Doppler frequency analysis of radar signals
First Claim
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1. A radar system which responds to distinctive Doppler step modulation resulting from the movement of human targets, comprising:
- a Doppler radar having a first intermediate frequency signal output modulated by a Doppler signal within a first low frequency range, a frequency modulation (FM) detector coupled to said radar to receive said first intermediate frequency and Doppler signal, said FM detector adapted to respond only to step frequency modulation on said first intermediate frequency, said step frequency being within a second range of low frequencies lower than said first frequency range and representing the frequency of movement of human targets, a plurality of parallel tuned filters operative within said second range of frequencies and connected to the output of said FM detector to split the detected step modulation frequencies into a number or contiguous frequency bands representing targets stepping at different rates, and a plurality of indicators respectively connected to the outputs of said filters to indicate the presence of moving targets at different step frequencies.
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Abstract
A Doppler radar is adapted to respond only to walking human targets by prding means to detect the frequency modulation of the Doppler signals caused by the oscillatory body movements of such walking targets. A frequency locked loop frequency modulation detector is provided for efficient detection of this so-called step frequency modulation, and the detected step frequencies are split into several bands representing targets walking at different step rates. Circuitry is shown for adapting this technique to continuous wave radars or range gated radars.
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Citations
5 Claims
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1. A radar system which responds to distinctive Doppler step modulation resulting from the movement of human targets, comprising:
- a Doppler radar having a first intermediate frequency signal output modulated by a Doppler signal within a first low frequency range, a frequency modulation (FM) detector coupled to said radar to receive said first intermediate frequency and Doppler signal, said FM detector adapted to respond only to step frequency modulation on said first intermediate frequency, said step frequency being within a second range of low frequencies lower than said first frequency range and representing the frequency of movement of human targets, a plurality of parallel tuned filters operative within said second range of frequencies and connected to the output of said FM detector to split the detected step modulation frequencies into a number or contiguous frequency bands representing targets stepping at different rates, and a plurality of indicators respectively connected to the outputs of said filters to indicate the presence of moving targets at different step frequencies.
- View Dependent Claims (2, 5)
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3. A Doppler radar system which responds to the distinctive Doppler step modulation resulting from moving human targets, comprising:
- a coherent range gated Doppler radar with a plurality of baseband range gate intermediate frequency outputs modulated by a Doppler signal within a first low frequency range, a multiplexing switch, a frequency modulation detector connected to said range gates sequentially by said multiplexing switch to receive said intermediate frequency outputs and Doppler signal, said frequency modulation detector being adapted to respond only to step frequency modulation on said intermediate frequency, said step frequency being within a second range of low frequencies lower than said first frequency range and representing the frequency of movement of human targets, said frequency modulation detector comprising a single sideband modulator to which said baseband Doppler signals are applied as an input to be heterodyned up in frequency and provide a second intermediate frequency output, a voltage controlled oscillator connected to the second input of said single sideband modulator and a second intermediate amplifier connected to the output thereof, a discriminator connected to the output of said second intermediate frequency amplifier, a low pass filter connected to the output of said discriminator, the output of said low pass filter connected to the control input of said voltage controlled oscillator, a paralleled filter bank connected to said low pass filter output comprising an array of stagger tuned filters covering the second range of low step frequencies, integrating detectors connected respectively to each of the filters of said filter bank, an array of indicators connected to respective integrating detectors and equal to the number of range gates of said radar, demultiplexing switches connecting said indicators to said detectors and synchronously operated with said multiplexing switch.
- View Dependent Claims (4)
Specification