Microwave Anechoic Chamber Research Articles

Analysis of Synchronization Angle Precision in RCS Measurement and its High Speed Synchronous Pulse Implementation

To meet the demand for high precision measurements of radar cross section (RCS) in microwave anechoic chamber, the effect of angle repeatability of position servo system in background cancellation technology is analyzed and its error mathematical model is presented. Then a method of high speed synchronization angle measurement based on CPLD is proposed, which improves the precision of synchronization angle measurement in any fixed angle interval. The experiment results show that this method can effectively solve the accuracy of target RCS when rotating.

FEATURES EXTRACTION OF ROTATIONALLY SYMMETRIC BALLISTIC TARGETS BASED ON MICRO-DOPPLER

It is potentially useful to perform target identification using micro-Doppler features because they contain information on the geometrical structure of the target. In this paper, the m-D effect of the rotationally symmetric ballistic target (BT) is analyzed which reveals that the m-D is not a form of sinusoidal modulation due to the slidingtype scattering. Inspired by the extended Hough transform (EHT), a method to extract all the six parameters of the BT is proposed. The m-D effect and the performance of feature extraction algorithm are demonstrated by the measured data in a microwave anechoic chamber.

A Mobile Asset Tracking System Architecture under Mobile-Stationary Co-Existing WSNs

The tracking of multiple wireless mobile nodes is not easy with current legacy WSN technologies, due to their inherent technical complexity, especially when heavy traffic and frequent movement of mobile nodes are encountered. To enable mobile asset tracking under these legacy WSN systems, it is necessary to design a specific system architecture that can manage numerous mobile nodes attached to mobile assets. In this paper, we present a practical system architecture including a communication protocol, a three-tier network, and server-side middleware for mobile asset tracking in legacy WSNs consisting of mobile-stationary co-existing infrastructures, and we prove the functionality of this architecture through careful evaluation in a test bed. Evaluation was carried out in a microwave anechoic chamber as well as on a straight road near our office. We evaluated communication mobility performance between mobile and stationary nodes, location-awareness performance, system stability under numerous mobile node conditions, and the successful packet transfer rate according to the speed of the mobile nodes. The results indicate that the proposed architecture is sufficiently robust for application in realistic mobile asset tracking services that require a large number of mobile nodes.

Broad band invisibility cloak made of normal dielectric multilayer

We present the design, fabrication, and performance test of a quasi three-dimensional carpet cloak made of normal dielectric in the microwave regime. Taking advantage of a simple linear coordinate transformation, we design a carpet cloak with homogeneous anisotropic medium and then practically realize the device with multilayer of alternating normal dielectric slabs based on the effective medium theory. As a proof-of-concept example, we fabricate the carpet cloak with multilayer of FR4 dielectric slabs with air spacing. The performance of the fabricated design is verified through full-wave numerical simulation and measurement of the far-field scattering electromagnetic waves in a microwave anechoic chamber. Experimental results have demonstrated pronounced cloaking effect in a very broad band from 8 GHz to 18 GHz (whole X and Ku band) due to the low loss, non-dispersive feature of the multilayer dielectric structure.

Micro-Doppler characteristics of sliding-type scattering center on rotationally symmetric target

The feature of micro-motion is one of the most effective features used for radar recognition in midcourse phase. At present, the study of feature extraction and recognition is usually based on the assumption that the micro-motion of the scattering center and warhead itself is the same, and the radar echo is sinusoid-FM signal. However, this assumption ignores the fact that the scattering center would slide on the warhead with the change of the aspect angle. In this paper, a complete micro-motion model is set for the scattering centers of different positions on the warhead, and the mathematical expression of the micro-Doppler of the sliding-type scattering center is obtained for the first time. The approximation of Taylor expansion under the background of missile confrontation is studied subsequently. The curve of this micro-Doppler is not the generally assumed sinusoid. Dynamic measurement of a precessional target in microwave anechoic chamber is done to vividly observe the sliding feature of the scattering center. The measurement results agree with the theoretic analysis in this paper. This research on micro-Doppler characteristics of sliding-type scattering center provides a more accurate model for the micro-motion simulation and feature extraction of precessional warheads.

