While the Yagi-Uda array has been studied for decades, one issue appears to have received less attention than perhaps it should, namely, the effects on performance of the array’s driven element length and its length-to-diameter ratio. This paper looks at that question. It shows that decreasing the L/D ratio increases impedance bandwidth, but it may shift the IBW band sufficiently far from the design frequency that other parameters such as gain and front-to-back ratio probably are adversely affected. It also shows that array performance is not relatively independent of element diameters. This paper also investigates the effect of lengthening the driven element, which can substantially improve IBW. Several iterations of a 3-element prototype and improved arrays are modeled with the Method of Moments and discussed in detail. A five step design procedure is recommended and applied to a Genetic Algorithm-optimized 3-element Yagi at 146 MHz. This array exhibits excellent performance in terms of gain, front-to-back ratio, and especially impedance bandwidth (nearly 14% for voltage standing wave ratio ≤ 2:1 with two frequencies at which 50 ? is almost perfectly matched). While the analysis and recommended design steps are applied to cylindrical array elements, which commonly are aluminum tubing for stand-alone VHF-SHF Yagis, they can be applied to other element geometries as well using equivalent cylindrical radii, for example, Printed Circuit Board traces for planar arrays. One consequence of lengthening the driven element while reducing its L/D ratio is that some reactance is introduced at the array feedpoint which must be tuned out, and two approaches for doing so are suggested.
This paper studies the design of water-saving irrigation system based on Internet of things. The structural model of the water-saving irrigation system was established, and the hardware and software of the control system were designed, with emphasis on the design and coverage calculation of the sensor nodes in the wireless sensor network. The wireless network and control system are tested, including network coverage, network connection, optimal communication distance and accuracy of data transmission. The experimental results show that the data transmitted by the wireless sensor is accurate and reliable, and the software and hardware of the automatic control system can work normally. The system can carry out intelligent irrigation timely and accurately.
This paper presents a study of a non-uniform pitch helical resonator (NPHR) structure and the coupling mechanisms to design dual-passband filters.The previous research analyzes NPHR as a type of step impedance resonator (SIR), however, it does not give analytical equations or prediction for the dual-resonance characteristics of the NPHR structure discussed in this paper.Consequently, a circuit model is proposed to analyze the dual-resonance characteristics of NPHRs.Analytical equations are derived, showing that the frequency ratio of a dual-band NPHR can be determined by the ratio of turns.EM simulation and experimental results have shown good agreement with the circuit analysis.The derived analytical equations from circuit model can be used for fast design of NPHRs.A step-width aperture is proposed to independently control the coupling coefficients at the each band of NPHRs.A third order dual-passband filter has been designed and fabricated.The filter has 3.3% and 3% fractional bandwidths at 789 MHz and 2402 MHz, respectively.The designed prototype filter shows that NPHRs can be utilized to realize compact filters with dual-band characteristics.The filter design can be extended from engineering perspective for application in wireless communication systems.
The effect of correlated fading reduces the performance gain in multi-antenna communications. Diversity combining is a well-known technique to reduce the effect of correlation. But still, it is an open problem to quantify as the diversity scheme is more efficient in enhancing the security of cellular multicast network mitigating the effects of correlation. Motivated by this issue, this paper considers a secure wireless multicasting scenario through correlated cellular networks in the presence of multiple eavesdroppers. The selection combining (SC) and switch and stay combining (SSC) techniques are considered in dual arbitrarily correlated Nakagami-m fading channels. The closed-form analytical expressions for the probability of non-zero secrecy multicast capacity and the secure outage probability for multicasting are derived to understand the insight into the effects of correlation on the SC and SSC diversity schemes and to quantify which diversity scheme is more efficient in enhancing the security of correlated multicast networks. The results show that, although the diversity gain reduces the effect of correlation, the diversity gain provided by the SC diversity scheme is more significant in mitigating the effect of correlation compared to the SSC diversity scheme. Due to the selection mechanism of SC diversity, it is more sensitive to the change of SNR of the eavesdropper’s channel compared to the case of the SSC diversity scheme.
