Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
Phased arrays antennas are designed to control their radiation characteristics by accurately setting the phase and amplitude distribution of the elements. Inaccurate control of the phase and amplitude can significantly alter the radiation pattern of an array. In fact, the operating principle of scanning arrays of elements for applications such as target tracking or mobile satellite communications, where the requirements for low side lobes and high gain are of very high importance, is primarily based on precise control of the phase and amplitude of the elements. For these reasons, the complexity of antenna measurement system design for phased array antennas measurements involves high accuracy and precise time synchronization between all the components of the system. This paper presents a comprehensive solution for accurate and reliable measurement of very large phased array antennas at high frequencies. The presented solution addresses the following issues: • Accurate positioning of the RF sensor / probe. • High-speed multi – frequency data collection. • High-speed multi - port data collection. • Programmable and real-time TTL position event triggers. • Pulse measurement. • Multi beam measurement. • Synchronization with the radar computer.
This paper discusses the use of a laser-tracking device to provide position information in x, y, and z that can be used in position correction algorithms to correct for any displacement error in the actual measurement. Planar near-field measurements require taking amplitude and phase information at accurate and equal point spacing on a plane in front of the antenna under test. The required position accuracy on this plane has been determined to be approximately ./50. As frequencies increase higher, the accuracy in point spacing position on the planar grid becomes more difficult to achieve.
Compact antenna test ranges such as the ESA/ESTEC CPTR are large facilities for the characterization of electrically and physically large antennas as well as end to end radiated payload testing. To achieve high accuracy measurements, time gating is used to filter out as many room effects as possible. The most common implementation of time gating is to perform a frequency sweep, Fourier transformation to the time domain followed by windowing, gating and back transformation to the frequency domain. All of this is at a time penalty. An alternative is to have a synchronised switching system to switch on and off the transmit power as well as switching on and off the receiver. Such a solution has been devised in a cooperative effort between EADS Astrium and the Munich University of Applied Sciences. The paper will present the capabilities of the Astrium HG2000 Hard Gate system (1) in the ESA/ESTEC CPTR, its implementation in the facility as well as presenting direct comparison of results obtained by the hard gate system with the conventional soft gate on both low gain and high gain antennas
Since the early days of spherical near-field far-field transformations a recommendation for the necessary number of polar modes has been given by , being the wavenumber and or the radius of the minimum sphere. The almost explosive development in computer speed and storage capacity witnessed during the last two decades has made trans-formations of fields from antennas exceeding thou-sands of wavelengths feasible, and a closer investiga-tion of the above expression seems to be appropriate. An improved expression for the number of modes, N, related to the antenna size and the required accuracy will be developed. The impact of truncation of the modal expansion at a given level will be illustrated. This is especially important for measurements where noise is present, or where there is undesirable scatter-ing from objects.
This paper describes the development, testing and evaluation of a new, automated system for calibration and AUT alignment of a planar near-field scanner that allows the calibration system to remain in place during AUT measurement and which can be used to support AUT alignment to the scan plane. During scanner calibration, probe aperture position measurements are made using a tracking laser interferometer, a fixture that positions the interferometer retro reflector at a precise location relative to the probe aperture and a probe roll axis that maintains the proper orientation between the retro reflector and the interferometer as the probe position is moved. Aperture scan path information is used to construct a best-fit scan plane and to define a Cartesian, scanner-based coordinate system. Scan path data is then used to build a probe position error map for each of the three Cartesian coordinates as a function of the nominal position in the scan plane. These error maps can be used to implement software-based corrections (K-corrections) or they may be used for active Z-axis correction during measurements. By using a set of tooling points on the antenna mount, an AUT coordinate system is measured with the interferometer. The system then directs an operator through a set of AUT adjustments that align the AUT with the planar near-field scanner to a desired accuracy. This paper describes the implementation and testing of the system on an actual planar scanner and AUT test environment, showing the improvement in effective scanner planarity.
ABSTRACT This paper describes a novel optical boresighting and alignment system used to mechanically align antennas on a compact antenna range at the North Island Naval Air Depot in San Diego, CA. The antenna range has a 5-axis (roll/upper slide/azimuth/elevation/lower slide) positioner used to measure various airborne antennas for production testing. The video alignment system implemented on this range uses two video cameras outfitted with telephoto lenses, one on the roll stage and the other on an antenna-mounting fixture. The system has been demonstrated to yield an accuracy of ±0.005 degrees. Prior to the start of testing the positioner is commanded to a “0” position and the cameras focus on a fixed optical target to provide the operator with a quick visual confirmation that the positioner is accurately aligned prior to testing. The video alignment system described has numerous advantages over other mechanical alignment techniques, is low cost, easy to use, and can be adapted to a variety of testing configurations.
