【作者】 王欣；

【导师】 刘庆想；

【作者基本信息】 西南交通大学 ， 电磁场与微波技术， 2010， 博士

【摘要】 对于新兴的高功率微波领域,高功率微波辐射技术的发展成为该领域发展的一个重要部分。由于高功率微波的一些特殊性质,对高功率微波天线也提出了一些特殊的要求。从径向线阵列天线的广泛调研可知,早期的径向线阵列天线多采用缝隙作为辐射单元,缝隙单元通过一定的排列组合可实现线极化或圆极化微波辐射,后期也有采用贴片微带天线和短螺旋天线作为辐射单元,但由于这些天线中存在着慢波结构或介质,使其无法应用于高功率微波领域。然而,随着高功率微波天线的发展,近些年来,种新型的高功率径向线螺旋阵列天线首次将径向线阵列天线引入到高功率微波领域,探索了高功率微波领域中一种新的天线形式。该天线通过采用新型的耦合探针,避免了介质的引入,为实现高功率径向线阵列天线奠定了基础,同时,这种天线自身具有体积小,效率高、功率容量大等特点,使其成为高功率微波天线发展的一个趋势,但这种阵列形式只实现了高功率圆极化波的辐射,因而,实现高功率线极化微波辐射的径向线阵列天线就成为另一个重要的研究内容。本文就以此为着眼点,以径向线馈电为基础,首次提出高功率线极化径向线阵列天线,并对其进行探索和研究。新型耦合探针的应用要求单元天线为同轴馈电,因此,同轴馈电的线极化单元天线成为首要研究的内容。首先,文中根据径向线馈电系统及整体天线特性对线极化单元提出了一系列要求；其次,依照要求对相关的线极化天线进行了探索研究,主要包括两方面：一方面,一些基本的包括电偶极子、环天线等形式最简单的线极化天线,以及在这些形式上探索、思考、拓展得到的新型单元天线形式；另一方面,探索圆极化合成线极化波的天线形式。最后,通过对比,选择各项特性均满足要求的水平单圆环线极化天线作为辐射单元。为了实现阵列天线轴向最大辐射,以及满足线极化单元激励要求,单圈圆环栅格布局径向线阵列天线成为首选且相对简单的形式,该布局中探针耦合处径向位置相同,耦合波满足等幅同相。但由于该布局中单元数目有限,天线增益相对较低,为了提高增益,需要增加单元数目,扩大圆环圈数,简单的单圈圆环栅格布局就不再满足要求。然而,采用多圈圆环栅格布局实现高功率线极化径向线阵列天线,其中存在着一个关键的问题：即：一方面,只有在径向线内微波路径上间隔为一个波导波长的径向位置处,耦合波的相位差为±2π(实际上是相同的),在这些位置上通过调节耦合波幅度使达到一致,激励相同的单元,就可实现阵列天线最大线极化辐射合成场强；而另一方面,又由平面阵列天线的特性可知,当阵列间距为一个波导波长时,将在可见空间内可能不止出现一个栅瓣,为了抑制栅瓣,必须在一定的范围内减小单元间距,这必然使得耦合口处存在着一定的相位差(不为±2π),激励相同的辐射单元就不能实现等幅同相激励。这两方面之间的矛盾即为问题的所在,因此,为了提高阵列天线的增益,则必须解决这一问题。经过分析,针对这一关键问题提出两种解决方案,方案一：径向线串联馈电,该方案中仍采用圆环栅格布局,但馈电径向线发生了一定的弯曲,以增加径向线内部的波程,合理的调节尺寸后可以使每圈相位差2π,达到等幅同相激励线极化单元天线；方案二：径向线并联馈电,该方案通过改变阵列天线栅格形式、利用多层馈电组合的方式,使馈电系统中每一条微波路径均匀相同,达到等幅同相激励线极化单元。鉴于方案一中弯曲径向线复杂的微波模式特性以及耦合探针的影响,使得整个方案的分析相对较为困难,文中具体地对方案二进行了研究,配合水平单圆环单元天线,共同形成了并联馈电高功率线极化径向线阵列天线。同时,文中对该天线相关的基础理论进行了总结和完善,主要包括：分析了阵列布局与天线性能的关系,由此获得阵列天线设计的参数；了解了径向线中的微波高频特性；分析研究了同轴到径向线转换接头中高阶模对S11参数的影响,加深了对这种带有调配结构的转换接头的认识,为以后整个阵列天线的模式分析提供基础。通过对初级功分器、子阵功分器、单元天线等关键环节的合理设计,对L波段高功率线极化径向线阵列天线进行了仿真,仿真结果表明：在中心频率1.57GHz下,天线增益为19.97dBi,口径效率为50.5%,轴向轴比为-52.06dB；在1.37GHz—1.77GHz的频率范围内,增益大于18.64dBi,口径效率大于37.2%,轴向轴比小于-46.45dB；在1.53GHz—1.76GHz的频率范围内,反射系数小于0.2(对应驻波比为1.5),初步证明了该天线实现的可行性。但其反射较大,口径效率较低,以及功率容量等问题,第5章就针对性地对其进行了优化设计,仿真结果表明：在中心频率1.57GHz下,天线增益为18.8dBi,口径效率为85.1%,轴向轴比为-40.07dB；在1.37GHz—1.77GHz的频率范围内,增益大于1 7.58dBi,口径效率大于64.26%,轴向轴比小于-40.07dB；在1.17GHz—1.68GHz的频率范围内,反射系数小于0.2(对应驻波比为1.5)；功率容量达到1GW。最后,在优化结果的基础上对该天线进行了实验验证,实验结果表明：中心频率下,阵列天线的增益为17.65dBi,口径效率为58.6%,驻波系数为1.19；在1.47—1.77GHz的范围内天线增益大于17.31dBi,轴比小于-38.6dB,天线口径效率大于54%,驻波系数小于1.4。实验结果与数值仿真结果基本一致,更进一步验证了高功率线极化径向线阵列天线的可行性,也具体地实现了该阵列天线。更多还原

【Abstract】 With the development of high-power microwave (HPM) technology, the HPM antenna has become an important part of the HPM system. Due to paticularities of HPM, HPM antenna shall satisfy some special requirments.At the early times, slot antennas which can radiate linear or circular polarized waves by certain arrangement are used as cells of the radial line array antenna. Patch microstrip antennas and low-profile helical antennas are used later. As there are slow wave structures and media in this kind of array antennas, they can’t be used in HPM areas. However, with the development of HPM antenna, a novel HPM radial line helical array antenna as a new kind of HPM antennas is proposed recently. In this antenna, a new kind of coupling probes is adopted which avoid the presence of media. These characteristics of the probe establish base for design of high-power radial line array antenna. At the same time, this antenna as a new means for high-power microwave radiation can fulfill