst a plurality of separate and distinct frequency channels in dependence on the frequency of said signals and separately outputting each said channel, whereby a plurality of received RFI signals of different frequencies is produced at the respective channel outputs associated with such frequencies and wherein a received pulsed RF signal is divided into constituent spectral components and said constituent spectral components are individually output from respective channels associated with respective constituent spectral components; counter signal generating means for producing a counter signal for each said channel;
each said counter signal corresponding to at least a respective RFI signal in a respective one of said plurality of channels, each respective counter signal being of essentially the same amplitude as and phase with said associated respective RFI signal;first combiner means, responsive to said separator means and to said counter signal generating means, for subtractively combining signals from each of said plurality of channels with the respective ones of said plurality of counter signals from said counter signal generating means to produce a corresponding plurality of difference signals, wherein each said RFI is effectively minimized and wherein the constituent components of a received pulsed RF signal are presented; and second combiner means, coupled to said first combiner means, for summing said plurality of difference signals to provide a composite output signal reproducing said pulsed RF signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. The method of preventing a plurality of spurious RF sources of different frequencies from producing interference with the detection and processing of desired radar echoes in a wide band pulse radar receiving system capable of receiving such different frequencies, comprising the steps of:
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separating received signals collectively representing spurious interference signals and the desired radar echo into a plurality of frequency sub-ranges, whereby each spurious signal falls into a respective one of said sub-ranges to produce a separate plurality of spurious signals of individual amplitude and phase together with a component of any desired radar echo that is simultaneously received; generating a counter signal for each separate spurious signal, each said counter signal being equal in amplitude and phase with the amplitude and phase determined from the spurious signal within each respective subrange; subtracting each counter signal from the corresponding spurious signal plus said desired echo component in each said subrange to produce a corresponding difference signal that is essentially a component of the desired radar echo; combining all said difference signals to produce a combined signal in which any interference signals have been minimized, whereby the combined signal represents essentially the desired radar echo. - View Dependent Claims (20, 21, 22)
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23. A radar system for transmitting and receiving a train of pulsed RF signals, whereby a reflecting surface on which said pulsed RF signals is incident reflects echoes thereof to said radar system, said radar system comprising a transmitter, directional antenna, receiver, said receiver receiving from said directional antenna and detecting a total signal occuring within a predefined pass band comprising an echo of a transmitted RF pulse signal and any RFI present within said pass band, and a signal processor for receiving and processing RF echoes during the presence of RFI, said signal processor including circuit means for reducing the effect of said RFI in the received detected signal, comprising:
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means for determining the amplitude of the detected RFI existing at the time of echo reception; and means for subtracting the amplitude of said detected RFI from the amplitude of the total detected signal to produce a difference signal representative of the desired echo, whereby said RFI is substantially eliminated. - View Dependent Claims (24, 25, 26)
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Specification