FDTD方法分析地面对超短波天线的影响

采用FDTD方法计算有耗地面上方偶极子天线的输入阻抗。推导天线输入阻抗的计算方法,采用表面阻抗边界条件对地面建模,用细导线方法对天线建模,并得到较为理想的结果。     

半消声室中离地升高声源的声场特性

按照ＩＳＯ３７４５规定，鉴定半消声室时，声中心贴在地面上（ｈ＝０），这时如果半消声室符合要求，则不呈现声场的复杂性，但半消声室的实际使用情况是，置于其中的大型机器设备，其声中心离地面均有一定高度ｈ（往往大于０．２ｍ乃至１．０ｍ），这时就出现直达声和反射声（主要是地面反射声）的较复杂的选加声场，这个声场与ｈ＝０的声场有很大不同。１．纯音声场的特性若是纯音声源，则在室内形成完全干涉声场，利用镜像法，我们计算了在不同直线路径上的干涉声场，并且在中科院声学所的半消声室内作了相应实验。若无反射声，则声场为…     

镜像法在隧道施工土体位移计算中的应用分析

本文根据隧道掘进过程中地层损失的分布规律，运用镜像法原理，通过数值积分法，对由地层损失引起的土体移进行了分析，并结合工程实例对土体位移变化情况进行了计算分析。本文首先分析了镜像法的推导原理，并对隧道掘进过程中的土层损失与土体位移进行了分析，结果显示，镜像法计算得到的位移值与实测值基本吻合，镜像法为隧道施工土体位移的计算提供新方法。     

微波通讯基站系统防雷设计方案

1 微波站进出线引起的雷害分析 微波站从其所处的环境条件看，有三种情况：一是城市站，多设在城市通信综合楼的楼顶：二是平原站，设于野外甲原地区，天线用铁塔支持，机房设在铁塔旁同一地面上：三是山上站，设于野外山上，机房建于山顶或山坡，天线架设在机房同一地面上或设在机房项。三种微波站中城市站和平原站环境条件较好．土壤电阻率低．地网易做，从调查看只要按照建筑物防雷规范设计，     

重力对大型环形可展天线展开动力学的影响研究

受限于火箭尺寸,大型星载环形天线在发射时收拢,入轨后在零重力环境下展至工作态。然而在地面实验重力环境下,克服重力的悬吊卸载系统并不能完全抵消重力场的全部影响,导致地面实验难以准确预测在轨展开动力学行为。因此,有必要借助仿真深入对比分析地面上重力加卸载展开与太空中无重力展开的动力学异同。该文基于柔性多体动力学的仿真方法,建立了天线在零重力和重力加卸载系统两种工况下的全尺寸展开动力学模型。仿真结果不但复现了地面实验的非同步展开现象,而且系统地给出了天线在整个展开历程中所有杆件载荷和驱动力的变化规律。并进一步基于能量分析,半解析地研究了重力对驱动力的影响。该文的研究不但有助于理解大型网状天线的展开动力学,为天线的机构设计、优化和地面实验设计提供技术支撑,而且提出的建模方法和得到的认识也可用于研究和理解其他大型网状天线。     

集合线对对数周期偶极子天线的影响

主要研究了对数周期偶极子天线．基于Pocklington积分方程和全域基函数，采用矩量法结合网络理论建立了天线算法模型；使用该模型计算了在天线阵和集合线共同作用下天线的辐射方向图，得出了集合线在不同频段上对天线辐射性能的影响，并通过截短延长线长度改善了天线低频段的辐射特性，增强了天线轴向方向性．     

地网对垂直偶极子天线辐射特性的影响

研究地网对垂直偶板子天线辐射特性的影响。建立了该天线的仿真模型，采用基于矩量法的仿真软件计算了铺设地网后垂直偶板子天线增益、输入阻抗、最大辐射仰角、3dB波瓣宽度等辐射特性。结果表明，地网中心偏离天线振子正下方0．75λ时能显著提高天线的增益，改变地网大小和铺设密度也能在一定程度上提高天线的增益。     

