Synthesis of compromise sum-difference arrays through time-modulation

In this study, time-modulation is exploited for the synthesis of monopulse sub-arrayed antennas. The solution of the compromise sum-difference problem is obtained by setting the set of static excitations to an optimal sum set and synthesising the `best compromise? difference pattern through a contiguous partition method based approach. The array elements are aggregated into sub-arrays controlled by means of radio frequency (RF) switches with optimised `on? time-durations. The switch-on instants of the pulse sequences are then computed by means of a particle swarm optimiser to reduce the interferences caused by the sideband radiations. A selected set of numerical results is reported to assess the potentialities of time-modulation in dealing with the synthesis problem at hand.     

Compact ultrahigh-frequency antenna designs for low-cost passive radio frequency identification transponders

Compact planar antennas for low-cost radio frequency identification (RFID) passive transponders are disclosed. The proposed ultrahigh-frequency antenna takes advantage of its unique topology to assure conjugate matching with essentially complex impedance of the electronic chip directly embedded into the radiator. Rectenna design issues are also emphasised. An original method to characterise IC chips and antennas as taken in its entirety of transponders is presented. The characterisation of the chip takes into account the impact of connecting antennas to the rectifier by flip-chip bonding process. The proposed experimental method allows finding chip impedance exactly as it seen by antennas. Refined rectifier circuitry effectively overcomes dependence of transponder performances on the type deviation of the connected antennas. Very good antenna performance is predicted theoretically and validated experimentally over an operating bandwidth of actual RFID systems.     

Radiation engineering of optical antennas for maximum field enhancement

Optical antennas have generated much interest in recent years due to their ability to focus optical energy beyond the diffraction limit, benefiting a broad range of applications such as sensitive photodetection, magnetic storage, and surface-enhanced Raman spectroscopy. To achieve the maximum field enhancement for an optical antenna, parameters such as the antenna dimensions, loading conditions, and coupling efficiency have been previously studied. Here, we present a framework, based on coupled-mode theory, to achieve maximum field enhancement in optical antennas through optimization of optical antennas' radiation characteristics. We demonstrate that the optimum condition is achieved when the radiation quality factor (Q(rad)) of optical antennas is matched to their absorption quality factor (Q(abs)). We achieve this condition experimentally by fabricating the optical antennas on a dielectric (SiO(2)) coated ground plane (metal substrate) and controlling the antenna radiation through optimizing the dielectric thickness. The dielectric thickness at which the matching condition occurs is approximately half of the quarter-wavelength thickness, typically used to achieve constructive interference, and leads to ～20% higher field enhancement relative to a quarter-wavelength thick dielectric layer.     

Finite-difference time-domain simulations of the effects of air gaps in double-shell extended hemispherical lenses

The effects of parasitic air gaps on the input impedance and radiation characteristics of dense double-shell integrated lens antennas are studied numerically at millimetre waves using the finite-difference time-domain method. The lens core is made up of Macor or silicon, and is coated with a quarter wavelength matching layer. Two kinds of gaps are compared: they are located either (i) between both shells of the lens, or (ii) between the lens base and the feed substrate. We show that their impact is much more critical in the second case, and that it becomes dramatic for silicon lenses, even with very thin gaps (smaller than ? ₀/100); the three major observed effects are the following: (i) strong shift of the resonant frequency, (ii) beam broadening and directivity loss, (iii) increase of the side lobe level.     

Design of compromise sum-difference patterns through the iterative contiguous partition method

An innovative approach for the synthesis of sub-arrayed monopulse linear arrays is presented. A compromise difference pattern is obtained through an optimal excitations matching method based on the contiguous partition technique integrated in an iterative procedure ensuring, at the same time, the optimisation of the sidelobe level (or other beam pattern features). The flexibility of such an approach allows one to synthesise various difference patterns characterised by different trade-off between angular resolution and noise/interferences rejection in order to match the user-defined requirements. On the other hand, owing to its computational efficiency, synthesis problems concerned with large arrays are easily managed, as well. An exhaustive numerical validation assesses the reliability and accuracy of the method pointing out the improvements upon state-of-the-art sub-arraying techniques.     

左手材料在天线中的应用研究进展

从理论上解释了左手材料用于天线设计时实现天线高指向性、高效率、小型化以及大扫描范围的原因,重点介绍了基于金属谐振结构和复合左/右手传输线(CRLH TL)结构的左手材料用于天线设计时的研究进展,指出金属谐振结构在提高天线方向性、增大天线增益、减小天线体积等方面具有很大优势,CRLH TL结构在提高天线带宽、增加天线频带、增大漏波天线扫描范围等方面具有潜在的应用价值。     

