US4568938A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Radar altimeter nearest return tracking
Assignee: Boeing North American Inc
•
Filing: 1981-12-14
•
Granted: 1986-02-04
•
Expires: 2001-12-14
Abstract
Abstract An FMCW distance measuring device is disclosed which enables increased accuracy by detecting the nearest return. A portion of the transmitted wave in an FMCW altimeter is mixed with the received signal indicating distance to ground to produce a beat frequency between the transmitted wave and the received wave. The beat frequency is a spectrum of frequencies, the lowest of which indicates the nearest return in a target area. The beat frequency spectrum is coupled for sampling by an analog-to-digital converter and then coupled to an apparatus for performing a Fast Fourier Transform to isolate the nearest return. In an altimeter, the Fast Fourier Transform of the return spectrum enables the FMCW radar to have an accuracy approaching that of pulsed radars without the associated disadvantages.
Inventors
- 👤 Thomas A. Ubriaco
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 02:38
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/02; G01S13/06; G01S13/08; G01S13/32; G01S13/34; G01S13/341; G01S13/88; G01S13/882
Claims Analysis
Total Claims: 17
Claim 1
Independent Claim
129 words
A distance measuring apparatus comprising; means for providing a linear modulating signal; means responsive to said linear modulating signal for generating a linearly variable frequency output signal; means for transmitting said variable frequency signal to a target; means for receiving a return spectrum of said variable frequency signal reflected from said target; means for mixing a portion of said variable frequency signal with said received reflected signal to produce a beat frequency spectrum; analog-to-digital converter means for converting said beat frequency spectrum to a digital output; Fast Fourier Transform means for transforming said digital output to individual frequency outputs each representative of a distance to the target; and means responsive to said Fast Fourier Transform means for displaying each of said frequency outputs as a distance to the target.
Claim 2
Dependent Claim
129 words
A distance measuring apparatus comprising; means for providing a linear modulating signal; means responsive to said linear modulating signal for generating a linearly variable frequency output signal; means for transmitting said variable frequency signal to a target; means for receiving a return spectrum of said variable frequency signal reflected from said target; means for mixing a portion of said variable frequency signal with said received reflected signal to produce a beat frequency spectrum; analog-to-digital converter means for converting said beat frequency spectrum to a digital output; Fast Fourier Transform means for transforming said digital output to individual frequency outputs each representative of a distance to the target; and means responsive to said Fast Fourier Transform means for displaying each of said frequency outputs as a distance to the target.
Claim 3
Dependent Claim
103 words
In an FMCW radar distance mesuring system including a modulator, a frequency generator for generating a variable frequency output in response to said modulator, a transmitter for transmitting said variable frequency to a target, a receiver receiving a reflected signal from said target, and a means coupled to mix transmitted and received energy to produce an analog beat frequency spectrum output, the improvement comprising: means for converting said analog beat frequency output to a digital output representative of individual frequencies of said beat frequency spectrum; and Fast Fourier Transform means for converting said digital output to individual frequency readings indicative of target distance.
Claim 4
Dependent Claim
103 words
In an FMCW radar distance mesuring system including a modulator, a frequency generator for generating a variable frequency output in response to said modulator, a transmitter for transmitting said variable frequency to a target, a receiver receiving a reflected signal from said target, and a means coupled to mix transmitted and received energy to produce an analog beat frequency spectrum output, the improvement comprising: means for converting said analog beat frequency output to a digital output representative of individual frequencies of said beat frequency spectrum; and Fast Fourier Transform means for converting said digital output to individual frequency readings indicative of target distance.
Claim 5
Dependent Claim
29 words
The apparatus of claim 2 further including means responsive to said Fast Fourier Transform means for displaying the lowest frequency in said detected spectrum as the nearest target distance.
Claim 6
Dependent Claim
89 words
In an FMCW radar distance measuring system having a means for transmitting a variable frequency signal to a target and means for receiving and outputting a frequency spectrum relating to the range of the target, the improvement comprising: Fast Fourier Transform means coupled to detect said frequency spectrum and provide an output representing at least the lowest frequency in said spectrum; and means coupled to the output representing at least the lowest frequency in said spectrum for displaying the frequency output as a measure of distance to the target.
Claim 7
Dependent Claim
89 words
In an FMCW radar distance measuring system having a means for transmitting a variable frequency signal to a target and means for receiving and outputting a frequency spectrum relating to the range of the target, the improvement comprising: Fast Fourier Transform means coupled to detect said frequency spectrum and provide an output representing at least the lowest frequency in said spectrum; and means coupled to the output representing at least the lowest frequency in said spectrum for displaying the frequency output as a measure of distance to the target.
Claim 8
Dependent Claim
104 words
A distance measuring apparatus comprising: means for generating a variable frequency signal; means for transmitting said variable frequency signal to a target; means for receiving a return spectrum of said variable frequency signal reflected from said target; and means for detecting individual frequencies in said return spectrum and providing an output representing target distance for at least the lowest of said detected frequencies, said means for detecting comprising, analog-to-digital converting means for converting the reflected variable frequency signal to a digital output, and a Fast Fourier Transform means for converting the digital output to individual frequency outputs each representative of distance to the target.
