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.