赋形反射面天线形变效应的研究

本文利用物理光学法（PO）分析了赋形双弯曲反射面天线在冲击波形变效应的影响下远区辐射场的变化，并由测试结果建立了反射面形变的数学模型，推导出了辐射场的计算方法。结果表明，由于反射面的局部形变，直接导致辐射方向图的恶化，并且随着形变部分面积的增大，水平面的副瓣抬高很大，不同部位的形变对方向图的影响也是不同的。中间部位形变对反射面方向图的影响要大于边缘形变对反射面方向图的影响。     

具有局部凸起形变反射面天线的方向图仿真

针对反射面天线受撞击表面形变问题,利用二次曲面交截椭圆建立局部凸起形变的数学模型,运用基于表面电流积分的物理光学方法计算辐射方向图,研究了天线发生形变后辐射特性随形变面积和形变位置的变化规律。结果表明,随着形变面积的扩大,副瓣电平逐渐升高;形变位于中心位置时,对方向图的影响最为显著。     

预测反射面天线馈源毁伤效应的混合算法

提出了一种预测反射面天线系统在馈源毁伤状态下辐射特性的混合算法.采用时域有限差分法(FDTD)分析了波导开口辐射器馈源穿孔毁伤时的初级辐射特性,利用物理光学法(PO)和物理绕射理论(PTD)分析了反射面天线的次级辐射特性.并采用非场分裂式完全匹配层(UPML)吸收边界条件、共形网格(Conformalmesh)技术提高计算精度和效率,取得了良好的效果,充分验证了混合算法的有效性.     

多孔毁伤时赋形反射面天线辐射特性的研究

利用基于表面电流积分的物理光学法对赋形反射面天线的远场辐射特性进行了建模和分析，比较了反射面完好时的计算结果与测试值，取得了良好的一致。着重研究了天线反射面多孔毁伤后辐射方向图特性受毁伤孔数、孔径及其位置的影响。分析发现，只有当孔径大于一定的尺寸(约0．20个波长)时，天线增益和副瓣电平才会发生明显变化。同时，毁伤孔径越大、越靠近反射面中心则天线增益的下降及副瓣电平的提高越显著。     

收发等波束的双频低副瓣多波束天线

介绍了一种可实现收发波束大小一致的工作于K/Ka频段的低副瓣反射面多波束天线系统。该天线系统采用高效率双频多模喇叭作为馈源,实现了收发频段共用同一反射面,极大地降低了系统的规模。通过对反射面口径场上幅度和相位的分布对天线二次辐射方向图的影响的分析,提出了一种在高频处对反射面引入副瓣照射的方法,从而实现了收发波束大小一致。该天线系统在收发频段均体现了良好的低副瓣、高载干比特性。     

赋形反射面天线毁伤效应研究

利用物理光学法分析了赋形双弯曲反射面天线在冲击波形变效应和破片打洞效应影响下远区辐射场的变化。由测试结果建立了反射面形变的数学模型，推导出了远区辐射场的计算方法，并提出了反射面打洞的模型及其辐射场的计算方法。结果表明：形变的位置和大小对天线辐射方向图的影响是不同的，破洞的位置和大小对天线辐射方向图的影响也是不同的，文中给出了详细的对比结果。     

表面具有形变反射面天线方向图的计算

大型反射面天线由于比较庞大、容易受外力的影响发生形变,因此计算表面具有形变反射面天线的方向图就变得尤为重要。反射面表面发生形变后,对辐射积分的处理会变得比较复杂,文中利用表面雅可比变换,对辐射积分进行处理,使得辐射积分的数学表示变得相对简单,将计算结果与GRASP仿真结果作了对比,结果基本一致,验证了方法的正确性。     

表面误差对双弯曲反射面天线副瓣的影响

天线反射面的表面误差会引起反射面天线的副瓣发生变化。为确定赋形波束双弯曲反射面天线反射面的表面误差与反射面天线副瓣最大值变化之间的关系,采用数理统计的方法,对受到随机表面误差影响的面电流积分,得到天线辐射场。随机表面误差用相关半径和Z向随机误差两个参量表示。根据随机表面误差求出其天线最大副瓣样本分布函数,较好地展现了表面误差引起的副瓣最大值变化,使得反射面天线表面误差引起的副瓣变化可预测,为天线反射面加工的精度要求提供了理论依据。     

超宽带低副瓣赋形反射面天线研制

本文介绍超宽带低副瓣赋形反射面天线的实验研究。经实测,研制的天线在Ｓ波段大于２５％的带宽内,水平面最大副瓣电平均值小于－３１ｄＢ,垂直面具有超余割平方波束,天线系统电压驻波比小于１．２３。同时,在更宽的频带内该仍然上仍十分优异的电气性能。     

球面三反射面天线的计算机辅助设计

本文介绍一种采用球面作主反射面的三反射面天线系统。该天线采用双副反射面对主反射面的球面散焦特性进行矫正,双副反射面由计算机辅助设计生成,固定主反射面不动,转动馈源及副反射面,可实现在空间一定区域内的扫描。由于馈源及副反射面是偏置的,该天线具有理想的副瓣特性和较高的口径效率。此外,本文还探讨了一些先进的计算机软件技术在反射面天线的分析及设计中的应用。     

