Time filter

Source Type

Lin L.K.,Nanjing University of Posts and Telecommunications | Lin L.K.,China Research Institute of Radio Wave Propagation | Zhao Z.W.,China Research Institute of Radio Wave Propagation | Zhang Y.R.,Nanjing University of Posts and Telecommunications | Zhu Q.L.,Xidian University
IET Radar, Sonar and Navigation | Year: 2011

A retrieval method is developed to obtain atmospheric refractivity profiles based upon the zenith delay of single ground-based global positioning system receivers. It is found that the key parameter in exponential wet refractivity model is the equivalent height of wet term Hw, while the errors between the integral of the wet terms of refractivity and the true values are single-peaked functions of Hw. Therefore the golden section method is utilised to retrieve Hw; moreover, the refractivity profiles are obtained. Meanwhile, the classic Hopfield model is used as the hydrostatic refractivity model. The experimental results with radiosonde data in Shanghai, China, and simulations using data from Qingdao, China, show that this method has demonstrated a good agreement with radiosonde profiles. © 2011 The Institution of Engineering and Technology.


Li G.,CAS Institute of Geology and Geophysics | Ning B.,CAS Institute of Geology and Geophysics | Patra A.K.,National Atmospheric Research Laboratory | Abdu M.A.,National Institute for Space Research | And 3 more authors.
Journal of Geophysical Research: Space Physics | Year: 2013

The daytime 150 km echoes, which are associated with the upper E region field-aligned irregularities, have been observed around the equatorial electrojet region but never before at magnetic latitudes near the northern anomaly crest region. We present first results of daytime 150 km echo over Sanya, China, a station located far away from the dip equator in the Northern Hemisphere. A layer of weak radar echoes with spectral width less than 10 m s-1 was seen in the height range from 145 km at 12:15 LT to 152 km at 13:45 LT on 21 July 2010. The interesting aspect is that the rare observation of daytime 150 km echoes with the small Sanya VHF radar was preceded by the occurrence of an unusual intermediate layer, which is identified as abnormal traces at the upper E region in corresponding ionograms. The abnormal intermediate layer associated with possible gravity wave activity (that implicates the presence of upper E region density gradients) could make a significant contribution to the growth of irregularities responsible for the rarely detected daytime 150 km echoes over Sanya. Key Points The 150 km echo is first of its kind from the northern anomaly crest region The presence of abnormal layer traces preceding the 150 km echo is a new point It provides direct evidence on the linkage of 150 km echo and intermediate layer ©2013. American Geophysical Union. All Rights Reserved.


Zhang J.-P.,Xidian University | Wu Z.-S.,Xidian University | Zhao Z.-W.,China Research Institute of Radio Wave Propagation | Zhang Y.-S.,China Research Institute of Radio Wave Propagation | Wang B.,Institute of Oceanographic Instrumentation
Chinese Physics B | Year: 2012

The maritime tropospheric duct is a low-altitude anomalous refractivity structure over the ocean surface, and it can significantly affect the performance of many shore-based/shipboard radar and communication systems. We propose the idea that maritime tropospheric ducts can be retrieved from ocean forward-scattered low-elevation global positioning system (GPS) signals. Retrieval is accomplished by matching the measured power patterns of the signals to those predicted by the forward propagation model as a function of the modified refractivity profile. On the basis of a parabolic equation method and bistatic radar equation, we develop such a forward model for computing the trapped propagation characteristics of an ocean forward-scattered GPS signal within a tropospheric duct. A new GPS scattering initial field is defined for this model to start the propagation modeling. A preliminary test on the performance of this model is conducted using measured data obtained from a 2009-experiment in the South China Sea. Results demonstrate that this model can predict GPS propagation characteristics within maritime tropospheric ducts and serve as a forward model for duct inversion. © 2012 Chinese Physical Society and IOP Publishing Ltd.


Yang L.,China Research Institute of Radio Wave Propagation | Fan J.,China Research Institute of Radio Wave Propagation | Jiao P.,China Research Institute of Radio Wave Propagation | Cao H.,China Research Institute of Radio Wave Propagation
Dianbo Kexue Xuebao/Chinese Journal of Radio Science | Year: 2013

The hybrid sky-surface wave system is a new HF radar system. The propagation mode associate with sky-surface wave is nonlinear and time-varying channel, and its availability is analyzed. Then, based on radar equation, the environment influence on time availability of the system are analyzed. The study method and its calculated examples of the time availability of the hybrid sky-surface wave radar which possesses given equipment capability and the target which possesses given radar cross section (RCS) are described. The influence of the time availability by the energy and RCS are pointed out. The study result is significant for the de-sign project of the system. Copyright © 2013 by Editorial Department of Chinese Journal of Radio Science.


