AMTA Paper Archive
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Simulation and Measurement of Locomotive Antennas in the Installed State Based on a Scaled Mockup
Accurate characterization of locomotive antennas is key to safe and robust railway signaling and control communication. With the introduction of new technologies and the foreseeable migration from the GSM-R standard towards FRMCS, new wireless applications and specifications arise, and suitable antenna solutions need to be developed and tested. Moreover, the rooftops of modern locomotives present a dense and harsh environment; therefore, potential antenna mounting spaces should be carefully evaluated to avoid undesirable degradations of the antenna radiation patterns. Due to the electrically large and complex structure of locomotives, full-scale testing is challenging to perform, especially under laboratory conditions. Antenna measurements with geometrically scaled models present a powerful alternative to address this issue. In this paper, we present and discuss antenna measurement results of a scaled locomotive mockup. The mockup incorporates two different cabin geometries, one with a step-like rooftop contour, and one with a smooth slightly tilted geometry. First, the optimum scaling factor was identified and validated through numerical simulations. Afterwards, antenna measurements with a scaled locomotive mockup were carried out in our automotive antenna measurement facility VISTA. The measured results were compared with the numerical simulations, where a good correlation above 80% was found. Secondly, the impact of the rooftop geometries, and superstructures on the roof has been investigated for a range of operational frequencies between 700 and 2600 MHz. The results reveal that the parasitic impact of the antenna environment becomes more pronounced at higher frequencies.
Challenges for the Automotive Industry on MIMO OTA Testing
The evolution of cellular communication technologies has been replicated by the automotive industry with modern vehicles being almost universally fitted, as a bare minimum, with a radio system, a cellular communication system and Bluetooth capability. Higher end vehicles have additional capabilities such as WiFi, GNSS, TPMS, smart keyless entry and smart start/stop feature. All these systems are highly integrated as part of the vehicle's infotainment unit and they must operate satisfactorily in a co-existing manner. Automotive wireless testing is currently facing several challenging aspects with one such aspect being MIMO OTA (Multiple-Input-Multiple-Output Over-The-Air) testing of the terrestrial cellular communication system of the vehicle. In this paper, we will examine the current approach for MIMO OTA testing in the 4G and 5G cellular environments and discuss various scenarios on how existing techniques can be adapted to support MIMO OTA testing in the automotive industry. MIMO OTA testing is typically carried out either using conducted testing techniques or using a Multi Probe Anechoic Chamber (MPAC); both these methods have their advantages and limitations and, to a certain extent, a degree of applicability to a very large article under test. This paper covers these two established MIMO OTA testing techniques and considers their applicability to the automotive MIMO OTA testing scene. Following on from this analysis and the challenges exposed herein, additional MIMO OTA test methods are put forward along with an assessment of how well they perform in an automotive test environment.
Achieving the Desired Performance from a Radar Cross Section Pylon Rotator
The desire to acquire Radar Cross Section (RCS) data on full scale models poses a number of challenges to the users of pylon / rotator systems. Typically, these full scale models have significant mass but have a relatively small foot print on which it is acceptable to mount the model to the rotational flange. The challenges to be addressed in this paper include designing a rotator that will have sufficient strength to support the weight of the model and the stress generated by the overturning moment. This rotator must have a sufficiently low profile and small volume so that it will conveniently fit within the model volume but still achieve a sufficient elevation travel to meet test objectives. This rotator must still properly close out the pylon at all elevation angles to prevent unwanted reflections. Additional design considerations include the test conditions and the test environment. A rigorous test requirement can demand special engineering features to mitigate the demands of relatively high scan speeds and extended run times. Environmental concerns including wind loads, temperature, humidity, and contaminants, must be factored into the design of modern RCS rotators. This paper presents the system design approach to address the requirements of a full scale model rotator. The paper examines consequences of selected potential design solutions and demonstrates the importance of performing trade studies.
A 240 GHZ Polarimetric Compact Range for Scale Model RCS Measurements
A fully-polarimetric compact radar range operating at 240 GHz has been developed for obtaining Ku-band RCS measurements on 1:16th scale model targets. The transceiver consists of dual fast-switching, stepped, CW, X-band synthesizers driving dual X24 transmit multiplier chains and dual X24 local oscillator multiplier chains. The system alternately transmits horizontal (H) and vertical (V) radiation while simultaneously receiving H and V. Software range-gating is used to reject unwanted spurious responses in the compact range. A flat disk and rotating circular dihedral are used for polarimetric as well as RCS calibration. Cross-pol rejection ratios of better than 45 dB are routinely achieved. The compact range reflector consists of a 60” diameter, CNC machined aluminum mirror fed from the side to produce a clean 27” FWHM quiet zone. In this paper a description of this 240 GHz compact range is provided along with an ISAR measurement example.
