Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-09-30
2001-07-24
Issing, Gregory C. (Department: 3642)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
Reexamination Certificate
active
06266011
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electronically scanned phased array antennas.
2. Description of the Related Art
The antenna beams of conventional surveillance and communications radar and other communications systems have been mechanically rotated, electrically controlled by phased arrays using phase shifters, or driven by mechanically actuated phase shifters in an attempt to increase range. In the 1950's, phased array technology progressed from mechanical to electronic phase shifters with a phase shifter that used a fixed delay line sandwiched by two frequency mixers (W. H. Huggins, “Generalized Radar Concepts with the use of Array Antennas,” Rand Corp., Report RM1854, December 1956). Similar techniques have been used in optical parallel-feed beam forming networks; R. Benjamin, C. D. Iaglanikis and A. J. Seeds, “Optical beam former for phased arrays with independent control of radiated frequency and phase,”
Electronics Letters,
vol. 26, pages 1853-1855, October 1990. In the early 1960's, digitally switched phase shifters used ferrites or diodes.
Although phased array antennas using electronic phase shifters offered distinct advantages over mechanically actuated aperture antennas (i.e. a nearly flat radiating aperture amenable to conformal structures, an electronically scanned beam providing an inertialess steering system, a superior life expectancy, a more effectively synthesized beam pattern for which a number of known algorithms are applicable, and adaptability to hostile environments, including the presence of radar jammers), they were costly and difficult to manufacture for higher frequencies. Phase shifters also experienced temperature-sensitivity, hysteresis and quantization errors, and were limited to the microsecond phase shifting time range (Skolnik,
Introduction to Radar Systems,
Chapter 8, “The Electronically Directed Phased Array Antenna in Radar,” pages 278-342, McGraw-Hill Publishing Co., 1980).
As an alternative to individual phase shifters, simple series-fed frequency-scan arrays have provided beam steering with virtually no phase shifter components except for fixed delay lines. See Skolnik, above, and M. Li, K. Chang, “Novel low-cost beam-steering techniques using microstrip patch antenna arrays fed by dielectric image lines,”
IEEE Trans. Antennas Propagation,
vol. 47, pages 453-457, March 1999. However, in these systems the radiating frequency changes as the beam is scanned, whereas a constant radiating frequency is normally desired.
SUMMARY OF THE INVENTION
The present invention seeks to provide a phased array antenna system and method that avoids the disadvantages of phase shifters discussed above, is more cost effective and yet allows for beam scanning without changing the frequency of the radiated signal. This is accomplished with an array of frequency mixers that correspond to the antenna elements of an antenna array, and a phase delay network that provides a scan control signal to the mixers with the required phase delays between the antenna elements. The mixers are connected in circuit with their respective antenna elements so that the system's scan angle is controlled by the frequency of the scan control signal, independent of the operating signal frequency for the antenna elements.
The phase delay network is preferably implemented with a time delay network, with the signal mixers tapping the time delay network at locations which correspond to the locations of their respective antenna elements. To transmit, a common mixing signal is mixed with each of the phase delayed scan control signals to yield progressively phase delayed transmission signals at a desired operating frequency, which are radiated by the antenna elements. In a receive mode the inputs from the antenna elements are mixed with their respective phase delayed scan control signals to yield mixer outputs with a frequency that is a function of both the scan control and operating signal frequencies. These outputs are accumulated and mixed with the scan control signal to yield the original operating signal. Appropriate filters are employed in both the transmit and receive modes to remove extraneous signals.
The invention can also be implemented with dual time delay networks. In the transmit mode the scan control signal and its complement, whose frequencies add up to the operating signal frequency, are counter-propagated through respective delay networks, from which they are tapped and mixed together at each of the mixers to yield the operating signal with appropriate phase delays for the various antenna elements. In a receive mode, scan control signal is tapped from one of the time delay networks and mixed with the incoming signals from the antenna elements, yielding outputs that are tapped into the other delay network to produce an output from which the operating signal can be extracted.
The invention is applicable to both single array antennas and, with appropriate phase offsets between them, multi-dimensional arrays.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.
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W.H. Huggins, “Generalized Radar Concepts with the use of Array Antennas”, Rand Corp., Report RM1954, (Dec. 1956).
R. Benjamin et al., “Optical beam former for phased arrays with independent control of radiated frequency and phase”, Electronics Letters, vol. 26, pp. 1853-1855 (Oct. 1990).
Skolnik, “The Electronically Directed Phased Array Antenna in Radar”,Introduction to Radar Systems, Chapter 8, pp. 278-342, McGraw-Hill Publishing Co., (1980).
M. Li et al., “Novel low-cost beam-steering techniques using microstrip patch antenna arrays fed by dielectric image lines”, IEEE Trans. Antennas Propagation, vol. 47, pp. 453-457, (Mar. 1999).
Issing Gregory C.
Koppel & Jacobs
Rockwell Science Center LLC
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