Time-of-flight radio location system

• US 5,661,490 A
• Filed: 04/23/1996
• Issued: 08/26/1997
• Est. Priority Date: 04/12/1993
• Status: Expired due to Term

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: McEwan, Thomas E.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US08/636,370
• Time in Patent Office: 490 Days
• Field of Search: 342/387, 342/388, 342/389, 342/391, 342/386, 342/463, 342/82, 342/125, 342/465
• US Class Current: 342/387
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 1/045 Receivers
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 13/0218 Very long range radars, e.g. surface wave radar, over-the-horizon or ionospheric propagation systems for meteorological use G01S13/95
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G01S 13/103 particularities of the measurement of the distance G01S13/12, G01S13/14, G01S13/16, G01S13/18 and G01S13/20 take precedence
• CPC Class Codes: G01S 13/106 using transmission of pulses having some particular characteristics G01S13/12, G01S13/22, G01S13/24, G01S13/26, G01S13/28 and G01S13/30 take precedence
• CPC Class Codes: G01S 13/18 wherein range gates are used
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 2013/9314 Parking operations
• CPC Class Codes: G01S 2013/9321 Velocity regulation, e.g. cruise control
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: G01S 7/285 Receivers
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors
• CPC Class Codes: H04B 1/7163 using impulse radio

Abstract

A bi-static radar configuration measures the direct time-of-flight of a transmitted RF pulse and is capable of measuring this time-of-flight with a jitter on the order of about one pico-second, or about 0.01 inch of free space distance for an electromagnetic pulse over a range of about one to ten feet. A transmitter transmits a sequence of electromagnetic pulses in response to a transmit timing signal, and a receiver samples the sequence of electromagnetic pulses with controlled timing in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The receive timing signal causes the receiver to sample the sequence of electromagnetic pulses such that the time between transmission of pulses in the sequence and sampling by the receiver sweeps over a range of delays. The receive timing signal sweeps over the range of delays in a sweep cycle such that pulses in the sequence are sampled at the pulse repetition rate, and with different delays in the range of delays to produce a sample signal representing magnitude of a received pulse in equivalent time. Automatic gain control circuitry in the receiver controls the magnitude of the equivalent time sample signal. A signal processor analyzes the sample signal to indicate the time-of-flight of the electromagnetic pulses in the sequence. The sample signal in equivalent time is passed through an envelope detection circuit, formed of an absolute value circuit followed by a low pass filter, to convert the sample signal to a unipolar signal to eliminate effects of antenna misorientation.

Claims

1. An apparatus for measuring time-of-flight of an electromagnetic pulse, comprising:

a transmitter which transmits a sequence of electromagnetic pulses in response to a transmit timing signal;

a receiver which samples the sequence of electromagnetic pulses with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples;

a timing circuit which supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver, the receive timing signal causing the receiver to sample the sequence of electromagnetic pulses such that time between transmission of pulses in the sequence and sampling by the receiver sweeps over a range of delays;

an envelope detector for converting the sample signal to a unipolar signal to eliminate effects of antenna orientation mismatch;

a sample detection circuit which in response to the sample signal and the timing circuit indicates a time-of-flight between the transmitter and the receiver of pulses in the sequence.

2. The apparatus of claim 1 wherein the envelope detector comprises an absolute value circuit followed by a low pass filter.

3. The apparatus of claim 1, wherein the transmit timing signal causes the transmitter to transmit the sequence of electromagnetic pulses at a pulse repetition rate, and wherein the receive timing signal sweeps over he range of delays in a sweep cycle such that pulses in the sequence are sampled at the pulse repetition rate and with different delays in the range of delays, such that the sample signal represents magnitude of a received pulse in the equivalent time.

4. The apparatus of claim 3, wherein the receiver includes automatic gain control circuitry to control magnitude of the sample signal in equivalent time.

5. An apparatus for detecting position of an object, comprising:

a transmitter, for placement on the object, which transmits a sequence of electromagnetic pulses in response to a transmit timing signal;

a receiver which samples the sequence of electromagnetic pulses with controlled timing, in response to a receive timing signal, and generates a sample signal in response to the samples;

a timing circuit which supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver, the receive timing signal causing the receiver to sample the sequence of electromagnetic pulses such that time between transmission of pulses in the sequence by the transmitter and sampling by the receiver sweeps over a range of delays;

an envelope detection circuit for converting the sample signal to a unipolar signal to eliminate effects of antenna orientation mismatch;

a pulse detection circuit which in response to the sample signal and the timing circuit generates a pulse detect signal when the sample signal reaches a threshold during a sweep; and

a signal processor, coupled with the pulse detection circuit, to indicate a position of the object in response to the pulse detect signal.

6. The apparatus of claim 5 wherein the envelope detection circuit comprises an absolute value circuit followed by a low pass filter.

7. The apparatus of claim 5, wherein the receiver includes an automatic gain control circuit.

8. The apparatus of claim 5, wherein the transmit timing signal causes the transmitter to transmit the sequence of electromagnetic pulses at a pulse repetition rate, and wherein the receive timing signal sweeps over the range of delays in a sweep cycle such that pulses in the sequence are sampled at the pulse repetition rate and with different delays in the range of delays, such that the sample signal represents magnitude of a received pulse in the equivalent time.

9. The apparatus of claim 8, wherein the receiver includes automatic gain control circuitry to control magnitude of the sample signal in equivalent time.

10. An apparatus for detecting position of an object, comprising:

a transmitter, for placement on the object, which transmits a sequence of microwave pulses in response to a transmit timing signal with a pulse repetition rate greater than about 1 megaHertz,

a receiver having an antenna, a sample gate coupled to the antenna, which samples which samples a signal on the antenna at the pulse repetition rate and with controlled timing in response to a receive timing signal, an amplifier coupled to the sample gate including automatic gain control such that pulses in the sequence are sampled to generate an equivalent time sample signal, and an envelope detector for converting the sample signal to a unipolar signal to eliminate effects of antenna orientation mismatch;

a timing circuit which supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver, the receive timing signal causing the receiver to sample the sequence of electromagnetic pulses such that time between transmission of pulses in the sequence by the transmitter and sampling by the receiver sweeps over a range of delays varying by less than 20 nanoseconds in a sweep duration of greater than about 10 milliseconds; and

a signal processor, coupled with the receiver, to indicate a, position of the object within a range of less than 10 feet in response to the equivalent time sample signal.

11. The apparatus of claim 10 wherein the envelope detection circuit comprises an absolute value circuit followed by a low pass filter.

12. The apparatus of claim 11 wherein the low pass filter has a passband having a linear phase characteristic and a stop band having a null at the periodicity of the sample signal.