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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.
Probe correction aspects for the spherical near-field antenna measurements are investigated. First, the spherical mode analyses of the radiated fields of several antennas are performed. It is shown that many common antennas are essentially so-called odd-order antennas. Second, the errors caused by the use of the first-order probe correction [1] for a rectangular waveguide probe, that is an odd-order antenna, are demonstrated. Third, a recently developed probe correction technique for odd-order probes is applied for the rectangular waveguide probe and shown to provide accurate results.
The input reflection coefficient of a probe-driven dielectric resonator antenna operating in the HEM11 mode is measured in the frequency range 8 to 13 GHz. The equivalent circuit of the antenna is postulated to be of Foster-type, with resistances added to account for the losses and for the radiation. The element values are data-fitted with the help of Marquardt optimization. The antenna is then covered with the conductive cap and the unloaded Q factor is determined. Based on the equivalent circuit values, the radiation efficiency is then computed from the measured data. The electromagnetic simulations of the structure are in agreement with the measured input reflection coefficient and the radiation Q factor.
A novel antenna miniaturization approach utilizing artificial transmission-line (ATL) structures whose impedance and phase velocity are mainly controlled by distributed reactive elements is explored. First, the slow- wave phenomena and impedance control in ATL will be demonstrated. Then, miniaturization of a resonating structure will be presented. Finally the application of ATL on antenna structure will be demonstrated. The proposed miniaturization approach is inherently suitable for broadband miniature antenna designs, such as spiral antennas, and provides additional design degree of freedom.
Exploitation of MIMO (Multiple-Input Multiple-Output) system in laptop type device, which size is adequate to integrate several antennas on it, would be the solution to increase attainable capacity e.g. in wireless local area networks (WLAN). Thus, a microstrip prototype antenna with two polarizations is developed for MIMO and also for diversity system purposes. Firstly, two antennas of this type were placed against to each other, which guarantees a good coverage over a whole propagation area. Secondly, two antennas of this type were placed next to each other. The simulated radiation patterns of the prototype antenna are used in the capacity studies of MIMO system using real indoor propagation data. The effect of shadowing by human body as well as different tilting angles of “laptop cover/screen” are considered. Further, different locations of the “device” in azimuth plane were considered identifying the fluctuation of the results due to the environmental and antenna properties. The developed antenna systems perform well as compared to the ideal dipole system.
In this paper the influence of mutual coupling on the capacity of a multiple-input multiple-output (MIMO) antenna system is demonstrated. No direct relation between the envelope correlation and the actual location and orientation of the antennas is found. Even though being essential for high MIMO capacity, configurations with the lowest envelope correlations are not necessarily the most suitable for a MIMO system. A certain bandwidth is required as well. Three planar inverted F-antennas (PIFA) located on the same 40 mm 100 mm ground plane. The antennas that haves a resonant frequency of 1.8 GHz yields envelope correlations ?e below 0.4.
Adaptive type smart antennas have not been implemented yet on the deployed UMTS systems, although UTRA-UMTS preview their operation and they also could improve capacity especially in a multiservice environment. This paper describes a set of novel measurement techniques that must be performed to evaluate the correct operation of a smart antenna system. The paper also describes the measurements carried out on a UMTS smart antenna prototype.
This paper presents the complete Antennas radiated performance measurement process within the frame of the AMC12 satellite program for SES-AMERICOM customer, from antenna sub-system level to spacecraft system level. Three long focal offset antennas are implemented on AMC12 spacecraft (see Figure 1-1). Each antenna was measured at both sub-system and system levels, within two different test ranges: • a Near-Field Antenna Test Range (NFATR), • a Compact Antenna Test Range (CATR), at sub-system and system levels respectively. Comparisons for co-polarization gain, XPD and co-polarization isolation between predictions and sub-system measurements on one part, between sub-system and system measurements on the second part will be presented. An effective correlation will be shown at each level. Two antennas are located on the West panel of the spacecraft. This configuration required to measure one antenna in presence of the adjacent reflector with the aim to validate the minimal coupling effect according to the conclusion of the antenna design. With this measurement method, all the physical effects are taken into account and the RF performances are directly representative of in- orbit spacecraft deployed configuration. Comparisons between sub-system level measurements and predictions will be presented.
