Radar Cross Section Measurements Research Articles

Application of Adaptive Pulse Compression in Cluttered Radar Cross Section Measurements

This article discusses a post-processing method to achieve highly accurate radar cross section (RCS) measurements in challenging test environments. In the ideal RCS measurement setup, the only received signal is the reflection from the object under test (OUT). However, this scenario is often not realizable in practice as outside measurements suffer from a multitude of scattering objects beyond the OUT, and even anechoic chambers have nonnegligible multipath clutter. Time-gating has been shown to be a powerful post-processing clutter suppression tool by temporally filtering any undesired return signals. However, this technique is only sufficient when there is ample spacing between the OUT and undesired return signals or when the sidelobes of one scatterer do not mask the return of a smaller nearby scatterer in the time domain. In the latter scenario, traditional time-gating techniques cannot separate the sidelobes from a nearby dominant scatterer overlapping with the main lobe of the OUT, and the RCS of the OUT cannot be extracted accurately. By applying the proposed stepped frequency continuous wave (SFCW) adaptive pulse compression (APC) algorithm, a range-dependent filter is created to iteratively estimate the range profile and suppress sidelobes allowing for temporal separation of the scatterers and accurate RCS estimation. To validate the concept, the RCS of a 15.2 cm sphere is extracted in two measurement configurations (with and without a large nearby dominating scatterer). The traditional matched filter data processing accuracy is compared to the proposed APC technique. Implementation of APC in post-processing yields a 71.2% improvement in average RCS error compared to traditional processing in the sphere-only measurement and an 88.2% improvement in the presence of a metal plate.

Standard Deviation of Spaceborne GNSS-R Ocean Scatterometry Measurements

This article analyzes the contribution of the delay-Doppler map (DDM) observation noise to the uncertainty of global navigation satellite system reflectometry (GNSS-R) ocean scatterometry observables and the retrieved wind speeds. For this purpose, the parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K^{p}$ </tex-math></inline-formula> , which is commonly used in the traditional microwave scatterometer, is introduced to characterize the relative standard deviation (RSD) of the GNSS-R normalized bistatic radar cross section (NBRCS) measurement. Based on the noise covariance of the DDM measurements, the analytic expressions of RSD are derived for two cases, i.e., the NBRCS computed with one single DDM bin at the specular point and the NBRCS computed from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M\,\,\times \,\,N$ </tex-math></inline-formula> DDM bins around the specular point. By analyzing the dependence of the RSD on different system, geometry, and instrument parameters, the simplified models of RSD are derived empirically. As a simple application of the proposed models, the wind speed retrieval errors are computed using parameters from the Cyclone GNSS (CYGNSS) mission. It shows that the wind speed retrieval error due to thermal noise and speckle can be an important error source for the overall wind speed retrieval performance, especially at high wind speed and with the high incidence angle GNSS-R measurements.

Wideband Measurement Techniques for Extracting Accurate RCS of Single and Distributed Targets

This article discusses both test setup and signal processing techniques to achieve highly accurate radar cross section (RCS) measurements across a wide bandwidth. This high accuracy is achieved through both postprocessing algorithms and test setup hardware modifications. The postprocessing techniques include calibration, clutter cancellation, and time-gating, all of which are applicable to a generic anechoic chamber setup. Specialized RCS measurement equipment such as a vector network analyzer (VNA) capable of producing nanosecond-length pulses is not necessary. However, strategic, inexpensive hardware modifications further improve measurement quality. Experiments are conducted at the University of Oklahoma in the far-field anechoic chamber to evaluate the effects of the postprocessing and setup variations on the measurement accuracy. Parameters including object support pedestal geometry, VNA intermediate frequency (IF) bandwidth, and azimuthal angle rotation are studied. Trade-offs between time, cost, and accuracy are considered in the context of these variables. By upgrading the measurement setup hardware and applying optimized processing techniques, the RCS average error is reduced from 3.2 dBsm to only 0.21 dBsm across the 2-18-GHz frequency range. The versatility of these techniques is then demonstrated by measuring a distributed target with an average error of 0.94 dBsm from 2 to 8 GHz when compared with simulation.

