【作者】 赵建森；

【导师】 张芝涛；

【作者基本信息】 大连海事大学 ， 轮机工程， 2013， 博士

【摘要】 等离子体天线是解决军舰在隐身作战中航行安全问题的有效途径,但天线研究与工程实现差距很大,尤其是带宽特性和电磁兼容性问题至今尚未得到实质性的解决。为展宽等离子体天线带宽和实现天线的电磁兼容性,本文建立了电磁波与等离子体相互作用、等离子体天线频带特性研究实验系统和等离子体及其激励.源电磁干扰实验系统,研究了等离子体天线的构成模式、等离子体对电磁波的传播特性、等离子体天线带宽特性和天线电磁兼容性。结合相关理论进行分析,得出如下结果：1.等离子体电子密度决定了电磁波在等离子体中的传播特性。电子密度越大,等离子体辐射电磁波的能力增强；在甚高频(VHF)频段,当入射信号频率增大时,会相应地存在一个最低电子密度使得等离子体可以有效地辐射电磁波信号,且最低电子密度随信号频率的增大而增大；等离子体在宽频带范围内对电磁波有较强吸收作用,尤其是当等离子体频率与电磁波频率相近时,会产生共振吸收。2.高频交流激励模式的激励通道和信号通道之间的强烈耦合使天线通信频带受限。在5-20kHz低频交流激励下,柱形等离子体天线具有较宽的阻抗和增益带宽,在100-250MHz范围内的方向图也相近。电容耦合模式是等离子体天线有效馈电模式,耦合电容适当增大可增加天线带宽。随等离子体电子密度增加天线带宽特性变好,但如果密度过大会加强等离子体对电磁波的反射,使带宽受限。适当增加线天线直径,会增加天线带宽,但直径过大,放电空间变大导致电子密度下降。3.直流与50Hz交流等离子体噪声源多,产生等离子体电子密度较小,稳定性较差,噪声电平较高。5-20kHz交流与40.68MHz交流等离子体噪声源相对较少,电子密度较高,噪声电平相对较低。当电磁波频率接近等离子体频率时,等离子体产生的场与电磁波信号耦合产生调制信号。适当增大电子密度可增加天线信噪比,但电子温度的增长会导致天线热噪声过大,需要折中考虑。针对高频交流等离子体激励源过强的辐射问题,可通过接地、滤波及屏蔽等方法大幅度降低电磁干扰,减小天线噪声。4.通过优化,研制了两台等离子体天线原理性样机—5-20kHz及40.68MHz交流等离子体线天线。5-20kHz交流等离子体天线在50-250MHz的增益与相同形状配置的金属天线相近,噪声电平也相差不大。40.68MHz交流等离子体天线由于滤波器的介入,工作频带稍窄。当入射信号频率较低时,等离子体天线的噪声很小。利用光-电时差法可较为准确地测量等离子体天线开启时间,经多次测试,两台等离子体天线的开启时间非常短,均为几十微秒量级。本文得出了在不大幅度损失增益的前提下拓宽等离子体天线工作带宽的方法及降低天线激励源电磁干扰及天线本身噪声的有效途径,在构建宽频带天线、实现电磁兼容性及天线应用于军舰安全等方面有一定的参考价值。更多还原

【Abstract】 Plasma antenna is an effective way to solve the warship-navigation-safety problem in the stealth combat, however, there is a big gap from antenna research to application in engineering, especially that the characteristics like bandwidth and electromagnetic compatibility (EMC) have not been solved actually. To broaden the bandwidth and fulfish the EMC, experimental systems for interaction between EM waves and plasma, bandwidth of plasma antenna, electromagnetic interference (EMI) of plasma and its power supply were established to investigate the construction models, propagation characteristics of EM waves in plasma, band-width properties and EMC. Combining theories, the results show that:1. Plasma electron density determines the propagation characteristics of EM waves in plasma, the larger the electron density, the stronger the radiation of plasma to EM waves. In the very high frequency (VHF) band, plasma can effecticely transmit the EM waves only when the plasma density is above the lowest electron density. The higher the radio frequency, the higher the lowest electron density for plasma to transmit EM waves. Besides, plasma can absorb the incident EM waves, especially when the frequency of EM waves equals to that of plasma, the resonance absorption occurs.2. In the system of high frequency (HF) ac plasma antenna the coupling between signal and excition channels is very strong, which restricts the communition bandwidth, and the radiation patterns between100to250MHz are similar.5-20kHz ac excition model shows good impedance and gain bandwidth. The bandwidth can be enhanced using capacitive coupling model. With the increase of electron density, the bandwidth is broadened. But too high electron density leads to higher reflection. Wire plasma antenna diameter increases to a certain extent cause the wider bandwidth of the antenna, however, too big the diameter is, too large discharge space causing lower electron density.3. There are too many noise sources in dc and50Hz ac plasma antenna, the plasma electron density excited by dc or ac power supply is very small and not stable, which cause large antenna noise. While there are relatively less noise sources in5-20kHz ac and40.68MHz ac plasma antennas, the electron density and temperature change small with time and the noise level is relatively low. When the EM wave’s frequency closes to the one of plasma, the plasma field will couple with the signals to produce the modulating signals. Suitable increasing the electron density can reduce the antenna noise, but the increase of electron temperature causes excessive thermal noise, which should be considered in a half way. With regard to the too strong radiation generated by RF power supply, the EMI can be largely reduced by means of grounding, shielding and filtering.4. Two antenna models-5-20kHz ac and40.68MHz ac plasma antennas are established through optimization, the gains of5-20kHz ac plasma antenna from50-250MHz are close to metal antenna with the same construction and size. The bandwidth of40.68MHz plasma antenna is relatively narrow for the imposed filter. And with the signal frequency higher, the noise is a little lower than that of5-20kHz ac plasma antenna. The switch-on time of plasma antenna can be rapidly and accurately measured by means of light-electricity time difference method. The switch-on times of the two plasma antennas are very short, about dozens of microsecond.The methods of broaden bandwidth of plasma antenna without a significant loss of gain and of reducing antenna noise are obtained in this article. It is of valuable reference in constructing broad-band antenna, fulfilling EMC and application in ship safety.更多还原