基于四元十字阵的低频换能器指向性检测方法

针对大型低频换能器指向性难以测量的问题,提出了一种基于四元十字阵的测量方法以获取大型低频换能器的指向性。利用到达四元十字阵阵元的时延差信息,结合双曲面交汇法对换能器进行定位,并根据四元十字阵阵元测得的声信号实现大型低频换能器指向性的测量;对定位算法进行理论仿真,设计并进行了湖上试验以测量模拟声源的指向性;对湖上试验测量数据进行计算分析,并与模拟声源在消声水池中的测量结果进行比较,两者-3 dB波束开角的测量结果相差在10%以内。此方法可以用于低频换能器指向性的测量。     

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.<>     

Multi-site production planning integrating procurement and distribution plans in multi-echelon supply chains: an interactive fuzzy goal programming approach

Motivated by a real case of an automobile company, this study proposes a multi-objective, multi-site production planning model integrating procurement and distribution plans in a multi-echelon supply chain network with multiple suppliers, multiple manufacturing plants and multiple distribution centres. The model incorporates four important conflicting objectives simultaneously: minimisation of the total cost of logistics, maximisation of the total value of purchasing, minimisation of defective items and minimisation of late deliveries subject to some realistic constraints. Due to the imprecise/fuzzy nature of the objectives’ aspiration levels and some critical data, an interactive fuzzy goal programming formulation is first developed. Then, a novel fuzzy approach is proposed to convert the FGP model into an auxiliary crisp formulation to find an efficient compromise solution. The proposed model and solution method are validated through some numerical tests. Computational results indicate the practicality and tractability of the proposed model and also the superiority of the proposed auxiliary crisp formulation in contrast to the current alternative fuzzy approaches.     

Method free from mismatching errors for measuring the loss of attenuators

Summary The method of evaluating the attenuation by measuring the ratio of voltages or powers in the lateral branches of two directional couplers, between which the attenuator is placed, provides a complete elimination of two of the three components of the matching error.In order to reduce residual errors, the directional coupler at the input of the attenuator must have a good directivity, and the directional coupler at its output must have small reflections from its flanges and from the load in its main branch.It is possible to eliminate completely in the first approximation the matching eror by using a sliding load (or any other method of phase adjustment).     

Fabrication and characterization of a three-dimensional feed-horn infrared antenna for an infrared detector

A three-dimensional feed-horn antenna for the 10-microm-wavelength infrared region has been suggested, characterized, and fabricated. It is applied to an infrared detector for efficient collection of infrared radiation and to reduce background noise. The optimum size of the horn antenna was designed for maximum antenna directivity. The three-dimensional feed-horn antenna mold was fabricated by rotating and tilting illumination, whereas the antenna plate was acquired through electroplating. Antenna characteristics were measured by coupling of the antenna with a microbolometer. Measurement results show that the directivity of the antenna is 16.1 dB and the background noise is reduced by a factor of approximately 2 compared with an open-structure infrared detector.     

Time-domain equalisation for discrete multi-tone transceivers: new results and performance analysis

The time-domain equaliser (TEQ) is a commonly used device to shorten the channel impulse response in a discrete multitone (DMT) receiver. Many methods have been proposed to design the TEQ with a capacity maximisation criterion. An implicit assumption used by existing methods is that circular convolution can be conducted for the noise signal and the TEQ. This assumption is not valid because the noise vector, observed in a DMT symbol, does not have a cyclic prefix. A similar assumption is also made for the residual inter-symbol interference (ISI) signal. Because of these invalid assumptions, the TEQ-filtered noise and residual ISI powers in each subcarrier were not properly evaluated. As a result, optimum solutions derived are not actually optimal. This paper attempts to resolve this problem. We first analyse the statistical properties of the TEQ-filtered noise signal and the residual ISI signal in detail, and derive precise formulae for the calculation of the TEQ-filtered noise and residual ISI powers. Then, we re-formulate the capacity maximisation criterion to design the true optimum TEQ. Simulations show that the proposed method outperforms the existing ones, and its performance closely approaches the theoretical upper bound.     

Mode matching for a passive resonant ring laser gyroscope

An analytical method of matching the mode of an input laser to the lowest-order mode of a passive resonant ring laser gyro is described, as are the steps in determining the location and focal length of cylindrical mode matching lenses. Results were obtained with no mode matching, with a compromise spherical lens, with horizontal mode matching only, and with the proper cylindrical mode matching lenses. Compared with no mode matching, the latter case shows that the amplitude of the lowest-order mode is increased approximately 2.5 times. In addition, the number and intensity of higher-order modes are reduced to near zero, and the relative intensity of the lowest-order mode to the higher-order mode increased from approximately 5 to approximately 60 times greater.     

