一种基于开口谐振环的高增益端射天线设计

基于开口谐振环(split-ring resonator, SRR)奇异的电磁特性, 设计并制备了一种覆盖C和X波段的高增益SRR-Vivaldi端射天线. 采用等效分析方法对SRR结构谐振特性进行了研究, 并将其应用于传统Vivaldi天线指数渐变槽线前方, 使SRR结构形成特殊谐振能力的引向器, 将天线表面电流集中于端射方向, 在保证天线尺寸和带宽不变的前提下, 实现了天线增益的有效提升. 仿真和测试结果表明, 新型SRR-Vivaldi天线在C波段增益平均提高75.44%, xoy面和xoz面半功率波束宽度都缩减20°以上; 在X波段增益平均提高24.46%, xoz面半功率波束宽度大约缩减25°. 该结构具有低成本、设计简单、便于加工、利于共形等优点, 为端射天线提高增益和增强定向性提供了新思路.     

Efficient and wideband horn nanoantenna

In this Letter, we present the design of a horn nanoantenna working at near-IR frequencies. The proposed layout consists of an Ag-air-Ag nanotransmission line terminated in a tapered horn. The antenna design is validated through proper full-wave numerical simulations, taking into account actual dispersion and losses of the involved materials. The numerical results show that the designed nanohorn is matched over a broad range of frequencies (more than 50% of fractional bandwidth) and radiates efficiently in the same frequency band (the realized gain is greater than 10 dBi). Such promising results may find application in different technical and scientific fields, ranging from smart lighting to optical wireless communications.     

Design considerations for rectangular microstrip patch antenna on electromagnetic crystal substrate at terahertz frequency

The effects of 2-D electromagnetic crystal substrate on the performance of a rectangular microstrip patch antennas at THz frequencies is simulated. Electromagnetic crystal substrate is used to obtain extremely broad-bandwidth with multi-frequency band operation of the proposed microstrip antennas. Multi-frequency band microstrip patch antennas are used in modern communication systems in order to enhance their capacity through frequency reuse. The simulated 10 dB impedance bandwidth of the rectangular patch microstrip antenna is 34.3% at THz frequency (0.6–0.95 THz). The radiation efficiency, gain and directivity of the proposed antenna are presented at different THz frequencies. The simulation has been performed using CST Microwave Studio, which is a commercially available electromagnetic simulator based on finite integral technique.     

Crucial role of the emitter-particle distance on the directivity of optical antennas

We demonstrate that the reflecting properties of a single particle nanoantenna can be extremely sensitive to its distance from a quantum emitter at frequencies lower than the plasmon resonance. The phenomenon is shown to arise from rapid phase variations of the emitter field at short distances associated with a phase of the antenna particle polarizability lower than π/4.     

变形螺旋天线的自动设计

 利用优化算法进行天线的自动设计是现代天线研究的一个重要趋势。采用NEC(Numerical Electromagnetics Code)天线数值计算程序和遗传算法，结合并行计算技术，实现了对螺旋天线的自动设计。在轴向模辐射，螺旋轴长80cm内和频率为600MHz的条件下，设计了增益高达12.68dB的均匀螺旋天线，比传统设计方法高3.28dB；在400～800MHz的频带内，对变形螺旋天线之一的锥削螺旋天线做了高增益设计，平均增益达12.28dB；对锥削螺旋-圆锥喇叭天线进行了优化设计，得到了比普通螺旋天线更佳的辐射性能。这些设计结果都是传统天线设计方法难以完成的，表明自动设计具有比传统天线设计方法更大的灵活性和更强的设计能力。     

天线阻抗特性对开关振荡器输出脉冲的影响

以单锥天线和螺旋天线作为开关振荡器辐射天线为例,采用等效电路模型和商业电磁仿真软件,分别对天线末端电压振荡信号和辐射电场脉冲进行了研究。研究结果表明:采用行波天线或者电长度与振荡器一致的振子天线作为辐射天线,都能够产生中心频率与振荡器本征频率一致的电磁脉冲信号;但采用振子天线时,振荡信号持续时间较短(Q值较低),频谱上能量较分散,带宽较宽,而采用行波天线则脉冲持续时间较长(Q值较高),频谱上能量较集中,带宽较窄。     

