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System and method for reducing interference in microwave motion sensors

  • US 7,872,604 B2
  • Filed: 12/20/2007
  • Issued: 01/18/2011
  • Est. Priority Date: 12/20/2007
  • Status: Active Grant
First Claim
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1. A security system comprising:

  • a first microwave sensor having a linearly polarized antenna with an electric field oriented at 45 degrees with respect to the horizon the linear polarized antenna transmits a microwave signal parallel to the plane of the horizon and receives reflected signals, wherein the transmitted microwave signal has an electric field at 45 degrees to the plane of the horizontal; and

    a second microwave sensor, the second microwave sensor further comprisingan oscillator configured to generate a microwave signal at a pre-determined frequency;

    a linearly polarized antenna having an electric field oriented at 45 degrees with respect to the horizon configured to transmit the microwave signal parallel to the plane of the horizon and to receive reflected signals, wherein the transmitted microwave signal has an electric field at 45 degrees to the plane of the horizontal;

    a signal processor coupled to the antenna and configured to process the reflected signals to determine a presence of a moving object; and

    a mixer coupled to the antenna and the oscillator and configured to mix the reflected signal with a portion the transmitted microwave signal to generate a corresponding inteimediate frequency wherein the linear polarized antenna of the first and second microwave sensors face each other and wherein the electric fields of the linear polarized antenna of the first and second microwave sensors are perpendicular to each other.

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