Scaled radar cross section measurement method for lossy targets via dynamically matching reflection coefficients in THz band

In the terahertz band, the dispersive characteristic of dielectric material is one of the major problems in the scaled radar cross section (RCS) measurement, which is inconsistent with the electrodynamics similitude deducted according to the Maxwell’s equations. Based on the high-frequency estimation method of physical optics (PO), a scaled RCS measurement method for lossy objects is proposed through dynamically matching the reflection coefficients according to the distribution of the object facets. Simulations of the model of SLICY are conducted, and the inversed RCS of the lossy prototype is obtained using the proposed method. Comparing the inversed RCS with the calculated results, the validity of the proposed method is demonstrated. The proposed method provides an effective solution to the scaled RCS measurement for lossy objects in the THz band.

Numerical approaches and analysis of optical measurements of laser radar cross-sections affected by aero-optical transmission

One of the concerns in the process of measuring laser radar cross-section (LRCS) using optical measurement methods is the aero-optical effect around a high-speed flow field. In this paper, a computational model for LRCS considering supersonic flow in a non-homogeneous medium is presented. First, by taking a typical 15° half-cone blunt cone as the research object, based on CFD calculation, the flow field distribution of the non-uniform medium around the high-speed vehicle is obtained. The ray-tracing method is used to calculate the light transmission in an aero-optical environment. An LRCS approach for arbitrarily complex targets in the aero-optical environment is then proposed, and the method is verified by analytical and numerical methods. Finally, the effects of incoming density, incoming Mach number, and material bidirectional reflectance distribution function (BRDF) parameters on LRCS measurements are investigated, and the errors caused by the steady aero-optical environment are analyzed. The results show that the maximum relative error of the measurement caused by the aero-optical environment in the direction of the shock-wave layer observation is significant when the Fresnel function approximation exponential function parameter is too large or when the root mean square (RMS) of the surface slope is too small in the BRDF parameters of the material. The influence of the aero-optical environmental flow field on the LRCS is characterized by a directional and regional distribution, determined by the incoming Mach number and shock-wave angle, with the influence of the incident flow density on the regional distribution being weakly correlated. The proposed method and calculation results are useful for the simulation, analysis, and calibration of LRCS measurements in complex aero-optical environments.

Compact Radar Cross-Section Measurement Setup and Performance Evaluation

Abstract. Radar cross-section measurements require the background reflections to be much lower than the reflections of the device under test. Although, anechoic chambers with special target holders meet this requirement, they are expensive and still have imperfections. To further reduce background reflections or to measure in environments where an anechoic chamber is not suitable, digital signal processing can be used to reduce background reflections. In this paper, a complete signal processing chain realized in Matlab is proposed, involving time gating of the measured target response and a background subtraction technique. Furthermore, the proposed signal processing includes a calibration procedure with either a single known calibration target or multiple known targets to improve measurement uncertainties. A compact measurement setup, consisting of a vector network analyzer and two horn antennas, is used to evaluate the overall performance and the advantages of a multiple known target calibration in a practical manner. The calibrated setup is able to measure the radar cross-section in a frequency range from 2 to 12 GHz with a mean error of less than 0.2 dB for both, VV and HH polarization combinations. It could also be shown, that a multi target calibration can result in an improvement of the measurement uncertainty by about 2.5 %.

Denoising With Inherent Scattering Characteristic for 2-D Radar Cross Section Measurement

Noises from the measurement sensors are inevitable in radar cross section testing due to the thermal agitation of electrons in imperfect conductors. Existing methods represented by wavelet threshold usually regard the measured data as a stationary stochastic signal, ignoring the inherent influence of the target under test, which inevitably removes the signal’s component when noise increases. This paper proposes a novel perspective on 2-D radar cross section measurement denoising, considering the target’s inherent scattering characteristics (ISC). In the proposed method, the noise and the target are firstly separated as far as possible in the generalized Fourier series domain while the target’s component is all preserved. Then, the noise is further suppressed by the scattered field reconstruction of the Hankel function. Finally, a metal sphere being a calibrator is introduced to improve the denoising ability. Both simulations and experimental studies demonstrate the superiority of our method compared with existing algorithms. Results indicate that the proposed method can achieve higher accuracy.

