Instantaneous measurement for radar target polarization scattering matrix

Adopting ＂simultaneous transmitting, simultaneous receiving＂ operational scheme, instantaneous polarization radar （IPR） can measure target polarization scattering matrix （PSM） using only once target echoes in two orthogonal polarization channels. Firstly, signal model and signal process are advanced under narrowband condition. Secondly, measurement performances of two typical IPR waveforms are analyzed in detail. At last, field experiments are carried out using X-band IPR system designed by National University of Defense Technology （NUDT）, China. Compared with results obtained by alternative polarization measurement scheme, following results can be obtained： the difference of relative amplitude measurement results is smaller than 2 dB and that of relative phase measurement results is smaller than 10？, verifying the validity of instantaneous polarization measurement scheme.

Wave Polarization Scattering and Transmission Property in Randomly Distributed Chiral Spheroids

In this paper, the scattering amplitude functions of a spatially-oriented chiral spheroid are derived. Polarization scattering from a layer of randomly distributed chiral spheroids in the Mueller matrix solution is obtained. Co-polarized and de-polarized backscattering and polarization degree for any polarized incidence are numerically calculated. Transmissions of coherent waves with four Stokes parameters through the layer are also discussed. Comparisons of polarization scattering from the chiral and achiral particulate media demonstrate the chirality effect on wave scattering and transmission.

Influence of temperature on strain-induced polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors

Electron mobility scattering mechanism in AlN/GaN heterostuctures is investigated by temperature-dependent Hall measurement, and it is found that longitudinal optical phonon scattering dominates electron mobility near room temperature while the interface roughness scattering becomes the dominant carrier scattering mechanism at low temperatures （~ 100 K）. Based on measured current-voltage characteristics of prepared rectangular AlN/GaN heterostructure field-effect transistor under different temperatures, the temperature-dependent variation of electron mobility under different gate biases is inves- tigated. The polarization Coulomb field （PCF） scattering is found to become an important carrier scattering mechanism after device processing under different temperatures. Moreover, it is found that the PCF scattering is not generated from the thermal stresses, but from the piezoelectric contribution induced by the electrical field in the thin A1N barrier layer. This is attributed to the large lattice mismatch between the extreme thinner AlN barrier layer and GaN, giving rise to a stronger converse piezoelectric effect.

Influence of the AlGaN barrier thickness on polarization Coulomb field scattering in an AlGaN/AlN/GaN heterostructure field-effect transistor

In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field(PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility.Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness.This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect.

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In_(0.18) Al_(0.82) N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.

Scattering of Circularly Polarized Terahertz Waves on a Graphene Nanoantenna

We present a surface current method to model the graphene rectangular nanoantenna scattering in the terahertz band with Comsol. Compared with the equivalent thin slab method, the results obtained by the surface current method are more accurate and efficient. Then the electromagnetic scattering of circularly polarized terahertz waves on graphene nanoantennas is numerically analyzed by utilizing the surface current method. The depen- dences of the antenna resonant frequency with the circularly polarized wave on width and length are consistent with those for the linear polarized waves. These results are proved to be useful to design et^cient nanoantennas in terahertz wireless communications.

Novel polarization filter design for wideband radar

Usually the polarization of the interference and the target backscattering may vary constantly, so the optimal receiving polarization of the polarization filter should be recalculated, which makes the filter realization very difficult. Also the predict method of the necessary parameters is not explained in most papers, which makes the polarization filter realization impossible. A novel modi- fied interference suppression （MIS） polarization filter is proposed, which resolves these problems by a new polarization designed strategy. The computation of this polarization filter is easy in most conditions, and the necessary parameters estimation method in real time is introduced, which makes polarization filter design possible.

