Radar level meter antenna by narrow microwave pulse, the pulse propagation in space at the speed of light, meet the measured medium surface, the part of the energy to be reflected back, by the same antenna. Emission pulses and the time interval of the received pulse and the antenna to the measured medium surface is proportional to the distance. Due to the electromagnetic wave propagation and very high speed, pulse and receiving pulse time interval is very small (nanosecond) it is difficult to confirm, 90X series of 26G radar level meter adopts a special demodulation technology, can accurately identify the transmitted pulse and pulse interval, thus further calculate the antenna to the measured medium surface distance.