新型无线局域网双频段微带贴片天线设计

 新型无线局域网双频段微带贴片天线采用50 Ω微带线进行馈电,采用在贴片切槽设计方式,实现了微带天线在双频段工作的要求。其中心工作频率分别为2.44 GHz和5.20 GHz,相应的工作带宽分别达到了200 MHz和1.20 GHz。该天线具有小尺寸、结构简单、制作简单,低成本和在各工作频点处具有良好的方向性等优点,而且只需简单修改辐射贴片上的缝隙尺寸参数,就可以实现对天线高频段和低频段的调节。     

新型无线局域网双频段微带贴片天线设计

新型无线局域网双频段微带贴片天线采用50 Ω微带线进行馈电,采用在贴片切槽设计方式,实现了微带天线在双频段工作的要求。其中心工作频率分别为2.44 GHz和5.20 GHz,相应的工作带宽分别达到了200 MHz和1.20 GHz。该天线具有小尺寸、结构简单、制作简单,低成本和在各工作频点处具有良好的方向性等优点,而且只需简单修改辐射贴片上的缝隙尺寸参数,就可以实现对天线高频段和低频段的调节。     

一种新型宽带定向性贴片天线设计

利用超材料概念,通过在接地面上蚀刻条形缝隙图案,并引入"八木"天线中的反射器和引向器的设计思想,设计并且制作了一种超宽带强定向型贴片天线.仿真结果表明,天线相对带宽为65.3%(6.9—13.6 GHz),带内回波损耗均在-10 d B以下,整个频段内天线的增益均在4.4 d Bi以上.由于接地板上蚀刻的超材料结构的左手特性影响了天线介质基底的等效媒质参数,天线电磁场的传播方向被改变,天线辐射场主要集中在水平方向而不是传统贴片天线的垂直方向.在传统的贴片天线上引入反射器和引向器增强了天线的方向性.实验结果与仿真结果有较好的一致性.     

宽带高功率贴片天线阵列辐射特性

 为提高宽带高功率微波辐射天线的总体功率容量和增益,研究了2×2宽带高功率贴片天线阵列的阵元互耦特性、馈电功分器设计及对宽带电磁脉冲的辐射特性。阵元采用宽带高功率双层贴片天线,分析了阵元反射和互耦系数随阵元间距的变化关系,结合增益变化曲线,选取阵元间距为30 cm。优化设计了1分4的同轴功分器,采用阻抗渐变方法,提高了功分器的带宽,使其在224~415 MHz时的反射系数小于0.1。模拟了带功分器的完整天线阵,结果表明天线阵带宽达到了57.4％,280~390 MHz频带范围内的增益大于12 dB,在360 MHz时达到最大增益14.23 dB,对中心频率320 MHz,带宽10％的宽带电磁脉冲辐射效率为868％,峰值功率增益大于11 dB。     

新型无线局域网双频段微带贴片天线设计北大核心CSCD

新型无线局域网双频段微带贴片天线采用50Ω微带线进行馈电,采用在贴片切槽设计方式,实现了微带天线在双频段工作的要求。其中心工作频率分别为2.44 GHz和5.20 GHz,相应的工作带宽分别达到了200 MHz和1.20 GHz。该天线具有小尺寸、结构简单、制作简单,低成本和在各工作频点处具有良好的方向性等优点,而且只需简单修改辐射贴片上的缝隙尺寸参数,就可以实现对天线高频段和低频段的调节。     

用于宽带高功率微波辐射的双层贴片天线特性

研究了用于宽带高功率微波辐射的双层贴片微带天线输入阻抗带宽和辐射特性,提出一种适合于高功率微波辐射的圆锥传输线馈电结构以减小传统馈电探针的引线感抗,使天线的功率容量提高到百MW级,同时作为同轴线到径向传输线的过渡变换,使反射系数降低近50%。通过数值计算分析了不同的介质基底厚度组合和贴片尺寸对天线带宽的影响,优化参数后的天线带宽达到了34.9%(电压驻波比小于3),带内平均增益高于6.5 dB,最大增益8.3 dB,主辐射方向上的远场辐射因子与馈入宽带脉冲幅度比值大于1.3。分析了天线的功率容量,模拟计算表明该天线可用于辐射幅值300 kV的宽带高功率微波。     

宽带高功率贴片天线优化设计与实验

研制了中心频率为300 MHz的宽带高功率贴片天线,并进行了高功率实验研究。采用Taguchi全局优化算法对双层贴片天线的结构参数进行优化设计,使其驻波比小于3的带宽达到60.2%,最大增益8.1 dB。为提高其功率容量,对贴片、介质基底和馈电结构进行了改进和相应的绝缘设计。小信号测试结果与理论计算吻合,实测带宽达到64.2%。高功率实验中,馈入峰值89 kV和-81 kV的双极的脉冲,辐射因子达到75.2 kV,等效峰值辐射功率为188.5 MW,辐射场频谱的3 dB带宽为46%,实测能量方向图与模拟结果相符,半能量角宽约为90°。     