China Galileo test range research and status

This article introduces the research and development for the China Galileo Test Range (CGTR) system, which includes indoor test environment (ITE) based on the microwave anechoic chamber, outdoor test environment (OTE) based on the pseudolite network and multimedia demonstration and training facility (MDTF) with multimode GNSS software receiver, application simulating facility, and multimedia platform. This article presents the key technical topics of CGTR and the system status by now. The topics are valuable for GNSS receiver testing, in indoor and outdoor test environment designing, multimode GNSS software receiver designing and GNSS application simulations.

Double screen frequency selective surface structure optimized by genetic algorithm

Double screen frequency selective surface(FSS) is a very effective means of realizing the invisibility of radar-cabin from the detection of radar wave since it can well realize the flattened effect and rapid decrease. In this paper, the thickness, the dielectric constant, the element graph and the arrangement periodicity of an FSS medium are investigated by Genetic Algorithm(GA) when electromagnetic waves are incident on the double screen FSS at varying angles, and an optimized FSS structure and transmission characteristics are obtained. Meanwhile, the relevant experimental samples are prepared by means of coating and lithography and are tested in microwave anechoic chamber. The results show that the optimized structure has a better stability with respect to incident angle of electromagnetic wave under the condition of 2GHz operation, thereby laying the foundation for the application of double screen FSS to curved surfaces at wide angles.

Modeling simulation and experiment of micro-Doppler signature of precession

Spatial precession is a special micro-motion of the spinning-directional target, and the micro-Doppler signature of the cone-shaped target with precession is studied. The micro-motion model of precession is built first, and then the micro-Doppler model is developed based on the proposed concept of micro-motion matrix, by which the theoretical formula of micro-Doppler signature of precession is derived. In order to further approach to the actual case, the occlusion effect is firstly considered in micro-Doppler, and the simulated result with occlusion effect is well in accordance with the measured result in microwave anechoic chamber, which suggests that the micro-motion model and micro-Doppler model of precession are both valid.

Novel compact 2.4/5‐GHz dual‐band T‐slot antenna for WLAN operations

AbstractThis paper proposes a novel compact dual‐band T‐slot antenna for 2.4/5‐GHz wireless applications. The proposed antenna is composed of two orthogonal slots in a 20 mm by 50 mm ground plane. The antenna was fabricated on a FR‐4 substrate (εr = 4.50, tan δ = 0.02) and was measured in a microwave anechoic chamber. The experimental data and the simulation results agree well with each other and show that the proposed antenna can completely cover both 2.4/5‐GHz bands with satisfactory radiation characteristics. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1236–1238, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22451

A MINIATURIZED PRINTED DIPOLE ANTENNA WITH V-SHAPED GROUND FOR 2.45 GHZ RFID READERS

In this paper, a miniaturized printed dipole antenna with the V-shaped ground is proposed for radio frequency identification (RFID) readers operating at the frequency of 2.45 GHz. The principles of the microstrip balun and the printed dipole are analyzed and design considerations are formulated. Through extending and shaping the ground to reduce the coupling between the balun and the dipole, the antenna’s impedance bandwidth is broadened and the antenna’s radiation pattern is improved. The 3D finite difference time domain (FDTD) Electromagnetic simulations are carried out to evaluate the antenna’s performance. The effects of the extending angle and the position of the ground are investigated to obtain the optimized parameters. The antenna was fabricated and measured in a microwave anechoic chamber. The results show that the proposed antenna achieves a broader impedance bandwidth, a higher forward radiation gain and a stronger suppression to backward radiation compared with the one without such a ground.

Detecting Each Position of Residual Reflections Using a Radiation Pattern Measurement Method for Eliminating Reflections by Distance Changing Technique

AbstractIn order to carry out high‐precision measurement of the radiation characteristics of antennas and to evaluate the reflection characteristics of microwave anechoic chamber used for antenna measurement, it is important to recognize the location and intensity of the unwanted reflection sources caused by the ambient environment. In this paper, the radiation pattern measurement proposed by the authors is applied for estimating the location of the reflection sources and their effects on the radiation pattern. In the proposed radiation pattern measurement method, the reflected waves are eliminated by the Fourier transform of the measured reflected electric field data obtained on varying the measurement distance. First, a method for estimating the locations of the reflected wave sources and their effects is theoretically shown from the radiation pattern of the reflected wave. This pattern is obtained after the direct radiation pattern obtained from the radiation pattern with the reflected wave suppressed is eliminated from the measured radiation pattern. From a verification experiment using a standard L‐band horn, the effectiveness of the method is verified. Second, a window function is applied to the measurement distance range so that the sidelobes of the Fourier transform spectrum are reduced. From the radiation pattern of the reflected wave obtained by applying a gating process to this Fourier spectrum at each angle, the effect of several reflection sources is estimated individually. From the results of computer simulation, the effectiveness of the proposed method is verified. Further, the range of applicability of the method is discussed. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(4): 33–43, 2002