A State of the Art Anechoic Chamber for Air vehicle Testing at Alenia Aeronautica
Electromagnetic Anechoic Chamber has recently been built by Alenia Aeronautica at Caselle South Plant: The Anechoic Chamber is a full anechoic chamber, and it has been designed to carry out electromagnetic vulnerability tests mainly on fighter and unmanned aircraft. In addition measurement can be carried out on many different vehicles that can be brought into the chamber through the main access door. A system to extract exhaust gas was installed in order to carry out tests on a wide variety of vehicles. The Anechoic Chamber has been designed to carry out both HIRF/EMC test and High Sensitivity RF measurement: in particular HIRF/EMC tests in the frequency range 30MHz ÷ 18GHz with the capability of radiating a very high intensity electromagnetic field and High Sensitivity RF measurement, including antenna pattern measurements on antennas installed on aircraft in the frequency range 500MHz ÷ 18GHz. During the design phase a 1/12th scale model of the chamber had been fabricated to assess the desired electromagnetic performance. In this phase of design the model was tested at the scale frequencies for Filed Uniformity, Site Attenuation and Free Space VSWR results. This study was published at the AMTA 2004 meeting. In addition to the physical model, during the construction phase, various computer simulations were performed to further define the detailed internal absorber layout and to define test acceptance methods for procedures not covered by the standards. The computer model analysis was conducted to identify areas of scattering that could be treated with higher performance absorbers to improve the chambers quiet zone performance. The identified “Fresnel Zones." have been treated with high performance absorbers optimized to provide improved performance at microwave frequencies. The absorber optimization was reported at the AMTA 2006 meeting. This optimization has allowed validation of the chamber according to the requirements of CIRSP 16-1-4 2007-02 in the range of frequency 30 MHz - 18GHz. The size (shield to shield) of chamber is 30m wide, 30m long and 20m high, and the 18m wide by 8.5m high main door allows the SUT access. The shielded structure is a welded structure of 3mm-thick steel panels which guarantees shielding effectiveness of more than 100 dB in the frequency range 100 kHz to 20GHz. The chamber includes a 10 meter diameter turntable to rotate a 30 ton SUT with an angular accuracy of ± 0.02° and a pathway to allow SUT access. Both the pathway and the turntable are permanently covered by ferrite tiles. A hoist system permits lifting of the SUT (max 25 tons) up to 10 meters from the turntable centre enabling EMC testing on aircraft with the landing gear retracted.
Measurement Accuracy of Stereolithography (SLA) Scale Models
Hand-made scale models in antenna measurements have been used since the late 1940s. Today, aircraft models are fabricated using a stereolithography (SLA) process and the Computer Aid Design (CAD) for manufacturing the full size aircraft. This is the fabrication method used for the V-22 1/15th scale model. Once the SLA machine is programmed, these models are very inexpensive to produce. In this paper, antenna patterns measured on the V-22 scale model are compared with antenna patterns measured on the aircraft in-flight. Comparison of the patterns shows high correlation. Figure 1 V-22 Aircraft
Validation and Verification of CEM Field Prediction Techniques Compared to IR Images of EM Fields for Complex Systems
An infrared (IR) measurement technique, based on thermal principles, is presented to independently validate and verify (V&V) numerical codes used for computational electromagnetic (CEM) field predictions. This technique is applied to scattering and to complex systems such as antennas on aircraft. The IR technique produces a thermal image of the EM field over any two-dimensional area, usually a plane, proportional to the intensity of the incident EM field being measured. This IR image can be compared to the predicted image of the field calculated with a numerical CEM code over the same plane that was used in the measurements to confirm the field levels. Precise thermal measurements on metallic scale models of canonical aircraft shapes are made in a controlled anechoic chamber environment to make scattered field measurements around the model. The temperature distribution is converted to field intensity and plotted as a false color image of the field and compared to similar plots from a selected CEM code. The field can also be visualized with this IR method. This is the first step in a progressive approach to compare results of more sophisticated geometries using a suite of CEM codes to confirm the results of the IR measurements to develop confidence in the complementary measurement and simulation methods.
