Transmitter Polarization Research Articles

Target decomposition using dual-polarization sentinel-1 SAR data: Study on crop growth analysis

Decomposition of synthetic aperture radar data has been carried out using fully polarised microwave bands. Considering the economical point of view, fully polarimetric SAR data is expensive to use for many applications like soil and agriculture, where, it is important to monitor frequently. With the advancement of human civilization, new agricultural techniques and crops are being developed to meet global food demand. With the development of crop growth, crop texture and dielectric properties varies, which is depicted in the backscattering values along with the crop growth. In this study, Sentinel-1 SAR data is used, which is freely available in dual polarimetric mode with a temporal revisit of 12 days with respect to the transmitter polarizations. In this work, we attempt to decompose the targets from dual polarised SAR data using entropy and alpha bands of H-A-α decomposition. The entropy and alpha band clusters are obtained by using K-means unsupervised classification is utilized for target decomposition. The clustering process is repeated 30 times for 100 iterations to obtain the optimum grouping of pixels. The clusters are plotted on the H-α plane to get an H-α plot of dual-polarization SAR data for target decomposition. The obtained H-α plot is used to identify the crop stages and its scattering mechanism at different growth stages. Crops grown in selected crop fields during the considered period include ginger, tobacco, rice, cabbage, and pumpkin. An attempt is made by plotting the time-series trends of early and late-planted crops with peak mature stages in terms of backscattering analysis, and the results were compared to the H-α plot to gain a better understanding of crop growth scattering mechanisms at various growth stages. Although the backscattering values for the VH and VV polarizations of crops are different, the temporal backscattering study showed the same trend for both polarizations with good similarity of VH polarization than VV for analyzing crop growth stages. The crop growth scattering mechanism on the H-α plane produced similar results to the temporal analysis.

Transmitter polarization optimization for space-time adaptive processing with diversely polarized antenna array

This paper considers the performance optimization of space-time adaptive processing (STAP) based on a diversely polarized antenna (DPA) array. A transmitter polarization design to enhance the detection performance is proposed. Accounting for the special structure of the polarization signal, we formulate the problem as a quasi-convex form based on the block majorization-minimization (MM) principle and solve it in an iterative framework. Compared with several existing methods, the proposed method has a quasi-convex form and can achieve better clutter suppression performance. We analyze the performance of conventional STAP and polarization-STAP (PSTAP), which indicates that the polarization diversity can help improve the performance of STAP for targets with low velocities, especially stationary ones. Simulations are conducted for validating the proposed methods and demonstrating their high performance.

Circularly Polarized Fabry-Perot Antenna Employing a Receiver–Transmitter Polarization Conversion Metasurface

This study presents a linear-to-circular polarization conversion metasurface (PCM) based on a novel unit cell for a circularly polarized (CP) Fabry-Perot (FP) antenna. The unit cell consists of a bottom linear-polarization patch and a top circular-polarization patch, which are separated by a metalized plane and connected by a metalized via. The bottom patch receives the power and transfers it to the top layer through the metalized via; the top layer then transmits the power into space. The metasurface is designed to have high reflectivity and an appropriate reflection phase to compose a resonate cavity with the ground plane. The capability of linear to circular polarization conversion is provided to the PCM by adjustment of the transmission magnitude and phase. A slot coupled patch antenna is used as the feeder due to its stable broadside radiation. The linearly polarized wave emitting from the feeder resonates in the cavity and then is converted into a CP wave when it comes out of the cavity. A prototype antenna is fabricated and measured. The measurement results show that the antenna has good circular polarization performance within the band of 9.8–10.2 GHz. The maximum gain of the antenna reaches 17.8 dBic at 10 GHz, with an aperture efficiency of 53%. The proposed antenna outperforms most of the previously reported CP FP antennas due to its low profile, high gain, and relatively high efficiency.

Polarimetric multiple-radar architectures with distributed antennas for discriminating between radar targets and deception jamming

The potential abilities of polarimetric multiple-radar architectures with distributed antennas in electronic counter-countermeasures (ECCMs) are analyzed based on differences between target echoes and deception jamming in scattering coefficients properties. According to the differences in generation mechanism between the target scatter and jamming, a signal model of real targets and deception jamming for two-dimensional vector sensors is established. By applying the Neyman-Pearson (NP) criterion and a hybrid NP-Maximum Posteriori (MAP) criterion, a two-stage detection/discrimination algorithm is proposed. In our proposed algorithm, the targets and jamming are detected in the first stage from a Gaussian noise background. Then, a discriminator based on the generalized likelihood ratio test is designed by exploiting the property of polarization discrimination. A theoretical analysis is also given to evaluate the performance of the second stage of the algorithm. Moreover, the discrimination performance can be improved by optimizing the transmitter polarization parameters. Simulation results indicate that the proposed ECCM strategy is effective against DRFM jamming, especially when JNR is high and transmit polarization is optimally designed.