Claim 9
Dependent Claim
104 words
A distance measuring apparatus comprising: means for generating a variable frequency signal; means for transmitting said variable frequency signal to a target; means for receiving a return spectrum of said variable frequency signal reflected from said target; and means for detecting individual frequencies in said return spectrum and providing an output representing target distance for at least the lowest of said detected frequencies, said means for detecting comprising, analog-to-digital converting means for converting the reflected variable frequency signal to a digital output, and a Fast Fourier Transform means for converting the digital output to individual frequency outputs each representative of distance to the target.
Claim 10
Dependent Claim
23 words
The apparatus of claim 5 further including means responsive to said detecting means for displaying said detected frequency outputs as separate target distances.
Claim 11
Dependent Claim
130 words
A distance measuring apparatus comprising: means for providing a modulating signal; means responsive to said modulating signal for generating a variable frequency signal; means for transmitting said variable frequency signal to a target; means for receiving a return spectrum of said variable frequency signal reflected from said target; means for mixing a portion of said variable frequency signal with said received reflected signal to produce a beat frequency spectrum, said means for modulating being operated to produce a constant beat frequency; means for detecting individual beat frequencies in said spectrum and providing outputs representing target distance for each detected beat frequency; and means responsive to the individual frequency outputs for controlling said means for modulating so that the lowest frequency return of said return spectrum produces said constant beat frequency.
Claim 12
Dependent Claim
130 words
A distance measuring apparatus comprising: means for providing a modulating signal; means responsive to said modulating signal for generating a variable frequency signal; means for transmitting said variable frequency signal to a target; means for receiving a return spectrum of said variable frequency signal reflected from said target; means for mixing a portion of said variable frequency signal with said received reflected signal to produce a beat frequency spectrum, said means for modulating being operated to produce a constant beat frequency; means for detecting individual beat frequencies in said spectrum and providing outputs representing target distance for each detected beat frequency; and means responsive to the individual frequency outputs for controlling said means for modulating so that the lowest frequency return of said return spectrum produces said constant beat frequency.
Claim 13
Dependent Claim
25 words
The apparatus of claim 7 further including a means responsive to said detecting means for displaying said detected beat frequency outputs as separate target distances.
Claim 14
Dependent Claim
76 words
A process for providing nearest return tracking in an FMCW radar comprising: transmitting an FMCW radar signal to a target; receiving a reflected return spectrum of said FMCW signal from said target; transforming said return spectrum from the time domain to the frequency domain by a Fast Fourier Transform; providing an output representing at least the lowest frequency of the transformed return spectrum; and displaying the frequency output as a measure of distance to the target.
Claim 15
Dependent Claim
76 words
A process for providing nearest return tracking in an FMCW radar comprising: transmitting an FMCW radar signal to a target; receiving a reflected return spectrum of said FMCW signal from said target; transforming said return spectrum from the time domain to the frequency domain by a Fast Fourier Transform; providing an output representing at least the lowest frequency of the transformed return spectrum; and displaying the frequency output as a measure of distance to the target.
Claim 16
Dependent Claim
103 words
A process for providing nearest return tracking in an FMCW radar comprising: transmitting an FMCW radar signal to a target; receiving a reflected return spectrum of said FMCW signal from said target; mixing a portion of the transmitted and received signal to create a beat frequency; transforming said return spectrum from the time domain to the frequency domain by a Fast Fourier Transform; providing an output representing at least the lowest frequency of the transformed return spectrum; and controlling the transmitted signal to produce a preselected constant beat frequency when said transmitted signal is mixed with the lowest frequency of the return spectrum.
Claim 17
Dependent Claim
103 words
A process for providing nearest return tracking in an FMCW radar comprising: transmitting an FMCW radar signal to a target; receiving a reflected return spectrum of said FMCW signal from said target; mixing a portion of the transmitted and received signal to create a beat frequency; transforming said return spectrum from the time domain to the frequency domain by a Fast Fourier Transform; providing an output representing at least the lowest frequency of the transformed return spectrum; and controlling the transmitted signal to produce a preselected constant beat frequency when said transmitted signal is mixed with the lowest frequency of the return spectrum.
References Cited (Backward Citations)
US3603990A
Cited
US3577143A
Cited
US3819920A
Cited
US4107679A
Cited
US4185285A
Cited
US4310903A
Cited
US4268828A
Cited
US4271412A
Cited
US4389649A
Cited
US4435709A
Cited
US4509049A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-02-03 | 1989-08-05 | 1990-02-04 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-02-03 | 1993-08-05 | 1994-02-04 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-02-03 | 1997-08-05 | 1998-02-04 | $7700.00 | Window Closed / Lapsed |