平面天线结构对电场强度分布的影响

建立电感耦合等离子体源（ＩＣＰＳ）平面天线的电磁场模型，并进行模拟计算。计算结果表明，天线环数较多时，电场强度分布较均匀，基片上离子流密度分布较均匀。若由平面形改为螺旋帽形，能改善电场强度分布，从而改善基片上离子流密度分布的均匀性。还讨论了天线结构对电场强度的影响。     

基于交叉缝隙的陷波可重构超宽带天线

本文设计了一种基于交叉缝隙的陷波可重构超宽带天线.通过采用3×3圆形超表面,有效拓展了天线的工作带宽.通过在矩形接地面上刻蚀两组交叉缝隙,并控制缝隙中设置的二极管的通断实现了天线的陷波可重构.所设计的天线尺寸较小,控制方式简单.结果表明,所设计的天线可以工作在超宽带和陷波模式下,超宽带模式的-10 dB带宽为3.5 G...     

一种井下仪器用RFID射频天线设计

针对井下高温、高压等恶劣环境对RFID射频天线的影响,设计了一种井下用的RFID射频天线。以非金属材料作为天线骨架,使用高温线缆作为缠绕线,同时在线圈外使用环氧树脂等灌封保护。通过地面及入井试验验证,该天线性能稳定,在地面及井下恶劣环境下能够准确读取RFID信息,可广泛应用在应用于智能滑套、随钻扩眼工具、矿山开发工具等。     

Ultra-wideband quasi-circular monopole antennas with rectangular and trapezoidal grounds

Two planar quasi-circular monopole antennas with rectangular and trapezoidal grounds are presented. The impedance bandwidths of the two antennas, defined by measured return loss better than 10 dB, are from 1.3 to 18.4 GHz and from 1.1 to 13.5 GHz, respectively. Both numerical and experimental results show that the proposed antenna with trapezoidal ground has significantly improved radiation performance, compared with the one with rectangular ground. Parameters and design considerations of the trapezoidal ground are discussed in detail. These novel monopole antennas have very wide impedance bandwidth, compact size and low fabrication cost, which are suitable for various broadband applications.     

A Novel Indirect Method to Determine the Radiation Impedance of a Handheld Antenna Structure

A novel indirect measurement technique is developed in which the input impedance of an unknown antenna structure is determined by measuring the change in the measured input impedance of a second probe antenna, while the unknown antenna is loaded at its input by a set of known impedances. The feasibility of the approach is explored using method-of-moment boundary element simulations of the interaction between two dipole antennas in free space. Examples of the measurement of the helical antenna of a terrestrial trunked radio (TETRA) handheld radio and a small portable device with an electrically small antenna are presented. The significant advantage of the technique in the accurate measurement of electrically small antennas is confirmed.      

The effect of substrate dispersion on the operation of square microstrip antennas

The effect of dispersive substrates upon the operation of microstrip antennas is evaluated with a simple and efficient finite-difference time-domain technique. Two single-feed corner-truncated patches with Debye-modeled substrates are simulated; the reflection coefficient and the input impedance are calculated and compared with the lossless case demonstrating that mainly the input impedance and slightly the resonant frequencies are influenced. An unsplit perfectly matched layer is also proposed for the termination of computational domains with dispersive media.     

Flush-mounted cylindrical-rectangular microstrip antennas

The analysis of flush-mounted cylindrical microstrip antennas is presented. The analysis is performed using method of moments in spectral domain, and results are obtained for radiation pattern and input impedance. The results are compared with those obtained for similar geometries, where the dielectric layers extend to infinity. The results show that the housing has not significantly altered the radiation pattern, but the input impedance is affected for small cavity sizes. It is also shown that the resonant frequency diminishes as the superstrate thickness increases.     