Pauli Phase Calibration in Compact Polarimetry

In this paper, we consider the problem of true transmitter polarization state estimation for circular compact SAR modes. We employ two methods—the first using point targets such as trihedral reflectors, and the second, a new method, based on the Pauli phase observed over distributed targets like forest canopy. We first show how compact modes allow estimation of the Pauli phase for reflection symmetric scatterers. We show that this phase remains remarkably constant over forest canopies, depending primarily on the dielectric constant of constituent volume particles. We show that small imperfections in the transmit polarization state then lead to large errors in this phase estimate. These errors can then be used as the basis for a calibration strategy that allows estimation of a set of candidate true transmitter states. These can then be compared with the trihedral estimates for validation. We illustrate using L-band compact data from the JAXA ALOS-2 satellite and C-band data from the ISRO RISAT-1 satellite.

Polarization insensitive performance of randomly structured antireflecting planar surfaces

The transmittance polarization extinction ratio of fused silica substrates with random antireflective surface structures (rARSS) was investigated. The antireflective structures were etched on both sides of the substrates to suppress Fresnel reflection from the two surfaces, and the substrates were processed with three different sets of etching parameters, resulting in samples with three distinct sets of surface characteristics. In addition, three of the samples were fabricated with identical processes on both sides, while one was fabricated with a different process on each side. Normal incidence transmission spectra, spanning wavelengths from 300 to 1900 nm, are presented for each double-sided substrate, and variable angle of incidence polarization measurements were taken at 633 nm. Although the spectral Fresnel reflection suppression of all of the samples was measured to similar levels at normal incidence, the polarized transmittance response was found to vary considerably, correlating with the surface morphology differences and the front-to-back surface roughness similarities between the samples. Polarization insensitivity was verified from normal incidence to Brewster’s angle. Comparisons with the ideal single-layer thin-film antireflection coating performance calculations show that rARSS samples are polarization insensitive over a larger range of angles and have a wide wavelength band of transmission enhancement.

Transmitter polarization optimization with polarimetric MIMO radar for mainlobe interference suppression

Polarization diverse design of the transmit waveforms based on the property of the target scattering matrix provides better performance than transmitting waveforms with fixed polarizations, especially for mainlobe interference suppression applications. In this work, we propose a radar system combines the advantages of multiple-input–multiple-output (MIMO) systems with the advantages offered by optimally choosing the transmitter polarizations, in order to achieve a better mainlobe interference suppression performance. The polarization diversity is employed in the transmit array, while the receive array adopts 2-D vector sensors to measure the horizontal and vertical components of the received signal. The optimal transmitter polarizations can be obtained by maximizing the output signal-to-interference-plus-noise ratio (SINR) in each coherent processing interval (CPI). In addition, the discrimination method for the target and the interference is studied in this paper, along with the target scattering matrix estimation method. Simulation results demonstrate that interference can be effectively discriminated and suppressed with the radar configuration, and better interference suppression performance is achieved with the optimal transmitter polarizations.

Rapid resistivity imaging for marine controlled-source electromagnetic surveys with two transmitter polarizations: An application to the North Alex mud volcano, West Nile Delta

To image the internal resistivity structure of the North Alex mud volcano offshore Egypt, the marine electromagnetics group at the Helmholtz Centre for Ocean Research Kiel (GEOMAR) developed and conducted a novel transient marine controlled-source electromagnetic experiment. The system, which was specifically developed to image the mud volcano, is also generally suitable for surveys of other small seafloor targets, such as gas-hydrate reservoirs, fluid-flow features, and submarine massive-sulfide deposits. An electric bipole antenna is set down by a remotely operated vehicle on the seafloor sequentially in two perpendicular polarizations at each transmission station. Two orthogonal horizontal electric field components are recorded on the seabed by an array of independently deployed nodal receivers (RXs). With two transmitter polarizations, the unique acquisition geometry of the system provides a very rich data set. However, for this geometric setup, conventional marine electromagnetic interpretation schemes (such as normalized magnitude variation with offset plots) have been difficult to implement. We have developed a simple imaging technique, which can be used for a first-step mapping of seafloor apparent resistivity with the GEOMAR system. Images can be produced in just a few minutes on a regular laptop computer, and the robustness of the approach was demonstrated using two synthetic data sets from simple seafloor models. The method was then applied to the real data acquired at the North Alex mud volcano in 2008. Results found increased apparent sediment resistivities of up to 4 Ωm near the center of the mud volcano occurring at source-RX offsets greater than 500 m, which mapped to apparent depths of greater than 150 m. This may be caused by large quantities of free gas or freshwater in the sediment pore space.

