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Calibration system and method for phased array antenna using near-field probe and focused null

  • US 6,636,173 B2
  • Filed: 12/20/2001
  • Issued: 10/21/2003
  • Est. Priority Date: 12/20/2001
  • Status: Active Grant
First Claim
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1. A system for calibrating at least one element of a transmit array antenna,said array antenna coupled to a signal generating means for generating a coherent reference phase signal to said at least one element, the signal emerging from said signal generating means transmitted as a beam from said array antenna, said beam producing a null and a focused difference pattern having peaks on either side of the null, said array antenna forming a finite plane of said elements, the plane having a center point and extreme edges, said system comprising:

  • a null probe having a face, said null probe rigidly positioned normal to the plane of said array antenna and at a distance in the near-field of said array antenna, said face of said null probe rigidly positioned over the center point of the plane thereby forming an angle between the center point and a point on one of the extreme edges of the plane of said array antenna, said null probe therein positioned over the center point of said array antenna corresponding to said null, said null probe, the center point, and the point on the extreme edge of the plane of said array antenna thereby forming a plane normal to the finite plane of said elements;

    a reference probe including a face, said reference probe rigidly positioned parallel to, and at an offset position away from, said null probe in the plane formed by said null probe, the center point and the point on the extreme edge of the plane of said array antenna, said reference probe rigidly positioned at the distance in the near-field of said array antenna such that said face of said reference probe is positioned over one of the peaks of the focused difference pattern of the null;

    said null probe receiving at the center point of said array antenna the null beam transmitted by said array antenna from said signal generating means to said at least one element, the beam received by said null probe coupled as a signal to a first attenuator, said first attenuator coupled to a first two-way splitter, said first two-way splitter receiving the signal from said null probe through said first attenuator;

    said reference probe receiving at said offset position from said null probe the beam transmitted by said array antenna from said signal generating means, the beam received by said reference probe coupled as a signal to a second attenuator, said second attenuator coupled to a second two-way splitter, said second two-way splitter receiving the signal from said reference probe through said second attenuator;

    a first mixer, said first mixer including as input ports a radio-frequency port and a local oscillator port, said first mixer including as an output port an intermediate frequency port;

    a second mixer, said second mixer including as input ports a radio-frequency port and a local oscillator port, said second mixer including as an output port an intermediate frequency port;

    said first two-way splitter splitting the signal received from said null probe through said first attenuator into a first signal, substantially 0 degree phase-shifted, which is coupled to said radio-frequency port of said second mixer, and into a second signal, substantially 90 degree phase-shifted, which is coupled to said radio-frequency port of said first mixer;

    said second two-way splitter splitting the signal received from said reference probe through said second attenuator into a first signal, substantially 0 degree phase-shifted, which is coupled to said local oscillator port of said second mixer, and into a second signal, substantially 0 degree phase-shifted, which is coupled to said local oscillator port of said first mixer;

    said first mixer combining the substantially 90 degree phase-shifted signal of said first two-way splitter and the substantially 0 degree phase-shifted signal of said second two-way splitter to yield an output signal at said intermediate-frequency port of said first mixer, said output signal at said intermediate-frequency port of said first mixer coupled to a first low-pass filter from which emerges a quadrature base-band component signal at substantially 0 degree frequency of the signal received from said null probe;

    said second mixer combining the substantially 0 degree phase-shifted signal of said first two-way splitter and the substantially 0 degree phase-shifted signal of said second two-way splitter to yield an output signal at said intermediate-frequency port of said second mixer, said output signal at said intermediate-frequency port of said second mixer coupled to a second low-pass filter from which emerges an in-phase base-band component signal at substantially 0 degree frequency of the signal received from said null probe;

    a processor, said processor receiving as an input signal said quadrature base-band component signal at substantially 0 degree frequency of the signal received from said null probe and as an input signal said in-phase base-band component signal at substantially 0 degree frequency of the signal received from said null probe, said processor processing said quadrature base-band component signal and said in-phase base-band component signal into data representing calibration reference values of said at least one element of said array antenna;

    a recorder for recording said data representing calibration reference values of said at least one element of said array antenna, said recorder receiving said data from said processor; and

    a beam steering controller for selecting the phases on said at least one element of said array antenna to form the difference null, and to vary the phase of said at least one element of said array antenna.

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