Meta-heuristic optimization algorithms for comparative analysis of uniform and non-uniform elliptical array antenna for enhanced gain

In this article, the synthesis of a non-uniform elliptical array antenna (EAA) is presented applying three relatively new, well-performing meta-heuristic optimization algorithms; quantum particle swarm optimization (QPSO), symbiotic organism search (SOS), and moth fly optimization (MFO) algorithms. The design objective allows simultaneous minimization of side lobes and maximization of gain by finding the best optimal combination of angular locuses of the antennas in the array structure. The proposed technique is efficient enough to resolve the underlying multi-objective problems at two principle planes of radiation and adaptable enough to the effective implementation of additional design constraints which make this design suitable for practical high-frequency applications as well as long-distance communication. The iterative accomplishment of the three algorithms is compared depending on the radiation parameters as well as statistical parameters. The outcomes are validated by performing a t test on the obtained data sets.     

A miniaturized multi‐wideband Quasi‐Yagi MIMO antenna system

A multi‐band directional multiple‐input–multiple‐output (MIMO) antenna system is presented based on a rectangular loop excited Quasi‐Yagi configuration. A 64% reduction in size is obtained using a rectangular meandered element as well as a small ground plane. The proposed two‐element MIMO antenna system covers the Telemetry L‐band and several LTE/WLAN bands. It has a wide measured bandwidth of 689 MHz (1.897–2.586 GHz) in the desired band centered at 2 GHz, and a measured bandwidth of more than 168 MHz across rest of the bands. The MIMO antenna system has a total size of 45 × 120 × 0.76 mm³, with a single element size of 55 × 60 × 0.76 mm³. The non‐desired back‐lobe radiation which is obtained using a small ground plane, is significantly reduced by using a novel defected ground structure (DGS) as compared with the complex techniques present in literature. The proposed DGS provides a high measured front‐to‐back ratio of 14 dB at 2 GHz and 11 dB in other bands. A maximum measured realized gain of 5.8 dBi is obtained in the desired band using a single parasitic director element. The proposed MIMO antenna system has a minimum measured radiation efficiency of 70%, isolation of 12 dB, and envelope correlation coefficient of 0.098 within all bands which ensures very good MIMO performance.     

An optimal circular antenna array design considering mutual coupling using heuristic approaches

This article shows the design of a non‐uniformly excited single ring circular antenna array (CAA) for the synthesis of optimal far‐field radiation characteristics. A recently proposed meta‐heuristic based optimization algorithm called gray wolf optimization (GWO) and state‐of‐the‐art swarm intelligence based evolutionary optimization technique known as particle swarm optimization with a distribution based update mechanism (PSOd) are individually applied to determine the optimum set of current excitation amplitude weights and the inter‐element spacing among the array elements to reduce the side lobe level and 3‐dB beamwidth considering the mutual coupling. The results obtained by employing PSOd and GWO are compared to those of the uniform radiation pattern and the recently published results of state‐of‐the‐art literature having equal sets of elements to show the superiority of employed approaches. Three different design examples of 8, 10, and 12 elements CAA are reported in this article to study the performances of PSOd and GWO algorithm‐based results over the results of other recently reported literature.     

Differential evolution to synthesize low sidelobe thinned isophoric time‐modulated planar array with increased directivity

In this article, a novel method for synthesizing rectangular planar array through thinning and time‐modulation is proposed. A new differential evolution based approach that generates a rank based population is adopted to find out the optimum element off position for thinning and ontime duration to modulate the antenna elements in time domain. The proposed synthesis method defines a preservative boundary at the array center where the antenna elements are not thinned and time‐modulated rather uniformly excited. It is shown that this proposed thinning and time‐modulation strategy with an optimum preservative boundary helps to realize low side lobe radiation pattern with increased directivity by controlling less number of optimization variables as compared to traditional approach. It also reduces the feed network complexity specifically for large antenna arrays.     

