Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 7 Articles
We propose a miniaturized band-pass frequency selective surface (FSS) with periodic unit cell structure. The proposed FSS is\nrealized by symmetrically bending the edges of the square loop aperture element, by which our proposed FSS increases the resonant\nlength, and, hence, reduces its size. In this FSS, each unit cell has a dimension of 0.0538??Ã?â??0.0538??, where ?? represents the\nwavelength of the corresponding resonant frequency. Both the theoretical analysis and simulation results demonstrate that our\nproposed FSS, having high polarization stability and angle stability, can achieve smaller size in comparison with the previously\nproposed structures...
Civil and military applications are increasingly in need for agile antenna devices which respond to wireless telecommunications,\nradars, and electronic warfare requirements. The objective of this paper is to design a new agile antenna system called\nelectromagnetic band gap (EBG) matrix. The working principle of this antenna is based on the radiating aperture theory and\nconstitutes the subject of an accepted CNRS patent. In order to highlight the interest and the originality of this antenna, we present\na comparison between it and a classical patch array only for the (one-dimensional) 1D configuration by using a rigorous full wave\nsimulation (CST Microwave software). In addition, EBG matrix antenna can be controlled by specific synthesis algorithms. These\nalgorithms use inside their; optimization loop an analysis procedure to evaluate the radiation pattern. The analysis procedure is\ndescribed and validated at the end of this paper....
This paper deals with spectrum sensing in an orthogonal frequency division multiplexing (OFDM) context, allowing an\nopportunistic user to detect a vacant spectrum resource in a licensed band. The proposed method is based on an iterative algorithm\nused for the joint estimation of noise variance and frequency selective channel. It can be seen as a second-order detector, since it is\nperformed by means of the minimum mean square error criterion.Themain advantage of the proposed algorithm is its capability to\nperformspectrumsensing, noise variance estimation, and channel estimation in the presence of a signal. Furthermore, the sensing\nduration is limited to only one OFDMsymbol.We theoretically show the convergence of the algorithm, and we derive its analytical\ndetection and false alarm probabilities. Furthermore, we show that the detector is very efficient, even for low SNR values, and is\nrobust against a channel uncertainty....
A novel design of a cognitive radar (CR) hybridized with a phased array radar (PAR) having a low probability of intercept (LPI)\ntransmit beam forming is proposed. PAR directed high gain property reveals its position to interceptors. Hence, the PAR high gain\nscanned beam patterns, over the entire surveillance region, are spoiled to get the series of low gain basis patterns. For unaffected\narray detection performance, these basis patterns are linearly combined to synthesize the high gain beam pattern in the desired\ndirection using the set of weight. Genetic algorithm (GA) based evolutionary computing technique finds these weights offline and\nstores to memory. The emerging CR technology, having distinct properties (i.e., information feedback, memory, and processing\nat receiver and transmitter), is hybridized with PAR having LPI property. The proposed radar receiver estimates the interceptor\nrange and the direction of arrival (DOA), using the extended Kalman filter (EKF) and the GA, respectively, and sends as feedback\nto transmitter. Selector block in transmitter gets appropriate weights from memory to synthesize the high gain beam pattern in\naccordance with the interceptor range and the direction. Simulations and the results validate the ability of the proposed radar....
Alow-cost, compact 8 Ã?â?? 8 Butler matrix based on a novel bilayer microstrip configuration is presented and implemented for 4.3GHz\ntelecommunication application. A back-to-back placed bilayer microstrip structure has been proposed to avoid using crossover. To\nexpand operational bandwidth of the Butler matrix, a three-branch line directional coupler has been employed as 3 dB/90Ã?° bridge,\nand a kind of improved two-order Schiffman phase shifter has been adopted as fixed phase shifter. For application of indoor wireless\ncommunication, a compact broadband 8 Ã?â?? 8 Butler matrix has been designed and fabricated. The measured results show that the\nreturn loss of the matrix is lower than -10 dB, the isolation is better than 17 dB, the power distribution error is less than Ã?±2.0 dB,\nthe phase error is less than Ã?±15Ã?°, and the relative bandwidth is more than 23%....
Thepaper proposes specialmultiple-input single-output synthetic aperture radar (MISO-SAR) andmultiple-inputmultiple-output\nSAR (MIMO-SAR) for bidirectional imaging, which can simultaneously illuminate two areas from different directions in azimuth.\nFor the proposed MISO-SAR, two subpulses with the same carrier frequency and phase coding are transmitted with different\nazimuth directions by switching the phase coefficients in the transmit modules, and echoes corresponding to the subpulses are\nreceived by the main lobe and the first grating lobe of the whole antenna. To suppress mutual interference, the two subpulses are\ntransmitted with different range-frequency bands, and their echoes are demodulated and recorded in different channels in the\nproposed MIMO-SAR. This paper presents the system design of these modes and analyzes their azimuth ambiguity to signal ratio\n(AASR). Besides, simulation results on points are carried out to validate the proposed bidirectional imaging modes....
The high cross-polarization of the microstrip integrated balun-fed printed dipole antenna cannot meet the demands of many\nengineering applications. This kind of antennas has high cross-polarization levels (about -20 dB). And we find that the high crosspolarization\nradiation is mainly produced by the microstrip integrated balun rather than the dipole itself. The very limited method\nto lower the cross-polarization level of this kind of antennas is to reduce the substrate thickness. In this paper, to improve the low\ncross-polarized performance, firstly, an equivalentmodel is presented to analyze the cross-polarization radiation. Secondly, a novel\nstructure with low cross-polarization is proposed. The microstrip integrated balun is enclosed by a center slotted cavity.The E-field\nof the microstrip integrated balun is transformed parallel to the dipole arms by the slot, so the radiation of the cross-polarized\ncomponent is suppressed. Measured results show that this structure can achieve a bandwidth wider than 40% while reducing the\ncross-polarization level to less than -35 dB within the frequency band....
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