Compensation of scatterer migration through resolution cell in inverse synthetic aperture radar imaging

To obtain the inverse synthetic aperture radar image of a target, certain rotation angles of the target with respect to radar line of sight during the coherent integration interval are required, migration of scatterers will take place. Actually, scatterer migration through resolution cells (MTRC) will happen inevitably in high-resolution radar imaging, which will result in image resolution degradation. Scatterer MTRC is discussed, then a simple and an efficient algorithm, the MTRC compensation algorithm (MTRCCA), is proposed to compensate MTRC. The relationship between the MTRCCA, range–doppler and polar formatting algorithms is also discussed. ISAR images from simulated and real data measured in a microwave anechoic chamber are presented to validate the proposed algorithm.

Frequency-selective surface for microwave power transmission

Using an equivalent-circuit model, frequency-selective surfaces (FSS's) with gridded- and double-square elements have been designed and tested for suppressing the harmonics radiation in microwave power transmission system. It is shown that the angular sensitivity of the frequency response of the FSS arrays can be reduced with a combination of TE- and TM-polarized incident waves or a circularly polarized incident waves instead of a single TE- or TM-polarized incident wave. The FSS arrays have also been measured in a microwave anechoic chamber and a good agreement is obtained between the theoretical calculations and experimental results.

Compact shielded exposure system for the simultaneous long-term UHF irradiation of forty small mammals II. Dosimetry

A four-antenna collinear array in an electromagnetically shielded chamber was designed and constructed to preferentially irradiate the brains of a large number of small mammals using cellular telephony microwave signals. Ten animals in special restrainers were positioned symmetrically around a centrally located antenna. These restrainers are resting on a circular structure made of acrylic plastic called a "carousel." Four carousels are stacked vertically, forming the array, inside a microwave anechoic chamber called a "chamberette." (Details of the design of this irradiator and of a 12-chamberette irradiation facility are given in a previous article.) In this article, the dosimetry on rats is reported. Both thermometric and thermographic measurements were performed. The average specific absorption rate (SAR) in brain tissue measured thermometrically was 0.85+/-0.34 W/kg per watt of net input power into the radiating antenna. This range agrees with the SAR levels reported in the literature for cellular telephones. Thermographic evaluation using splittable phantoms showed that most of the energy absorbed by the rats is concentrated in and around the brain. Moreover, it was found that the SAR in brain tissue can vary considerably for rats of similar weights, depending on position of the rats' heads inside the restrainers, and that there exists a significant dependence of SAR on animal weight. These variations may be of importance in the interpretation of results of lifelong studies. The data presented clearly show that the chamberette is, dosimetrically, a suitable irradiation system for electromagnetic bioeffects studies in the cellular communication frequency range, especially when a large number of laboratory animals is required.

Compact shielded exposure system for the simultaneous long‐term UHF irradiation of forty small mammals II. Dosimetry

A four-antenna collinear array in an electromagnetically shielded chamber was designed and constructed to preferentially irradiate the brains of a large number of small mammals using cellular telephony microwave signals. Ten animals in special restrainers were positioned symmetrically around a centrally located antenna. These restrainers are resting on a circular structure made of acrylic plastic called a “carousel.” Four carousels are stacked vertically, forming the array, inside a microwave anechoic chamber called a “chamberette.” (Details of the design of this irradiator and of a 12-chamberette irradiation facility are given in a previous article.) In this article, the dosimetry on rats is reported. Both thermometric and thermographic measurements were performed. The average specific absorption rate (SAR) in brain tissue measured thermometrically was 0.85 ± 0.34 W/kg per watt of net input power into the radiating antenna. This range agrees with the SAR levels reported in the literature for cellular telephones. Thermographic evaluation using splittable phantoms showed that most of the energy absorbed by the rats is concentrated in and around the brain. Moreover, it was found that the SAR in brain tissue can vary considerably for rats of similar weights, depending on position of the rats' heads inside the restrainers, and that there exists a significant dependence of SAR on animal weight. These variations may be of importance in the interpretation of results of life-long studies. The data presented clearly show that the chamberette is, dosimetrically, a suitable irradiation system for electromagnetic bioeffects studies in the cellular communication frequency range, especially when a large number of laboratory animals is required. Bioelectromagnetics 20:81–93, 1999. © 1999 Wiley-Liss, Inc.