Demonstration of an Inverted Steward Platform Target Suspension System using Lightweight, High Tensile Strings
This paper presents the design, development and testing of an inverted Stewart platform for suspending and positioning targets during RF antenna and signature testing. Previous string target support systems use multiple string attachment point configurations that do not allow the target roll or pitch to be modified during the azimuthal data collection. This presentation will discuss an in-house development of a scale model target support system that allows for high accuracy simultaneous target roll and pitch positioning. The inverted Stewart platform also offers unique stability of the target by damping out the torsional pendulum motion typically encountered in conventional string support systems. In this paper we will also discuss the advantages and disadvantages of the string support concepts and provide design guidance for a building an inverted Stewart platform support system. If possible, a simple squat calibration standard will be measured to assess the quality and precision of this novel support system.
RCS Time Domain Near Field measurement and 2D ISAR
This paper presents a Radar Crossed Section (RCS) time-domain near-field measurement and its Inverse Synthetic Aperture Radar (ISAR) imaging. The target includes a pyramidal horn and a metallic aircraft scale model. A pulse generator excites the transmit antenna and a digital sampling unit collects the data at the receiving side. A time gating window is subsequently applied to reject the multiple reflections. An efficient 3-D algorithm for ISAR based on time-domain near-field data is presented. The test results for six cases demonstrate excellent ISAR images. In particular the geometry of 3-D reconstructed target can be displayed in perspective manner. The advantage of using time-domain near-field measurements is three-fold. First, it reduces measurement time in the order of one-tenth compared to frequency-domain measurements. Second, it mitigates the multiple reflection effects via time gating. Third, near-field measurements require relatively little real estate which reduces the cost tremendously since a compact range is not needed.
Techniques in Scaling the Performance of Dielectric Microwave Absorber for use in Scale Model Anechoic Chambers
The use of electromagnetic scale models for evaluating the expected performance of a large test facility prior to its construction has been found to be useful in providing insight on how various absorber layouts effect the ultimate performance of the full scale test chamber. This report details the expected and measured performance of a series of absorber sets used in a 1/12 scaled model of a very large anechoic chamber to be used for both EMC and microwave measurements. Electromagnetic scaling of dielectric absorbers involves not just the geometry of the absorbers but also the amount of conductive carbon loading required to achieve a given reflectivity at the scaled frequencies. The goal is to scale performance over a very broad frequency range. It was found that absolute physical scaling is not always possible. Expected and measured performance of the scaled absorbers is detailed over the scaled frequency range of 360 MHz to 12 GHz. Selected measured chamber performance is included for Free Space VSWR, site Attenuation, and Field Uniformity to demonstrate the effectiveness of the scaling.
Alenia HIRF - EW Model Study
ORBIT/FR is presently under contract to provide Alenia Aeronautics with the HIRF – EW test facility to perform radiated field immunity testing of aerospace vehicles with high electromagnetic field intensity: radiated emission measurements, which belong to EMC testing; electronic warfare and antenna pattern tests. This unique facility will combine specific EMC, EME, EW measurements as well as specific antenna measurements. An anechoic-shielded chamber therefore, represents the ideal solution to perform these tests, because it provides the electromagnetic shielding and protection against the internal and external electromagnetic environments. While in many cases as little as -10 dB of round trip reflection may be adequate for EMC testing applications, in the EW tests to be performed at frequencies higher than 500 MHz, is required a fairly lower level of reflectivity. The facility will include an anechoic-shielded chamber (ASC) where the System under Test (SUT) is installed and operated in its functional modes to perform susceptibility tests and emission tests. The ASC will be equipped with a turntable having the capability of arranging the System Under Test (SUT) in front of the radiating antennas at different aspect angles. The ASC will provide internal size of 30 x 30 x 20 (H) m. The pyramidal absorber material shall be permanently installed on ASC ceiling, vertical walls and doors. As far as the floor is concerned two configurations are possible: proposed facility. The model will be described and the effort to scale the performance of the full size absorbers. The development and fabrication of scale model antennas. The establishment of measurement techniques, which will allow the correlation of the scale model measurement to the computer model performance predictions and the potential performance of the completed full size chamber.