Li T.,China Research Institute of Radio Wave Propagation | Li X.,China Research Institute of Radio Wave Propagation | Feng J.,China Research Institute of Radio Wave Propagation | Lu Z.,China Research Institute of Radio Wave Propagation
Dianbo Kexue Xuebao/Chinese Journal of Radio Science | Year: 2013

Layer characteristics of ionosphere lead to multi-mode propagation of over-the-horizon radar (OTHR) echo signal, significant broadening of ground-sea clutter spectral, and sharp dropping of the OTHR target detection capability of ship. A selection method of single-mode operating frequency based on full-band fixed-frequency detection is proposed. The core issue of this method is to obtain the information of propagation mode number of backscatter fixed-frequency detection which changes with the distance. An extraction algorithm of propagating modes number based on feature decomposition is proposed, which achieve the extraction of model number distribution in full-band. Ultimately, the operation frequency selection of single mode is also achieved. The simulation results and experimental data verify the method is effective. Copyright © 2013 by Editorial Department of Chinese Journal of Radio Science.


Zhang J.-P.,Xidian University | Wu Z.-S.,Xidian University | Zhu Q.-L.,China Research Institute of Radio Wave Propagation | Wang B.,China Research Institute of Radio Wave Propagation
Progress in Electromagnetics Research | Year: 2011

A new four-parameter modified refractivity profile (M-profile) model for the evaporation duct is introduced in this paper. In the estimation of radio refractivity structure from sea clutters, a parametric M-profile model is normally employed. The conventional M-profile model for evaporation ducts is the one-parameter log linear model, which has some potential disadvantages in describing the observed M-profiles which would result in rough results of evaporation duct estimation. Based on this model, three new parameters are introduced and a four-parameter M-profile model is proposed here. This model has the ability to (a) more accurately match real-world M-profiles, (b) well replicate the observed clutter field, and (c) show clutter power or path loss sensitivity to each model parameter. All these abilities are necessary for robust refractivity estimations. The performance of this model is tested and validated through the estimation for two truly measured M-profiles.


Zhang X.-Y.,South China University of Technology | Zhang Y.-B.,South China University of Technology | Wang X.-Y.,China Research Institute of Radio Wave Propagation | Hu B.-J.,South China University of Technology
Journal of Electromagnetic Waves and Applications | Year: 2012

This paper presents a bandpass filter with electricallytunable center frequency and bandwidth. The proposed filter employs a centrally-loaded resonator with three varactors. The odd-mode and even-mode resonant frequencies of the resonator can be flexibly controlled by changing the voltage of the corresponding varactors. The adjustability of center frequency is achieved by adjusting both odd- and even-mode resonant frequencies, and the tuning of bandwidth can be achieved by probably adjusting the discrepancy between odd- and evenmode resonant frequencies. To improve the selectivity, the source-load coupling is utilized to generate transmission zeros. The performance of this electronically tuned filter is promising in terms of continuous center frequency and bandwidth tunings. For validation, both theory and experimental results are provided. It is shown that the filter could operate within the frequency range from 525 MHz to 655 MHz and be applicable to cognitive radio systems.


Deng S.,Shandong University | Fan Y.,Shandong University | Li Z.,China Research Institute of Radio Wave Propagation | Sun Q.,Shandong University
Petroleum Science | Year: 2011

In order to identify fractured reservoirs and determine their fracture parameters with a high definition array laterolog, we built a fracture-induced anisotropic formation model with a parallel fracture group. The three-dimensional finite element method is used to simulate the responses of the array laterolog, and then the primary inversion method is utilized. Numerical simulation shows that when the fracture spacing is small, the array laterolog response of the fracture group is the same as that of a formation with macroscopic electrical anisotropy. The apparent resistivity of the array laterolog is approximately inversely proportional to fracture porosity. The anisotropy depends on the fracture porosity in the fractured formation, which accordingly results in response variation of the array laterolog. The higher the fracture dip, the larger the apparent resistivity. When the fracture dip is low the difference between the deep and shallow apparent resistivities is small, and when the dip is high the difference turns out to be positive. The fracture parameters were inverted using the Marquardt non-linear least squares method. The results, both fracture porosity and dip show a good match with parameters in the actual formation model. This will promote the application of the array laterolog in evaluating fractured reservoirs. © 2011 China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg.


Zhang J.-P.,Xidian University | Wu Z.-S.,Xidian University | Zhang Y.-S.,China Research Institute of Radio Wave Propagation | Wang B.,Shandong Academy of Sciences
Progress in Electromagnetics Research | Year: 2012

A method for retrieving evaporation duct height (EDH) is instroduced in this paper. The proposed technique employs the changes in radar sea clutter power observed at different heights as input information. It identifies the EDH associated with the modeled clutter change pattern that best matches measured change patterns. The performance of the method is evaluated in terms of RMS errors in retrieving actual EDHs that range from 0 to 40 m. The comparison of the proposed method with the conventional clutter pattern matching method shows that the former more effectively retrieves actual EDHs.


Liu S.-Q.,South China University of Technology | Hu B.-J.,South China University of Technology | Wang X.-Y.,China Research Institute of Radio Wave Propagation
IEEE Communications Letters | Year: 2012

In this letter, we consider hierarchical cooperative spectrum sensing based on two-threshold energy detection in cognitive radio networks. In order to solve the sensing failure problem in conventional two-threshold energy detection, soft combination of the observed energy value from different cognitive radio users is investigated. Encouraged by the performance gain of soft combination of energy falling between the two thresholds, we further propose a new softened hard combination scheme to reduce the communication overhead. Results show that the proposed method achieves a good tradeoff between sensing performance and communication overhead. © 2012 IEEE.

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