Investigation of a slot nanoantenna in optical frequency range

Following the analogy of radio frequency slot antenna and its complementary dipole, we propose the implementation of a slot nanoantenna (SNA) in the optical frequency range. Using finite-difference time-domain (FDTD) method, we investigate the electromagnetic (EM) properties of a SNA formed in a thin gold film and compare the results with the properties of a gold dipole nanoantenna (DNA) of the same dimension as the slot. It is found that the response of the SNA is very similar to the DNA, like their counterparts in the radio frequency (RF) range. The SNA can enhance the near field intensity of incident field which strongly depends on its feedgap dimension. The resonance of the SNA is influenced by its slot length; for the increasing slot length, resonant frequency decreases whereas the sharpness of resonance increases. Besides, the resonance of the SNA is found sensitive to the thickness of metal film, when the latter is smaller than the skin depth. The effect of polarization of incident field on the EM response of the SNA was examined; the field enhancement is optimum when polarization is parallel to the feedgap. Finally, we calculate the radiation patterns of the DNA and SNA and compare them with those of the RF dipole antenna. The radiation pattern of the SNA is found to be independent of its slot length when excited at resonant frequency. To the best of our knowledge, this is the first study on a slot antenna in the optical frequency.     

Analysis of single band and dual band graphene based patch antenna for terahertz region

A microstrip patch antenna is designed using a very thin layer of graphene as the radiating patch, which is fed by a microstrip transmission line. The graphene based patch is designed on a silicon substrate having a dielectric constant of 11.9, to radiate at a single frequency of 2.6 THz. Further, this antenna is made to resonate at dual frequencies of 2.48 THz and 3.35 THz, by changing the substrate height, which is reported for the first time. Various antenna parameters such as return loss, VSWR, gain, efficiency and bandwidth are also determined for the single and dual band operation. For the single band operation, a bandwidth of 145.4 GHz and an efficiency of 92% was achieved. For dual band operation, a maximum bandwidth of 140.5 GHz was obtained at 3.35 THz and an efficiency of 87.3% was obtained at the first resonant frequency of 2.48 THz. The absorption cross section of the antenna is also analysed for various substrate heights and has maximum peaks at the corresponding resonating frequencies. The simulation has been carried out by using a full wave electromagnetic simulator based on FDTD method.     

Quantum theory for plasmon-assisted local field enhancement

We applied quantum theory for nonlocal response and plasmon-assisted field enhancement near a small metallic nanoscale antenna in the limit of weak incoming fields. A simple asymmetric bio-inspired design of the nanoantenna for polarization-resolved measurement is proposed. The spatial field intensity distribution was calculated for different field frequencies and polarizations. We have shown that the proposed design the antenna allows us to resolve the polarization of incoming photons.     

Coplanar waveguide-fed compact planar ultra-wideband antenna with inverted L-shaped and extended U-shaped ground for portable communication devices

To simultaneously cover multiple wireless services and protocols, the antenna in communication devices should operate over a wide and ultra-wide frequency band. The use of wide/ultra-wideband antennas not only lessens the number of antennas necessary to cover multiple frequency bands but also decreases the system complexity, size, and costs. To operate over the ultra-wide frequency band, in this paper a CPW-fed small antenna is reported for portable communication devices. The anticipated antenna comprises a bow-tie-shaped patch and two ground planes. One inverted L-shaped and one extended U-shaped ground plane are asymmetrically placed with the main radiator which helps the antenna prototype to realize a functional band of 3.05 – 11.25 GHz (VSWR ≤ 2). In the functional band, the studied antenna accomplished a maximum peak gain of 4.98 dBi and maximum efficiency of 94.4%. Moreover, it exhibits symmetric omnidirectional radiation patterns and good time-domain behavior. The lucrative characteristics such as simple design, very small size (24.5 × 20 mm²), ultra-wide operating band, good gain and efficiency, stable radiation characteristics, and good time-domain characteristics make it a potential candidate to be used in portable communication devices.     