A microwave anechoic chamber for radar-cross section measurement

A microwave anechoic chamber has been developed at the Department of Electrical Engineering, University of Malaya, for monostatic and bistatic radar-cross-section measurements. The structure of the chamber is a quarter-section geodesic dome, with a 12 foot radius, and raised three feet above the floor. An antenna railing system is installed inside the chamber. The antennas can be moved along the rails in the elevation direction, with the microwave beam pointing at the center of the dome where the target is located. This design enables a very large combination of incidence and scattering angles in bistatic measurements. Four transmitting antennas are fixed at different elevation angles next to one of the antenna rails. By using an azimuth-over-elevation positioner as the pedestal for the target, and by positioning the movable antenna along that rail beside those fixed transmitting antennas, monostatic measurements with incidence angles ranging from 0 to 90 degrees can be accomplished. A vector network analyzer is utilized to measure the amplitude and phase of the radar returns. An IEEE-488.2 interface bus is used to control various hardware components, as well as to perform data acquisition. A computer program was written to automate the measurement system. Data are stored in raw format, and processed later with dedicated software, so that different processing methods and parameters can be applied. This paper highlights the design and construction of the microwave anechoic chamber, as well as the measurement-system configuration for scattering-cross-section measurements.

Radar target recognition using a radial basis function neural network

The problem of radar target recognition based on high resolution range profiles is investigated in this paper, using a radial basis function network (RBFN). After analysing the signatures of the range profile, an effective preprocessing method is proposed to obtain stable and shift invariant patterns which are classified by RBFN. Then the classification mechanism of RBFN is described, suggesting that the RBFN has better performance than the conventional kernel classifier. It is shown from theoretical analysis and experimental results which were obtained with data acquired in a microwave anechoic chamber that the method proposed in this paper offers promise for target recognition.

Radar target recognition based on neural network

The problem of radar target recognition using range profiles is investigated in this paper, based on a Radial Basis Function Network(RBFN). A preprocessing method is proposed, which performs amplitude average of the range profiles to obtain more stable patterns. After pointing out the limitedness of traditional empirical formula, this paper also gives a method of estimating the shape parameter σ of a Gaussian kernel function according to spatial distribution of the training samples. It is shown that the method proposed in this paper offers promise for target recognition, from both the theoretical analysis and the experimental results of rotating platform imaging based on data acquired in a microwave anechoic chamber.

Super-resolution range-Doppler imaging

The general observation model for range-Doppler imaging is established from the point of view of multiple scatter-point localisation, and the optimum imaging procedure based on the maximum likelihood principle is given. Pursuing simplified procedures, the authors present three super-resolution range-Doppler imaging methods, including the linear prediction data extrapolation DFT (LPDEDFT), the dynamic optimisation linear least-squares (DOLLS), and the Hopfield neural network nonlinear least-squares (HNNNLS) methods. The live data of a metallised scale model B-52 aircraft mounted on a rotating platform in a microwave anechoic chamber and a flying Boeing-727 aircraft as well as the simulated data of an aircraft were processed. The imaging results indicate that, compared to the conventional Fourier method, a higher resolution for the same effective bandwidth of transmitted signals and total rotation angle of the object may be obtained by these super-resolution approaches.

Simple high-frequency diffraction analysis of microstrip antenna on large cylinder

The aim of this Letter is to investigate the electromagnetic field surrounding an electrically large convex cylinder on which a microstrip antenna is mounted. Being capable of calculating the various types of field, i.e. directly incident field, reflected field and diffracted field on the plane perpendicular to the cylinder axis, the selfconsistent GTD formulation is employed. In accordance with such a formulation, a two-magnetic-line-current radiation model for the patch is given. Measurement is also performed in a microwave anechoic chamber for the purpose of validation of the proposed theory.