Antenna Polarization Optimization for Target Detection in Non-Gaussian Clutter

Adaptive polarization design of radar antenna has recently become the focus of attention in radar polarization community. A polarimetric detector against non-Gaussian clutter with transmitter polarization optimization has been proposed in this paper. First, the radar data model including the realistic dependence of the clutter on the transmitted polarization is introduced. Then the polarimetric detector with transmitter polarization optimization is developed. By employing the simulation, we demonstrate that the polarization waveform optimization can bring the significant performance gain on target detection as compared to the conventional full-polarization approach. Besides, jointly optimizing transmitter and receiver polarization to form a scalar measurement is confirmed not to achieve a better detection performance than vector measurement with only transmitter polarization optimization.

Spectrum Sensing for Cognitive Radios Based on Directional Statistics of Polarization Vectors

In this paper, we propose a new blind spectrum sensing method based on the polarization characteristic of the received signal, which is completely represented by the orientation of a polarization vector. We first discuss a spectrum sensing model based on polarization vectors' orientation. Then we develop the directional statistics of polarization vectors that contain both the signal and noise or noise only. The distinctive difference between the two statistics can be used to decide whether the primary signal exists or not. Based on this, by using the well-known generalized likelihood ratio test (GLRT) paradigm, a new polarization sensing algorithm GLRT-polarization vector (GLRT-PV) is proposed. By applying directional statistics, we derive closed-form expressions for the probability of false alarm and the probability of detection under both dual-polarized additive white Gaussian noise (AWGN) and Rayleigh-fading channels. Our numerical simulation and experimental results show that the proposed method exhibits better performance than other existing methods in the case of unknown primary transmitter polarization and/or presence of noise power uncertainty.

OPTIMAL POLARIZATION DESIGN FOR DIRECTION FINDING USING MIMO ELECTROMAGNETIC VECTOR-SENSOR ARRAY

In this paper, transmitter polarization optimization is flrstly proposed to improve the accuracy of azimuth-elevation arrival angles estimation within MIMO electromagnetic vector-sensor array (EMVA). Minimizing of Cramer-Rao bound is used as cost function for the optimal design of transmitting signal polarization. Computer simulation results verify that the optimal polarization design provides increased estimation accuracy of direction flnding in MIMO-EMVA, compared with that of using flxed polarization of transmitting signal. Moreover, the optimal polarization design retains all advantages of using flxed polarization of transmitting signal for MIMO-EMVA direction flnding.

Design of transmission multilayer polarizer for soft X-ray using a merit function

A new method of designing soft X-ray transmission multilayer polarizer for use at a single wavelength using a merit function has been eveloped. A merit function of product of p-transmittance throughput and logarithm of transmittance polarization ratio was chosen. Characteristics of Mo/Si multilayer calculated using the merit function at 13.0 nm have been compared with those calculated using the traditional method by the present authors and those reported so far. The merit function has given the most optimal results of throughput of 30.0% and polarization ratio of 202. The polarizers of much higher polarization ratio or much larger p-transmittance can be designed by choosing the number of layers and optimizing the thickness of each layer to maximize the merit function. Using this method, the roughness effect has been studied on Mo/Si and La/B multilayer polarizers at 13.0 nm and 6.7 nm, respectively. It was found that the influence of roughness is crucial in shorter wavelength region.

