Near-field calibration system for phase-array antennas

• US 6,084,545 A
• Filed: 07/12/1999
• Issued: 07/04/2000
• Est. Priority Date: 07/12/1999
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Purdy, Daniel Sanford, Ashe, Jeffrey Michael, Lier, Erik, Volman, Vladimir, Jacomb-Hood, Anthony Wykeham
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/352,508
• Time in Patent Office: 358 Days
• Field of Search: 342/165, 342/174, 342/360, 342/372, 342/374
• US Class Current: 342/360
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

A near-field calibration arrangement for a phased-array antenna determines the phase shifts or attenuation of the elemental control elements of the array. The calibration system includes a probe located in the near field, and a calibration tone generator. The tone generator is coupled to the probe in the case of calibration of a receive antenna, and to the signal port of the array in the case of calibration of a transmit antenna. A code generator generates sets of values, with each set being orthogonal to the others. The codes are applied to the control input port of the array antenna, so that the codes encode the tone passing through the antenna. The encoded tones are applied to a decoder and processor, which processes the signals to determine the phase shift or attenuation associated with each bit of the control signal.

Claims

1. An antenna system, comprising:

an transmit antenna array including a signal port and also including a beam conditioning or beam-forming control input port coupled to at least controllable phase shifters;

a transmit calibration probe affixed at a nominal location in the near field of said transmit antenna array;

transmit antenna switching means including at least common, calibration, and transmit ports, said common port being coupled to said signal port of said transmit antenna array;

a source of transmit antenna array calibration signals;

transmit antenna array calibration signal coupling means coupled to said source of transmit antenna array calibration signals and to said calibration port of said transmit antenna switching means, for controllably coupling said transmit antenna array calibration signals to said signal port of said transmit antenna array, so that said transmit antenna array calibration signal, when applied to said signal port of said transmit antenna array, is transmitted by said transmit antenna array;

calibration encoding means for sequentially generating sets of values, each set of values being orthogonal to other sets of values;

transmit antenna encoding signal coupling means coupled to said calibration encoding means and to said beam conditioning control port of said transmit antenna array, for, during calibration, coupling said calibration encoding signals to said beam conditioning control port of said transmit antenna array, for thereby sequentially setting at least some of said phase shifters of said transmit antenna array with said plurality of sets of values, whereby said transmit antenna array calibration probe receives said transmit antenna array calibration signals sequentially encoded with mutually orthogonal values;

an receive array antenna including a signal port and also including a beam conditioning control input port coupled to at least controllable phase shifters of said receive array antenna;

a receive calibration probe affixed at a nominal location in the near field of said receive antenna array;

receive antenna switching means including at least common, calibration, and receive ports, said common port of said receive antenna switching means being coupled to said signal port of said receive antenna array;

a source of receive antenna array calibration signals;

receive antenna array calibration signal coupling means coupled to said source of receive antenna array calibration signals and to said receive calibration probe, for controllably coupling said receive antenna array calibration signals to said receive calibration probe, whereby said receive antenna array calibration signal is transmitted by said receive calibration probe and is received by said receive antenna array;

receive antenna encoding signal coupling means coupled to said calibration encoding means and to said beam conditioning control port of said receive antenna array, for, during calibration, sequentially setting at least some of said phase shifters of said receive antenna array with said plurality of sets of values, whereby said receive antenna array produces, at said signal port, receive antenna array calibration signals sequentially encoded with mutually orthogonal values;

a transmit/receive calibration switch including transmit signal port, receive signal port, and a common port, for coupling signals applied to one of said transmit signal port and said receive signal port to said common port;

first encoded signal coupling means coupled to said transmit calibration probe and to said transmit signal port of said transmit/receive calibration switch, for coupling said transmit antenna array calibration signals sequentially encoded with mutually orthogonal values to said transmit/receive calibration switch, whereby said transmit antenna array calibration signals sequentially encoded with mutually orthogonal values are produced at said common port of said transmit/receive calibration switch in an transmit antenna array calibration mode of operation;

second encoded signal coupling means coupled to said signal port of said receive antenna array switching means and to said common port of said receive antenna switching means, for, in a calibration mode of operation, coupling said receive antenna array calibration signals sequentially encoded with mutually orthogonal values to said calibration port of said receive antenna switching means, whereby said receive antenna array calibration signals sequentially encoded with mutually orthogonal values appear at said calibration port of said receive antenna switching means;

third encoded signal coupling means coupled to said calibration port of said receive antenna switching means and to said receive port of said transmit/receive calibration switch, whereby said receive antenna array calibration signals sequentially encoded with mutually orthogonal values are produced at said common port of said transmit/receive calibration switch in an receive antenna array mode of operation;

