Radar altimeter nearest return tracking
AssigneeRockwell International Corporation
InventorThomas A. Ubriaco
Life of this patent
Estimating the term…
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.
Claims10
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.
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.
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.
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.
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.
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.
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.
Dependencies are inferred from the claim text.