Signal Processing Of Microwave Interferometer Measurement System

Microwave interferometer is used to the measurement of electron density in the wake of hypervelocity projectiles. This is important to the development of aerospace and national defence.This paper briefly introduces the theory and design of the microwave interferometer. We achieve the signal processing part that is the output of the result. It plays a key role in this system. Compared with the conventional one, this system has a distinguished characteristic that the whole signal processing is finished on the computer with software. The software has two major parts: data acquisition and signal processing.We achieve the voltage data acquisition with the DAQ card PCI-9820 that made up with ADLINK. This card has 14 bits resolution, 60M/s sampling rate .The software of the card we design using graphical language LabVIEW and C++. Either of them can meet the system. Multiple ranges and multiple trigger modes choosing, calibration of card, data display, data saving and reading are all accomplished in software. We also talked about the difference between two methods.We achieve phase measurement using zero-crossing method. First, we calculate out the zero point in a simple numeral method, then we get the phase according to the fact that the symbol of phase changed is opposite in the positive-slope and the negative-slope of triangle wave. This method has the following characteristics: easy to calculate, simple to realize and high precision. We can get electron density with the calculated phase and some common model formula (such as sphere and cone) in the wake of hypervelocity projectiles. Finally, we can get a curve of electron density changing with the time or the position. This is the result required of system.This software of signal processing system has many advantages such as precisely, stability, using easily and so on.