一种低旁瓣圆形活塞高频换能器研究

文章主要研究了一种低旁瓣圆形活塞高频换能器,采用去环非均匀分布方法实现低旁瓣,推导了去环非均匀圆形活塞换能器的指向性函数表达式,建立了指向性仿真模型,并采用Matlab软件进行仿真优化,对不同去环位置和不同去环宽度的圆形活塞换能器旁瓣级变化规律进行了分析,并通过添加匹配层拓展带宽。制作了一款低旁瓣圆形活塞宽带高频换能器,并进行测量。实测结果与仿真基本一致,换能器实测最大旁瓣级为-22.4 dB,较均匀圆形活塞换能器旁瓣级降低了4.8 dB,中心频率为325 kHz,-3 dB带宽为150 kHz。     

Plasmonic antennas for directional sorting of fluorescence emission

Spontaneous emission of fluorescent molecules or quantum dots is radiated along all directions when emitters are diluted in a liquid solution, which severely limits the amount of collected light. Besides, the emission direction does not carry any useful information and cannot be used to sort different molecules. To go beyond these limits, optical antennas have been recently introduced as conceptual tools to control the radiation properties for nanoemitters fixed on a substrate. Despite intense recent research, controlling the luminescence directivity remains a challenge for emitters with random positions and orientations, which is a key for several biomolecular screening applications. Here, we present full directional control of the fluorescence emission from molecules in water solution by an optical antenna made of a nanoaperture surrounded by a periodic set of shallow grooves in a gold film. For each emission wavelength, the fluorescence beam can be directed along a specific direction with a given angular width, hereby realizing a micrometer-size dispersive antenna. We demonstrate the fluorescence beaming results from an interference phenomenon and provide physical optics guidelines to control the fluorescence directivity by tuning the groove-nanoaperture distance. This photon-sorting capability provides a new approach for high-sensitivity screening of molecular species in solution.     

Fuzzy multi-objective optimisation for master planning in a ceramic supply chain

In this paper, we consider the master planning problem for a centralised replenishment, production and distribution ceramic tile supply chain. A fuzzy multi-objective linear programming (FMOLP) approach is presented which considers the maximisation of the fuzzy gross margin, the minimisation of the fuzzy idle time and the minimisation of the fuzzy backorder quantities. By using an interactive solution methodology to convert this FMOLP model into an auxiliary crisp single-objective linear model, a preferred compromise solution is obtained. For illustration purposes, an example based on modifications of real-world industrial problems is used.     

二阶镶拼圆管矢量接收换能器研究

文章介绍了一种二阶镶拼圆管矢量接收换能器的设计方法，获得了类偶极子指向性以及波束宽度更为锐化的类四极子指向性。利用理论计算以及有限元仿真分析了镶拼圆管的指向性以及接收灵敏度，并实际制作了二阶镶拼圆管矢量接收换能器。在消声水池的测试表明，灵敏度测试结果与有限元仿真计算结果吻合较好，镶拼圆管矢量接收换能器类偶极子指向性图-3 dB波束宽度在95°左右，类四极子指向性图-3 dB波束宽度在40°左右，二阶矢量指向性图波束宽度明显比一阶矢量指向性图波束宽度更加锐化。     

求解远场声辐射问题的一种快速边界元法

针对传统边界元法奇异性的固有缺陷,研究一种求解结构辐射声场的间接边界元法。通过在内域虚拟曲面上配置一系列单偶极子源,等效模拟结构外辐射声场,并根据单元体积速度匹配法的边界条件方案,给出数值计算辐射声场的间接边界元模型。结合球冠形辐射器的仿真算例,表明该间接边界元法在求解远场声特性时具有较高的计算效率和精度,为分析设计具有大空间指向性的辐射器提供参考。     

小型化线列阵研究

介绍了一种小型化线列阵,阵结构与常规线列阵最大的不同在于阵元间距小于四分之一波长。通过理论分析和仿真计算优化了各阵元的最佳权系数,获得了良好的指向性,得到了实验的证明。小型化线列阵的指向性图具有四大特点：①单向性：仅在半空间出现一个轴对称的主波束,无栅瓣和次瓣。②端射特性：主波束出现在线阵的轴射方向。③超指向性：在阵的尺寸远小于二分之一波长条件下不仅可以获得良好的指向性图,并且波束宽度随阵元间距的减小而减小。④恒定束宽特性：在阵元间距小于八分之一波长条件下,波束宽度随频率变化非常平缓。这种小型化基阵也可用于大型基阵如拖曳阵和展开式体积阵的子基阵,进行低频宽带信号的检测。     

Some potential antenna applications of high-temperature superconductors

A review of possible applications of high-temperature superconductors (HTS) to antennas and antenna feed networks is presented. The frequency range of consideration is 1 MHz to 100 GHz. Three antenna application areas seem appropriate for HTS material. (1)Electrically small antennas and their matching networks: An increase in efficiency is possible for electrically short antennas, but at the expense of bandwidth. Substantial radiated power levels (on the order of kilowatts) can be handled by the best HTS material. Substantial improvement may be realized by making only the matching network of HTS material. (2)Feed and matching networks for compact arrays with enhanced directive gain (superdirective arrays): HTS material should permit such arrays to be fabricated that have high efficiency. (3)Feed networks for millimeter-wave arrays: Low-loss feed networks using HTS microstrip transmission lines give many decibels improvement in gain.