人体附近天线的辐射特性

使用解析方法研究了无线人体局域网(WBAN)通信中穿戴式天线的辐射特性.将人体简化为有耗介质椭圆柱体,采用椭圆柱面波展开和阻抗边界条件(IBC),利用收、发天线的互易原理,推导了置于人体附近的短振子天线之方向性图和增益的解析表达式.计算了不同极化取向以及离人体不同间距对天线辐射特性的影响.经与软件仿真和实验测试结果对比...     

Maximisation of signal/noise ratio in array with broadened zero

A technique for synthesising a maximally-flat zero in antenna array while maximising the signal/noise ratio is described. It is shown that the optimum radiation pattern consists of a main beam, a cancellation beam and its pattern derivatives. The properties and characteristics of the pattern are also discussed.     

Position-only planar hexagonal array antenna pattern nulling with simultaneous side lobe reduction at multiple azimuth planes

This article presents a study on the placement of multiple nulls as well as minimization of side lobe level in the radiation pattern using a planar hexagonal antenna array structure in two different vertical planes. The desired null depth is achieved to suppress the interference signal by the position-only control of the uniformly excited isotropic antennas in the array structure. The immediate solution to the mentioned computational problem is reached by various meta-heuristic optimization algorithms such as teaching learning-based optimization (TLBO), symbiotic organism search (SOS), and moth fly optimization (MFO) within a considerably reduced processing time with a control over the design constrains. Various examples for diversified scenarios are demonstrated to place multiple deep nulls in the radiation pattern without compromising the pattern constraints and all other radiation pattern characteristics. This experiment sought to illustrate and quantify the unique benefits and limitations of proposed technique using three considered meta-heuristic optimization algorithm.     

A monopole antenna loaded by a hemispherical dielectric resonator

The input conductance, radiation pattern, and radar cross section (RCS) of a monopole loaded by a hemispherical dielectric resonator (DR) are studied. The effects of the DR on the monopole characteristics are investigated. Measurements were carried out to verify the theory. It is found that the input conductance, radiation patterns, and RCS are strongly affected by the DR.     

柱面共形蝶形微带天线的阻抗特性和方向图研究

研究了小曲率半径有限长度圆柱体上共形蝶形微带天线的阻抗特性和方向图.给出了不同曲率半径下的柱面共形蝶形微带天线反射损失和方向图的仿真结果.实际制作和测试了柱面共形微带天线的单元和二元阵列天线,仿真结果与实测结果比较吻合.研究表明:当圆柱半径较小时,不但方向图改变,而且谐振频率下降、阻抗带宽明显减小;当圆柱长度缩短时,方向图的起伏增大.     

Radiation from an axially slotted anisotropic plasma-clad cylinder

This paper presents an analytical solution for the radiation field of an axially slotted, infinite, circular cylinder which is covered with a uniform layer of an anisotropic plasma sheath. Numerical results are obtained and radiation patterns plotted for various degrees of plasma anisotropy. It is shown that the radiation pattern undergoes rapid changes for certain ranges of plasma parameters and forms well-defined, directive beams for other ranges. Curves showing the effect of the thickness of the plasma sheath on the radiation characteristics are also given.     

单元方向图对阵列综合性能影响分析

在阵列天线综合问题中,传统方法假设各辐射单元各向同性且忽略互耦效应。工程应用中这些忽略会给计算结果带来较大的误差。本文首先建立了天线单元方向图对天线阵列性能影响的数学模型,对阵列指向精度、目标方向图赋形等问题进行了仿真对比分析。为了克服由单元方向图带来的误差,将阵中单元方向图代入优化过程中,算例表明该措施的有效性。考虑了阵列边缘单元辐射特性差异对阵列性能的影响。仿真结果表明在优化过程中考虑这些差异可以进一步提高计算精度。     

Analysis of skew antenna around a square tower for UHF TVbroadcasting

The authors discuss the installation and characteristics of a UHF skew antenna mounted on a tower that already supports seven other VHF arrays used for TV broadcasting. The skew antenna consists of four antenna arrays arranged in a circle with a radius of about 3 m and radiating tangentially. The phase difference between the antenna arrays is 90°. The skew antenna system produces a good omnidirectional pattern, but when located on the tower the reflections from the flat face and the wedge diffractions modify the pattern. The calculation of the horizontal radiation pattern using the geometrical theory of diffraction is compared with the measured pattern. Both the UHF antenna's radiation pattern and its mutual interference are compared with the existing VHF antennas     

Radiation characteristics of corrugation loaded dielectric-coated conducting cylinder

The radiation characteristics of a corrugation loaded dielectric coated conducting cylinder are investigated theoretically for the infinite periodic and finite structures. For the infinite periodic structure, the mode matching method is applied. The integral equation is derived for the finite structure by use of the Fourier transform and mode expansion. The influences of the corrugation width, corrugation depth, dielectric thickness, cylinder radius, and finite corrugation number on the radiation characteristics (leakage constant, phase constant, and radiation pattern) are investigated. The results of the finite periodic corrugations are compared with those of the infinite extent structure and good agreement is found. To reduce the high side lobe of the uniform periodic structure, nonuniform quasiperiodic corrugation arrays are considered. The surface wave radiated by the structure having end-fire radiation pattern is also investigated.     