A Novel Approach towards the Designing of an Antenna for Aircraft Collision Avoidance System

TCAS/ACAS (Traffic/Aircraft Collision Avoidance System) is an airborne system designed to increase cockpit awareness of nearby aircraft and to service as a last defense against mid-air collisions between the aircrafts. In the existing system, four monopole stub elements are used as TCAS directional antenna and one blade type element is used as TCAS Omni-directional antenna. The transmission and reception frequencies of the TCAS antenna are 1.03G Hz and 1.09G Hz respectively. The existing TCAS antenna has some drawbacks such as low gain, large beamwidth, frequency and beam tuning/scanning issues etc. Antenna issues like unwanted signals reception may create difficulties in identifying the possible threats. In this paper, the focus is on the design and development of a novel Microstrip Antenna Array which can be used for TCAS/ACAS application. Two proposed antenna models are presented here – a Unit Element Dual Feed Microstrip Dual Patch Slotted Antenna and a Compact Microstrip Antenna Array. These are designed in CST tool to meet the current needs of aircraft Collision Avoidance System and to overcome the possible limitations associated with the existing techniques. The performance and other antenna characteristics have been explored from the simulation results followed by the antenna fabrication and measurement. A good Reflection Coefficient and VSWR with proper 50 Ω Impedance Matching, narrow Beamwidth, perfect Directional Radiation Pattern, high Gain and Directivity at the operating frequencies make this proposed antenna a good candidate for TCAS application. The proposed antenna would be expected to meet the requirements of the advanced avionics standards in terms of design simplicity, lightweight and high performance.     

不同参数对三瓦翻转压力坝轴承承载能力的影响

建立三瓦压力坝轴承的几何模型并求解得到油膜厚度分布。基于雷诺方程建立滑动轴承理论模型,采用单元流量平衡法来离散复杂轴瓦结构的Reynolds方程并用MATLAB求解,得到轴承承载力。采用载荷约束条件和模式搜索相结合的方式求解定载荷方向下的轴承静态特性,并得到载荷收敛的油膜厚度分布与压力分布。分别改变压力坝轴承结构参数,分析各参数对轴承承载能力的影响。结果表明：椭圆率和轴承长径比对轴承承载力影响较大,其他参数的影响都相对较小;随着椭圆率和轴承长径比的增加轴承承载力提高。     

Ku波段双极化宽带阵列天线

在Ku波段的微带阵列天线贴片单元基础上,进行了低旁瓣阵列的设计。设计了切比雪夫阵列、切比雪夫分布与等幅分布综合的16×16阵列,利用CST软件对这些阵列进行仿真。通过比较仿真结果,选择旁瓣电平较低的切比雪夫分布与等幅分布综合的16×16阵列进行加权处理。结果表明,权值为0．9、阵元间距为0．7A的16×16切比雪夫分布与等幅分布综合阵列,旁瓣电平小于-26dB,阵元电流相差较小,达到了性能指标要求。     

摄像机谱特性和矩阵电路

本文说明三管摄像机理想谱特性的负叶是正确色重现所必需的,并且证明,矩阵电路可以精确实现这些负叶。这使我们不再停留在“通过基色信号的加减运算,近似得理想曲线”的说法。     

Analysis and prediction of shock-induced near-field acoustics from an exhaust pipe

In this study an acoustic problem of a single shock wave moving through a circular pipe instead of a real pulsating flow with blast waves is considered. Due to the failure of a linear acoustic theory for the problem of interest, the method of computational fluid dynamics is employed to analyze the present problem. For this purpose, the axisymmetric Euler equations are solved by a high-resolution method which consists of a fifth-order weighted essential non-oscillation scheme for spatial discretization and a fourth-order Runge–Kutta method for time integration. In order to reduce the large computational time on a single computer, parallel computation with seven personal computers has been conducted. The detailed flow and sound pressure fields inside and downstream of the pipe are studied. The near-field sound pressure level downstream of the pipe was computed. The sound lobe and its orientation are investigated. In particular, an interesting phenomenon of spatial variation of velocity components associated with the sound lobe is reported. It is found that the spatial variations of the streamwise velocity component and pressure are in phase. However, the spatial variations of the radial velocity component and pressure are out of phase. Moreover, the generation mechanism of acoustics is attributed to the fact of the back-and-forth reflections of upstream-moving expansion waves generated at the pipe wall corner when the shock wave diffracts around the corner. The back-and-forth wave reflections result in the formation of interlacing high- and low-pressure regions that change with time.     

废气引射抽尘流场数值模拟

通过对原废气引射抽尘装置的三维引射掺混流场进行模拟计算分析,并根据数值模拟结果对喷管结构进行改进,以使其更好地满足涡轮增压发动机的使用需要。原结构的数值模拟结果与实际实验相吻合,计算结果与实际物理过程符合。在本文中给出了主喷管喷嘴形状进行改进后的流场模拟情况,并对结果进行分析讨论。本文的计算方法可以有效地用来预测引射流量比和揭示混合流场特性。