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Time filter

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Lu D.,CAS Institute of Semiconductors | Pan B.,CAS Institute of Semiconductors | Chen H.,Beijing Institute of Radio Measurement and Metrology | Zhao L.,CAS Institute of Semiconductors
Optics Letters | Year: 2015

A widely tunable optoelectronic oscillator (OEO) based on a self-injection-locked monolithic dual-mode amplified feedback laser (DM-AFL) is proposed and experimentally demonstrated. In the proposed OEO structure, the DMAFL functions as an active tunable microwave photonic filter (MPF). By tuning the injection current applied on the amplifier section of the AFL, tunable microwave outputs ranging from 32 to 41 GHz and single sideband phase noises below .97 dBc/Hz at 10 kHz offset from the carriers were realized. © 2015 Optical Society of America.


Che Z.-P.,Beijing Institute of Radio Measurement and Metrology
Hedianzixue Yu Tance Jishu/Nuclear Electronics and Detection Technology | Year: 2011

There are many methods about time interval measurement such as count method, vernier method, analog inter-plug, delay line inter-plug and time-to-voltage method. After having analyzed and compared these methods, It provided a new method with high precision and large range, and showed the principle and technique of the design. The method had successfully applied to GPS rubidium clock, and it will provide a good reference scheme for other designs.


Wang W.,Beijing Institute of Radio Measurement and Metrology
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2014

Vacuum thermal insulation of the thermostat control unit of hydrogen atomic clockwas physically modeled, numerically simulated with software package Ansys, and experimentally evaluated to reduce the negative impact of environmental temperature on its accuracy. The influence of the thermal insulation conditions, such as the pressure in the vacuum layer, vacuum wall materials, and environment temperature, on the temperature sensitivity was evaluated. The prototyped vacuum thermal insulator was designed, constructed, and tested. The test results show that the newly-developed vacuum thermal insulationsignificantly reduced the temperature sensitivity of the hydrogen atomic clock from 1×10-14/°C to 2.5×10-15/°C, close to the best result reported (1×10-15/°C).


Jiao Z.,Tsinghua University | Yang J.,Tsinghua University | Yeh C.,Tsinghua University | Yeh C.,Beijing Institute of Radio Measurement and Metrology | Song J.,China Institute of Technology
IEEE Geoscience and Remote Sensing Letters | Year: 2014

In this letter, a modified three-component model-based decomposition method is proposed to solve the problem of instability present in the Freeman decomposition method. We incorporate the similarity parameter and introduce a new constraint that describes the relationship between the powers of scattering components. The proposed method minimizes a continuous objective function under a set of constraints, which results in the stability of the decomposition method. Furthermore, a fast algorithm for solving the optimization problem is developed to accelerate computation. We demonstrate the stability of the proposed decomposition method by using the E-SAR polarimetric data acquired over the Oberpfaffenhofen area. © 2013 IEEE.


Wang J.,Beijing Jiaotong University | Yang Y.,Beijing Institute of Radio Measurement and Metrology | Miao J.,Beihang University | Chen Y.,National Key Laboratory of Metrology and Calibration Technology
IEEE Transactions on Antennas and Propagation | Year: 2010

Internal calibration source provides reference data for remote sensing system. Realistic calibration source is constructed by finite periodic structure, and hence, the emissivity calculation is different from the infinite periodic array case. In this paper, conventional indirect method based on the scattering field is modified first, so that it can be used to calculate the emissivities of finite homogeneous objects. Subsequently, a new method based on antenna concept is proposed for calculating the differential scattering coefficients and emissivities of the inhomogeneous finite objects. The methods are then applied to finite circular pyramid arrays covered with an absorbing material, and the results are analyzed. Furthermore, the effect of the illuminating scope of incident wave on the emissivity and differential scattering coefficient of circular finite pyramid array is studied. © 2006 IEEE.

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