Practical calibration method for instantaneous polarization radar systems utilizing a metal sphere

A practical calibration method is proposed for instantaneous polarization radar systems.The method only needs one measurement by using a metal sphere.The distortions of system and the actual polarization scattering matrix（PSM）of target can be obtained.First,an instantaneous polarization radar system is presented.The system can obtain PSM by a single pulse echo.The dual-polarization antenna can transmit and receive two orthogonal polarization waves.The multilayer micro-strip patch antenna is adopted for this kind of radar system.Second,based on the multi-port network theory,the operation and system errors of instantaneous polarization radar system are analyzed.By making assumption on the cross-talk factors of antenna,distortion matrices of R and Tare derived.Finally,the calibration method based on instantaneous polarization measurement is introduced.Simulation results show the performance of this calibration method.The values of calibrated PSM are in agreement with the actual ones after calibration.

Aggregate dust model to study the polarization properties of comet C/1996 B2 Hyakutake

The observed linear polarization data of comet Hyakutake are studied at wavelengths λ=0.365 μm,λ=0.485 μm and 0.684μm through simulations using Ballistic Particle-Cluster Aggregate and Ballistic Cluster-Cluster Aggregate aggregates of 128 spherical monomers.We first found that the size parameter of the monomer,x ～ 1.56-1.70,turned out to be the most suitable which provides the best fits to the observed dust scattering properties at three wavelengths：λ=0.365 μm,0.485μm and 0.684μm.Thus,the effective radius of the aggregate （r） lies in the range 0.45 μm ≤ r ≤ 0.49 μm at λ=0.365 μm;0.60 μm ≤ r ≤ 0.66 μm at λ=0.485 μm and 0.88 μm ≤ r ≤ 0.94 μm at λ=0.684 μm.Now using superposition T-MATRIX code and the power-law size distribution,n（r） ～ r-3,the best-fitting values of complex refractive indices are calculated for the observed polarization data at the above three wavelengths.The best-fitting complex refractive indices （n,k） are found to be （1.745,0.095） at λ=0.365 μm,（1.743,0.100） at λ=0.485 μm and （1.695,0.100） at λ=0.684 μm.The refractive indices derived from the present analysis correspond to a mixture of both silicates and organics,which are in good agreement with the in situ measurement of comets by different spacecraft.

Refractive Focusing of Interstellar Clouds and Intraday Polarization Angle Swings

Intraday variations of compact extragalactic radio sources in flux density and polarization are generally interpreted in terms of refractive scintillation from the continuous interstellar medium of our Galaxy. However, continuous polarization angle swings of - 180° （for example, the one observed in the QSO 0917＋624） could not be interpreted in this way. Qian et al. have shown that the polarization angle swing observed in the QSO 1150＋812 can be explained in terms of focusing-defocusing effect by an interstellar cloud, which occults two closely-placed polarized components. Here we further show that the polarization angle swing event observed in the QSO 0917＋624 can also be explained in this way. We also found evidence for the cloud eclipsing a non-polarized （core） component during a short period out- side the swing. A particular （and specific） plasma-lens model is proposed to model-fit the polarization swing event of 0917＋624. Some physical parameters related to the plasma-lens and the source components are estimated. The brightness temperatures of the two lensed components are estimated to be -1.6× 10^13 K. Thus bulk relativistic motion with a Lorentz factor less than -20 may be sufficient to avoid the inverse - Compton catastrophe.

Polarized imaging dynamic light scattering for simultaneous measurement of nanoparticle size and morphology

The performance of nanoparticles is often affected by particle size and morphology.Currently,electron microscopy or atomic force microscopy is typically utilized to determine the size and morphology of nanoparticles.However,there are issues such as difficult sample preparation,long processing times,and challenges in quantitative characterization.Therefore,it is of great significance to develop a fast,accu-rate,and statistical method to measure the size and morphology of nanoparticles.In this study,a new method,called polarized imaging dynamic light scattering(PIDLS),is proposed.The nanoparticles are irradiated with a vertical linearly polarized laser beam,and a polarization camera collected the dynamic light scattering images of particles at four different polarization directions(0°,45°,90°,and 135°)at a scattering angle of 90°.The average particle size and distribution are obtained using the imaging dy-namic light scattering method at 0°polarization direction,and the morphology of the particles is ob-tained based on the depolarization patterns of the scattered light.The optical sphericityΦis defined based on the degree of linear polarization(DoLP).It is also implemented for the quantitative evaluation of the sphericity of the nanoparticles,including spherical,octahedral,nanoplate,nanorod,and linear ones.Together with the Poincarésphere parameterψ,the morphology of the nanoparticles can be roughly identified.In addition,PIDLS enables the measurement of particle size and morphology distributions simultaneously for evaluating the uniformity of particles.The effectiveness of PIDLS is verified by the measurement of five kinds of industrial titanium dioxide as well.