一种波束赋形可调的导航天线设计

提供一种新的调节半功率波束宽度的思路,并设计了一款可实现波束宽度变换以应用于不同波束赋形场景的北斗二号B3频段的导航天线。基于四阵元双馈源的微带贴片天线阵列,在HFSS有限元仿真软件中根据理论进行建模仿真并优化。在保持右旋圆极化的基础上,不用改变阵列的结构,只需适当调节各个阵元激励的幅度与相位,就能实时缩小或者扩大半功率波束宽度,分别实现主瓣方向可调的定向波束赋形与宽波束赋形以应对不同的工作环境,并且具有定向抗干扰能力。仿真结果表明:定向波束赋形与宽波束赋形在B3中心频点的最大增益分别约为7.13,3.56 dBi,半功率波束宽度分别为52°,119°,3 dB轴比宽度分别为90°,166°;在整个B3频段内各个馈电端口反射系数低于?11 dB,相邻端口隔离度低于?28 dB。设计的波束赋形方式可调的导航天线适用于在无遮挡的开阔空间与特定的遮挡环境之间经常切换的工作场景,改善传统的机动式导航终端在“城市峡谷”等高遮蔽角环境下增益较低的缺点。     

一种紧凑型宽谱辐射源

采用快前沿Marx发生器直接驱动辐射天线,设计了一种紧凑型宽谱辐射源。Marx发生器采用3 300 pF低电感陶瓷电容器作为储能电容,采用螺旋形空芯电感作为充电电感,通过各级气体火花开关迅速放电,在负载上建立了陡化前沿的输出电压波形。系统设计为同轴一体化结构,整个Marx发生器放置在一个密封的金属圆筒内,通过充氮气或者六氟化硫气体来绝缘。辐射系统包括振荡器及辐射天线两部分,系统辐射场中心频率为206 MHz,辐射因子40 kV,可重复频率10 Hz运行。     

一种高功率共面馈电脉冲辐射天线的设计实验

设计了一种高功率共面馈电脉冲辐射天线。该天线馈源采用双组电大尺寸共面极板馈臂,将馈电点置于焦点处,与直径2.1 m的抛物反射面相配合,实现超宽谱短脉冲的有效定向辐射。提出了一种由同轴输入到4端输出的高功率馈电巴伦,解决了高功率情况下同轴线到4馈臂共面馈电问题。对所设计天线进行测试实验,结果表明:在馈电脉冲宽度为450 ps、峰值电压为142 kV时,辐射因子达到800 kV。     

Performance enhancement of a compact patch antenna using an optimized EBG structure

In this paper, an Electromagnetic Band Gap (EBG) based structure is proposed and simulated with other conventional structures on a thick substrate, to tackle the narrow bandwidth problem in microstrip patch antenna, and to take advantage of using a high permittivity substrate in terms of compactness. However, using this later degrades the antenna’s radiation pattern and gain even further. An optimized mushroom like EBG structure using Genetic Algorithm (GA) is used to cover the frequency band of interest, two different bandgap characterization methods were used to determine it. The results show significant improvements in terms of the bandwidth, gain and radiation pattern compared to the use of thick substrate.     

Antipodal radiation pattern of a patch antenna combined with superstrate using transformation electromagnetics

This paper aimed to show the design and performances of a flat superstrate placed above an L-band patch antenna. Obtained from the Transformation Electromagnetics technique, this superstrate enables to produce an antipodal radiation with a quasi-null radiation in the broadside direction. From the analytical transformations used for the calculation of the constitutive parameters, material permittivity and permeability profiles of the superstrate are deduced. Then, the field distribution and radiation patterns of the whole structure confirm the antipodal radiation behavior.     

A new multi frequency compact microstrip antenna

A single layer, single feed, multi frequency, compact rectangular microstrip antenna is proposed. Resonant frequency has been reduced drastically by cutting unequal rectangular slots at the edge of the patch along with two tiny circular slots created inside the patch to improve return loss. Antenna size has been reduced by 64% with an increased frequency ratio (the ratio of second or higher resonant frequency to the first resonant frequency).     

On the acoustic radiation modes of compact regular polyhedral arrays of independent loudspeakers

Compact spherical loudspeaker arrays can be used to provide control over their directivity pattern. Usually, this is made by adjusting the gains of preprogrammed spatial filters corresponding to a finite set of spherical harmonics, or to the acoustic radiation modes of the loudspeaker array. Unlike the former, the latter are closely related to the radiation efficiency of the source and span the subspace of the directivities it can produce. However, the radiation modes depend on frequency for arbitrary distributions of transducers on the sphere, which yields complex directivity filters. This work focuses on the most common loudspeaker array configurations, those following the regular shape of the Platonic solids. It is shown that the radiation modes of these sources are frequency independent, and simple algebraic expressions are derived for their radiation efficiencies. In addition, since such modes are vibration patterns driven by electrical signals, the transduction mechanism of compact multichannel sources is also investigated, which is an important issue, especially if the transducers interact inside a shared cabinet. For Platonic solid loudspeakers, it is shown that the common enclosure does not lead to directivity filters that depend on frequency.     

