Direct Measurement of Small Antenna Radiation Efficiency by Calorimetric Method

A novel method for radiation efficiency measurement of small-size radiators such as mobile phones and other handheld wireless devices is presented. The method is based on the accurate determination of the power which is dissipated in the antenna under test using a calorimetric approach. The principle of the method, some of its variants, and the experimental setup are described. Application of the method is demonstrated for several test objects with different efficiencies. Accuracy is validated by comparison of calorimetric radiation efficiency against numerical estimates and independent measurements using the reflection efficiency method, a generalized variant of the Wheeler cap method, whose basic limitations are briefly discussed. Due to the calorimetric principle employed in the proposed new method, it qualifies equally well as a highly accurate reference method for radiation efficiency measurements and as a low-cost alternative to three-dimensional pattern integration and Wheeler cap type efficiency estimates.     

Impedance-Matching Technique for an Infrared Folded Dipole Antenna

Journal of Infrared, Millimeter, and Terahertz Waves - Modifications of the geometry of a folded dipole antenna operating in the infrared were studied with the objective to increase the antenna...     

A Procedure for Estimating the Power Pattern of a Narrow-Beam Antenna

In EMC analysis it is often required to assess the mutual interference between stations without detailed knowledge of the antenna patterns involved. Typically, only the mainbeam gain is available from large-scale spectrum-management data systems. This paper formalizes a simple method for estimating the power pattern of narrow-beam antennas from this admittedly insufficient information. Estimated patterns are compared with measured antenna patterns.     

Synthesis and Validation of a Cu Meta-BasedWideband Microwave Absorber on an Antenna Array

Meta copper (Cu) material called nanotwin crystalline copper metal (C2101, Kopu Tharma Loham) fabricated on the basis of ancient Indian metallurgical techniques has been originally used here as an absorbing material. The research attempted here is to explore the electromagnetic properties experimentally over a wide range of frequency covering X, Ku, K and Ka bands. The dielectric constant and loss tangent of Cu meta material are high in the X range making it a good candidate for the successful design of an absorber. Along with that, the melting point of Cu meta is also increased to 1135°C which is otherwise 1085°C as per international copper standards, hence making the absorber thermally stable. The particle size of Cu meta material, when measured with the x-ray diffraction method, is decreased from 50 μm to 100 nm, placing it in a nanomaterial category. An absorption bandwidth of 35.58 GHz is obtained, ranging from 1 GHz to 36.58 GHz. After testing, the absorber is finally integrated with a two-element rectangular patch array for substantial applicability. The radiation pattern plot shows a remarkable reduction in side lobe level of the array from 3.737 dB to 1.158 dB after placing the Cu meta material absorber. The beam width narrows down from 70° to 44° with a slight increase in the amplitude of the major lobe from 5.494 dB to 6.341 dB while retaining the pattern symmetry.     

基于遗传算法的任意布阵天线方向图优化

建立了一种通用的适应度函数式，通过遗传算法对八元阵优化，逼近二项式分布和切比雪夫分布，验证了算法的正确性。通过对八元阵方向图不同目标的优化，说明该算法及适应度函数的设计对任意布阵天线方向图多目标优化的有效性。     

偏焦偏置抛物面天线的辐射特性

以馈源横向偏焦量Δy作为变化因素分析了偏焦偏置抛物面天线的远场辐射特性.在采用坐标转换、相位计算的基础上运用口径场法推导了远区电场的近似表达式,并对不同偏焦量Δy下的天线方向图进行了计算和比较分析.结果表明,随着偏焦量Δy的增大,天线主波瓣偏离抛物面的焦轴线角度越大,天线增益越小;而且主波瓣宽度越宽,旁瓣的不对称性越明显,第一旁瓣的相对强度也越大.     

遗传算法在阵列天线方向图综合设计中的应用

本文采用遗传算法来完成阵列天线方向图综合的优化设计。     

一种超宽带天线的辐射特性分析

超宽带系统一般采用超宽带短脉冲信号,因而其天线系统也必须为宽带的。给出了一种新型的超宽带天线,该天线为置于镜像面上且具有离散指数电阻加载的单偶极子。通过时域有限差分法分析了电阻加载对天线辐射性能和波形的影响。计算结果表明,通过选择一定的电阻加载形式,可以消除由于天线未端阻抗不匹配而引起的二次反射,使天线具有较好的辐射波形和一定的带宽,从而能够满足实际超宽带系统的需要。     

遗传算法在阵列天线方向图综合中的应用

遗传算法是一种高效的搜索算法。本文采用遗传算法对18元天线阵列方向图进行综全优化设计，并与用Woodward法得到的结果进行了比较。     

The Radiation Properties of a Novel Wire Antenna for the Security Fence Radar

The radiation properties of a novel wire antenna are investigated. The main part of this antenna is a sinusoidal wire undulator, which radiates by coupling electromagnetic energy from a Goubau line located near the antenna. Far-field patterns and S-parameters composed of three sets of antenna are measured. The measured patterns are compared with the calculated ones and the phase and attenuation constants of all the antennas are calculated. Frequency behavior and the dependency on the antenna dimensions of those wave parameters are investigated. Measured and calculated field patterns are also compared with the MoM patterns and some properties of the wave propagating along structure are explained by using MoM current distributions. It is shown that a broadside transversal radiation occurs in a narrow frequency band. The radiation intensity strongly depends on the coupling distance between the Goubau line and the sinusoidal undulator. This antenna is used as the basic element of the security fence radar antenna array working at 1.25 GHz in the L-band, which detects intruders approaching the fence. The performance of the antenna in the array is investigated and the near field distribution of the array is measured. The received signals caused by an intruder are given. The effects of rain and wind are also considered. The results suggests that the security fence radar introduced in this study can be used for the perimeter control of closed areas such as airports, malls, etc.      

