| When a high speed spacecraft flies in reentry aerosphere stage, a phenomenon of electromagnetic attenuation increasement rapidly is able to occur. The reentry plasma is generated by the interaction between spacecraft and aerosphere. The plasma is a main cause of electromagnetic attenuation rapid augment so much as the communication blackout occurment. In this paper, the electromagnetic wave attenuation caused by plasma and the mitigation technique are studied through different method such as theoretical analysis, simulated calculation, and experimental measurement.Plasma in reentry aerosphere stage is a kind of electric liquid with high electron density, collision frequency and dispersive characteristic. The electromagnetic attenuation caused by plasma is consisted with the electromagnetic wave absorption and reflection of plasma, and the gain reduced by mismatch of antenna impedance. To describe the macrography characteristic of plasma, the Druce dispersion model is able to employ to analyze the interaction of electromagnetic wave and plasma as much as antenna and plasma. To research the electromagnetic wave attenuation of plasma, the theory of vertical incidence and oblique incidence in homogeneous plasma, and vertical incidence in nonhomogeneous is analyzed, and power absorption coefficient and power return loss of electromagnetic wave is simulated. The reentry plasma can change the initial antenna characteristic. To research the characteristic of antenna covered with plasma, a dipole antenna in plasma is researched. The theory of impedance and radiation characteristic is analyzed, and the input impedance, return loss and radiation pattern of the antenna is simulated. A horn antennacovered with plasma is proposed to analyze the antenna on spacecraft, and the return loss, electric field intensity and radiation pattern of the antenna is simulated.To verify the results of theory and simulation analysis, a experiment scheme is proposed to measure the electromagnetic wave attenuation of plasma. The experiment scheme includes a plasma flat slab consist of several plasma tubes by low voltage gas discharge. The plasma flat slab can simulate the reentry plasma characteristic of the spacecraft. After determine the average electron density of the plasma flat slab, the plasma flat slab is put on the transmitting antenna,and the attenuation and the antenna characteristic of electromagnetic wave in plasma are measured by transmitting and receiving horn antenna.It is important for the communication protection of high speed spacecraft to mitigate the electromagnetic wave attenuation caused by the plasma. Based on the liquid property of plasma, a configurationis proposed to change the characteristic of the reentry plasma, and the realignment model of plasma electron density is analyzed. When the total number of electron is fixed, the electron density of plasma is arranged normal to the polarization. To analyze the mitigation of electromagnetic wave attenuation based on microwave network theory, ahe model consisted with transmitting antenna and receiving antenna is proposed. The impedance and radiation characteristic is researched. The measurement results show the electromagnetic wave attenuation is mitigated, and the gain is increased. In this model, the transmitting antenna is covered with plasma. The parameter of the plasma electron density model is optimized, and the impedance characteristic and radiation characteristic in every frequency band is simulated and analyzed. The results show the proposed plasma model can reduce the absorption and reflection of electromagnetic wave, reduce the return loss of antenna, and increase the gain of antenna. The results in experiment show the proposed method can mitigate the electromagnetic wave attenuation, and improve the antenna characteristic.For some high speed spacecrafts with high electron density plasma jet, a method is proposed to form a plasma antenna by plasma jet with high electron density. Based on the similar metal characteristic of plasma and metal antenna theory, the impedance characteristic and radiation characteristic of plasma monopole antenna is analyzed. The plasma antenna used on the spacecraft can be formed with appropriate feeding and configuration design. To analyze the antenna characteristic, the columnar plasma antenna and conical plasma antenna fed by coaxial line are simulated and analyzed. To adapt the reentry environment, a columnar plasma antenna with ground covered by plasma is researched. To adapt the application of reentry spacecraft, a columnar plasma antenna model fed by metal ring is proposed, and a dielectric ring is used between the feeding metal ring and columnar plasma to avoid the high temperature ablation. The columnar plasma antenna fed by metal ring surround by plasma is researched. A columnar plasma antenna fed by metal ring is designed and measured. The experiment results show the plasma can radiate the electromagnetic wave.To adapt the ues of wideband communication system, some wideband plasma antennas are proposed, such as circular plasma monopole antenna and elliptic plasma monopole antenna based on circular monopole theory. The impedance characteristic and radiation characteristic of these antennae are simulated and analyzed. The results show that the band width of the novel plasma antenna is extended markedly.The electromagnetic wave attenuation of high speed reentry in aerosphere stage is analyzed in detail. Based on the liquid property of plasma and the similar metal characteristic of plasma, two methods of electromagnetic wave attenuation mitigation are proposed. The model of electromagnetic wave attenuation mitigation is designed and analyzed by theory and simulation, and the experiment is proposed and researched. The simulation and experiment results are the consultation for flight experiments. |
PDF Full Text Request