US 20030132880 A1
The Precision Position Measurement System (PPMS) measures the location of the source of electromagnetic radiation in 3-D physical space to accuracies on the order of fractions of a wavelength using phase difference measurements among
US 20030132880 A1
The Precision Position Measurement System (PPMS) measures the location of the source of electromagnetic radiation in 3-D physical space to accuracies on the order of fractions of a wavelength using phase difference measurements among several receiving antennas, one of which is designated as the reference. All signal processing is done at the transmitter's RF frequency and in a single receiver with distributed RF signal amplification. Spatially distributed RF amplification is used to achieve sufficient signal strength for phase measurement without using up/down conversion receivers thereby eliminating sources of error due to local oscillator instability.
1. A method and apparatus for measuring the physical location of a source of radiated electromagnetic energy comprising:
several means for receiving said radiated electromagnetic energy, one of which will be referred to as the reference signal;
a means for measuring the phase of each of said received electromagnetic energy with respect to said reference signal; and,
a process for computing the position of the transmitter in which said phase differences are used to calculate the physical position of the transmitter.
2. A method and apparatus for measuring the physical location of a source of radiated electromagnetic energy comprising:
several means for receiving said radiated electromagnetic energy, one of which will be referred to as the reference signal;
several spatially separated means for amplifying said received electromagnetic energy;
several means for comparing the phase of said amplified received electromagnetic energy with respect to said reference signal; and,
a process for computing the position of the transmitter in which said phase differences are used to calculate the position of the transmitter.
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 The field of endeavor to which this invention pertains is primarily Class 342 (Communications: Directive Radio Wave Systems and Devices) and can be further classified in:
 subclass 21 (Base Band System),
 subclass 127 (Determining Distance, Phase Comparison),
 subclass 437 (Directive, Beacon or receiver, Direction-finding Receiver only, With plural fixed antenna pattern comparing, including more than two antennas),
 subclass 451 (Directive, position indicating, by computer), or
 subclass 457 (Directive, position indicating, land vehicle location).
 There exists a need to accurately measure the position of objects and track their movement in a real-world, real-time environment. Examples of this need range from measuring the state of highly maneuvering, autonomous vehicles to tracking wildlife for basic scientific research as well as clandestine tracking of unintended electromagnetic emissions. Additional applications of this technique include:
 biological feedback to virtual reality systems by measuring the positions of the extremities of the human moving through the virtual space,
 tracking multiple interacting autonomous vehicles,
 operator input for telerobotics, and,
 measuring the position of and tracking actors on stage.
 Existing systems for performing precision position measurements are generally expensive (optical, radar), susceptible to interference (wide bandwidth time-difference-of-arrival), require narrow field of view sensors which must themselves move or beam-steer to track the object (optical/radio frequency), are of limited range (magnetic, electrostatic), and/or require high-power transmitters (radar, sonar). The advantages of this new system are several, including:
 the receiving antennas have no unusual requirements except for spatial diversity,
 the receiving antennas can be fixed or moving with their position known,
 the bandwidth of the receivers is extremely narrow and only determined by the speed of movement of the transmitter being tracked,
 the accuracy of the position measurement is determined by the geometry of the receiving antennas, the carrier frequency of the transmitted signal, and the ability to resolve the phase differences in the received signals, and,
 multiple objects can be measured simultaneously through frequency or time division multiplexing
 It is well-known that the position of a continuous wave (CW) transmitter can be tracked to an accuracy determined by the stability of its carrier frequency generating oscillator and the signal receivers' local oscillators while at the same time using a very narrow receiver bandwidth. This can be done by measuring the cycle-by-cycle change of the carrier phase with reference to receivers with extremely stable local oscillators which yield relative range changes of fractions of a wavelength radially from each of the receiving antennas. The intersection of these multiple radii fix the position of the transmitter. If the initial position of the vehicle is not precisely known, an approximate position of the transmitter can be used to begin the tracking process with the absolute position being refined as more and more measurements are taken. If the initial vehicle position is precisely known, then an absolute track can be maintained from track initiation through a sequence of measurements. If it is not known, then an approximate position can be used for initialization and subsequent measurement used to refine the position.
 The drawback of this approach is that the position accuracy is determined by the stability of all of the oscillators involved, not just the transmitting oscillator's stability. For example, normal 