一种直线阵列天线辐射散射特性折中设计方法

给出直线阵列天线的辐射散射特性阵元间距折中设计方法。运用该方法对8单元贴片阵列进行仿真验证,结果表明设计的贴片阵列可以在满足辐射性能的基础上,带内和带外单站RCS的强散射点得到了有效抑制,使其在绝大多数入射角处于低散射状态,从而证明了该方法可以快速、有效地指导兼顾辐射性能的低散射阵列设计。     

A Computer Calculation of the Far Field Radiation Pattern of an Antenna Array

A computer program has been investigated and developed for the calculation of the far field radiation pattern of an antenna array. This paper contains an IBM 360/65 program for the calculation of the far field pattern with accuracy checks on the pattern obtained by using radio stations KXIC and WSUI, both located in Iowa City, Iowa, as assumed normals. Two theories of solving the far field calculation problem with the SDS-92/TR-48 hybrid computer are submitted.     

Optimal Antenna Radiation Characteristics for Diversity and MIMO Systems

This paper proposes a method for determining the antenna element radiation characteristics that maximize diversity gain given a specific power angular spectrum of the propagation environment. The method numerically constructs the eigenfunctions of the covariance operator for the scenario subject to constraints on the radiated power and allowable level of supergain. The discussion also focuses on how the resulting radiation characteristics approximately optimize average capacity for multiple-input multiple-output communications. Computational results reveal that optimal antenna characteristics can provide significantly more diversity gain than that offered by the characteristics of a simple design. An example computation using genetic algorithm optimization demonstrates that a numerically optimized practical design can be designed whose performance is relatively close to that of the optimal array.      

无线通信系统中的智能天线技术

文章就智能天线的两大类,多波束天线和自适应天线阵,阐明了智能天线的定义、组成和实现方式,比较了智能天线中智能算法,进而分析了智能天线在视距和多径环境下的性能。最后结合应用进展,文章探讨了实现智能天线的难点和发展前景。     

Variable Antenna Load for Transmitter Efficiency Improvement

A wireless radio transmitter with an integrated variable-impedance antenna is demonstrated. The transmit signal is connected via a switch to the antenna at one of several feed points that correspond to different load impedances that are optimal for the power amplifier at different transmit power levels. It is shown that this can be used to improve the efficiency of the transmission at low and medium transmit powers. The variable antenna load is demonstrated with a planar inverted-F antenna, but the method can be applied to any antenna with suitable impedances.     

An Accurate Equivalent Behavioral Model of Antenna Radiation Using a Mode-Matching Technique Based on Spherical Near Field Measurements

A new and simple method for modeling an antenna under test (AUT) from spherical near-field (NF) measurements is presented. This method utilizes NF data to determine an equivalent behavioral model composed of magnetic and electric dipoles placed over a fictitious sphere surrounding the AUT. A spherical wave expansion (SWE) of the measured NF is developed to derive a linear relation between the transmission coefficients of the AUT and the transmission coefficients of each dipole. Dipole transmission coefficients are determined using the translational and rotational addition theorems. Finally, a least square method is employed to compute the excitation of each current source. Once the equivalent model is obtained, it can be used to study the behavior of the original AUT in different environments. Computations with electromagnetic simulation data illustrate the accuracy of the proposed method and the reliability of the derived model.     

Radiation Q of a Small Antenna Enclosed in an Oblate Spheroidal Volume: Transverse-to-Axis Polarisation

Radiation quality factor, Q, of an electrically small lossless structure that fits an oblate spheroidal volume for transverse-to-axis polarisation is investigated. Q is evaluated for different size and shape of a spheroid by integrating numerically the stored energy associated with radiation. It is found that Q depends on the distribution of power amongst the various spheroidal modes, and a minimum of Q is achieved by suitable optimisation of the relative amplitudes of these modes. A graphical comparison between the minimum Q of a transversally polarised oblate and an axially polarised prolate spheroid is provided for ellipticities in the range 0.2,…,1. The inverse of the obtained minimum Q serves as an estimate for the bandwidth potential of an arbitrary, linearly polarised lossless radiator inside that volume.     

The Millimeter Wave Radiation of a Dielectric Leaky-Wave Antenna Coupled with a Diffraction Grating for the Broadside Radiation: Narrow-Face Interaction

A dielectric leaky-wave antenna (DLWA) coupled with a metallic diffraction grating is experimentally investigated in millimeter-waves. The interaction between dielectric line and grating is from the narrow-face of dielectric and it is contactless. Measured patterns are compared with simulated ones. The antenna parameters (HPBW, side lobe levels, etc.) are also obtained. The most significant achievement of this antenna is to obtain broadside radiation without any suppression, which occurs due to the periodicity of grating. This situation is not available for the most of the periodic leaky-wave antennas. This antenna type can be used as a broadside radiator by this property as well as a frequency scanning purposes.     

大功率中波天线与大功率调频天线共塔系统的设计与实践

河南人民广播电台对郑州市近郊龙湖发射台中波天线进行了改造,以较低的投入增强了城市调频覆盖,对解决城市无合适调频发射场地,同时改善中波发射台生存环境等问题进行了探索.     

车载天线辐射方向图分析

车体及地面对车载天线性能的影响关系着车载通信系统的性能优劣,车载天线辐射方向图可以直观地表示天线的收发性能,因此对车载天线的辐射方向图进行研究具有工程价值.文中应用一致性几何绕射理论进行定性分析,然后采用基于矩量法(MOM)的FEKO软件,仿真分析了有限大平面上的鞭状天线以及某装甲车载鞭状通讯天线,位于车体不同位置时对其方向图的影响.研究结果对车载天线优化配置设计有一定参考价值.