In a proposed digital signal-processing technique, a radio receiver would control the phasing of a phased-array antenna to aim the peaks of the antenna radiation pattern toward desired signal sources while aiming the nulls of the pattern toward interfering signal sources. The technique was conceived for use in a Global Positioning System (GPS) receiver, for which the desired signal sources would be GPS satellites and typical interference sources would be terrestrial objects that cause multipath propagation. The technique could also be used to optimize reception in spread spectrum cellular-telephone and military communication systems.
During reception of radio signals in a conventional phased-array antenna system, received signals at their original carrier frequencies are phase-shifted, then combined by analog circuitry. The combination signal is then subjected to downconversion and demodulation.
In a system according to the proposed technique (see figure), the signal received by each antenna would be subjected to down conversion, spread-spectrum demodulation, and correlation; this processing would be performed separately from, and simultaneously with, similar processing of signals received by the other antenna elements. Following analog down conversion 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 pseudorandum-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. The technique could also be applied to other code-division multiple-access communication systems.
This work was done by Charles E. Dunn and Lawrence E. Young of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Electronics/Computers category.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
NASA Management Office–JPL
(818) 354-7770.
Refer to NPO-20031.
This Brief includes a Technical Support Package (TSP).
Receiver Would Control Phasing of a Phased-Array Antenna
(reference NPO-20031) is currently available for download from the TSP library.
Don't have an account?
Overview
The document outlines a significant innovation in phased-array antenna technology developed by NASA's Jet Propulsion Laboratory (JPL). This innovation addresses the limitations of conventional phased array systems, which typically rely on analog hardware for combining radio-frequency signals after phase shifting. In contrast, the new approach allows for the downconversion, spread spectrum demodulation, and correlation of RF signals from each antenna element to be performed in parallel. This digital processing enables the synthesis of independent antenna patterns for each signal source, offering substantial advantages over traditional methods.
The primary problem addressed by this innovation is the need for GPS antennas to maximize gain toward GPS signal sources while minimizing gain toward interfering signals. The new system allows for the independent direction of gain and nulls for each GPS signal being tracked by the receiver. This capability is not limited to GPS but also applies to other Code Division Multiple Access (CDMA) radio systems, enhancing their performance in environments with multiple signal sources.
The solution involves processing RF signals from each antenna element through downconversion, followed by digital processing to eliminate residual carriers. The processed signals are then correlated with a local model Pseudorandom Noise (PRN) code, which is standard in GPS processing. The accumulated values from these processes are combined in software, applying appropriate phase shifts to synthesize an antenna pattern directed toward the desired signal source while creating nulls to mitigate interference from multipath sources or other unwanted signals.
This innovative approach not only improves the performance of GPS and CDMA systems but also has broader implications for various aerospace-related applications. The document emphasizes the potential for this technology to enhance signal tracking and reception in challenging environments, thereby contributing to advancements in navigation and communication systems.
Overall, the document serves as a technical support package detailing the advancements in phased-array antenna technology, highlighting its potential applications and benefits in improving signal processing and reception capabilities in modern communication systems.