Finite-difference time-domain model for the feeding gap of coaxial probe driven antennas

In the finite-difference time-domain (FDTD) method, a simple and realistic feed model for coaxial probe driven antennas is proposed here. The feed zone of the antenna may be considered as an equivalent source in view of the antenna theory and a load port in view of the transmission line theory. The proposed feed model is constructed by combining the infinitesimal-gap source condition of the antenna and the equivalent load condition of the feed line. It leads to perform no additional FDTD cell modelling of the line. The transient reflected voltage and the input impedance of cylindrical monopole antennas fed by coaxial lines are calculated numerically and then compared with the accurate measurement and a full fine-grid. The FDTD results of the proposed model have a good agreement with the measured data and the fine-grid results.     

Space Electromagnetic and Plasma Sensor (SEAPS): A Laboratory Prototype for a Space Payload

Space electromagnetic and plasma sensor is a proposed space payload consisting of an electric field vector sensor—a tri-axial arrangement of monopoles in a mutually orthogonal configuration—and a magnetic field vector sensor, which is a tri-axial arrangement of mutually perpendicular loop antennas. Both operate between 0.5 and 20 MHz in order to acquire the complete 3D polarization matrix. The antennas, which are meant to be electrically short, are matched with a high input impedance amplifier, followed by gain blocks, filters and a six-channel data acquisition system. Some of the proposed goals of the project include study of the low frequency Sun, plasma interactions between the solar wind and Earth’s magnetosphere, lunar atmosphere, and radio emission from other planets within the solar system. This article describes the construction of a laboratory prototype and preliminary calibration results.     

Rectangular microstrip antennas

Abstract

The theory of rectangular microstrip antennas based on the line resonator model and the cavity model are summarized. The theoretical and experimental values of input impedance and radiation patterns are compared, and the discrepency between these two values are explained. A parallelogram microstrip antenna is constructed, and the input impedances are compared to those of the rectangular microstrip antenna.     

Application of dual-mode filter techniques to the broadband matching of microstrip patch antennas

Structures such as square or circular microstrip patch antennas may support two orthogonal resonant modes. The paper presents a new method of utilising the dual-mode property to increase the bandwidth of microstrip antennas. The input impedance of such a dual-mode antenna may be represented as a second-order ladder network of coupled resonators, where each resonator is coupled to a load resistor. A theoretical method for evaluating the coupling values in the network is presented, enabling the bandwidth of a dual-mode antenna to be maximised. A theoretical bandwidth improvement of up to 3:1 is achieved when compared to a single-mode antenna. This is confirmed with an experimental dual-mode circular microstrip patch antenna     

Thin-wire finite-difference time-domain model for insulated and resistively loaded cylindrical antennas driven by coaxial lines

A thin wire-based finite-difference time-domain (FDTD) model for a simple analysis of insulated and resistively loaded cylindrical antennas fed by coaxial lines is proposed. The resistive loading and the coaxial feed line are approximated to equivalent resistors along the antenna axis and the equivalent source over the infinitesimal feed gap, respectively. The effects of the insulation are corrected by employing thin-wire approximation and the boundary condition. A full coarse-grid FDTD algorithm is then implemented without additional grid refinements for the insulation, the resistive loading and the feed line. As a function of insulation properties and resistive loading profiles, the transient reflected feed voltage and the input impedance of antennas are calculated numerically. The validity of the proposed model is proved by comparing it with the results of the full fine-grid FDTD.     

Superstrate effects on slot-coupled microstrip antennas

An analysis for studying the superstrate (cover) effects on the slot-coupled microstrip antennas is presented. The approach is based on the reciprocity theorem and uses the grounded double- and single-layer dielectric slab Green's functions in a moment method solution for the unknown slot fields and patch currents. From these fields and currents, various characteristics of the antenna can be extracted, such as the radiation efficiency, directivity, input impedance, and resonant frequency. Numerical calculations showing superstrate effects on these antenna characteristics are presented. The input matches obtained from proper adjustment of the slot and patch dimensions are discussed.<>