A Phase Hologram Based Compact RCS Range for Scale Models
A compact radar cross section (RCS) test range for scale model measurements is being developed. The test range is based on a phase hologram that converts the feed horn radiation to a plane wave needed for RCS determination. The measurements are performed at 310 GHz using continuous wave operation. A monostatic configuration is realized using a dielectric slab as a directional coupler. The main advantage of a scale model RCS range is that the dimensions of radar targets are scaled down in proportion to the wavelength. Therefore, RCS data of originally large objects can be measured indoors in a controlled environment. So far simple test objects such as metal spheres have been measured. The feasibility of the phase hologram RCS range has been verified. The basic operation and first measurement results of the monostatic measurement range are reported here.
A Hybrid Inflatable Dish Antenna System for Spacecraft Communications
An inflatable communication antenna is a subject of current space research because of its potential for enabling high-bit-rates. However, a significant problem associated with inflatable technology is the “all-or-nothing” scenario, where success of the mission depends on successful deployment of the antenna. For this reason, few satellite programs are willing to take the risk of using an inflatable unless it is mission enabling. The Hybrid Inflatable Antenna, a concept developed by the Johns Hopkins Applied Physics Laboratory and ILC Dover, addresses the risk by providing a backup capability within the inflatable dish. This system combines a fixed parabolic dish with an inflatable reflector annulus that greatly increases antenna area. For example a 1-meter diameter dish can be increased to 4-meter resulting in a 16X improvement in reflector surface. A prototype Hybrid Inflatable Antenna has been successfully fabricated and tested. This scale model demonstrates that a highly accurate reflector surface can be formed via inflation.
RCS Measurements in an Anechoic Chamber in V/UHF Band: Ray Tracing Model and Exact Simulation
CAMELIA is a large RCS measurements facility (45m.12m.13m in dimensions) that is operated at both SHF and V/UHF frequencies. In the V/UHF band, coupling between the target and the walls can be exhibited, due to non directive transmitting/receiving antenna, and low efficiency absorbers, that must be eliminated to derive the intrinsic response of the target To this aim, we have first developed a 1:10 small scale model of the chamber, that is operated in the SHF band. It enables the experimental simulation of RCS measurements in the V/UHF band, and confirmed the interpretation of the electromagnetic phenomena in the large scale facility ([l]). Then, two theoretical algorithms were developed, modeling these coupling phenomena. The first one is a simple ray tracing model, requiring as input data the measured reflection coefficient of the walls, the radiation pattern of the transmitting/ receiving antenna and the bistatic RCS of the target. The second one introduces an analytical model for the antenna and its images with respect to the walls, and calculates the near field scattered by the target. The measurement of several targets bas been modeled, and a good agreement bas been obtained. The advantages and drawbacks of each method are discussed.
Quasi-Optical Waveguide Modeling Method for Scattering Matrix Measurements in the Near Millimeter and Submillimeter Wave Regions
Earlier (AMTA'97, AMTA'98), we have proposed a new low-cost laboratory method named the quasi-optical waveguide modeling (QWM) method to study power and amplitude-phase scattering characteristics of objects, in particular the RCS of targets or their scale models, in the near millimeter (NMM) and submillimeter (SMM) wave regions. A specific feature of this technique in that an investigated object (or its scale model) is mounted inside a quasi-optical waveguide structure in the form of a hollow dielectric waveguide (HDW), in which the scattering characteristics of the waveguide dominant HE11 mode are determined. These characteristics are related to the wanted scattering characteristics of the test object in free space by definite relationships. At the same time the HDW serves several functions: it forms a quasiplane incident wave within the scattering area where test object is placed, performs the low-loss and low-distortion transmission of the scattered wave carrying information of the object being tested to the receiver, effectively filters the unwanted modes arising at the scattering on the test object, and insulates the measurement area from the ambient conditions containing parasitic sources. In this paper we consider the possibility of using the QWM method to study polarization backward scattering characteristics of physical objects, in particular the complex elements of the scattering matrix with relative phase (SMR). A quasi-optical polarimetric micro-compact range (PMCR) based on the circular HDW and quasi-optical devices has been developed and built. The measurement results of the SMR and backward scattering patterns of a reference object as a square metallic cylinder obtained in the PMCR for the different linear polarization basic sets at the 4-mm wave band are presented. The comparison between the experimental results for the reference object and the theoretical data calculated by the geometrical theory of diffraction have shown a good agreement, and demonstrated the possibilities of the QWM method, and its good perspectives for backward scattering polarization characteristics modeling in the NMM and SMM wave regions.