SCATTERING AND RADIATION CHARACTERISTICS OF STEP DISCONTINUITY IN LEFT-HANDED SLAB WAVEGUIDE OPERATING IN EVANESCENT SURFACE MODE

The scattering and radiation characteristics of a step discontinuity in left-handed (LH) slab waveguide operating in evanescent surface mode of TE and TM polarization are analyzed by a method, which combines the rigorous mode-matching method with the multi-mode network theory. In the analysis the radiation problem is transformed into a propagation problem so as to tremendously simplify the calculation procedure. The dispersion properties of the grounded planar LH slab waveguide for both ordinary and evanescent surface modes are examined, from which the left-hand property of the operating mode is testified. The relative scattered power and radiation pattern of the step are given for the first time, from which the backward radiation of the stepped LH guide is clearly demonstrated. The frequency scanning characteristics of the step under consideration in this paper are just opposite to that of the ordinary antenna, which makes the considered structure promising candidate for new type of planar antennas.     

Resonance and radiation of a superstrate-loaded spherical-circularmicrostrip patch antenna

The effects of the dielectric superstrate cover on the resonance and radiation problems of a spherical-circular microstrip patch antenna are studied, using the Green's function formulation in the spectral domain and the Galerkin moment method calculation. Numerical results for the resonant frequency, half-power bandwidth, and radiation pattern of the superstrate-loaded antenna are presented. The effects of curvature on these characteristics are also shown     

Radiation of a travelling-wave antenna in plasma in the whistler frequency band

The far field, the radiation pattern, and the radiation impedance of a traveling-wave antenna oriented in plasma along the external magnetic field in the resonance region of the whistler frequency band are studied. It is shown how the main characteristics of the antenna depend on its length and the current propagation constant along the antenna wire.     

三维全向天线的设计和实验

本文从设计方面介绍了三维全向天线的工作原理、构成及其特性。还从实验方面阐述了方向图不圆度的测量及减小不圆度的措施     

Novel wideband circular polarization antenna with quasi-hemispheric radiation pattern and low level of cross-polarization

A novel type of circular polarization radiator in the form of a turnstile antenna with spiral-twisted vibrators and bulk cruciform reflector is suggested. Numerical simulation results of the antenna’s characteristics conducted using the author-developed crystal_CR software application, which implements the calculation method invented by the authors, are presented. The obtained radiation characteristics are confirmed by calculations in Ansoft HFSS 9.1 software. Due to optimization of vibrator and reflector geometry the main polarization radiation pattern whose shape is close to hemisphere with cross-polarization level below ?27 dB in any direction in the front semi-space is achieved.     

Experimental analysis of metal coated dielectric waveguides

This paper concerns the experimental characteristics of metal coated dielectric waveguides with a rectangular surface corrugation. Waveguide are designed to operate at a second Bragg frequency of 90 GHz. The period, height and the duty cycle of a rectangular grating were calculated using the chosen frequency. A metallic layer of aluminum is sputtered on one side of the slab waveguide. The purpose of the metallic layer is to simulate a layer of high density plasma on the surface of the waveguide similar to that obtained by optical excitation of semiconductor structures. Experiments were performed to examine the far field radiation pattern, attenuation constant and the dispersion relation. Due to the presence of the plasma layer there will be an angular shift in the far field radiation pattern. We have observed angular shifts of about 20? in the radiation pattern of the waveguide before and after coating. Measurements are made in the frequency range of 88–95 GHz. This waveguide structure can be used to design an electronically steerable antenna and an electronic phase shifter operating in the millimeter-wave frequency band.     

TM-wave radiation from grooves in a dielectric-covered ground plane

This article describes the radiation characteristics from multiple rectangular grooves in a dielectric-covered ground plane. The theoretical far-zone radiation pattern is compared with the measured data at 10 and 11 GHz using a wavenumber conversion procedure     

Application of Characteristic Modes and Non-Foster Multiport Loading to the Design of Broadband Antennas

A conceptual framework is proposed to systematically design antennas with broadband impedance and pattern characteristics using multiple reactive loads. Antennas of arbitrary geometry can have their bandwidths expanded using this technique. The technique is applied to a narrow band thin wire dipole antenna to demonstrate its main features. It is shown that the loaded antenna resonates a desired current over a wide frequency band. The loads are shown to require non-Foster elements when realized. Simulations demonstrate the broadband characteristics of both the dipole input impedance and radiation pattern.      

双频基站天线中的反射板形状设计

蜂窝移动通信系统中的基站天线通常由直线阵列加反射板构成,而反射板的形状主要影响天线的前后比特性及水平面辐射方向图.该文对适合于基站天线的几种典型反射板形状进行优选,并采用矩量法线栅技术仿真计算了各种反射板形状对天线辐射性能的影响,根据仿真结果给出了满足基站天线双频辐射要求的反射板形状.     

Radiation by a straight thin-wire antenna embedded in an isotropicchiral medium

Radiation characteristics of a straight thin-wire antenna embedded in an isotropic chiral medium are explored. The radiation field contains both left-circularly polarized (LCP) and right-circularly polarized (RCP) components. The radiation pattern is found to be symmetric about the plane &thetas;=π/2, azimuthally isotropic, and TEM (transverse electromagnetic) in nature; however, all three of these features are found as well for isotropic achiral media. Some specific features of the radiation field on certain constant spherical surfaces are also examined. If the antenna is reduced to a point dipole, it is shown that the radiation resistance is enhanced by the presence of chirality in the embedding medium, and the antenna LCP gain differs from the RCP gain     

Radiation characteristics of microstrip arrays with parasitic elements

The radiation characteristics of microstrip antennas consisting of one centre-fed patch and several identical parasitic patches are studied experimentally. The configurations investigated include a five-element cross and three- and seven-element linear arrays. A significant increase in gain is obtained by using close interelement spacing, with no degradation in pattern characteristics.