유동환경용 FSS 전극 유전체 장벽 방전 구조 플라즈마 발생기의 X-Band 내 RCS 감소 효과

In this study, an frequency selective surface (FSS) electrode of a dielectric barrier discharge (DBD) plasma generator, with a two-dimensional planar target, for radar cross section (RCS) reduction is proposed and measured. The electrode of the proposed plasma generator is based on a cross FSS array conductor. Therefore, it is possible to minimize the amount of RCS change according to the efficient plasma discharge and polarization of the signal from the radar. In addition, a frame of FR-4 dielectric material is placed between the 4.572 mm gap of the ground surface and the electrode to reduce RCS owing to stable plasma discharge in a fluid environment in which the aircraft operates. The proposed plasma generator is fabricated to determine the optimal plasma discharge and RCS measurement. The measurement results showed a 2.9 dB RCS reduction in the X-band.

Meteoroid Mass Estimation Based on Single‐Frequency Radar Cross Section Measurements

AbstractBoth high‐power large aperture radars and smaller meteor radars readily observe the dense head plasma produced as a meteoroid ablates. However, determining the mass of such meteors based on the information returned by the radar is challenging. We present a new method for deriving meteor masses from single‐frequency radar measurements, using a physics‐based plasma model and finite‐difference time‐domain (FDTD) simulations. The head plasma model derived in Dimant and Oppenheim (2017), https://doi.org/10.1002/2017ja023963 depends on the meteoroids altitude, speed, and size. We use FDTD simulations of a radar pulse interacting with such head plasmas to determine the radar cross section (RCS) that a radar system would observe for a meteor with a given set of physical properties. By performing simulations over the observed parameter space, we construct tables relating meteor size, velocity, and altitude to RCS. We then use these tables to map a set of observations from the MAARSY radar (53.5 MHz) to fully defined plasma distributions, from which masses are calculated. To validate these results, we repeat the analysis using observations of the same meteors by the EISCAT radar (929 MHz). The resulting masses are strongly linearly correlated; however, the masses derived from EISCAT measurements are on average 1.33 times larger than those derived from MAARSY measurements. Since this method does not require dual‐frequency measurements for mass determination, only validation, it can be applied in the future to observations made by many single‐frequency radar systems.

Position Error Detection and Compensation for Far-Field Radar Cross-Section Measurement

The calibration process is an essential kernel step in far-field radar cross-section measurement. Nevertheless, in the turntable test scenario, the calibrator cannot always be placed at the rotation center of the turntable. Because the geometric center and the rotation center of the upper surface of the turntable are not always coincident. To address this issue, we propose an error estimation method to predict and correct the calibrator position error caused by this issue; an error estimation method is proposed based on the vector rotation theory. Initially, the scattered power of the calibrator is recorded in the monostatic test mode. Then, the collected data are normalized and median filtered. Next, the position error vector is evaluated by determining the values of the radius and the polar angle of the calibrator in the experimental coordinate system. Simulation and experimental results show that the predicting accuracy with the proposed method is higher than 86%, which confirms the efficiency of this method.

Ku- and Ka-Band Ocean Surface Radar Backscatter Model Functions at Low-Incidence Angles Using Full-Swath GPM DPR Data

This paper presents the results of the first characterization of coincident Ku- and Ka-band ocean surface normalized radar cross section measurements at earth incidence angles 0°–18° using one year of wide swath Global Precipitation Measurement (GPM) mission dual frequency precipitation radar (DPR) data. Empirical geophysical model functions were derived for both bands, isotropic and directorial sensitivity were assessed, and finally, sea surface temperature (SST) dependence of radar backscatter, at both bands, were investigated. The Ka-band exhibited higher vector wind sensitivity for a low-to-moderate wind speeds regime, and the SST effects were also observed to be substantially larger at Ka-band than at Ku-band.