RCS Measurement in an Anechoic Chamber in the U/VHF Band: Comparison with Experimental 1:10 Scale Simulation
CAMELIA is a large RCS measurement facility (45m.12m. 13m in dimensions) whose compact range is optimized in the SHF band (1-18 GHz). Exploiting it at lower frequencies requires the modification of the absorbers and the use of huge broad band horns as RF sources (since the compact range is now not well adapted). To help understanding the radioelectric behavior of the large scale facility, we have developed a 1:10 small scale model as well as 1:10 scale horns, that are operated in the SHF band. It enables the experimental simulation of RCS measurements in the V/UHF band. Thus, all dimensions and frequencies are homothetic, only electromagnetic properties of materials are not. RCS measurements of several canonical targets have been performed in both facilities and compared. Due to non directive transmitting/receiving antenna, coupling between the targets and the wans has been exhibited. A simple ray tracing model, taking into account the measured reflection coefficient of the walls and the bistactic RCS of the target, shows good agreement with the measurements.
1.56 THz Spot Scanning Radar Range for Fully Polarimetric W-Band Scale Model Measurements
A radar transceiver operating at 1.56 THz has recently been developed to obtain coherent, fully polarimetric W-band (98 GHz) RCS images of 1:16 scale model targets. The associated optical system operates by a scanning a small focused beam of swept frequency radiation across a scale model to resolve individual scattering centers and obtain the scaled RCS values for the centers. Output from a tunable microwave source (10 - 17 GHz) is mixed with narrow band submillimeter-wave radiation in a Schottky diode mixer to produce the chirped transmit signal. Two high-frequency Schottky diode mixers are used for reception of the V-pol and H-pol receive states, with a fourth mixer providing a system phase reference. The full 2x2 polarization scattering matrix (PSM) for each resolved center is obtained following off-line data processing. Measurement examples of five simple calibration objects and a tank are presented.
Design of a 75-103 GHz RCS Measurment System for High Resolution Imaging
The purpose of millimeter wave RCS measurements is often to evaluate the performance of scale model aircraft. To representative ISAR it is important that also the resolution cell size is scaled in proportion to the frequency. A typical bandwidth used for full scale aircraft measurements at 10 GHz is 2 GHz. This means that for at a 1:10 scale model measured at 100 a bandwidth of 20 GHz should be used. By modifications of a HP83558A W-Band antenna measu rement equipment, a powerful RCS measurement equipment covering 75 - 103 GHz with high receiver have been achieved. The hardware modifications and the radar and turntable performance are presented. This paper also shows the W-Band requirements for the SAAB indoor RCS measu rement facility in Linkoping, Sweden, and how these requirements are fulfilled. RCS measurements have been performed on 1:50 and 1:10 model aircraft. These measurements are discussed and ISAR images with resolution cell sizes down to 10 mm x 10 mm are presented.
Evaluation of Scattering Level of TT&C Antennas with Geometrical Scale Modeling Technique
Omnidirectional antennas are typically used as Tracking, Telemetry and Command (TT&C) antennas for satellites. However, the omnidirectional patterns of TT&C antennas located on satellite structures are susceptible to substantial scattering and polarization mismatch loss, especially at the initial mission stage. Consequently, it is very important to properly evaluate the extent of these effects for each of the initial mission configurations. In this paper, measurement techniques to achieve proper evaluation of scattering level and polarization mismatch loss for TT&C antennas of NASA's Tracking and Data Relay Satellite (TDRS) are presented. The paper encompasses a test approach, a test procedure and test results. Application of these test techniques is essential to the TDRS TT&C antenna qualification program.
524 GHz Polarimetric Compact Range for Scale Model RCS Measurements, A
A fully-polarimetric compact range operating at 524 GHz has been developed for obtaining Ka-band RCS measurements on 1:16th scale model targets. The transceiver consists of a fast switching, stepped, C W , X-band synthesizer driving dual X 4 8 transmitmultiplier chains and dual X 4 8 local oscillator multiplier chains. Software range-gating is used to reject unwanted spurious responses in the compact range. A motorized target positioning system allows for fully automated sequencing of calibration and target measurements over a desired set of target aspect and depression angles. A flat disk and a dihedral at two seam orientations are used for both polarization and R C S calibration. Cross-polarization rejection ratios of better than 45 d B are routinely achieved. The compact range reflector consists of a 1.5m diameter aluminum reflector fed from the side to produce a 0. 5 m diameter quiet zone. Targets are measured in free-space or on a variety of ground planes designed to model most typical grou nd surfaces. A description of this 524 GHz compact range along with 30 ISA R measurement examples are presented in this paper.
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