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Digitally synthesized phased antenna for multibeam global positioning

In a system according to the proposed technique (see figure), the signal received by each element of the array antenna would be subjected to downconversion, and spread-spectrum demodulation and correlation as necessary; this processing would be performed separately from, and simultaneously with, similar processing of signals received by the other antenna elements. For the GPS implementation, following downconversion to baseband, the signals would be digitized, and all subsequent processing would be digital. In the digital process, residual carriers would be removed and each signal would be correlated with a locally generated model pseudo random-noise code, all following normal GPS procedure. As part of this procedure, accumulated values would be added in software and the resulting signals would be phase-shifted in software by the amounts necessary to synthesize the desired antenna directional gain pattern of peaks and nulls. The principal advantage of this technique over the conventional radio-frequency-combining technique is that the parallel digital baseband processing of the signals from the various antenna elements would be a relatively inexpensive and flexible means for exploiting the inherent multiple-peak/multiple-null aiming capability of a phased-array antenna. In the original intended GPS application, the peaks and nulls could be directed independently for each GPS signal being tracked by the GPS receiver. This will improve the SNR simultaneously for each GPS signal being tracked while steering multiple nulls toward sources of interference. The technique could also be applied to other code-division multiple-access communication systems.
NASA's Jet Propulsion Laboratory has developed a novel technique to control the phasing of a phased-array antenna to improve the signal-to-noise ratio (SNR) and reduce interference from jamming and multipath propagation in a cost-effective manner. Compared to single-antenna systems, phased-array antennas are ideal for use in GPS receivers, because adding the outputs of separate antenna elements improves SNR and reduces interference. Despite these advantages, conventional phased-array antenna systems are prohibitively expensive because received signals are phase shifted and then combined using analog circuitry. JPL's phased-array antenna system uses digital synthesis techniques that eliminate the need for costly analog circuits and can be orders of magnitude more precise than the analog techniques used in conventional systems.

Inexpensive, flexible means of exploiting the advantages of phased-array antennas


Communications systems - GPS, cellular telephone, military, and FM radio


Charles E. Dunn, Jr., Lawrence E. Young

Patent Number: 
Internal Laboratory Ref #: 
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Patent Issue Date: 
January 7, 2005
Far West
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