Simulation of a cylindrical reflector by conducting circular cylinders

A cylindrical reflector is simulated byNparallel circular conducting cylinders of arbitrary radius and distribution along the trajectory of the continuous reflector surface. The resulting radiation pattern of the transmitting reflector antenna is computed as the backscattering pattern of the circular cylinders due to a line source excitation. The results for largeNare compared with published data for a cylindrical parabolic reflector by Kinzel and for a corner reflector by Tsai. It is shown that the beamwidth and first sidelobe level can be improved by using cylinders of unequal radii and spacing but that, contrary to expectation, further improvement by increasing the number of cylinders is not necessarily possible.     

Reflector sidelobe degradation due to random surface errors

It is well known that the sidelobe structure of a reflector antenna is highly susceptible to random surface errors, and that in most applications it is not adequate to investigate only the average behavior of the antenna. In this study, an attempt is made to determine the probability distribution of the sidelobe level of a reflector antenna subject to some random surface errors. Specifically, the random pattern function is considered and its sidelobe level studied using the level-upcrossing theory. Both the degradation of the maximum sidelobe and the degradation of the sidelobe region with respect to an International Radio Consultative Committee (CCIR) sidelobe envelope are obtained. The theoretical results are found in excellent agreement with those obtained by Monte Carlo simulations. Finally, some useful tolerance charts are presented.     

A high aperture efficiency, wide-angle scanning offset reflectorantenna

A unique single offset reflector antenna has been designed which provides as much as ±30° of scanning in azimuth while maintaining a much higher aperture efficiency than a torus antenna. Like a torus antenna, different portions of the reflector are illuminated for each scanned beam. The reflector profile curve in the plane of scan is found by least squares to minimize the error for the beams with the greatest scan angle, and then polynomial terms of up to sixth order which minimize nonplanar phase errors are added to produce a three-dimensional reflector surface. Numerical simulation indicates very good results for all 0.5° beams in the ±30° azimuth field of view, with peak gain no more than 0.3 dB below ideal and highest side-lobe levels no worse than 13.3 dB below the peak gain. Additionally, comparable performance can be extended to the elevation plane out to 15°/-30°, although full azimuth performance becomes compromised at extreme elevation scan angles. By using an offset design, there is no blockage of the outgoing beam by the feed array assembly for azimuth scanning. With better feed performance than comparably sized paraboloids, and being more compact than similar torus reflectors, this novel antenna should find numerous uses in spacecraft and terrestrial applications     

Optimization of microstrip feed geometry for prime focus reflectorantennas

The radiation characteristics of a circular microstrip antenna are studied numerically. Surface integral equations are used to formulate the problem from the boundary conditions and moment methods are used to reduce the integral equations to a matrix equation. An analytic method is used to design a microstrip feed and to achieve symmetric radiation patterns with low cross polarization and backlobe levels. The backlobe level is reduced by adding a quarter-wavelength choke to the side wall or the ground plane of the antenna and the bandwidth is improved by stacking two layers. The performance of the feed with the reflector antenna is also considered. One of the feeds was fabricated and tested. Satisfactory agreement between the computed results and the measurement data was obtained. The microstrip feed has a very small size which should reduce its blockage of the reflector aperture     

Radiation properties of parabolic torus reflector

General radiation-pattern formulas for a torus reflector antenna have been developed using physical optics. These expressions are valid at arbitrary feed locations not only within the primary focal arc but also for beam scanning with squinted feed horn illuminations. Numerical results were obtained at 22 GHz for an experimental 1.25 m×2.5 m torus reflector in both elevational beam scanning and extended azimuthal scanning outside the primary ±15° field of view. An elevation scanning range of 7° showed only a 1 dB gain reduction. The 20° azimuth beam (i.e. 5° extended azimuth scanning) showed a 1.4 dB gain reduction. Comparison between calculated and measured patterns showed agreement in beamwidth and most pattern features. The discrepancy between calculated and measured sidelobe levels in the azimuthal plane is attributed to imperfection enhancement by the horizontal oversize of the reflector     

Analysis of one-dimensional zonal reflectors

A one-dimensional zonal reflector is a conducting surface which is uniform in one direction and has a zonal profile in the other. Similar to a cylindrical reflector, it converts a cylindrical wave from a line-source into an outgoing plane wave. The radiation performance of such reflectors with TM-wave illumination is analyzed by the method of moments (MoM). The influence of corner diffraction and zoning on the sidelobe level is investigated. Three types of configurations are considered, which include the parabolic zonal reflector and two stepwise zonal reflectors of different configurations. It is found that corner diffraction makes a significant contribution to the sidelobe level, but zoning intrinsically raises the far-out sidelobes. Numerical results show that the near-in sidelobes of the stepwise zonal reflector can be significantly decreased by adjusting the geometrical configuration