Microwave Resonant Cavity Discharge Breakdown Characterization and Emission Spectral Analysis
Recently,there has been a significant increase in the power density of microwave components in spacecraft communication systems due to their development towards high power and miniaturization.This has raised the risk of radio frequency breakdown,which poses a challenge to the safe functioning of these systems.This paper conducts an experimental study on the discharge breakdown of microwave components in order to address the issue of detection during the discharge process.This study uses a specially designed microwave resonant cavity with air,nitrogen and oxygen as background gases.Using the global detection by signal nulling and local means by emission spectroscopy,the changes in breakdown characteristics from multipactor to low-pressure gas discharges are investigated.The results show that the breakdown thresholds of the discharges show a tendency to decrease and then increase in the pressure range of 100～1 000 Pa,which is in line with the typical variation of"Paschen's law".When the background gases are nitrogen and air,the breakdown threshold reaches the lowest level at 400～500 Pa,with the lowest values of 31.8 dBm and 30.9 dBm,respectively.And the lowest value of 31.3 dBm at 600～700 Pa in the oxygen environment.Under the same dimensions and working conditions,the breakdown level depends on the input power and the difficulty of ionizing the gap gases.In the left half-branch of the curve,the breakdown power decreases continuously,due to the lower pressure,the number of gas molecules in the interstitial space is less,the chance of collision during the movement of the electrons is smaller,the mechanism to maintain the discharge is mainly caused by the multiplication of secondary electrons after scattering of the electrons with the inner wall material,which belongs to the category of multipactor,and it is mainly determined by the surface properties of the inner wall and the input power together.While in the right half-branch of the curve,with the gradual increase in pressure,the level of breakdown depends on the ionization difficulty and the input power of the interstitial gas.The number of gas molecules in the gap increases,and the chances of collision ionization reactions between electrons and particles increase.The number of secondary electrons gradually decreases,and the weight of the total charged particles decreases.The number of ions of different species increases instead,and the weight becomes higher,and the mechanism of triggering the breakdown gradually changes to the low-pressure discharge due to the proliferation of the number of plasmas by the multiplication of secondary electrons in the initial stage.Comparison of the emission spectra reveals that under the background gases of nitrogen and air,the emission spectra generated when the discharge occurs are relatively similar,with the more pronounced intensity of the emission spectral lines appearing in the second positive band system of nitrogen at 337.1 nm for the N2 jump,and also at 314 nm for the OH intensity due to the small amount of water vapor contained in the background environment.When the background gas is oxygen,the overall emission spectrum and the intensity are low,and only the O jump lines at 704.2 nm and 777.5 nm can be observed,while no obvious OH lines are detected.Besides,the gas pressure can affect the concentration size of each particle in the plasma by changing the particle generation and consumption paths.Since OH comes from external water pollution,the oxygen is additionally treated by water-bath and tested again.It is found that the difference between the two test results are relatively small,indicating that the presence of water molecules has less influence on the ionization process of oxygen within a certain pressure range.
Radio frequency breakdownEmission spectraGas dischargeSpace microwave componentsPlasma
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