Antenna design and distribution of the LOFAR super station

The Nançay radio astronomy observatory and associated laboratories are developing the concept of a “Super Station” for extending the LOFAR station now installed and operational in Nançay. The LOFAR Super Station (LSS) will increase the number of high sensitivity long baselines, provide short baselines, act as an alternate core, and be a large standalone instrument. It will operate in the low frequency band of LOFAR (15–80 MHz) and extend this range to lower frequencies. Three key developments for the LSS are described here: (i) the design of a specific antenna, and the distribution of such antennas; (ii) at small-scale (analog-phased mini-array); and (iii) at large-scale (the whole LSS).     

Plasmonic abilities of gold and silver spherical nanoantennas in terms of size dependent multipolar resonance frequencies and plasmon damping rates

Absorbing and emitting optical properties of a spherical plasmonic nanoantenna are described in terms of the size dependent resonance frequencies and damping rates of the multipolar surface plasmons (SP). We provide the plasmon size characteristics for gold and silver spherical particles up to the large size retardation regime where the plasmon radiative damping is significant. We underline the role of the radiation damping in comparison with the energy dissipation damping in formation of receiving and transmitting properties of a plasmonic particle. The size dependence of both: the multipolar SP resonance frequencies and corresponding damping rates can be a convenient tool in tailoring the characteristics of plasmonic nanoantennas for given application. Such characteristics enable to control an operation frequency of a plasmonic nanoantenna and to change the operation range from the spectrally broad to spectrally narrow and vice versa. It is also possible to switch between particle receiving (enhanced absorption) and emitting (enhanced scattering) abilities. Changing the polarization geometry of observation it is possible to effectively separate the dipole and the quadrupole plasmon radiation from all the non-plasmonic contributions to the scattered light.     

高增益宽带圆极化Vivaldi天线阵的设计

提出了一种由新型Vivaldi天线单元构成的22十字交叉圆极化天线阵。Vivaldi天线单元采用边缘渐变对拓的锯齿结构,提高了天线在4.7～7.0 GHz频带内的增益,其反射系数低于-10 dB的带宽为2.4～11.0 GHz,具有超宽带线极化特性。圆极化天线阵测量结果显示,在4.5～7.0 GHz频带范围内,其轴比均低于3 dB,且整个频带范围内增益达11～13 dBi。     

一种基于共享孔径Fabry-Perot谐振腔结构的宽带高增益磁电偶极子微带天线

设计了一种工作于X波段的基于共享孔径Fabry-Perot(F-P)谐振腔结构的宽带高增益磁电偶极子微带天线,并设计了三种不同尺寸的双层频率选择表面(FSS)单元,通过共享孔径布阵组成了超材料覆层.利用三种FSS单元的相位补偿特性,有效拓展了覆层天线的增益带宽.实测和仿真结果均表明,加载超材料覆层后,磁电偶极子天线在7.8—12.3 GHz内S_(11)-10 d B,相对带宽达到44.7%,覆盖整个X波段.天线增益在7.9—12.1 GHz内均有明显的提高,最大提高了7 d B.相较于传统的F-P谐振腔结构覆层天线,设计的基于共享孔径的F-P谐振型超材料覆层天线能够明显拓展天线增益带宽,在新型宽带高增益天线设计方面具有广阔的应用前景.     

过模波导器件的迭代设计方法

从模式保留和转换的角度, 过模波导器件可分为模式转换器、模式保留器和模式综合器. 传统方法只解决其中一种器件的设计或者对器件的某个指标进行改进. 本文在深入分析耦合波理论之后, 提出了过模波导器件的迭代设计方法, 从原理上解决了过模波导器件的设计问题. 该方法能够统一设计三类过模波导器件, 通过添加不同的结构控制方法, 可得到转换效率更高、带宽更宽、结构更紧凑、满足不同工程需求的器件, 而且还能有效设计一些新型器件. 给出了两个设计实例: 双频TM₀₁–TE₁₁模式变换器和光壁馈源喇叭. 双频TM₀₁–TE₁₁模式变换器的两个工作频点为8.75 GHz和10.3 GHz, 波导半径为16 mm, 在两个频点转换效率为99%以上. 光壁馈源喇叭实现TE₁₁模式向高斯束的转换. CST仿真结果验证了这两个器件设计的正确性和有效性. 关键词： 耦合波理论 模式转换器 模式过渡器 迭代法     

