Measuring Distance to a Radio Emitter from a Moving Vehicle

This patent describes a system for a single moving vehicle to passively determine the distance to a radio signal source by comparing the timing and phase changes of signals received by two spaced antennas.

What it covers

The patent describes a system to measure the distance (range) to a radio signal source without sending out its own signal. It uses at least two antennas on a single vehicle (Claim 1). A receiver processes the signals, sending video signals to a "time of arrival computing means" to determine the direction (bearing) to the source. Simultaneously, intermediate frequency (IF) or radio frequency (RF) signals go to a "phase rate computer means" (Claim 1). This phase computer measures how quickly the phase difference between the two antennas changes over time, producing a "phase rate beat frequency voltage" (Claim 1). A "modifying means" adjusts the bearing signal based on factors like antenna spacing, drift angle, and ground speed (Claim 4). Finally, a "combining means" uses this adjusted bearing signal and the phase rate information to calculate and output the range to the radio source (Claim 1). For example, a military aircraft could use this to locate an enemy radar without revealing its own position.

What it doesn't cover

• —Does not cover systems that actively transmit a signal to determine range, such as traditional radar.
• —Does not cover range determination using only one antenna, as it requires at least two physically separated antennas (Claim 1).
• —Does not cover systems that determine range solely based on time of arrival without also using phase rate information (Claim 1).
• —Does not cover systems that do not account for vehicle movement parameters like drift angle or ground speed when modifying the bearing signal (Claim 4).
• —Does not cover range finding where the antennas are not physically separated, as physical separation is a core requirement (Claim 1).

The clever bit

The novelty lies in combining both the difference in signal arrival times (for bearing) and the rate of change of the phase difference (for range) between two antennas on a single, moving platform. This allows for a complete range solution from a single vehicle, which was a significant challenge for passive systems.

Why it matters

This patent, assigned to the US Department of Navy, describes a method for a single vehicle to determine the range to an emitter without radiating its own signals. This capability is crucial for military applications, allowing a tactical vehicle to locate enemy radar or communication systems while remaining undetected. Such passive ranging techniques enhance situational awareness and survivability in hostile environments.

Real-world examples

• 1.Electronic warfare support measures (ESM) systems on military aircraft
• 2.Radar warning receivers (RWR)
• 3.Intelligence, surveillance, and reconnaissance (ISR) platforms
• 4.Radio direction finding (RDF) systems with ranging capabilities