This paper describes the methodologies and processes used for the development, installation, alignment and qualification of a Compact Range Rolled Edge Reflector purchased by the MIT Lincoln Laboratory and installed at their test facility located at Hanscom Air Force Base. The Ohio State University, under contract to MIT Lincoln Laboratory, performed the electromagnetic design and analysis to determine the desired surface shape and required mechanical accuracy of various zones of that surface. The requirement for operation over a very broad frequency range (400 MHz to 100 GHz) resulted in a surface specification that was both physically large (24 ft × 24 ft) and included extremely tight tolerance requirements in the center section. The mechanical design process will be described, including the generation of a solid “Master Surface” created from the “cloud” of data points supplied by The Ohio State University, verification of the “Master Surface” with The Ohio State University, segmentation of the reflector body into multiple panels, design, fabrication and factory qualification of the structural stands, panel adjustment mechanisms, and panels. Results of thermal cycling of the reflector panels during the fabrication process will be presented. The processes used for installation of the reflector and the alignment of each panel to the “Master Surface” will be presented and discussed. Final verification of the surface accuracy using a tracking laser interferometer will be described. Color contour plots of the reflector surface will be provided, illustrating the final surface shape and verifying compliance to the surface accuracy requirement
More and more wireless services such as satellite radio (SDAR), navigation systems, OnStar, and mobile telephones are installed in GM vehicles. This has created a need to make quick and accurate vehicle antenna measurements. For the frequency range of 500 MHz to 6 GHz, one solution is to use a spherical near-field system. The Satimo rapid probe array technology was selected to develop a vehicle antenna test system (ATS) to reduce test time and maintain data accuracy. The ATS was designed to operate inside of an existing GM electromagnetic compatibility (EMC) anechoic chamber equipped with a nine-meter turntable. The ATS was completed and received XM certification in the first quarter of 2004. The ATS performs multi-frequency dual-polarized complex measurements for every one-degree in azimuth and elevation, over a full hemisphere, in approximately five minutes. The autonomous transport and deployment system, allows the ATS hardware to be removed and the chamber returned to its EMC configuration. This paper presents the ATS design and a summary of the verification test results. A detailed uncertainty budget, as defined by NIST, is also presented.
In this paper, we describe a new method for improving the true-position accuracy of a very large, spherical near- field measurement system. The mechanical positioning subsystem consists of 10-meter diameter, 180 circular- arc scanner and an MI Technologies MI-51230 azimuth rotator and position controller. The principle components of the error correction method are the error measurement system, the position correction algorithm, and a pair of very high precision, mechanical error correction stages. Using a tracking laser interferometer, error maps are constructed for radial, planar and elevation errors. A position correction algorithm utilizes these discrete-point error maps to generate error correction terms over the continuous range of the elevation axis. The small position correction motions required in the radial and planar directions are performed using the mechanical correction stages. Corrections to the position of the elevation axis are made using the primary elevation axis drive. Results are presented that show the geometry of the spherical scanning system before and after error correction. It is observed that the accuracy of the radial, planar and elevation axes can be significantly improved using the error correction system.
ELTA is now in the process of designing and building a new spaceborn SAR “TECSAR” – Israel Synthetic Aperture Radar (SAR) X-Band lightweight satellite. TECSAR contains an ultra-light weight high accuracy Paraboloid deployable reflector antenna. TECSAR’s electronic beam steering capability is achieved by using a feed array in the focal plane. For future testing at ELTA, Israel, an horizontal Planar near-field antenna test range (7m x 8m scan) has recently been completed by ORBIT/FR to allow testing of large fully integrated space antennas as stand alone as well as integrated with a satellite The paper will describe: o Short TECSAR SAR antenna description o The special requirements of the measurement system o System design and measured performance
Satimo’s STARGATE probe array systems are now well established as an efficient tool for testing radiated performances of wireless devices and antennas. Since 1998, about forty STARGATE measurement systems have been successfully installed worldwide. Recently, a range of new applications have also demonstrated the suitability of probe arrays for large radiating structures and directive antennas. These new generation of measurement set-ups present innovative aspects regarding their rapidity, dynamic range, and accuracy. This paper will describe several novel antenna testing concepts based on probe arrays that cover automotive, aerospace, and military applications and a wide range of frequencies. The basic difference between traditional approaches using single probe and the STARGATE approach using an array of probes will be explained along with probe array calibration procedures. An error analysis budget using the conventional NIST error terms will be presented including the specific terms related to the use of probe arrays. Also a discussion will be made on some of the key technical challenges to making large probe arrays including such issues as dynamic range, mechanical tolerances, and data truncation effects.
