Fang Guangyou

An Inverse Electromagnetic Scattering Method for One-Dimensional Inhomogeneous Media

A frequency-domain inversion scheme for reconstructing the permittivity profile of one-dimensional inhomogeneous media is proposed. The generalized reflection coefficients and the generalized transmission coefficients of the inhomogeneous media are used as the input data of the inverse model. A Newton-like iterative algorithm known as the generalized pulse-spectrum technique with the Tikhonov regularization is applied to solve the inverse problem. Novel boundary conditions are proposed for the inverse problem and therefore the permittivity at the boundary of the inhomogeneous media is not required as prior knowledge. The choice of frequency points of the frequency-domain method is also investigated. Numerical examples are carried out to validate the inversion technique. Good agreements between the reconstructed profiles and the true profiles are shown.

The Radio Frequency Interference Mitigation in Ionospheric Sounding

Operating in noisy radio frequency environments has been a very important issue in high-frequency sounding these years, especially the narrow-band interference. So it is urgent to find an effective method to eliminate the interference. The algorithm of radio interference mitigation introduced in this paper is used to remove the radio frequency interference (RFI). It could estimate the exact frequency, amplitude and phase of the interference signal via spectral analysis and subtract the interference signal from the received signal in time domain. This algorithm has been well proved by data from ionosonde and perfect result could be seen from the comparison between the RFI mitigation-processed data and the unprocessed data. It is obviously that not only has been the interference eliminated, but also the SNR has been improved.

The Absorbing Properties of Two-Dimensional Plasma Photonic Crystals

Plasma photonic crystals composed of periodic plasma and dielectric materials have attracted considerable attention because of their tunable photonic band gaps, but only their band structures or negative refractive index properties have been addressed in previous works. In this paper, through studying the transmission and reflection characteristics of two types of two-dimensional plasma photonic crystals, it is found that plasma photonic crystals play an important role in absorbing waves, and they show broader band and higher amplitude absorption characteristics than bulk plasmas. Also, the absorption of plasma photonic crystals can be tuned via plasma parameters; varying the collision frequency can make the bandwidth and amplitude tunable, but cannot change the central frequency, whereas varying the plasma frequency would control both the location and the amplitude of the absorbers. These features of plasma photonic crystals have potential for terahertz tunable absorber applications.

Chang’E-3 scientific payloads and its checkout results

The scientific objectives of ChangE-3 mission were to: examine the texture, mineralogy, and structure of the local lunar terrain; determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites; image the Earths plasmasphere and operate an ultraviolet astronomy camera on the moon. Four kinds of scientific instruments are chosen as the payloads for ChangE-3 lander, which include topography camera, lunar optical telescope, extreme ultraviolet imager and landing camera so on. And other four kinds of scientific instruments are chosen as the payloads for lunar rover, which include panoramic cameras, lunar radar, IR acousto-optic spectrometer, X-ray spectrometer and so on. This paper mainly introduces scientific exploration mission, the scientific payloads design and construction. The checkout results are also described in detail.

The Realization of Terahertz Image Reconstruction with High Resolution Based on the Amplitude of the Echoed Wave by using the Phase Retrieval Algorithm

An indirect imager working at terahertz band is presented and implemented, which is suitable for high-resolution planar object detection. The proposed imager employs a simple quasi-optics design to transmit and to receive terahertz waves, and adopts incoherent detection technology to extract the intensity of echoed signal, which results in a relatively low complexity and cost. Moreover, the Fienup Fourier phase-retrieval algorithm is successfully modified and is applied to retrieve the phase of the echoed signal and reconstruct the target image. Imaging experiments on typical planar objects are performed with the imager working at 0.2 THz, and the experimental results demonstrate the good performance of the proposed imager and validate the effectiveness of the reconstruction algorithm.

A Wideband SMM Antenna with Gap and Dielectric Loadings

A wideband four-arm spiral mode micro strip (SMM) antenna, which is loaded by dielectric and gap, is introduced in this paper. This antenna, which operates at mode 0, uses a shallow back cavity to suppress back radiation. Gap-loading and dielectric-loading are used to decrease the voltage standing wave ratio (vswr) of the antenna. A capacitive gap is introduced by a metal ring strip around the spiral, and a nylon disk is attached to the supporting substrate to introduce dielectric-loading. Measured results show that vswr of the antenna is noticeably lowered by dielectric- and gap-loading (fractional bandwidth of vswr

The Design and Implementation of FPGA-based Deep Ground-Penetrating Radar Host Control System

The Ground Penetrating Radar (GPR) is a technique that utilizes the radio waves to map structure and features of objects buried in the ground. In this paper, we design a host control system (HCS) of GPR based on a maximum length binary sequence, abbreviation M-sequence, to implement the detecting of deep level objects on earth, and we realize the design of software and hardware for the HCS of GPR. Using single field-programmable logic array (FPGA) as the core, the HCS improves the flexibility of the system, reducing power consumption. Experiments show that the HCS can complete the tasks of generating transmitting, echo signals sampling, data transmission, controlling the work modes with parameters, meeting the design specifications requirements.

The Applying of Compressed Sensing in M-Sequence UWB Radar

A maximum length binary sequence, in short an M-sequence, is a special kind of pseudo-random binary sequence(PRBS). It can be well used in Ground Penetrating Radar(GPR) because of advanced characteristics. Compressed Sensing(CS) provides a way to sample the signal below the Nyquist rate, but it relies on two principles: sparsity, which pertains to the signals of interest, and incoherence, which pertains to the sensing modality. M-sequence matrix has been proved satisfying RIP property. In this paper we will introduce a M-sequence GPR system and the CS theory will be used to reconstruct the signal when the original signal is extracted. The experiment results will also be given.

Electromagnetic Scattering and Inverse Scattering of Layered Media with a Slightly Rough Surface

An electromagnetic (EM) scattering model for layered media covered by a 3D infinite rough surface and the corresponding inversion technique are investigated. The work aims at remote sensing the surface roughness and dielectric constant for different depths of bear soil through radar measurement data. The forward problem is carried out by the wave decomposition method. The small perturbation method (SPM) and EM boundary conditions are employed to solve the integral equations introduced by the wave decomposition method. The second-order SPM solution of the scattering field is involved in the computation of the forward problem for the first time. The backscattering coefficients of multiple frequencies, multiple angles and multiple polarizations are employed to create a nonlinear optimization problem. A genetic algorithm is introduced to help the inversion procedure approach to the global minimum of the cost function. Examples are carried out to validate the inversion technique. The inversion results show good agreement with the forward problem with given parameters and pose good tolerance to the input data with the additive white Gaussian noise.

Moving Targets Localization for Dual Frequency Continuous Wave Radar Using Time Domain Analysis

Technology that can be used to precisely detect and monitor the presence of moving subjects from a distance and through barriers can be a powerful tool supporting a large range of applications. To this end, dual frequency continuous wave (CW) radar, which estimates the localization of targets based on the phase difference between two closely spaced frequencies, has been shown a cost-effective approach. In this paper, we propose a simple method to determine the localization of multiple moving targets using a dual frequency continuous wave radar. Different from the traditional imaging algorithm, the proposed new technology concentrates its computation mostly in time domain, which not only successfully avoids the leakage effect caused by the discrete Fourier transform (DFT), improving the accuracy of the detection results, but also addresses the targets separation problem even in frequency ambiguous zones. Besides, it also helps dealing with result matching problem which is of significant importance in certain practical applications. Simulation results are presented to validate the technique.