Reseach On Frequency Sweep Microwave Interfero Meter System

The high-speed flying object will produce a high-temperature unbalanced plasma trail when it enters the atmosphere again. The trail will bring a lot of problems, for example, they can interfere with wireless communications between the object and the ground station. They will also affect guided-flight of the object. Even in several cases it can cause “black” problem, which the signal was seriously interrupted. Studying the characteristics of ultra-high speed fight plasma wake can improve the recognition of ultra-high speed flight targets and provide support for ultra-high speed flight penetration. Ballistic target device is used for simulating flight re-entry, and the sweep microwave interferometer system can be used for measuring the electron density of plasma with the ballistic target wake. This paper studies the frequency sweep microwave interferometer technology and the structure of the system, by getting a plasma caused by the phase information to get the electron density of plasma.Firstly, the basic characteristic of the non-magnetized plasma which propagates in electromagnetic wave is analyzed. The variation of phase and amplitude which change along with frequency is obtained, which lays the basis for the design of the system.Secondly, this paper adopts frequency sweep microwave interferometer to measure plasma electron density. The principle of frequency sweep microwave interferometer is analyzed in detail, and the bandwidth and time delay of sweep frequency sweep microwave interferometer is deduced theoretically(caused by the path difference of the referred branch and the test branch), from which we get the algorithm of phase. The method of zero-phase-detecting is used for extracting phase.Many important parameters such as the frequency of signal source, the bandwidth of medium frequency and the type of antenna are analyzed in this paper. Considering the requirements of amplitude of the system, reflection branch is added to the system, which can measure both phase and amplitude.Finally, some of the key parts of the system, mainly the mixer and detector, are calibrated and analyzed. System debugging is mainly divided into dynamic time response test and the error precision of phase of the quiescent state, the phase and amplitude of the quiescent.This paper completed the research of frequency sweep microwave interferometer, together with debugging and testing of microwave interferometer. In this paper, the error of measurement is analyzed and the feasibility of the system is verified.