Solution for polarimetric radar cross section measurement and calibration

The exact radar cross-section （RCS） measurement is difficult when the scattering of targets is low. Ful polarimetric cali-bration is one technique that offers the potential for improving the accuracy of RCS measurements. There are numerous polarimetric calibration algorithms. Some complex expressions in these algo-rithms cannot be easily used in an engineering practice. A radar polarimetric coefficients matrix （RPCM） with a simpler expression is presented for the monostatic radar polarization scattering matrix （PSM） measurement. Using a rhombic dihedral corner reflector and a metal ic sphere, the RPCM can be obtained by solving a set of equations, which can be used to find the true PSM for any target. An example for the PSM of a metal ic dish shows that the proposed method obviously improves the accuracy of cross-polarized RCS measurements.

Lattice deformation in epitaxial Fe3O4 films on MgO substrates studied by polarized Raman spectroscopy

The lattice structures of epitaxial Fe3O4 films deposited on MgO were studied systematically using polarized Raman spectroscopy as a function of film thickness,where interesting phenomena were observed.Firstly,the spectral conflict to the Raman selection rules(RSRs)was observed under cross-sectional configuration,which can be attributed to the tetragonal deformation in the growth direction due to the lattice mismatch between Fe3O4 and MgO.Secondly,the blue shift and broadening of Raman peaks evidenced the decrease of the tensile strain in Fe3O4 films with decreasing thickness.Thirdly,distinct from the other Raman modes,the lowest T2g mode exhibited asymmetric lineshape,which can be interpreted using the spatial correlation model.The increased correlation length introduced in the model can well explain the enhanced peak asymmetry feature with decreasing thickness.These results provide useful information for understanding the lattice structure of epitaxial Fe3O4 film.

The influence of the channel electric field distribution on the polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors

Based on the measured capacitance–voltage（C–V） curves and current–voltage（I–V） curves for the prepared differently-sized AlN/GaN heterostructure field-effect transistors（HFETs）, the I–V characteristics of the AlN/GaN HFETs were simulated using the quasi-two-dimensional（quasi-2D） model. By analyzing the variation in the electron mobility for the two-dimensional electron gas（2DEG） with the channel electric field, it is found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field（PCF） scattering. The 2DEG electron mobility difference is mostly caused by the PCF scattering which can reach up to 899.6 cm^2/（V·s）（sample a）, 1307.4 cm^2/（V·s）（sample b）,1561.7 cm^2/（V s）（sample c） and 678.1 cm^2/（V·s）（sample d）, respectively. When the 2DEG sheet density is modulated by the drain–source bias, the electron mobility for samples a, b and c appear to peak with the variation of the 2DEG sheet density, but for sample d, no peak appears and the electron mobility rises with the increase in the2 DEG sheet density.

Influence of Schottky drain contacts on the strained AlGaN barrier layer of AlGaN/AlN/GaN heterostructure field-effect transistors

Rectangular Schottky drain AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate contact areas and conventional AlGaN/AlN/GaN HFETs as control were both fabricated with same size. It was found there is a significant difference between Schottky drain AlGaN/AlN/GaN HFETs and the control group both in drain series resistance and in two-dimensional electron gas （2DEG） electron mobility in the gate–drain channel. We attribute this to the different influence of Ohmic drain contacts and Schottky drain contacts on the strained AlGaN barrier layer. For conventional AlGaN/AlN/GaN HFETs, annealing drain Ohmic contacts gives rise to a strain variation in the AlGaN barrier layer between the gate contacts and the drain contacts, and results in strong polarization Coulomb field scattering in this region. In Schottky drain AlGaN/AlN/GaN HFETs, the strain in the AlGaN barrier layer is distributed more regularly.

