Earth-penetrating radar with inherent near-field rejection

• US 7,548,181 B1
• Filed: 06/29/2006
• Issued: 06/16/2009
• Est. Priority Date: 06/29/2006
• Status: Expired due to Fees

• Current Assignee: Stolar Incorporated
• Original Assignee: Stolar Incorporated
• Inventors: Bausov, Igor
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): GALT, CASSI J
• Application Number:
  US11/478,757
• Publication Number:
  US 20090167589A1
• Time in Patent Office: 1,083 Days
• Field of Search: 342/22, 342/90, 342/129, 342/159, 342/175, 342/179, 342/195
• US Class Current: 342/22
• CPC Class Codes: G01S 13/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 13/885 for ground probing prospecting or detecting using electromagnetic waves G01V3/12
• CPC Class Codes: G01S 13/89 for mapping or imaging
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

A ground-penetrating radar comprises a transmitter for launching pairs of widely separated and coherent continuous waves. Each pair is separated by a different amount, such as 10 MHz, 20 MHz, and 30 MHz. These are equivalent to modulation that have a phase range that starts at 0-degrees at the transmitter antenna which is near the ground surface. Deep reflectors at 90-degrees and 270-degrees 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.

Claims

1. An earth penetrating radar, comprising:

a software-defined transceiver (SDT) programmed as a geologic-media penetrating radar with multi-channel direct digital synthesizer (DDS) for synthesizing many coherent first and second frequency continuous waves ω

_H1,ω

_L1, ω

_H2,ω

_L2, etc., as individual pairs and each member of a separated from the other member in the pair in frequency by n-MHz, m-MHz, etc.;

a feedback enabled pre-distorter for dynamically predistorting each of said pairs of first and second frequency continuous waves to account for non-linearities in following stages and antennas;

a power amplifier and antenna for launching corrected versions of said coherent pairs of said first and second frequency continuous waves into the earth and a first interface;

a receiver and antenna for collecting a relatively strong signal reflected from said first interface and substantially weaker signals reflected from deeper buried objects and interfaces of material with contrasting dielectric constants;

a down-converter and demodulator disposed in the SDT and for demodulating in-phase, I=sin(ω

_mτ

₁)sin(ω

_cτ

₁)+sin(ω

_mτ

₂)sin(ω

_cτ

₂), and quadrature-phase Q=sin(ω

_mτ

₁)cos(ω

_cτ

₁)+sin(ω

_mτ

₂)cos(ω

_cτ

₂) signals for each pair of transmitted first and second frequency continuous waves, wherein ω

_m represents a modulation frequency, ω

_c represents a virtual carrier frequency, τ

₁ represents the echo delay time occurring for reflections from said first interface near the antenna, and τ

₂ represents the echo delay time occurring for more distant reflections from buried objects and interfaces; and

a computer and display for showing a user the depth of said buried objects and interfaces by simultaneously solving for all echo delay times τ

₂ for each differently separated pair of first and second frequencies;

wherein, echo delay time τ

₁ is near zero and near reflection surface terms including it are manipulated by a configuration of constituent parts to zero out in the step of computing and displaying.

2. The radar of claim 1, further comprising:

an up and down conversion quadrature mixer for translating said first and second frequency continuous waves.

3. A radar, comprising:

means for synthesizing coherent continuous waves at first and second frequencies as pairs separated in frequency by a constant or variable n-MHz;

means for predistorting the magnitudes and phases of each of said continuous waves at first and second frequencies to account for non-linearities in following stages and antennas;

means for launching corrected versions of said coherent pairs of said continuous waves at first and second frequencies from a power amplifier and antenna into the earth through a first interface to deeper objects and interfaces of materials with contrasting dielectric constants;

means for receiving relatively weaker signals reflected from buried said deeper objects and interfaces of material with contrasting dielectric constants in the presence of relatively stronger signals reflected from said first interface;

means for demodulating any signals received to produce an in-phase I=sin(ω

_mτ

₁)sin(ω

_cτ

₁)+sin(ω

_mτ

₂)sin(ω

_cτ

₂), and a quadrature phase, Q=sin(ω

_mτ

₁)cos(ω

_cτ

₁)+sin(ω

_mτ

₂)cos(ω

_cτ

₂), wherein ω

_m represents a modulation frequency, ω

_c represents a virtual carrier frequency, τ

₁ represents the echo delay time that is near zero and occurring for reflections from said first interface near the antenna, and τ

₂ represents the echo delay time occurring for more distant reflections from buried objects and interfaces;

means for suppressing said relatively stronger signals reflected from said first interface; and

means for computing and displaying the depth of said buried objects and interfaces by solving the echo delay times τ

₂.

4. The radar of claim 3, further comprising:

means for up-conversion to allow the means for synthesizing to operate at lower frequencies than those radiated by the antenna.

5. A method of electronic imaging into the earth, comprising:

transmitting double-sideband, suppressed carrier signals, ω

_c, that comprise pairs of coherent continuous waves separated by different amounts by a modulation frequency, ω

_m;

coherently demodulating reflections of said double-sideband, suppressed carrier signals received from a plurality of interfaces of material near a transmitting and receiving antenna in which such materials have contrasting dielectric constants;

suppressing a strong near field echo with a delay time, τ

₁, in said reflections that approaches zero, wherein, quadrature detection, mixing, and down-conversion are combined so 0-degree and 180-degree reflections effectively drop out in demodulation;

preferring weaker near field echoes with delay times, τ

₂, in said reflections that are substantially removed from zero; and

producing radar images of objects outlined by reflections from said plurality of interfaces of material with delay times, τ

₂.