A six-element Yagi-Uda array is optimally designed using Central Force Optimization (CFO) with a small amount of pseudo randomly injected negative gravity. CFO is a simple, deterministic metaheuristic analogizing gravitational kinematics (motion of masses under the influence of gravity). It has been very effective in addressing a wide range of antenna and other problems and normally employs only positive gravity. With positive gravity the six element CFO-designed Yagi array described here exhibits excellent performance with respect to the objectives of impedance bandwidth and forward gain. This paper addresses the question of what happens when a small amount of negative gravity is injected into the CFO algorithm. Does doing so have any effect, beneficial, negative or neutral? In this particular case negative gravity improves CFO’s exploration and creates a region of optimality containing many designs that perform about as well as or better than the array discovered with only positive gravity. Without some negative gravity these array configurations are overlooked. This Yagi-Uda array design example suggests that antennas optimized or designed using deterministic CFO may well benefit by including a small amount of negative gravity, and that the negative gravity approach merits further study.
The advanced design of a 10 × 1 linear antenna array system with the capability of frequency tunability using GT3-23001 liquid crystal (LC) is proposed.The design for this reconfigurable wideband antenna array for 5G applications at Ka-band millimeter-wave (mmw) consists of a double layer of stacked patch antenna with aperture coupled feeding.The bias voltage over LC varies from 0 V to 10.6 V to achieve a frequency tunability of 1.18 GHz.The array operates from 25.3 GHz to 33.8 GHz with a peak gain of 19.2 dB and a beamwidth of 5.2˚ at 30 GHz.The proposed reconfigurable antenna array represents a real and efficient solution for the recent and future mmw 5G networks.The proposed antenna is suitable for 5G base stations in stadiums, malls and convention centers.It is proper for satellite communications and radars at mmw.
This paper investigates the effect of adding three extensions to Central Force Optimization when it is used as the Global Search and Optimization method for the design and optimization of 6-elementYagi-Uda arrays.Those extensions are Negative Gravity, Elitism, and Dynamic Threshold Optimization.The basic CFO heuristic does not include any of these, but adding them substantially improves the algorithm's performance.This paper extends the work reported in a previous paper that considered only negative gravity and which showed a significant performance improvement over a range of optimized arrays.Still better results are obtained by adding to the mix Elitism and DTO.An overall improvement in best fitness of 19.16% is achieved by doing so.While the work reported here was limited to the design/optimization of 6element Yagis, the reasonable inference based on these data is that any antenna design/optimization problem, indeed any Global Search and Optimization problem, antenna or not, utilizing Central Force Optimization as the Global Search and Optimization engine will benefit by including all three extensions, probably substantially.
The Internet of Things (IoT) is an emerging network infrastructure with more than five devices owned by a single user.Wireless connectivity forms the backbone of such infrastructure.IoT uses diverse wireless communication technologies such as IEEE 802.15.4,Wi-Fi, Zigbee, Bluetooth, RFID, BLE (Bluetooth Low Energy), and various other cellular technologies.Wi-Fi is most suitable for IoT Home or office networks.Practically wireless signals do not adhere to the boundaries of the office or home, or organization and impose inherent security risks like information leakage, unauthorized access, other security and privacy threats to networking infrastructure.Therefore Authorization/Association of devices is one of the main security concerns.This paper discusses how unauthorized access to wireless networks (Wi-Fi) can be secured by improving existing WPA2 protocol security.
This paper presents the design and the experimental characterization of a new multi-band antenna consisting of three folded monopoles dedicated to mobile communication systems. The originality of this paper is to get the PMR (Professional or Private Mobile Radio) band with the GSM (Global System for Mobile Communications), DCS (Digital Cellular System) and UMTS (Universal Mobile Telecommunications System) bands. The main lobe of the antenna radiates in the zenith direction with a linear polarization over all bands. It is interesting to design the proposed antenna in order to obtain better performances in terms of directive radiation pattern (especially in the PMR band) in comparison with the already existing antenna systems in the wireless market for similar purposes. The prototype was studied with the software CST-MWS (Micro wave studio 2012). The antenna has been designed and successfully measured.
With the ever-growing requirement for higher data rates, terminals supporting multiple-input multiple-output (MIMO) technologies are being developed for next-generation. As for wireless device manufacturers, a radio performance evaluation of multi-antenna terminals in desired environments is mandatory before product release. This paper discusses the Over the Air (OTA) performance evaluation of antenna diversity systems in Indoor and Outdoor multi-path propagation channel models inside anechoic chamber, in terms of correlation coefficients and diversity gain (DG). These channel models have been emulated in terms of angles of arrivals (AoA) and cross-polarization ratio (XPR) with Rayleigh fading. For this purpose, SATIMO SG24 measurement system has been used. However, the actual configuration of this system is not able to emulate desired realistic environments. Therefore, an innovative methodology based on the SG24 probes control has been developed. The obtained results in simulations and measurements have shown a good agreement.