IEEE Standard 1502-2020: IEEE Recommended Practice for Radar Cross-Section Test Procedures [Stand on Standards

The measurement of radar crosssection (RCS) became very important in the 1960s, and many RCS test ranges were designed and built between 1960 and 1995. These test ranges and their procedures for testing, calibration, and usage typically were different because they reflected the visions of the scientists and engineers who designed them. In fact, performing RCS measurements is oftentimes as much of an art as it is a science. Moreover, the requisite measurement process is necessitated by the measurement facility, the target size, the frequency range, and the desired measurement fidelity. Consequently, the practices adopted by one facility are often not entirely transferrable to another. The objective of IEEE Standard 1502 is to standardize these practices as much as possible by providing a standard of practice across the RCS measurement community (test range operators, managers, data processors). To that end, this standard incorporates the common practices of experts in the field.

Novel Approach to Determine Spinning Satellites’ Attitude by RCS Measurements

AbstractThis paper proposes a novel approach for determining the three-dimensional (3D) attitude of on-orbit satellites in a spin condition using radar cross-section (RCS) measurements. The core id...

플라즈마의 특성 분석을 위한 수정된 로렌츠 분산 모형 기반 FDTD 알고리즘

In this paper, to analyze the dispersive characteristics of plasma, a dispersive model suitable for the finite-difference time-domain (FDTD) method is proposed. The dispersive characteristics of plasma with varying electrical properties according to frequency were accurately and efficiently expressed using the modified Lorentz dispersive model. The coefficient of the modified Lorentz dispersive model was extracted by applying complex curve fitting based on the weighted least squares method. The method of applying the modified Lorentz dispersion model to the FDTD is discussed. The plasma model based on the modified Lorentz dispersion model proposed in this paper was verified to match the data of the dielectric barrier discharge (DBD) plasma generator from dielectric slab equivalent modeling. The accuracy of the proposed FDTD algorithm based on the modified Lorentz dispersive model was verified by comparison with the results of the broadband radar cross-section (RCS) measurement experiment.

Radar cross section measurement of road debris in 79 GHz-band

Radar cross section measurement of road debris in 79 GHz-band

Fundamental Improvement to the Efficiency of On-Chip mmWave Phased Arrays Using MEMS Suspension

A major shortcoming of current silicon-based millimeter-wave (mmWave) on-chip antennas is the low radiation efficiency (<; 50%). In this letter, we present a novel on-chip antenna array with the radiation efficiency >80% at 60 GHz. The proposed array addresses the issues of on-chip air-suspension using micro electro mechanical systems (MEMS) processes, thus elevating the hovering radiating elements on a substrate at the height of 35 μm (0.007 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ). The micofabricated SU-8 posts serve as the vertical support, ensuring mechanical stability and monolithic integration. The simulated -10 dB fractional bandwidth of this array is 5.5% or 3.4 GHz at 60 GHz. Further, the designed array is capable of scanning of ±55° in the E plane and ±58° in the H-plane. The noncontact backscattering method is proposed and employed to derive the radiation efficiency from measured radar cross-section (RCS) data. RCS measurements are performed using a precision six-axis robotic arm with the spatial repeatability of 20 μm (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /250). The measured radiation efficiency is 82% at 60 GHz. The measured peak gain of 9 × 9 array is 23.3 dBi versus simulated 23.6 dBi. Fundamental enhancement in suspended array efficiency is achieved by eliminating unwanted radiation in the silicon substrate. Compared to other on-chip integration approaches, the proposed array can be monolithically integrated on a silicon substrate while maintaining high radiation efficiency.

A Calibration Method of Phase Error Caused by Target’s Position Error

A method is proposed in this paper to correct the position error in radar cross section (RCS) calibration. In radar RCS measurement system, in order to get the accurate information, the amplitude and phase calibration are very important to remove the error influence. The measurement results are influenced by multipath effect, laboratory background, target position, environmental noise and so on. In this paper, the position error correction is under consideration. Firstly, the method of getting target position is derived. Following this, the phase error caused by it can be got rid of to get more accurate data. Finally, we show the extensive simulation results and experiment results of typical cylinder, which all demonstrate the validity of the method.