High-gain composite microstrip patch antenna with the near-zero-refractive-index metamaterial

A high-gain rectangular microstrip patch antenna which is covered by a single layer metamaterial (MTM) superstrate with the near zero refractive index is proposed. The refraction of the metamaterial at frequency 3.51 GHz–3.57 GHz is very close to zero. The metamaterial with the near zero refractive index is placed 42 mm above an ordinary rectangular microstrip patch antenna. The effectively zero refractive index behavior of metamaterial superstrate can gather the wave emitted from the microstrip patch antenna and collimate it toward the normal direction of the antenna. The finite element method (FEM) and the finite difference time domain (FDTD) method are used to study the characteristics of this antenna. The results of the two methods indicate that the realized gain of the proposed antenna is increased by more than 6 dB, and the antenna has a flatness high gain in the predicted frequency band, where the proposed MTM is designed to have a near zero index of refraction. Therefore, the high-gain antenna is effectively enhanced based on the near-zero-refractive-index metamaterial.     

一种高增益低雷达散射截面的新型圆极化微带天线设计

设计了一种基于人工电磁材料覆层的高增益低雷达散射截面(radar cross section, RCS)圆极化微带天线. 人工电磁材料覆层是由介质板及其两侧的人工周期表面构成, 上表面是加载集总电阻的方环贴片, 具有宽带吸波特性; 下表面是开条带缝和圆环缝的金属贴片, 具有部分反射特性. 将其加载到圆极化微带天线上方, 通过覆层上表面的电阻可吸收入射的雷达波, 结合下表面与接地板构成Fabry-Perot谐振腔的多次反射, 可实现圆极化微带天线辐射和散射性能的同时改善. 实测结果表明: 加载人工电磁材料覆层后, 天线的相对轴比带宽由5.9%扩展为7.1%; 天线增益在整个工作频带内都得到了提升, 最大提高了6.61 dB; 天线RCS在宽频带宽角域内实现了明显的减缩, 在天线工作频带内也实现了3 dB以上减缩. 实测结果与仿真结果符合较好.     

Compact ellipse shaped patch with ground slotted broadband monopole patch antenna for head imaging applications

This paper represents an ellipse-shaped patch with a ground slotted broadband patch antenna for microwave head imaging systems. The proposed antenna constructs with a simple ellipse shaped square patch and modified slotted plane. The proposed design is very simple to fabricate and is enclosed in a microwave imaging system. The slotted patch, and the partial ground plane improves the antenna's efficiency, operating frequency range, and gain. The size of the proposed antenna is 70 × 60 × 1.5 mm³ with the electrical dimension being 0.277λ × 0.238λ × 0.006λ at a lower frequency of 1.19 GHz and connected to a 50Ω microstrip feeding line. This antenna is printed onto a low-cost FR-4 substrate whose relative permittivity is 4.4, and whose thickness is 1.5 mm. CST and HFSS software have been used for simulation and thereafter successful completion of the measurements and the fabrication. The comprehensive simulation exhibits that this design provides a bandwidth of 2.37 GHz (1.19 – 3.56 GHz) and 100% of the fractional bandwidths (% BW) with the reflection coefficient of <-10 dB. This antenna on FR-4 can produce an average gain of around 3.63 dBi with 5.95 dBi peak gain at whole operation frequencies. The prototype has a peak radiation efficiency of approximately 97% across the active frequency spectrum with 93% of average. The antenna does have an improved fidelity-factor (> 90 %) with a shorter group-delay. Several design modifications have been performed to get perfect, effective, and suitable results for microwave imaging applications. A 3D-realist Hugo head model is fitted with a single antenna and a 9-antenna array component to verify the performance of both the single antenna, and the configured array antenna. The antenna penetrates the brain human tissues satisfactorily. Across the operational range, the specific absorption rate (SAR) attains a limit of <1 W/kg. The analysis of both numeric and experimental evidence clearly indicates that the suggested antenna is ideal for microwave head-imaging implementations.     

A shock-detecting sensor for filtering of high-order compact finite difference schemes

A new shock-detecting sensor for properly switching between a second-order and a higher-order filter is developed and assessed. The sensor is designed based on an order analysis. The nonlinear filter with the proposed sensor ensures damping of the high-frequency waves in smooth regions and at the same time removes the Gibbs oscillations around the discontinuities when using high-order compact finite difference schemes. In addition, a suitable scaling is proposed to have dissipation proportional to the shock strength and also to minimize the effects of the second-order filter on the very small scales. Several numerical experiments are carried out and the accuracy of the nonlinear filter with the proposed sensor is examined. In addition, some comparisons with other filters and sensors are made.