This paper describes our contribution in the ANR (Agence Nationale de la Recherche) project called GELOCOM (GEo-LOCalisation de telephOnes Mobiles) managed by the THALES Communications company, dedicated to the emergency localization of cellular phones.This contribution takes place in the field of antennas, with the development of broad-band systems: a circular array of six elements with separated outputs for the receiving part.In this paper, we present the design and the characterization of broad-band double ellipse array antenna.This special structure is chosen in order to obtain a good omnidirectional radiation pattern, enhance the gain and maximize the V/H polarization ratio.In comparison with the already existing antenna systems in the wireless market for similar purposes, the proposed antenna has considerably shown better performance which makes it competitive among other antenna models.For the design and optimization of antennas, we use CST MWS software.The antennas have been designed and successfully measured.
As antennas are inherently included recommended in Over-The-Air (OTA) testing, it is important to also consider realistic channel models for the multiple-input multiple-output (MIMO) device performance evaluation. This paper aims to emulate realistic multi-Path propagation channels in terms of angles of arrivals (AoA) and cross-polarization ratio (XPR) with Rayleigh fading, inside an anechoic chamber, for antenna diversity measurements. In this purpose, a practical multi-probe anechoic chamber measurement system (MPAC) with 24 probe antennas (SATIMO SG24) has been used. However, the actual configuration of this system is not able to reproduce realistic channels. Therefore, a new method based on the control of the SG24 probes has been developed. At first time, this method has been validated numerically through the comparison of simulated and analytical AoA probability density distributions. At the second time, the performance of an antenna diversity system inside the SG24 has been performed in terms of the correlation coefficient and diversity gain (DG) using an antenna reference system. Simulated and measurements results have shown a good agreement.
Electronic commerce which denotes the process of electronic transaction via internet has led to a very significant improvement in the level of growth, development, efficiency and productivity of global economies. In order to benefit from the economic opportunities offered by electronic commerce, Nigerian government and business organizations needs to effectively integrate Information and Communication Technologies (ICTs) as the major component of e-commerce campaign initiatives. The discussion in the paper is centered on e-commerce and ICTs and their resultant effect on Nigeria's economic growth and development. This paper has presented an in-depth discussion of the various types of e-commerce, the major contributions of e-commerce to the economic growth of Nigeria and finally the challenges that impede the growth of e-commerce in Nigeria were identified and the possible recommendations for solutions to those challenges were provided.
This paper presents a novel method for polarized antenna transmission utilizing a differential technique. The method uses a linear cross-polarized antenna, for example, a vertical and horizontal polarized antenna, improving performance and power efficiency of wireless communications. Hence a linear relationship between the capacity of the systems and the number of cross-polarized antennas exists. The result shows the fact that this method enhances the SNR comparing to other systems. This solution is simple, compact and does not require any bandwidth expansion.
In this paper, we describe 2 kinds of printed dipole arrays and compare the performances of these arrays in term of reflexion coefficient, radiation pattern and dimensions. It is interesting to design array in order to obtain better performances in term of omnidirectional radiation pattern in comparison with single element. We choose this elementary source in order to obtain compact array with good performances. These antenna arrays are designed to have omnidirectional radiation pattern with horizontal polarization. We present an application dedicated to compact base station in the last section.
Monitoring and recording large time series of data and making them available for studying—are the key roles of environmental monitoring systems. This study produce review of three different measurement monitoring systems (NSUNET, WAHASTRAT and MERIEXWA) with same design, which were placed during different time frame in the Northern Serbia (Vojvodina Province). Each of three monitoring systems has different demands and requirements which were addressed accordingly in their design. Power supply conditions for two systems are primary cells and solar panels, while NSUNET has constant power supply only during nighttime. Data is transmitted in MERIEXWA using binary protocol, WAHASTRAT using http, while NSUNET sends data over ftp. Same topology is used in all systems—each node sends data directly to the central location (in case of NSUNET two locations are provided for backup purposes). NSUNET system sends data using specific structure and stores them as plain text files. It also has different approach for time synchronization and monitoring issues. The main result of this study is to present how to create system that provides good quality and unchanged data from monitoring sensor to the end user while maintaining whole data structure transmission costs low. Furthermore, data collected from NSUNET were used in order to assess the influence of urbanization on regional climate modification, which leads to the creation of urban climate. Propositions for new system development combining best from all three systems are discussed.