Compact polarimetry based on symmetry properties of geophysical media: the /spl pi//4 mode

We assess the performance of synthetic aperture radar (SAR) compact polarimetry architectures based on mixed basis measurements, where the transmitter polarization is either circular or orientated at 45/spl deg/(/spl pi//4), and the receivers are at horizontal and vertical polarizations with respect to the radar line of sight. An original algorithm is proposed to reconstruct the full polarimetric (FP) information from this architecture. The performance assessment is twofold: it first concerns the level of information preserved in comparison with FP, both for point target analysis and crop fields classification, using L-band SIRC/XSAR images acquired over Landes forest and Jet Propulsion Laboratory AIRSAR images acquired over Flevoland. Then, it addresses the space implementation complexity, in terms of processed swath, downloading features, power budget, calibration, and ionospheric effects. The polarization uniqueness in transmission of this mixed basis mode, hereafter referred to as the /spl pi//4 mode, maintains the standard lower pulse repetition frequency operation and hence maximizes the coverage of the sensor. Because of the mismatch between transmitter and receiver basis, the power budget is deteriorated by a factor of 3 dB, but it can partly be compensated.

Electrical properties of sol-gel processed PLZT thin films

Sol-gel processed lanthanum-modified lead zirconate titanate (PLZT) thin films consisting of two different perovskite phase contents were fabricated on indium tin oxide coated Corning 7059 glass substrates with two different heating schedules: direct insertion at 650° C for 30 min and at 500° C for 2h. Optical transmittance spectra, polarization versus electric field curves, relative dielectric constant versus frequency and capacitance versus d.c. bias voltage curves of the samples were investigated. The samples showed a good transparency of over 70% and interference oscillation. A thin film consisting of mainly perovskite phase showed a slim loop hysteresis in the polarization versus electric field curve and in the capacitance versus d.c. bias voltage curve, indicating the presence of ferroelectric domains, but a film consisting of mainly pyrochlore phase did not. The dielectric constant and loss factor of the thin film consisting of mainly perovskite phase were about 90 and about 0.2, respectively, at relatively low frequency and showed dispersion of the dipolar polarization of permanent dipole moment in the ferroelectric perovskite phase in the frequency range between 10 kHz and 1 MHz.

The Resonance Structure of the Bistatic Radar Scattering Cross Section of Randomly Oriented Dipoles

A definitive method for the calculation of the bistatic radar scattering cross section of a cloud of randomly oriented conducting wire dipoles has been developed by Dedrick et al. [6]. It is based on a Stokes parameter formalism, thus containing complete information regarding transmitter and receiver polarizations. Since the single-wire cross section exhibits strong resonance effects, it is of interest to investigate to what extent these resonance phenomena are affected by the orientation average in a cloud of randomly oriented wires. To study this question, we present comprehensive three-dimensional graphs of the relevant bistatic cross sections plotted versus scattering angle and frequency, as well as of the various polarization functions, using the Einarsson wire cross section. The results indicate the degree to which the resonance features persist in both cross section and polarizations after orientation averaging.

On the polarimetric contrast optimization

The problem considered is one of finding the polarization state of an antenna such that a power ratio due to two different objects is optimized. It is reduced to an optimization problem of two Hermitian forms which can be simultaneously diagonalized using a well-known linear-algebraic construction. The corresponding polarization vectors are found. The calculations are performed directly on the expression for the energy density of the reflected wave as a function of the transmitter polarization and are, therefore, decoupled from the receiving antenna parameters. Such decoupling is particularly convenient in bistatic applications.

Average radar cross section for arbitrary transmitter and receiver polarizations with application to wire scatterers

An expression is derived for the average backscattering cross section of an obstacle for arbitrary transmitter and receiver antenna polarizations. Results are given for straight wires, circular loops, and one-turn helices.

Diffraction of Ultra-Short Radio Waves

WE have pointed out1 that ultra-short radio waves polarized with the electric vector vertical are propagated into the shadow of hills more readily than horizontally polarized waves. We have since observed the opposite effect for receiver positions beyond hills but just outside their shadow. Fig. 1 represents roughly the terrain over which these results, shown in the table, were obtained. The transmitter T was near the top of one ridge and the field strength investigated over the region ABCD ; horizontally and vertically polarized radiation was emitted in turn from the transmitter on a wave-length of 3 metres, and the aerial at the receiver oriented to correspond for each measurement with the appropriate transmitter polarization. Over the region ABC within the geometrical shadow of the ridge having a crest at A, the vertical electric field, in agreement with our earlier note, was greater than the horizontal field, the ratio of these two fields, as will be seen from the table, being unity near the edge of the shadow at A and C and a maximum near the bottom of the valley at B. Just outside, however, the horizontal field was greater than the vertical, the ratio showing a flat maximum.