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.