同轴馈源性能改善的方法

同轴馈源是用于反射面天线双频共用馈源的一种重要形式,其内导体为工作在高频段的圆波导馈源,同轴区域为工作在低频段的同轴馈源.如何提高同轴区域低频段馈源的性能,是这种馈源研究的主要内容.采用电磁仿真和实验的方法研究了同轴馈源辐射方向图等化的技术途径,测试结果与仿真结果吻合,并达到了预期的设计指标,验证了技术途径的有效性.     

一种新型双频段共用馈源设计

提出了一种新的同轴式S/X双频共用馈源的设计方法,用于解决卫星通信与测控天线对于双频共用、双频单脉冲跟踪馈源的需求问题。运用模式匹配法分析了同轴馈源的电磁场特性,给出了利用同轴馈源的TEM模用于单脉冲跟踪的新思路,仿真设计了同轴喇叭和主要波导器件并加工实物进行测试。实测结果表明,在S和X 2个频段,馈源驻波比均小于1.35,轴比低于1.2 d B,边缘照射电平约为-15 d B,差方向图零深低于-30 d B,满足工程应用要求。     

单脉冲雷达多模馈源分析与设计

详细分析了单脉冲雷达四喇叭三模馈源的原理和设计方法,指出馈源模比的变化和口径面相位分布的不一致,都会对馈源的方向图产生影响,考虑这些因素,经过严格推导,得出了这种馈源方向图的完整解析表达式。利用该结果,分析频率和模比对馈源方向图的影响,设计最优的馈源模比,计算出理想的馈源的和差方向图。并进一步对馈源的相位中心进行了分析,给出了频率和喇叭1：7面的相位分布对相位中心的影响结果。这些都会对工程设计具有一定的指导意义。     

S/X双频共用同轴馈源

提出了一种用于射电望远镜50m天线、S/X双频共用且对S、X双频段具有不同照射角的同轴馈源设计方法,S、X两个频段的相对工作频带宽度均为20%,S频段为同轴馈源,内导体为圆波导馈源工作在X频段。采用电磁仿真和实验的方法研究了同轴馈源辐射方向图-10dB点波束宽度的调整方法和减小同轴馈源电压驻波比和轴比的技术途径。对同轴馈源方向图、电压驻波比和轴比进行了测试,测试结果与电磁仿真结果比较吻合。     

超宽带嵌套同轴波导组合馈源的实验研究

超宽带波导馈源在反射面天线中有着巨大的应用潜力。本文分析设计了一个四腔体60：1带宽(1～60GHz)的超宽带嵌套同轴波导组合馈源。文中详细讨论了馈源的性能，该馈源在整个工作频带内有小于-10dB的反射损耗。馈源的每个同轴波导腔工作于圆极化TE11模。馈源的相关参数由实验测量(1～8GHz)和有限元法仿真(8～60GHz)得到。     

毫米波多模单脉冲喇叭馈源的分析与设计

对多模单脉冲喇叭馈源的理论和设计方法进行了研究。针对高次模的模比计算和控制难点,提供了一种准确的分析理论,给出了高次模的产生规律和模比的计算方法。在此基础上分析设计了一个毫米波多模单脉冲喇叭馈源并加工了实物,其实测结果表明,该馈源具有带宽宽（>5%）、驻波比小（<1.2）、和差矛盾小（<1.5 dB）、方位和俯仰面方向图对称性好的特点,与理论分析结果、仿真设计结果非常吻合,达到了预期的设计效果。     

焦面场分析与相控阵馈源设计

该文介绍了焦面场的计算方法及其与反射面焦径比的关系,分析了焦面场与馈源口径场的联系,并建立了基于焦面场分析进行相控阵馈源设计的方法,包括确定单元间距、阵列规模以及实现目标方向图所需要的激励.按照这一方法,分别以未赋形卡塞格伦天线和前馈抛物面天线为对象,设计了各自的相控阵馈源以实现赋形波束的效果,并在后者上验证了波束扫描性能.通过仿真,天线性能实现了预定目标,证明了设计方法的有效性.     

新型宽带馈源的设计方法

提出了一种新型宽带馈源的建模方法,利用此方法能方便地对各个频段的宽带馈源建立仿真模型。利用该建模方法设计了2-15 GHz宽频带馈源,并利用Ansoft HFSS仿真软件对设计的馈源进行了仿真,给出了馈源在2GHz,8 GHz和15 GHz的仿真方向图,方向图等化很好,并且具有几乎相等的10 d B波束宽度。加工实物并进行了测试,测试结果良好,验证了设计方法的正确性。该馈源已经应用在射电日像仪CSRH-II期工程中,天线性能优良,满足设计技术指标要求。     

共反射面双频段单脉冲馈源设计

叙述了共反射面双频段单脉冲馈源的一种设计方法，该馈源采用了各自频段的喇叭馈电，实现了双频共面馈电的技术要求。根据馈源的理论方向，计算了天线的理论方向图。     

同轴波纹喇叭内部高频馈源特性研究

同轴波纹喇叭可用作双频段馈源或多频段馈源.纵槽波纹喇叭可以作为同轴波纹喇叭的内部高频馈源,除具有良好的辐射特性外,还具有较小的口面面积.文中利用模式匹配法对同轴馈源的内部高频馈源进行理论分析与研究,并对实际馈源进行了测试.实测结果与计算结果基本一致,从而验证了分析方法的正确性.     

