# US 2013/0154873 A1 · Method and system for measuring a distance with narrowband radar > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154873 A1 - Document ID: US20130154873A1 - Status: Published application - Kind: A1 - Application number: 13/326,496 - Filed: 2011-12-15 - Published: 2013-06-20 - Earliest claimed: 2011-12-15 - Assignees: GM Global Technology Operations LLC - Inventors: Guy RAZ; Ron Rotstein - Web page: https://patentgrep.com/patent/US20130154873A1 ## CPC - G01S 13/08: Systems for measuring distance only (indirect measurement G01S13/46) - G01S 7/4004: {of parts of a radar system} - G01S 7/4052: {by simulation of echoes} - G01S 7/4091: {during normal radar operation} - G01S 13/931: of land vehicles - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract A system includes a radar antenna and a radar controller. The radar controller generates two narrowband radar signals, each narrowband radar signal having substantially constant frequency, the frequencies of the two narrowband radar signals differing from one another. The controller operates the radar antenna to transmit each of the generated narrowband radar signals as a transmitted signal, each transmitted signal being characterized by a transmitted power. The controller also measures a received power of received signals that are received by the radar antenna, each received signal including a portion of a corresponding one of the transmitted signals that was returned from an object or from a calibration surface at a known calibration range. A processor operating in accordance with programmed instructions calculates a range to the object on the basis of the transmitted and received powers. ## Claims ### Claim 1 A method comprising: transmitting a first transmitted narrowband radar signal having a substantially constant first frequency, the first transmitted narrowband radar signal being characterized by a first transmitted power; concurrently transmitting a second transmitted narrowband radar signal having a substantially constant second frequency, the second transmitted narrowband radar signal being characterized by a second transmitted power; measuring a first received power of a first received measurement signal that includes at least a portion of the first transmitted narrowband radar signal that was returned from an object, and a second received power of a second received measurement signal that includes at least a portion of the second transmitted narrowband radar signal that was returned from the object; calculating an atmospheric attenuation factor based on the transmitted and received powers; calculating a range of the object based on the calculated atmospheric attenuation factor and on an atmospheric attenuation coefficient factor. ### Claim 2 (depends on 1) The method of claim 1, wherein the atmospheric attenuation coefficient factor is calculated by measuring a first received calibration signal power of a first received calibration signal that includes at least a portion of the first transmitted narrowband radar signal that was returned from a calibration surface, and a second received calibration signal power of a second received calibration signal that includes at least a portion of the second transmitted narrowband radar signal that was returned from the calibration surface, and calculating the atmospheric attenuation coefficient factor based on the transmitted powers, on the measured received calibration signal powers, and on the known calibration range; ### Claim 3 (depends on 2) The method of claim 2, wherein measuring the first received calibration signal power or the second received calibration signal comprises averaging a plurality of measurements. ### Claim 4 (depends on 1) The method of claim 1, wherein transmitting the first narrowband radar signal or the second narrowband radar signal comprises transmitting a directional beam of radar radiation toward either the object or the calibration surface. ### Claim 5 (depends on 1) The method of claim 1, wherein the first frequency and the second frequency are selected such that a radar cross section (RCS) of the object or of the calibration surface is substantially identical for the first narrowband radar signal and the second narrowband radar signal. ### Claim 6 (depends on 5) The method of claim 5, wherein the first frequency is selected such that an atmospheric attenuation coefficient corresponding to the first frequency is greater than a predetermined upper threshold fraction of a peak attenuation for an atmospheric attenuation peak, and the second frequency is selected such that an atmospheric attenuation coefficient corresponding to the second frequency is less than a predetermined lower threshold fraction of the peak attenuation for the same atmospheric attenuation peak. ### Claim 7 (depends on 1) The method of claim 1, wherein calculating the atmospheric attenuation factor comprises calculating a logarithm of a quotient of a power reduction of the first received power relative to the first transmitted power, and of a power reduction of the second received power relative to the second transmitted power. ### Claim 8 (depends on 6) The method of claim 6, wherein calculating the range of the object comprises calculation a quotient of the calculated atmospheric attenuation factor and the calculated atmospheric attenuation coefficient factor. ### Claim 9 (depends on 1) The method of claim 1, wherein the calibration surface comprises a region of a roadway substantially at the calibration range. ### Claim 10 (depends on 1) The method of claim 1, comprising measuring a relative velocity of the object by comparing a shift in frequency between the received measurement signal and its corresponding transmitted narrowband radar signal. ### Claim 11 (depends on 1) The method of claim 1, comprising varying the first frequency or the second frequency. ### Claim 12 A system comprising: a radar antenna; a radar controller to: generate two narrowband radar signals, each narrowband radar signal having substantially constant frequency, the frequencies of the two narrowband radar signals differing from one another; to operate the radar antenna to transmit each of the generated narrowband radar signals as a transmitted signal, each transmitted signal being characterized by a transmitted power; and to measure a received power of received signals that are received by the radar antenna, each received signal including a portion of a corresponding one of the transmitted signals that was returned from an object or from a calibration surface at a known calibration range; and a processor operating in accordance with programmed instructions to calculate a range to the object on the basis of the transmitted and received powers. ### Claim 13 (depends on 12) The system of claim 12, wherein the radar antenna is directional so as to transmit the transmitted signal directionally toward, or to receive the received signal directionally from, the object or the calibration surface. ### Claim 14 (depends on 12) The system of claim 12, wherein the radar antenna comprises a separate transmission antenna to transmit the generated narrowband radar signal, and a receiving antenna to receive the received signal. ### Claim 15 (depends on 12) The system of claim 12, wherein the controller is configured to measure a shift in frequency between the received signal and its corresponding transmitted signal. ### Claim 16 (depends on 12) The system of claim 12, incorporated in a vehicle. ### Claim 17 (depends on 16) The system of claim 16, wherein the calibration surface comprises a section of a roadway at the calibration range. ### Claim 18 (depends on 12) The system of claim 12, wherein the frequencies of the two narrowband radar signals are selected such that an RCS of the object or of the calibration surface is substantially identical for both of the two narrowband radar signals. ### Claim 19 (depends on 18) The system of claim 18, wherein the frequency of a one signal of the of the two narrowband radar signals is selected such that an atmospheric attenuation coefficient corresponding to the frequency of the one signal is greater than a predetermined upper threshold fraction of a peak attenuation for an atmospheric attenuation peak, and the frequency of the other of the two narrowband radar signals is selected such that an atmospheric attenuation coefficient corresponding to the frequency of the other signal is less than a predetermined lower threshold fraction of the peak attenuation for the same atmospheric attenuation peak. ### Claim 20 (depends on 12) The system of claim 12, wherein the radar controller is configured to change the frequency of at least one of the two narrowband radar signals.