Large satellites antennas are best measured in specially designed compact range systems designed for aerospace applications, located in a clean room environment. This testing requires very large, high accuracy positioners to accommodate full size satellites. Typical requirements include positioning accuracy of 0.003 degrees for a payload of 5 tons. ORBIT/FR has recently delivered to Astrium a unique payload positioner system specifically built for such high accuracy applications. This positioner provides the ability to accurately locate satellite payloads in the Astrium compact range system chamber to within the tolerances necessary to perform all radiated payload tests for specification compliance. In order to realize the required accuracy performance, an extremely stable positioner construction is required, such that near-perfect orthogonality between the rotary axes is maintained, and minimum structural bending is exhibited. This level of construction quality is realized by a unique elevation axis bearing configuration, in conjunction with an adjustable counter-weight system. In addition, very high accuracy absolute optical encoders are used; these exhibit higher accuracies than the traditional Inductosyn type of encoder. All axes are equipped with brakes on the primary axis to eliminate backlash. Alignment requirements further accentuate the need to be able to position to within a few thousandths of a degree. This in turn places difficult requirements on low speed operation and on the control system. This paper details the design and performance of such a positioning system as measured for two compact range installations utilized for satellite antenna testing applications.
Probe position errors, specifically the uncertainty in the theta and phi position of the probe on the measurement sphere, are one of the sources of error in the calculated far-field and hologram patterns derived from spherical near-field measurements. Until recently, we have relied on analytical results for planar position errors to provide a guideline for specifying the required accuracy of a spherical measurement system. This guideline is that the angular error should not result in translation along the arc of the minimum sphere of more than ?/100. As a result of recent simulation and analysis, expressions have been derived that relate more specifically to spherical near-field measurements. Using the dimensions of the Antenna Under Test (AUT), its directivity, the radius of the sphere (the minimum sphere) enclosing all radiating surfaces and the frequency we can estimate the errors that will result from a given position error. These results can be used to specify and design a measurement system for a desired level of accuracy and to estimate the measurement uncertainty in a measurement system.
For a planar near-field range, it is sometimes convenient to use a linearly polarized probe to measure a circularly polarized antenna. The quality of the circular polarization of the test-antenna is determined by the measured axial ratio. This requires the amplitude and phase from two near-field scans, one scan with the probe polarization oriented horizontally and another vertically. A lateral probe position error between the horizontal and vertical orientations can occur if the probe is not aligned properly with the probe polarization rotator. This particular probe position error affects the accuracy of the axial ratio in the main beam if the beam of the test antenna is not perpendicular to the scan plane. This paper presents analysis and measurement examples that demonstrate the relationship between the errors in the axial ratio and the lateral probe position. It is shown that the axial ratio, within the main beam, is not sensitive to the lateral probe position error when the beam is normal to the scan plane. However, the error in the axial ratio in the main beam can be quite significant with a small lateral probe position error if the antenna beam is tilted at an angle with respect to the scan plane. A simple phase correction algorithm is presented that is useful for measured data from an electrically large aperture.
Probe calibration is a prerequisite for performing high accuracy near-field antenna measurements. One convenient technique that has been used with confidence for years consists of using two auxiliary antennas in conjunction with the probe-to-be-calibrated. Inherent to this technique is a calibration of all three antennas. So far the technique has mostly been applied to measure polarization and gain characteristics. It is demonstrated how the technique can be extended to also measure an antenna’s phase-versus-frequency characteristic.