A simple feed model that reduces time steps needed for FDTD antennaand microstrip calculations

The finite-difference time-domain (FDTD) method is being widely applied to antenna and microstrip calculations. One aspect of this application is accurately and efficiently modeling antenna and microstrip feeds within the constraints of the FDTD approximations. Several relatively straightforward approaches have been suggested, including gap and frill feeds. More complicated approaches, which involve including the coaxial feed cable in the FDTD calculation space, have also been suggested. A related aspect is the desirability of reducing the number of time steps required for the FDTD calculations to converge, especially for transient excitation. We illustrate that for many geometries a simple gap model with an internal source resistance provides accurate results while greatly reducing the number of time steps required for convergence     

The Treatment of Thin Wire and Coaxial Structures in Lossless and Lossy Media in FDTD by the Modification of Assigned Material Parameters

It has been shown recently that the use of modified assigned material parameters (MAMPs) within the finite-difference time-domain (FDTD) method provides a systematic, readily extensible, accurate, and efficient approach to the electromagnetic analysis of microstrip structures. In this paper, it is shown that this technique can also be applied with equal effect to lossless and lossy coaxial lines, wires in a lossy medium such as earthing grids, and more complex structures which include coaxial feeds and shorting posts. The modified parameters are calculated directly from the known asymptotic fields near the wire and do not rely on the concept of "equivalent radius." Results are given which show equal or superior performance compared to those obtained using other methods but with the added advantage of flexibility and rigor     

Considerations on performance evaluation of cavity-backed slotantenna using the FDTD technique

The finite-difference time-domain (FDTD) method is considered a versatile and efficient tool for the solution of Maxwell's equations in complex structures for any time dependence. We show an antenna feed model suitable for performance evaluation of a cavity-backed slot antenna using the FDTD technique. The gap voltage and the coaxial feed models are examined, and their input characteristics and absolute gains are compared. Analytical results show that the input characteristics are estimated with fewer time steps for the coaxial model than for the conventional gap voltage model. Furthermore, we show how to calculate absolute gains and radiation patterns using the coaxial model and a sinusoidal voltage source at the desired frequency. The computed results of the absolute gain converge after the fifteenth period of the voltage source for the coaxial model and are in good agreement with the experimental results. On the other hand, the absolute gain is observed to fluctuate when the gap voltage model is used. The performance evaluation and comparison reveals that the coaxial model is an appropriate feed model for use in the analysis of the performance of the cavity-backed slot antenna using the FDTD technique. The good agreement of the FDTD results with the experimental measurements demonstrates the effectiveness of the model and the method proposed     

An Equivalent Feed Model for the FDTD Analysis of Antennas Driven Through a Ground Plane by Coaxial Lines

For the finite-difference time-domain (FDTD) analysis of antennas excited by coaxial lines, an equivalent model of the antenna feed is presented here. Under the quasi-static approximation, the coaxial aperture is simply represented as the equivalent magnetic-frill current and the equivalent load circuit including the effects of the coaxial line. It leads us to a simple modification of the standard FDTD update equation at the aperture without any additional cell modeling of the line. The validity of the proposed model is confirmed by comparing of the FDTD results and the measured data.      

Optimization of transient feeding to parallel-plate transmission lines from coaxial line

The transient feeding to parallel-plate transmission lines from coaxial line is optimized by using the Finite-Difference Time-Domain (FDTD) method and a simple FDTD feed model. Observing the reflected voltages, this letter presents the optimal feeding position and ratio of width to height for a given input impedance of the coaxial line.     

Coaxial feeds for high aperture efficiency and low spillover of paraboloidal reflector antennas

Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H11modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of100degto160deg. Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.     

Full-Wave Analyses of Coaxial to Waveguide Adapters by the FDTD Method

The finite-difference time-domain (FDTD) method is applied to the full-wave analyses of the electrical properties of millimeter wave coaxial to waveguide adapters. The results are useful for the design of wideband coaxial to waveguide adapter.     

Artificial Neural Network Models for Coaxial to Waveguide Adapters

Artificial neural networks provide fast and accurate models for the modeling, simulation, and optimization of microwave and millimeter wave components. In this paper, a multilayer perceptron neural network (MLPNN) is used to model a millimeter wave coaxial to waveguide adapter. The MLPNN is electromagnetically developed with a set of training data that are produced by the full-wave finite-difference time-domain (FDTD) method. One type of the designs of experiments, the central composite technique, is used to allow for a minimum number of FDTD simulations that is needed to be performed. The MLPNN models are useful for the CAD of wideband coaxial to waveguide adapter.     

开口式微波加热器的研究

应用时域有限差分法(FDTD)分析和计算了一种开口式同轴加热装置。同时讨论和计算了为防止微波泄漏而设计在腔体外围的扼流槽的作用。测量结果与计算结果有相当高的一致性。表明这种装置可以在中心处产生高温,而在设计相关的微波装置时,使用时域有限差分法又是十分有效的。     

Thru characteristics of a coaxial gap (FDTD model and measurements)

Thru characteristics of a coaxial cable interrupted by a small gap are modeled and measured. Finite-difference time-domain (FDTD) modeling is applied in cylindrical coordinates to semirigid coaxial cable and to the intervening gap material. Both dispersive and nondispersive gap materials are investigated. Gap loss and phase shift are accurately predicted by this two-dimensional model which accounts for TEM and TM modes in the gap and coaxial apertures. An application of the model is to establish reference data for thin sample permittivity or moisture measurements