high-power capacity, high efficiency, miniaturized. But this array form realized circular polarized radiation only, therefore HPM linear polarized radial line array antenna becomes another important aspect in research. In this paper, HPM linear polarized radial line array antenna is proposed firstly on the basic of radial line feed, and series of exploration and research are made in this paper.The novel coupling probe requires the feed port of the cell antenna is coaxial feed, so linear polarized cell of coaxial feed become the most inportant aspect of the reseach. At first, series of requirements to the linear is proposed to the cell based on the radial line feed system and characteristic of the whole array antenna. Then, in the area of the linear polarized antennas are investigated based on the requirements in these two aspects:(1) a lot of basic antenna shapes including dipole and loop antennas and their new form etc. are investigated; (2) antennas of linear polarized radiation composed by circular polarized antennas are investigated on the other side. Finally, a planar single circular linear polarize antenna is chosen which satisfies each characteristic as a radiation cell by contrast.To realize the characteristic of the maximal radiation in coaxial direction and satisfy the requestment of linear polarized stimulation, single circular grid radial line array antenna which has a simple form becomes the best choice. In this array, each radial position of the probes is the same and the magnitude and the phase of coupling waves is the same. As the number of the array cell is limited, the gain of the antenna is low. To improve the gain, the number of the cells and the circles is need to increase, as a simple single circular grid can’t meet all the requestments. However, there is a most important question when using multi-ring grid array to realize HPM linear polarized radial line array antenna. Only when the distance of the wave path of the radial lines isλ(wavelength in the waveguide), the differencing of coupling wave phase is±2π(as a matter of fact, it’s the same), it is possible to realize highest resultant field intensity of the maximum of the linear polarized radiation on these positions by regulating the amplitude of the coupling wave and simulating the same cells; On the other side, from the characteristic of the planar array antenna it is known that when the spacing isλ(wavelength in the waveguide), there are more than one grid lobes appear. To restrain the grid lobes, the distance of the cell must be reduced which make the coupling port have some phase differencing.(which is not equal±2π), simulate on the same radiation cells cannot realize same magnitude and phase simulation. To improve the gain of the array antenna, this is the most important question.To solve this question, this paper proposed two solutions to the key problem by analyzing. Solution 1:Radial line is fed in series, in this project, the layout of circular grid is still adopted, while the radial line bent to a certain extent which is in order to increase the wave-path in the internal of the waveguide. There can be 2πphase-difference among different circles by adjusting the dimension properly, finally the linear polarized antenna is excited by the excitation with equal