A field disturbance sensing system has an antenna, an oscillator producing a high-frequency signal, a first detector circuit, a second detector circuit, a combining network configured to couple the high-frequency signal to the antenna, and to couple the high-frequency signal and a reflected high-frequency signal to the first detector and to the second detector. An algebraic combining network sums a first detected signal having first detected high-frequency signal and a first detected reflected signal from the first detector circuit and a second detected signal having second detected high-frequency signal and a second detected reflected signal from the second detector circuit to produce a detected output signal. The first detected reflected signal is added to the second detected reflected signal and the first detected high-frequency signal is subtracted from the second detected high-frequency signal. A controller configured to convert the detected output signal to a speed between the antenna and a target.