| Plasma antennas have gradually received worldwide attention,with the advantages of reconfiguration,low radar cross section(RCS),and low thermal noise.In recent years,the compact operation of communication system onboard ships has drawn much attention.However,traditional metric wave antennas suffer from large sizes and volumes,complex feeding network,and limited operating bandwidth.Moreover,it also requires the antennas to be with low radar cross section(RCS)property,which makes it difficult be detected by radar.We use the novel plasma antenna to replace the traditional metal antenna.It has increased the operating bandwidth by virtue of the reconfigurable property of plasma,and reduced RCS value by the interaction between plasma and microwave,which effectively overcome the fundamental problems.This paper focuses on some key technical problems of miniaturized antennas,reconfigurable antennas,plamsa energizing,and measurements work of the metric wave antenna.The specific topics of this thesis are as follows:(1)Basic theory of plasma antenna: For the application of radiation,the plasma frequency,collision frequency and the relationship between the plasma frequency and the frequency of electromagnetic wave are crucial parameters.This paper introduces the physical properties of plasma and focuses on the radiation of a plasma antenna,which based on the fundamental theory of plasma physics.We apply the plasma fluid model,momentum equation,and Maxwell equation to research on the coupling effect between ions and electrons.The plasma frequency and collison frequency are important parameters in Drude scattering model.CST software conducts the simulations.The results of metal and plasma antennas are compared,and conclusions are obtained.The far field magnetic vector and electric potential of dipole antenna based on plasma cylinders are analyzed in detail.Thus,the poynting vector for radiation of the antenna is obtained.Meanwhile we obtain the current distribution along the line by using Fourier expansion.Finally,we analyze the reconfigurable property of plasma antenna,the thermal noise of plasma antenna,and compare them with metal antennas.(2)Production of plasma and methods of plasma activation: This paper applies the non-magnitized cold plasma.The plasma tube is made of the cylindrical quartz,and the power supply source is from 13.56 MHz radio frequency(RF)source.The gas pressure and the gas composition of the plasma in quartz tube are discussed.We calculate the gas pressure when the plasma frequency is 5 GHz,which corresponds to the VHF and UHF operating band of the antenna.For commercial application,this paper uses the method of microwave interference to measure the plasma density and the plasma stability,thus,we can evaluate the performance of the proposed plasma.Furthermore,we discuss four kinds of methods to activate plasma,which are direct current activation,RF activation,pulse activation,and microwave activation.The operating method of the source in this paper is introduced.In order to obtain the plasma with high power,this paper proposes the pulse generator with high power and high pulse repetition frequency(PRF)based on drift step recovery diodes(DSRD).Moreover,we design the eight-way stripline radial combiner with high power volume and ultra-wideband tree structure of stripline combiner with MW power.We fabricate the combiners and conduct the measurement work.(3)Very high frequency(VHF)/Ultra high frequency(UHF)reconfigurable plasma antenna:The bandwith of the traditional VHF/UHF antenna is insufficient.The volume of the antenna is large while its gain is low.In order to operate with an ultra-wideband,we propose the two arms loaded monopole antenna,the parasitic monopole antenna,and the top loaded plasma monopole antenna.These antennas all achieve the wideband operation.Howerver,there still many problems in radiation,direction and miniaturized operation.This paper applies the discone structure,and inverts the cone to improve the impedance match.In order to operate in the lower band and enhance the gain,plasma cages are loaded above the cone antenna.LR parallel structure is loaded in the middle of the antenna to achieve impedance match in lower band.Meanwhile,the matching network is introduced to the feeding port.We discuss the relationship between the radiation patterns and the ground,and the optimization process is proposed.We simulate the antenna model,and research the impedance characteristics,the radiation performances and the RCS properties.(4)Operating system and measurement work of reconfigurable plasma antenna:This paper proposes the operation system of the plasma antenna.The radiation signal is isolated from the activated signal.We design some microwave components,such as Butterworth high pass filter(HPF),Butterworth low pass filter(LPF),and Pi type lumped distributed power divider.The measurement results conducted by network analyzer confirm the availability of the microwave components.We introduce the fabrication process of the plasma antenna and metal antenna.The measurements of standing wave,gain and RCS are conducted in chamber.The results of impedance match and the radiation gain show a good performance.The results of plasma antenna are consistent with that of the metal antenna.Meanwhile,the RCS of plasma is lower than that of the metal antenna.We propose the measurement system of normalized radiation patterns for VHF/UHF antenna.The system composes of the portable spectrum analyzer mounted above the unmanned aerial vehicle(UAV).Moreover,we measure the radiation patterns in pitching plane and azimuth plane,respectively,at100 MHz and 400 MHz.The innovation points of this paper can be summarized as follows:Firstly,this paper proposes an inverted-discone antenna and impedance matching methods to achieve broadband operation at VHF/UHF bands with a miniaturized structure(?/10 at 30 MHz).With the reconfigurable property of plasma,the antenna achieves a 17:1 bandwidth.Secondly,Plasma tubes are used to radiate power instead of metal bars,the advantage is not only to achieve wideband operation with its reconfigurable property,but to reduce the RCS of the antenna.Thirdly,This paper proposes the measurement system of the far field of VHF/UHF antenna.We measure the RCS of the antenna from L band to Ku band in chamber with the length of 17 m.UAV with signal receiving system is applied to measure the patterns of the proposed antenna,VHF/UHF antenna pattern is difficult to measure with traditional method because of the limited space of chamber. |
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