Electron mobility in the linear region of an AlGaN/AlN/GaN heterostructure field-effect transistor

We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas （213EG） with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.

Parasitic source resistance at different temperatures for AlGaN/AlN/GaN heterostructure field-effect transistors

The parasitic source resistance（RS） of AlGaN/AlN/GaN heterostructure field-effect transistors（HFETs） is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage（C–V） and current–voltage（I–V） characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field（PCF） scattering exhibits a significant impact on RSat the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.

The signal selection and processing method for polarization measurement radar

Based on the ambiguity function, a novel signal processing method for the polarization measurement radar is developed. One advantage of this method is that the two orthogonal polarized signals do not have to be perpendicular to each other, which is required by traditional methods. The error due to the correlation of the two transmitting signals in the traditional method, can be reduced by this new approach. A concept called ambiguity function matrix （AFM） is introduced based on this method. AFM is a promising tool for the signal selection and design in the polarization scattering matrix measurement. The waveforms of the polarimetric radar are categorized and analyzed based on AFM in this paper. The signal processing flow of this method is explained. And the polarization scattering matrix measurement performance is testified by simulation. Furthermore, this signal processing method can be used in the inter-pulse interval measurement technique as well as in the instantaneous measurement technique.

Understanding angle-resolved polarized Raman scattering from black phosphorus at normal and oblique laser incidences

The selection rule for angle-resolved polarized Raman(ARPR)intensity of phonons from standard grouptheoretical method in isotropic materials would break down in anisotropic layered materials(ALMs)due to birefringence and linear dichroism effects.The two effects result in depth-dependent polarization and intensity of incident laser and scattered signal inside ALMs and thus make a challenge to predict ARPR intensity at any laser incidence direction.Herein,taking in-plane anisotropic black phosphorus as a prototype,we developed a so-called birefringence-linear-dichroism(BLD)model to quantitatively understand its ARPR intensity at both normal and oblique laser incidences by the same set of real Raman tensors for certain laser excitation.No fitting parameter is needed,once the birefringence and linear dichroism effects are considered with the complex refractive indexes.An approach was proposed to experimentally determine real Raman tensor and complex refractive indexes,respectively,from the relative Raman intensity along its principle axes and incident-angle resolved reflectivity by Fresnel’s law.The results suggest that the previously reported ARPR intensity of ultrathin ALM flakes deposited on a multilayered substrate at normal laser incidence can be also understood based on the BLD model by considering the depth-dependent polarization and intensity of incident laser and scattered Raman signal induced by both birefringence and linear dichroism effects within ALM flakes and the interference effects in the multilayered structures,which are dependent on the excitation wavelength,thickness of ALM flakes and dielectric layers of the substrate.This work can be generally applicable to any opaque anisotropic crystals,offering a promising route to predict and manipulate the polarized behaviors of related phonons.

Impact of polarization mode dispersion and nonlinearities on 2-channel DWDM chaotic communication systems

This paper has designed 2-channel dense wavelength division multiplexing （DWDM） chaotic sys- tem at the frequencies of 193.1 and 193,2THz, respec- tively. The optical chaotic signals were produced by using the semiconductor laser that is numerically modeled by employing laser rate equations. These two channels were multiplexed and then propagated through single mode optical fiber （SMF） of 80kin length with dispersion compensating fiber of 16 km length. Erbium doped fiber amplifier （EDFA） was used to compensate the power losses in the SMF. In lhis paper, we investigated the effects of polarization mode dispersion （PMD） and nonlinearities especially stimulated Raman scattering （SRS） on 2 channel DWDM chaotic communication system by varying the length of the SMF and value of differential group delay （DGD）.