Spread spectrum detector
First Claim
1. Apparatus for detecting spread spectrum signals comprising:
- an antenna;
a swept local oscillator;
means for heterodyning the output of said local oscillator with a signal at said antenna;
means for squaring the output signal from said heterodyning means;
a dispersive filter having a rate twice that of said local oscillator, said filter being coupled to the output of said squaring means, and means for gating the output from said filter in timed relationship to the sweep of said local oscillator, whereby the presence and center frequency of a direct sequence spread spectrum signal may be ascertained.
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Abstract
A spread spectrum detector utilizes compressive receiver techniques and squaring of the incoming signal to detect the presence of a spread spectrum signal and to obtain its center frequency, with the squaring cancelling the pseudo-random code. Once having determined the center frequency, the gated output of the compressive receiver'"'"'s dispersive delay line may be directly demodulated without resort to code correlation, by applying the output of the dispersive delay line to a narrowband filter set to the detected center frequency. Narrowband interfering signals are rejected by a continuous comb filter, hard limiters for the filter outputs and a summing device. The same narrowband signal rejection can be accomplished by hard limiting the output of the compressive receiver delay line and then returning to the time domain with an additional dispersive delay line having a dispersive characteristic inverse to that of the compressive receiver delay line. Pseudo-random quadrature phase shifts may be cancelled out by raising the incoming signal to the fourth power.
73 Citations
14 Claims
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1. Apparatus for detecting spread spectrum signals comprising:
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an antenna; a swept local oscillator; means for heterodyning the output of said local oscillator with a signal at said antenna; means for squaring the output signal from said heterodyning means; a dispersive filter having a rate twice that of said local oscillator, said filter being coupled to the output of said squaring means, and means for gating the output from said filter in timed relationship to the sweep of said local oscillator, whereby the presence and center frequency of a direct sequence spread spectrum signal may be ascertained. - View Dependent Claims (2, 3, 4)
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5. Apparatus for ascertaining the presence and center frequency of a direct sequence spread spectrum signal comprising:
an antenna, a swept local oscillator, means for heterodyning the output of said local oscillator with a signal at said antenna, means for squaring the output signal from said heterodyning means, dispersive filter means having a rate twice that of said swept local oscillator, said filter being coupled to the output of said squaring means, and means for gating the output signal from said filter means in timed relationship to the sweep of said local oscillator. - View Dependent Claims (6, 7, 8, 9)
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10. A method of minimizing the effect of narrowband high-power signals on the detection of spread spectrum signals comprising:
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receiving a band of signals having varying frequencies; sweeping said frequency band; heterodyning said swept signal with said received signal; squaring said heterodyned signal; filtering said squared signal at a rate which is double the rate in which said band is swept; gating said filtered signal; dividing the frequency of said gated signal into contiguous subbands; hard limiting the signals in each of the subbands; and summing the hard limited signals in the subbands. - View Dependent Claims (11, 12, 13)
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14. Apparatus for ascertaining the presence and center frequency of a direct sequence spread spectrum signal comprising:
an antenna, a swept local oscillator, means for heterodyning the output of said local oscillator with a signal at said antenna, means for raising the output signal from said heterodyning means to the fourth power;
dispersive filter means having a rate four times that of said swept local oscillator, said filter being coupled to the output of said fourth power means, and means for gating the output signal from said filter means in timed relationship to the sweep of said local oscillator.
Specification