analog-to-digital conversion means including an input port coupled to said common port of said transmit/receive calibration switch, for converting into digital form those analog signals applied to said input port of said analog-to-digital conversion means, to thereby generate a digital version of said transmit antenna array calibration signals sequentially encoded with mutually orthogonal values in said transmit antenna array calibration mode of operation and a digital version of said receive antenna array calibration signals sequentially encoded with mutually orthogonal values in said receive antenna array calibration mode of operation;

signal processing means coupled to said analog-to-digital conversion means, for decoding that one of said digital version of said transmit antenna array calibration signals sequentially encoded with mutually orthogonal values and said digital version of said receive antenna array calibration signals sequentially encoded with mutually orthogonal values which is produced by said analog-to-digital conversion means, to thereby generate signals representing the relationship between a bit applied to each of said phase shifters and the resulting phase.

2. A system according to claim 1, wherein each of said first and third signal coupling means comprises an electromagnetic filter for rejecting unwanted frequencies, to thereby generate filtered signals.

3. A system according to claim 1, wherein each of said first and third signal coupling means comprises an electromagnetic filter for rejecting unwanted frequencies, to thereby generate filtered signals, and a frequency converter coupled to said filter for frequency converting said filtered signals.

4. A system according to claim 3, wherein each of said frequency converters is a downconverter.

5. A system according to claim 1, further comprising:

traffic signal processing means coupled between said receive port of said receive antenna switching means and said transmit port of said transmit antenna switching means.

6. A near-field calibration system for calibrating at least one of the phase and amplitude controllers of the individual elements of a phased-array antenna which may be operated in a normal signal-handling mode and in a calibration mode, in which said phased-array antenna includes a signal port for each individual beam which said antenna generates, and also includes a control signal input port to which control signals are applied for control of said phase and amplitude controllers, said calibration system comprising:

a calibration probe located at a fixed position relative to said phased-array antenna, and within the near-field of said phased-array antenna;

a calibration tone generator for generating a calibration tone signal, said calibration tone generator being (a) coupled to at least one of said signal ports of said phased-array antenna for the case in which said phased-array antenna is used as a transmit antenna during normal operation, and (b) coupled to said calibration probe for the case in which said phased-array antenna is used as a receive antenna during normal operation;

calibration encoding means coupled to said beam conditioning control port of said phased-array antenna, for, during calibration, sequentially setting at least some of said phase shifters of said phased-array antenna with a plurality of sets of values, each of said sets of values imposing a coding on the calibration tone signal, to thereby sequentially generate calibration signals encoded with sets of values, each set of values so encoded onto said calibration signals being orthogonal to other sets of values with which said calibration signals are encoded, whereby, in the case in which said phased-array antenna is used as a transmit antenna during normal operation, said calibration probe receives said calibration tone signals sequentially encoded with mutually orthogonal values, and in the case in which said phased-array antenna is used as a receive antenna during normal operation, said calibration tone signals sequentially encoded with mutually orthogonal values are generated at said at least one of said signal ports of said phased-array antenna;

a decoder for decoding signals encoded with said mutually orthogonal values, for generating decoded signals therefrom;

encoded signal coupling means (a) coupled to said calibration probe and to said decoder in the case in which said phased-array antenna is operated as a transmit antenna in said normal mode of operation and (b) coupled to said decoder and to said signal port of said phased-array antenna in the case in which said antenna is operated as a receive antenna in said normal mode of operation, for coupling said encoded signals to said decoder, as a result of which said decoder generates said decoded signals;

a processor coupled to said decoder, for processing said decoded signals for generating signals representing at least the values of one of phase shift and attenuation; and

coupling means coupled to said processor and to said antenna control unit, for coupling to said antenna control unit said signals representing at least the values of one of phase shift and attenuation.

7. A method for calibrating an array antenna, said method comprising the steps of:

generating a calibration tone signal;

in the case of a transmit antenna, applying said calibration tone signal to the signal input port of said array antenna, and in the case of a receive antenna, applying said calibration tone signal to a probe antenna located in the near field of said array antenna;

sequentially generating encoding signals including sets of values, each set of values being orthogonal to other sets of values;

applying said encoding signals to a control input port of said array antenna for control of at least the phase shifters thereof, whereby said calibration tone signal traversing said array antenna is encoded with said values to thereby produce encoded calibration signals;

coupling said encoded calibration signals to a decoder, for decoding said sets of values to produce decoded signals; and

processing said decoded signals to produce signals representative of the phase shift resulting from said encoding signals.