Microwave radiometer, as one of the most useful tools in remote sensing of earth resources and environment, has been developed rapidly The recent research in this area is to concentrate how to improve spatial resoluti...
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ISBN:
(纸本)0819429627
Microwave radiometer, as one of the most useful tools in remote sensing of earth resources and environment, has been developed rapidly The recent research in this area is to concentrate how to improve spatial resolution. But the methods, which depend on increasing antenna aperture or decreasing carrier wavelength to obtain high spatial resolution, are inapplicable to aerospace engineering. The synthetic aperture technique needs the coherence effect of active microwave transmitted signal, so it cannot be used by passive radiometer. In this paper, a new approach is introduced. Firstly, the radiation of far-field target is received by two-dimensional (2-D) linearantennaarray. The incident signals received by all array elements have an amount of delay among them. These coherent signals of same wave front are amplified individually and applied to piezoelectric transducers of a multi-channel Bragg cell. The electronic signals are converted into traveling acoustic waves in acousto-optic cell. The refractive index of crystal is changed proportionally to the input voltages. When collimated laser is incident upon the crystal, Bragg diffraction occurs. Fourier transform lens produces optically a two-dimensional Fourier Transform of the signals in a charge-coupled device (CCD) plane. The direction and radiation intensity of arrival signal can be obtained simultaneously. Since the radiation signal of some far field target in the antenna coverage can be detected individually, that means the spatial resolution of radiometer can be improved. Theoretical derivation will be given in detail in this paper.
Generation of multi beams with equal height is complex and involved. The literature to trial with this problem is very limited. However, an effort is made in this present work to generate such complicated patterns usi...
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ISBN:
(纸本)9781538659953
Generation of multi beams with equal height is complex and involved. The literature to trial with this problem is very limited. However, an effort is made in this present work to generate such complicated patterns using state-of-the-art optimization algorithms. Few arrays are considered to generate multi beam by applying Firefly and PSO algorithms. The values of parameters of elements in arrayantennas are varying in nature. The results realized by applying Firefly and PSO algorithms are correlated and normalized patterns are conferred in U domain. Communication between multiple users is made easy by using antennas with multi beam. The trial of this work is very significant as the generated pattern doesn't exhibit any side lobe and hence EMI problem is eliminated.
Vehicle-related communications are a key application to be enabled by Fifth Generation (5G) wireless systems. The communications enabled by the future Internet of Vehicles (IoV) that are connected to every wireless de...
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Vehicle-related communications are a key application to be enabled by Fifth Generation (5G) wireless systems. The communications enabled by the future Internet of Vehicles (IoV) that are connected to every wireless device are referred to as Vehicle-to-Everything (V2X) communications. A major application of V2X communication systems will be to provide emergency warnings. This thesis evaluates Long-Term Evolution (LTE) and Dedicated Short Range Communications (DSRC) in terms of service quality and latency, and provides guidelines for design of cooperative LTE-DSRC systems for V2X communications. An extensive simulation analysis shows that (1) the number of users in need of warning has an effect on latency, and more so for LTE than for DSRC, (2) the DSRC priority parameter has an impact on the latency, and (3) wider system bandwidths and smaller cell sizes reduce latency for LTE. The end-to-end latency of LTE can be as high as 1.3 s, whereas the DSRC latency is below 15 ms for up to 250 users.
Also, improving performance of systems is as much as important as studying about latency. One method to improving performance is using a better suitable antenna for physical communication. The mobility of vehicles results in a highly variable propagation channel that complicates communication. Use of a smart, steerable antenna can be one solution. The most commonly used antennas for vehicular communication are omnidirectional. Such antennas have consistent performance over all angles in the horizontal plane; however, rapidly steerable directional antennas should perform better in a dynamic propagation environment. A linear array antenna can perform dynamical appropriate azimuth pattern by having different weights of each element. The later section includes (1) identifying beam pattern parameters based on locations of a vehicular transmitter and fixed receivers and (2) an approach to find weights of each element of linear array antenna. Through the simulations with our approach an
This article presents an approach to design a non-uniformly excited linear array antenna (LAA) and an alternate solution to LAAs in the form of time-modulated lineararrays (TMLA) for optimum far-field radiation patte...
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This article presents an approach to design a non-uniformly excited linear array antenna (LAA) and an alternate solution to LAAs in the form of time-modulated lineararrays (TMLA) for optimum far-field radiation pattern synthesis. The performance analysis of both the antennaarrays is studied, and the advantages and limitations of the proposed design approaches are presented with numerical outcomes. The far-field radiation pattern is optimized to reduce the interference by simultaneously lowering the sidelobe levels and increasing the directivities of LAAs and TMLAs. A recently proposed meta-heuristics computation technique called whale optimization algorithm (WOA) is employed to get the optimal results. The current excitation amplitude and the inter-element spacing of the 16-element LAA are optimized with WOA to attain the desired results. However, due to the large dynamic range ratios (DRRs) of excitation weights, array feed network complexities are increased, which restricts the design of typical LAAs. TMLAs can be regarded as an alternative solution where the problem of large DRRs as well as the design complexities of LAAs are eliminated. The concept of 'time' is vital in time-modulation as it plays the role of an added degree of freedom realized by periodically turning ON and OFF the radio-frequency switches with an electronic control circuit to achieve an enhanced array radiation pattern. WOA is utilized to determine the optimal switch-ON time periods for each array element and the optimal inter-element spacing of a 16-element TMLA. A set of numerical results validates the advantages of TMLAs over LAAs, and the limitations of TMLAs with respect to LAAs are also indicated. The performance of both the arrays is then compared with other published literature results to establish the superiority of the proposed approach.
A continuous-switching type arrayantenna receiver has been proposed in order to reduce the deterioration due to fast-fading channel variations and improve communication performance. The receive antennas are placed in...
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ISBN:
(纸本)9781467366533
A continuous-switching type arrayantenna receiver has been proposed in order to reduce the deterioration due to fast-fading channel variations and improve communication performance. The receive antennas are placed in a lineararray, and by sequentially switching the elements in the opposite direction to the direction of the train travel, it has been possible to fix the signal receiving point virtually. Through the development of a scale-model experiment of high-speed movement using the prototype antenna, in this paper we show that it is possible through optimized antenna element selection and appropriate signal processing to reduce the fading rate and improve the performance of an OFDM system. A software simulation based on the Worldwide Interoperability for Microwave Access (WiMAX) physical layer parameters was made and data transmitted at RF in a 5 MHz bandwidth with symbol rate appropriately scaled to simulate a range of fading speeds. The receive antennaarray consisting of eight elements traverses a track at a virtual speed of 180 km/h and the error rate performances with and without switching are compared.
In this paper, we propose a system for detection of the missing people employing UAV which is able to move quickly and has a wide view from the air in the disaster area. However, an airplane type UAV does not always h...
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ISBN:
(纸本)9781467386678
In this paper, we propose a system for detection of the missing people employing UAV which is able to move quickly and has a wide view from the air in the disaster area. However, an airplane type UAV does not always have a stable flight due to strong wind, rolling, and pitching. In order to detect and to respond the missing people promptly using the UAV, we propose the system which uses a phased arrayantenna and an angle detector. To implement the system, we assemble the phased arrayantenna and carry out an experiment to measure the characteristics of directivity, the directivity control characteristics, the return loss of the antenna, and the received power level to compare using and not using the phased arrayantenna in terms of efficiency and functionality. The experiment results show that the proposed system increase the received power level by adjusting the directivity of the antennas with short delay time. The results also confirm that the proposed system is practical in decreasing victims of disasters.
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