{
  "patent_number": "US 3789410",
  "country": "US",
  "title": "How to Calculate Distance to a Radio Signal Using Two Antennas",
  "original_title": "Passive ranging technique",
  "summary": "A 1970s Navy system that calculates the distance to a radio-emitting target by measuring the tiny time and phase differences between signals arriving at two separate antennas.",
  "what_it_does": "This system determines how far away a radio-emitting source is without the source knowing it is being tracked. It uses two antennas placed at a known distance from each other to capture incoming radio waves. By measuring the difference in the time it takes for a signal to reach each antenna, the system calculates the bearing (direction) to the source. It then uses a phase rate computer to analyze the 'beat frequency'—a pattern created by the interaction of the signals—to determine the distance. This allows a vehicle to locate a target passively, meaning it does not need to send out its own radar pulses that would reveal its own position.",
  "what_it_does_not_cover": [
    "Does not cover active radar systems that emit signals to detect targets.",
    "Does not cover systems that use more than two antennas for triangulation.",
    "Does not cover methods that rely on signal strength (RSSI) to estimate distance.",
    "Does not cover systems that require the target to cooperate or transmit a specific identification code."
  ],
  "filed": "1972-01-07",
  "granted": "1974-01-29",
  "expires": "1992-01-07",
  "status": "expired",
  "holder": "US Department of Navy",
  "holder_url": "https://patentbrief.org/company/us-department-of-navy",
  "inventors": [
    {
      "name": "L Smith",
      "url": "https://patentbrief.org/inventor/l-smith"
    },
    {
      "name": "K Sayano",
      "url": "https://patentbrief.org/inventor/k-sayano"
    }
  ],
  "times_cited": 16,
  "tags": [
    "telecommunications",
    "mechanical",
    "aerospace"
  ],
  "abstract": "A system for passively determining range to a threat emitter from a single tactical vehicle based upon the change in the difference of phase of a radio frequency carrier between two physically spaced antennas.",
  "url": "https://patentbrief.org/patent/us/3789410/gps-timation-navigation",
  "markdown_url": "https://patentbrief.org/patent/us/3789410/gps-timation-navigation/md",
  "google_patents_url": "https://patents.google.com/patent/US3789410",
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}