Highly accurate antenna and payload measurements in antenna test facilities require highly accurate alignment and boresight determination. The Angle of Arrival (AoA) of the plane wave field in the quiet zone of the CCR Compensated Compact Range CCR 75/60 of EADS Astrium GmbH, installed at Alcatel Space in Cannes . France, has been measured using three different methods (optical geometrical determination using theodolites, Radar Cross Section (RCS) maximization, planar scanner phase plane alignment). The proposed paper describes the three methods and the performed measurement campaign and provides the correlation between the resulting angles via a comparison of the results. The achieved absolute worst case values of lower than 0.005° demonstrates the high level of accuracy reached during the campaigns.
This paper describes and discusses relevant performance issues concerning the quiet zone illumination of a baseline interferometer antenna using a compact range system. Typical baseline interferometer antennas are utilized for precision direction finding applications, and are designed on the principle of detecting the incoming phase wave front as a means to determine the direction of arrival of the detected signal. Quiet zone illumination of the antenna using a compact range deviates from the ideal illumination by introducing some levels of amplitude and phase taper and ripple. Unwanted relative differences in the illumination of the individual elements of the interferometer antenna will introduce errors in the subsequent analysis of the direction finding accuracy and precision of the array. Sources of these errors are examined in this paper, and relevant compact range performance trade-offs are discussed to optimize the range. Considerations are given to both utility of the range, as many interferometer antennas are broadband EW type arrays, and thus require single feed, single test broadband measurements, as well as to the accuracy in characterizing the performance of the interferometer over its full operating bandwidth. In addition, this paper discusses the analysis of high precision compact range field probe data, and the subsequent application of relevant statistical parameters to characterize the data. The analysis techniques utilized highlight the important performance features required of the compact range to effectively test baseline interferometers. The implementation of an automated utility is described that applies the relevant corrections, and applies the statistical algorithms, to the data to effectively reduce the data and summarize it in a fashion that provides immediate utility to the field probe test operator.
MTI Technology and Engineering Ltd. in Israel has installed an antenna test facility for the development and production testing of communication link antennas. Link antennas are typically high gain, medium size (< 2 ft) and medium to high frequency (10 to 50 GHz), with strict requirements on sidelobes, back-radiation and cross-polarization. Production testing is typically done on the main cuts. The facility is also used for PTMP and WLL antennas down to 2 GHz. This is an ideal requirement for a small size compact range. The ORBIT/FR single reflector compact range with a cylindrical quiet zone of a size 4 x 4 ft (diameter x length) was selected. The performance is compliant to international regulations (e.g. FCC, ETSI, DTI-MPT), and has a cross polarization as low as –40 dB for 0.4-m antennas. The total chamber size is 31 x 18 x 15 ft (L x W x H). The positioner system is roll over model tower over azimuth over lower slide. The instrumentation is Agilent 8530 based. The system was installed and qualified in late 2002. Qualification was performed from 2 to 50 GHz for quiet zone field probing and antenna sidelobe level accuracy testing. A system description, as well as an excerpt of the qualification data are presented in the paper.
Preliminary investigations for cohering multiple apertures into a single distributed aperture were performed at the Georgia Tech Research Institute. Data were collected on complex targets in near realtime with two individual HP8510 Network Analyzer systems controlled by a single data acquisition computer as an interferometeric measurement. The data were analyzed and presented for high-accuracy angular resolution by examining the amplitude and phase difference between the two network analyzers. In addition, further upcoming tests on the Georgia Tech Research Institute far-field range will be outlined, showing how both measured angular resolution improvement and power-aperture gain product will be collected over a wideband frequency range.
The Air Force Research Laboratory (AFRL) Materials Measurement Laboratory (MML) is a state of the art facility for the characterization of the electromagnetic properties of materials at radio frequencies. The two-fold mission of the MML is to provide material characterization services to AFRL and to conduct R&D to develop or improve RF material characterization technology. The goal of the MML is to perform—or develop the ability to perform—material property measurements to the highest degree of accuracy possible with state of the art test equipment. Characterization measurements range from determination of RF reflection or transmission loss to the extraction of the dielectric permittivity and magnetic permeability of material samples. The MML has the ability to characterize material samples from below 100 MHz to above 18 GHz over material test sample temperatures ranging from – 150oC to greater than 1000oC. While maintaining capabilities using ‘standard’ material measurement techniques (circular coax and rectangular waveguide), the MML’s most highly utilized system is based on the GTRI focused arch apparatus. The MML also employs resonant cavity fixtures, open-ended coax probes and impedance meters to provide a capability to evaluate material samples of a wide variety of shapes and sizes.