DOUBLE-SIDEBAND SUPPRESSED-CARRIER RADAR TO NULL NEAR-FIELD REFLECTIONS FROM A FIRST INTERFACE BETWEEN MEDIA LAYERS
First Claim
11. An earth-penetrating radar method, comprising:
- using a near measurement mode and a far measurement mode for predistortion and calibration of a transmitted waveform and a carrier suppression;
setting a radar first to near measurement mode to measure near-antenna signals reflected from a first interface by setting a phase of a modulation signal to θ
m to 0 (π
) during a calibration;
processing a near measurement mode, wherein a first sideband is tuned off and a magnitude and phase are a measurement of a second sideband alone;
repeating a measurement for an opposite sideband;
adjusting magnitudes of said sidebands to be equal in value and adjusting the phase θ
m to produce 0-degrees;
adjusting θ
c is adjusted to zero to compensate for a frequency response in the radar and antennas;
then switching to a far measurement mode that sets such that any first interface reflection is suppressedusing polarized antennas for any additional suppression; and
using a software-defined transceiver for phase-coherent detection of the depth of said second interface reflection.
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Abstract
A ground-penetrating radar comprises a software-definable transmitter for launching pairs of widely separated and coherent continuous waves. Each pair is separated by a constant or variable different amount double-sideband suppressed carrier modulation such as 10 MHz, 20 MHz, and 30 MHz Processing suppresses the larger first interface reflection and emphasizes the smaller second, third, etc. reflections. Processing determines the electrical parameter of the natural medium adjacent to the antenna.
The modulation process may be the variable or constant frequency difference between pairs of frequencies. If a variable frequency is used in modulation, pairs of tunable resonant microstrip patch antennas (resonant microstrip patch antenna) can be used in the antenna design. If a constant frequency difference is used in the software-defined transceiver, a wide-bandwidth antenna design is used featuring a swept or stepped-frequency continuous-wave (SFCW) radar design.
The received modulation signal has a phase range that starts at 0-degrees at the transmitter antenna, which is near the first interface surface. After coherent demodulation, the first reflection is suppressed. The pair of antennas may increase suppression. Then the modulation signal phase is changed by 90-degrees and the first interface signal is measured to determine the in situ electrical parameters of the natural medium.
Deep reflections at 90-degrees and 270-degrees create maximum reflection and will be illuminated with modulation signal peaks. Quadrature detection, mixing, and down-conversion result in 0-degree and 180-degree reflections effectively dropping out in demodulation.
45 Citations
16 Claims
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11. An earth-penetrating radar method, comprising:
-
using a near measurement mode and a far measurement mode for predistortion and calibration of a transmitted waveform and a carrier suppression; setting a radar first to near measurement mode to measure near-antenna signals reflected from a first interface by setting a phase of a modulation signal to θ
m to 0 (π
) during a calibration;processing a near measurement mode, wherein a first sideband is tuned off and a magnitude and phase are a measurement of a second sideband alone; repeating a measurement for an opposite sideband; adjusting magnitudes of said sidebands to be equal in value and adjusting the phase θ
m to produce 0-degrees;adjusting θ
c is adjusted to zero to compensate for a frequency response in the radar and antennas;then switching to a far measurement mode that sets such that any first interface reflection is suppressed using polarized antennas for any additional suppression; and using a software-defined transceiver for phase-coherent detection of the depth of said second interface reflection. - View Dependent Claims (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13)
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9. The radar of claim 7, further comprising:
a circuit to prevent spurious signals from conflict with the mixed-down intermediate frequency (intermediate frequency) amplifier passband signal, wherein, ω
o−
ω
1, ω
o+ω
2, ω
2 and ω
1, and heterodyne frequencies ω
3 and ω
4 are each outside the passband of any intermediate amplifier (ω
IF≠
ω
m, ω
1, ω
2, ω
3, and ω
4).
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10. The radar of claim 7, further comprising:
-
an intermediate amplitude band pass center frequency ω
IF=ω
4−
ω
2=ω
1−
ω
3, wherein, ω
2≠
ω
1 and ω
3≠
ω
4, the suppressed carrier frequency,and the heterodyne frequency is and a distance to any target continues in the phase terms ω
mτ and
ω
cmτ
.
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12. The earth-penetrating radar method of claim 11, further comprising:
dynamically predistorting each of a pair of first and second continuous waves'"'"' magnitude and phase to account for frequency response nonlinearities with a feedback-enabled predistorter when operating in a near measurement mode.
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13. The earth-penetrating radar method of claim 12, further comprising:
-
predistorting any received waveform phase by computing an inverse tangent of an intermediate-frequency signal in phase (I) and quadrature (Q) components and then dividing by ω
cm;wherein, θ
c measured and set to cause θ
c+ω
cmτ
to be zero so a first interface reflection will occur at τ
=0.
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13-1. The earth-penetrating radar method of claim 12, further comprising:
-
predistorting a modulation phase by first measuring a magnitude of an intermediate frequency signal as a predistorted waveform suppressed carrier frequency is incremented in any FMCW or SFCW radar operating frequency range; and solving simultaneous equations for cos(ω
mτ
) and a range to a target.
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14. An earth-penetrating radar, comprising:
-
a power amplifier and antenna for launching corrected versions of coherent pairs of said first and second continuous wave frequencies into a geologic heterogeneous media with different constituent electrical parameters for causing first, second, etc. interface reflected waves to be received; a receiver and antenna for collecting signals reflected from a first interface and other signals reflected or scattered from buried objects and interfaces of material with contrasting electrical parameters; a down-converter and coherent demodulator for coherent demodulating of an in-phase I=cos(θ
m+ω
mτ
1)cos(θ
c+ω
cmτ
1)+cos(θ
m+ω
cmτ
2)cos(θ
cm+ω
cτ
2)+ . . . , and Q=cos(θ
m+ω
mτ
1)sin(θ
c+ω
chτ
1)+cos(θ
m+ω
mτ
2)sin(θ
c+ω
cmτ
2)+ . . . , where ω
m is a processor-controllable phase shift (π
/2, 0, 3π
/2, 2π
), . . . , ω
m is the modulation frequency of a double-sideband suppressed carrier or phase-modulated signal, and θ
c is a carrier phase with a frequency of ω
cm;a processor for determining the magnitude of each reflection as M=|cos(θ
m+ω
mτ
)| for each pair of transmitting continuous waves, wherein τ
1 represents the echo delay time occurring for reflections from the surface near the antenna and τ
2 represents the echo delay time occurring for more distant reflections from buried objects and interfaces;a device for predistortion that results in a modulation signal phase θ
m being set to zero when π
1=0 in a far measurement mode calibration process, and a predistorted modulation signal phase is set to a near measurement mode and then measured in a far measurement mode to determine a distance (R) to a second interface by measuring ω
mτ
in the intermediate frequency. - View Dependent Claims (15, 16)
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Specification