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Zheng W.C.,Huazhong University of Science and Technology | Zhang L.,Huazhong University of Science and Technology | Li Q.X.,Huazhong University of Science and Technology | Leng Y.,Air Force Early Warning Academy
IEEE Transactions on Antennas and Propagation

Smart antennas have received increasing interest for mitigating interference in the multiple-input-multiple-output (MIMO) wireless local area network (WLAN). In this paper, a dual-band dual-polarized compact bowtie dipole antenna array is proposed to support anti-interference MIMO WLAN applications. In the antenna array, there are 12 antennas, six for horizontal polarization and six for vertical polarization. In order to achieve dual linear polarizations and beam switching, six horizontal antennas are placed in a sequential, rotating arrangement on a horizontal substrate panel with an equal inclination angle of 60° to form a symmetrical structure, while the other six antennas for vertical polarization are inserted through slots made on the horizontal substrate panel. Furthermore, six pairs of meandered slits are introduced to reduce the mutual coupling between horizontal antennas in the lower band. A prototype of the array with a dimension of 150×150×60mm3 is manufactured and exhibits the characteristics of high isolation, good front-to-back ratio, and average gains of 4.5 and 5 dBi over the 2.4- and 5-GHz band, respectively. The MIMO performance of the array is analyzed and evaluated by mutual coupling, the total active reflection coefficient (TARC) and the envelope correlation coefficient. The anti-interference capability of the array is also investigated by the experiment. © 2013 IEEE. Source

Wang Q.-B.,Wuhan University | Zhou C.,Air Force Early Warning Academy | Wu J.,Wuhan University | Lu T.,Wuhan University
Optics Communications

Using the GGA+U method, we have calculated the optical properties of vanadium (V) doped ZnO with and without single intrinsic (zinc or oxygen) vacancy. Vanadium introduces a new band in the band gap. The new band betters conduction and causes a red shift of the optical properties. Vanadium causes a weak absorption in the infrared region. Zinc vacancy suppresses the infrared absorption and shifts absorption to higher energy. Besides the infrared absorption, oxygen vacancy causes an intense absorption in the visible and near-ultraviolet region. Our study explains the different experiments and extends the use of V-doped ZnO. © 2013 Elsevier B.V. Source

Wang Q.-B.,Wuhan University | Zhou C.,Air Force Early Warning Academy | Chen L.,Wuhan University | Wang X.-C.,Wuhan University | He K.-H.,Wuhan University
Optics Communications

To comprehend the optical properties of the recent-predicted NiAs phase ZnO under pressure, we used the generalized gradient approximation plus U (GGA+U) method to calculate the properties. The GGA+U method is more suited for the strong correlated NiAs phase. The direct band gap increases with increasing pressure. The calculated band gap shows that NiAs phase is an insulator, while the real part ε1(ω) shows the NiAs phase expresses metallic behavior around 18.6 (22.5 GPa) and 26.0 eV (215 GPa). The relation between the imaginary part ε2(ω) and PDOS was also discussed. The calculated optical constants show the NiAs phase is transparent and can be used in the vacuum ultraviolet region. We also compared the optical constants of NiAs with wurtzite and CsCl phases ZnO at according transition pressure. And the new-appeared peaks of optical constants can be used to identify the phase transition. The blue-shift optical constants of NiAs phase ZnO can be used to measure pressure after carefully calibrated. Our research provides a reference for identifying and using the NiAs phase ZnO under pressure. © 2013 Elsevier B.V. Source

Luo H.,The Academy of Management | Chen J.-W.,Air Force Early Warning Academy | Bao Z.,Air Force Early Warning Academy
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology

Skywave Over-The-Horizon Radar (OTHR) can achieve long range detection via the ionosphere reflection. However, time-varying ionosphere and multipath effect will lead to serious clutter spectrum spread in long Coherent Integration Time (CIT). It increases difficulty degree of the detection of slow-speed targets. To deal with contaminated echo in the case of the two spreading Bragg peaks overlapping, an ionospheric contamination correction scheme based on Short Time MUSIC Transform (STMT) and improved Phase Gradient Autofocus (PGA) method is proposed. In the scheme, coarse estimation of ionospheric phase contamination can be obtained and compensated by using STMT transform, then an adaptive sliding window filter is utilized to extract the first order clutter (calibration signal). After that, the remanent ionospheric phase contamination can be estimated and compensated accurately by using improved PGA method. Theoretical analysis and simulation results show that the scheme has a good performance on correcting the situation of two spreading Bragg peaks overlapping. Source

Zhan L.-X.,The Academy of Management | Tang Z.-Y.,Air Force Early Warning Academy | Zhu Z.-B.,Air Force Early Warning Academy
Xi Tong Gong Cheng Yu Dian Zi Ji Shu/Systems Engineering and Electronics

The signal-to-noise ratio(SNR) of small radar cross section(RCS) targets can be improved by coherent integration. But the maneuvering of targets causes range cell migration and Doppler cell migration. The reasons of above problems are analyzed from the two-dimensional(2-D) frequency domain, and based on this, a novel method of long term coherent integration is proposed. In fast frequency-slow time domain the Keystone transform is taken and the range cell migration is corrected, then a quadratic phase compensation function is multiplied and the objective function is constructed to search the acceleration in the compensation function. The characteristic of the new method is that the maximum value of the objective function equals to the coherent integration value, and this reduces the operational quantity and improves the operation speed. The simulation results verify the effectiveness of the proposed method. Source

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