Research On The Electromagnetic Properties Of Plasma Based Microwave Interferometer

When the aircraft flies in thin air, the air among the surface of flying object will be partially ionized when the flight speed reaches a certain value, which forms a plasma sheath and plasma wake. Owing to the presence of the plasma layer, the communications between the ground station and aircraft will be affected, and communication disruption may be caused when it becomes heavier. Meanwhile, aircraft can also be screened by diagnosticing plasma wake of aircraft. Much work has been done among foreign scholars in order to study the electromagnetic properties of these aircraft attached to the surface of the plasma layer. However, in our country, the research of plasma started relatively late. So, aiming at some urgent remained problems in the domestic research of electromagnetic characteristics of plasma, this paper has focused on the research on the following content:Firstly, the measurement technique of plasma based on the reflection method of microwave is studied. Under the condition of the oblique incident flat wave, with the method of geometrical optics, the reflected wave and reflection coefficient expressions under the plasma boundary conditions is deduced in detail. According to the reflection coefficient expressions, the relationship between the reflection coefficient and electron density is simulated and analyzed with different electromagnetic frequencies. The electron density range of different frequencies available is obtained, which lays the theoretical basis for the design of reflectometer.Secondly, the measurement technique of microwave transmission is discussed. First, the basic principle of the transmission of diagnostic techniques is analyzed with the relationship between the attenuation constant, phase constant and collision frequency, electron density in plasma. The available measurement range of electron density of plasma is obtained with the method of transmission wave by simulation and analysis.Then, by reflection, transmission interference method and interference method analysis, the main advantage of reflection method is available for a variety of aerospace equipment. In the actual atmosphere, the electromagnetic properties of surface plasma wake among the device can be measured; the drawback is that there is a multi-value problem, which the subsequent data processing is more complex. The main advantage of the transmission method is that calculation is more accurate and multi-value problem does not exist; the disadvantage is not available for the measurements of the airborne wake electron density. Advantages of the method of interference is simple hardware structure and low cost; main disadvantage is that the error is relatively large when the measured electron density is less than1110.Finally, according to the principle of modulation and demodulation, three types of channel model of modulation and demodulation in the plasma environment are built. Based on the model, 2ASK, 4FSK, QPSK demodulator BER expression is deduced separately. Through simulation and analysis, 2ASK, 2FSK, QPSK BER is obtained with different plasma electron density. The best way of communication(2FSK non-coherent demodulation) in the plasma environment is determined in comparison with the expression of BER and the results of simulation, which lays the basis for subsequent research.