amplitude and phase. Solution 2:Radial line is fed in parallel, in this project, In order to make every microwave route in the feed system have the same wave-path, grid form of array antenna is changed and multi-layer feed is adopted. Finally the excitation of linear polarized element antenna is in-amplitude and in-phase.As the effect of complex wave mode characteristics of the bend radial line and the coupling probes, the analysis of first solution is difficult. So second solution is investigated in this paper, combined with the horizontal ring cell antenna, parallel connection feed HPM linear polarized radial line array antenna is formed. Meanwhile, theoretical elements related to the antenna are summarized and ameliorated systemically based on the basic principle in this paper including these aspects:the connection between the overall arrangement of the array and antenna performance is analysed, basing on this analysis, parameters in the array design are abtained; characteristics of the microwave high frenquency are comprehend; the infection to S11 parameter by the mode in the coaxial-line-radial-line junction is theoretic analyzed and calculated, knowledge about this structure is deeply recognized which establish theoretical base for the mode analysis of the whole array antenna.Base on this reasonable design of the primary power divider, array unit divider and the cell antennas etc, numerical simulation and measurement of the HPM linearly-polarized radial line array antenna of L-band is simulated. Simulation results indicate that this structure is feasible to realize the linear polarized radial waveguide array antenna. The Gain of the antenna is 19.97dBi at the frequency of 1.57GHz, The aperture efficiency is 50.5%,the axial ratio is-52.06dB. In the range of 1.37 GHz to1.77 GHz, the gain is over 18.64dBi, The aperture efficiency is above 37.2%, the axial ratio is below-46.45dB; In the range of 1.53 GHz to 1.76 GHz, the reflecting coefficient is below 0.2 (which is the same as VSWR is 1.5). The resules above prove that this antenna is feasible, but there are some questions in this antennas, the reflection of this antenna is a little high and the aperture efficiency is low, the power capacity is not big enough. To solve these questions, optimum simulation is carried on in the chapter 5. The simulation results indicate that the Gain is 18.8dBi at the central frency of 1.57GHz, the aperture efficiency is above 64.26%,the axial ratio is-40.07dB, in the range of 1.37 GHz tol.77 GHz, the Gain is over 17.58dBi, the axial ratio is below-40.07dB, in the range of 1.17 GHz to 1.68 GHz, the reflecting coefficient is below 0.2(which is the same as the VSWR equals 1.5); the power capacity can reaches 1GW.Finally, experiment is carried on the basic of the results of the numberical simulation. It shows that on the central frequency of 1.57GHz, the gain of the array is 17.65dBi, the aperture efficiency is 58.6%, the VSWR is 1.19; In the range of 1.47 to 1.77 GHz, the Gain is over 17.31dBi, the axial ratio is below-38.6dB. The aperture efficiency is over 54%, and the VSWR is lowre than 1.4. The experimental results is almost accorded with simulated results which means that HPM radial line array antenna can meet the property of a linear polarized radiation.更多还原