UHF-Band Radar Cross Section Measurements With Single-Antenna Reflection Coefficient Results

This article discusses the challenges and advantages of measuring radar cross section (RCS) using reflection coefficient measurements from a single-antenna test setup. In practice, arranging two ultrahigh-frequency (UHF) antennas in a quasi-monostatic configuration is difficult due to their large physical size. In addition, the coupling power between the two antennas can be much larger than the signal of interest, imposing further limitations on this configuration. However, traditional RF measurement hardware and postprocessing algorithms are combined to extract RCS across frequency and azimuthal angle accurately with the $S_{11}$ values collected from a single antenna. This is made possible by using vector background subtraction and time-gating windowing techniques to suppress multipath reflections, clutter, and mismatch reflection while increasing the measurement’s dynamic range. The test setup utilizes the National Instruments LabVIEW software for control and automation, a General Purpose Interface Bus (GPIB)-enabled vector network analyzer, and a rotary table allowing for experiments to be conducted in an anechoic chamber or an outdoor measurement range. Experiments are conducted at the University of Oklahoma in the far-field anechoic chamber and outdoors using the components mentioned above to validate the derived algorithms and measurement concepts. The chamber setup is calibrated using a metal sphere to extract the RCS of a smaller metal sphere. The initial RCS extraction had an average error of 4.9 dBsm over the 300–1000-MHz frequency range using only calibration and vector background subtraction. After applying time gating, the error is further reduced to 0.54 dBsm. The implemented test setup is accomplished using traditional measurement equipment and a single antenna allowing for a portable, flexible, and low-cost solution for RCS measurements in the UHF band.

Near-Field to Far-Field RCS Prediction on Arbitrary Scanning Surfaces Based on Spherical Wave Expansion.

Near-field to far-field transformation (NFFFT) is a frequently-used method in antenna and radar cross section (RCS) measurements for various applications. For weapon systems, most measurements are captured in the near-field area in an anechoic chamber, considering the security requirements for the design process and high spatial costs of far-field measurements. As the theoretical RCS value is the power ratio of the scattered wave to the incident wave in the far-field region, a scattered wave measured in the near-field region needs to be converted into field values in the far-field region. Therefore, this paper proposes a near-field to far-field transformation algorithm based on spherical wave expansion for application in near-field RCS measurement systems. If the distance and angular coordinates of each measurement point are known, the spherical wave functions in an orthogonal relationship can be calculated. If each weight is assumed to be unknown, a system of linear equations as numerous as the number of samples measured in the near electric field can be generated. In this system of linear equations, each weight value can be calculated using the iterative least squares QR-factorization method. Based on this theory, the validity of the proposed NFFFT is verified for several scatterer types, frequencies and measurement distances.

An octagonal-shaped conductive HC12 & LIBERATOR-40 thread embroidered chipless RFID for general IoT applications

This paper presents the design, fabrication and testing of two embroidered chipless octagonal-shaped RFID tags on cotton fabric for wearable applications. The first tag is designed by using silver-coated polyamide conductive fibre (HC12) and the second tag is embroidered by using highly conductive Vectran (LIBERATOR 40) which is highly conductive multifilament yarn spun from Liquid Crystal Polymers (LCP), on cotton fabrics. In contrast to the traditional RFID tag, the chipless RFID tagging, the ID code is not saved in the memory, instead, it uses the physical features of the tag to send data. The proposed tag's design uses a Frequency Selective Surface (FSS) technique for the frequency range of 8–18 GHz. These tags are designed using CST studio and precisely fabricated by using commercial ZSK Technical Embroidery System JCZA (0109–550). The tag design is composed of six concentric octagonal loop resonators with one unitary element. The electromagnetic scattering waves behaviour and Singularity Expansion Method (SEM) based circuit modelling for the octagonal-shaped tag is performed, and the coupling coefficients are evaluated. The desired data bits are obtained by a series of comparative experiments for Radar Cross Section (RCS) in an anechoic chamber. The experimental results obtained show that the 4-bit data is accurately retrieved with the variation of distance by up to 1.8 m at 0 dB m. Moreover, the average transition from minimum ‘0’ to maximum 1’ is -27 dB for both designs. Furthermore, the experimental results for on-body RCS measurements and the bending effects on both tags down to 7 mm is observed. This octagonal embroidered Chipless RFID tag is a fully textile design which is compact and can be deployed commercially in various IoT applications.