Radiofrequency magnetic resonance coils and communication antennas: Simulation and design strategies

Coils simulation and design is a fundamental task to maximize Signal-to-Noise Ratio in Magnetic Resonance applications. In the meantime, in the last years the issue of accurate communication antennas analysis has grown. Coil design techniques take advantage of computer simulations in dependence on the magnetic field wavelength and coil sizes. In particular, since at high frequencies coils start to behave as antennas, modern Magnetic Resonance coil development exploits numerical methods typically employed for antennas simulation.This paper reviews coil and antenna performance parameters and focuses on the different simulation approaches in dependence on the near/far field zones and operating frequency.     

Babinet-Inverted Optical Nanoantenna Analogue of Electromagnetically Induced Transparency

A Babinet-inverted optical nanoantenna analogue of electromagnetically induced transparency based on the coupling between two magnetic dipole antennas and a magnetic octupole antenna in a Au film waveguide is demonstrated. Simulation results indicate that a pronounced elimination occurs in the radiating spectrum due to the coupling-induced radiation suppression. A two-oscillator electromagnetically induced transparency model is used to describe the antenna. The coupling coefficient between the magnetic dipole antennas and the magnetic octupole antenna is calculated using the model and is found to decline exponentially with the increase of the distance between them. Such an antenna can be directly integrated with optical waveguides or transmission lines,thus is of fundamental significance for the applications in nano-optics, such as the optical device miniaturizations and photonic circuit integrations.     

Optimization of Circular Ring Microstrip Antenna Using Genetic Algorithm

Circular ring microstrip antennas have several interesting properties that make it attractive in wireless applications. Although several analysis techniques such as cavity model, generalized transmission line model, Fourier-Hankel transform domain and the method of matched asymptotic expansion have been studied by researchers, there is no efficient design tool that has been incorporated with a suitable optimization algorithm. In this paper, the cavity model analysis along with the genetic optimization algorithm is presented for the design of circular ring microstrip antennas. The method studied here is based on the well-known cavity model and the optimization of the dimensions and feed point location of the circular ring antenna is performed via the genetic optimization algorithm, to achieve an acceptable antenna operation around a desired resonance frequency. The antennas designed by this efficient design procedure were realized experimentally, and the results are compared. In addition, these results are also compared to the results obtained by the commercial electromagnetic simulation tool, the FEM based software, HFSS by ANSOFT.     

超薄宽带平面聚焦超表面及其在高增益天线中的应用

针对相位梯度超表面在灵活操控电磁波与提高天线增益中的潜在应用,提出一种新型的宽带超表面单元,实现了在较宽频带范围内操控电磁波波前与提高天线增益.本文首先设计了一种圆环十字形对称单元来控制反射波的相移量,单元厚度为1 mm,尺寸为0.3λ_0(λ_0=20 mm),工作频段15—18 GHz,而后验证了由该单元组成的相位梯度超表面在15—18 GHz范围内对电磁波的奇异反射与聚焦特性.最后将设计的反射聚焦超表面应用于提高天线增益中,仿真与测试结果均表明,天线最高增益在15—18 GHz内平均增加了11 d B且-1 dB增益带宽为15—18 GHz(相对带宽为18.2%).由于厚度薄、重量轻、频带宽,设计的该单元拓展了相位梯度超表面在微波领域的应用,有望为高增益天线的实现提供新的方法.     

Millimeter wave components for electronically controllable antennas

Many present and future military and commercial systems operating at millimeter wave frequencies require the use of sophisticated electronically controllable antennas for maximum capability and flexibility. Electronic control of the antenna pattern is provided by electronically switchable phase control of each radiating element such as that achieved in phased array antennas or via electronically reconfigurable antenna feeds referred to as beam forming networks (BFN). Multibeam antennas provided by BFN'S can be realized using switches, variable power dividers (VPD), and phase shifters. Ferrite materials and associated application technology are being utilized to achieve these switchable RF control components at millimeter wave frequencies. The performance achievable in ferrite switchable circulators, variable power dividers and phase shifters in the frequency region from 20 to 100 GHz is discussed.