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
Upcoming space exploration missions will have microwave instruments operating well beyond 100 GHz. Test techniques and instrumentation have to keep up with these developments. Although most of these instruments operate in a few narrow bands, a test engineer, faced with the combined requirements of a range of instruments will prefer full octave band coverage. As a goal, he would like to have the same functionality as at lower frequencies, i.e. sweep or step frequency capability, high dynamic range, coherent, computer controllable and compatible with existing receiver equipment (HP8530). A concept based on a Backward Wave Oscillator, locked by PLL to a synthesizer was chosen for the 110-170 GHz band. For the next leap, the 170-260 GHz band, a solid- state concept based on multipliers has been chosen. The experience with both systems and the pro’s and cons will be clarified
The purpose of this paper is to present antenna measurement techniques of antenna modules for Satellite Digital Audio Radio System (SDARS). SDARS employs dual-transmitter broadcasting formats which include simultaneous transmission of signals from both satellites and terrestrial transmitters. An SDARS antenna efficiently receives both satellite and terrestrial signals: it has relatively good circularly polarized gain at high elevation angles and acceptable linearly-polarized gain at the horizon. Popular SDARS antennas are small ground- depended patch antennas etched on ceramics and ground- independent mast antennas such as quadrifilars. Ceramic patch antennas have a relatively narrow bandwidth of operation. Thus, tuning such antennas to the right frequency is critical. The measurement techniques presented help engineers and technicians evaluate SDARS antennas and determine whether they are correctly designed. We shall describe hardware platforms for evaluating impedance, radiation characteristics, and real-world performance. Parameters such as VSWR, antenna gain, axial ratio, as well as receiver satellite C/N and terrestrial BER will be discussed.
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.
A UWB dual linear polarized feed design for taper chambers was implemented and tested. The low frequency limit of a typical taper chamber was investigated. An improved design that includes a quad- ridge feeding structure allows for operating at lower frequencies was developed.
A calibration uncertainty analysis was conducted for the Air Force Research Laboratory’s (AFRL) Advanced Compact Range (ACR) in 2000. This analysis was a key component of the Radar Cross Section (RCS) ISO-25 (ANSI-Z-540) Range Certification Demonstration Project. In this analysis many of the uncertainty components were argued to be small or negligible. These arguments were accepted as being reasonable based on engineering experience. Since 2000 the ACR radar has been replaced with an Aeroflex Lintek Elan radar system. A new measurement uncertainty analysis was conducted for the ACR using the Elan radar and for a general (non-calibration) target. We present results comparing the previous results to the current analysis results.
We have been developing an uncertainty analysis of RCS calibrations and measurements in the 2 – 18 GHz range at the Etcheron Valley RCS outdoor ground-bounce facility. In this study we report on the results of the uncertainty analysis primarily at 11.3 GHz, but results at some other frequencies are also discussed. We plan to address all components of uncertainty, and present here in some detail the procedures used to determine the uncertainties due to nonplanar illumination, drift, noise-background and nonlinearity. We use a measurement-based approach to obtain upper-bound estimates for the component uncertainties, which are combined using root-sumsquares (RSS) to obtain the overall uncertainty. The uncertainties at any frequency can be determined using these measurement procedures.
This paper describes the RCS measurement test facilities, CHEOPS, STRADI and SOLANGE which are operated in the Technical Center for Information Warfare (CELAR) in France, with a particular focus on SOLANGE. CHEOPS is an anechoïc chamber convenient for the measurement of small missiles as well as antennas measurement. STRADI is an outdoor facility, which is convenient for measurement of land vehicles, helicopters and large antennas. SOLANGE is an indoor RCS measurement facility used to measure long missiles and aircraft. Originally built in 1985, SOLANGE has been continuously upgraded to fulfill all customers requirements in the field of RCS measurement. Thanks to the in house radar instrumentation and data processing software, SOLANGE can reach a very good performance on small or big RCS targets from 200 MHz to 18 GHz. The UHF/VHF capacity has been recently enhanced thanks to the upgrade of the positioning system and the cooperation between CELAR and CEA.
The Institute for Integrated Circuits of the Fraunhofer Gesellschaft recently acquired a combined spherical nearfield / far-field (SNF/FF) antenna measurement range with a shielded anechoic chamber for verifying passive and active antenna design concepts. A single 9-pin digital control connector allows the range to remain sealed from external RF, while maintaining full motion and data acquisition control. This set-up uses two different illuminators, separated 180° as seen from the AUT. This combined SNF/FF configuration gives the opportunity to perform intra-range measurement comparisons (SNF vs. FF) with not only the distance between AUT and illuminator being varied, but also with the measurement zone being reversed. In this manner, a comparison between SNF and FF measurements also compares the quality of two sides of the measurement chamber.
The optimum source antenna in an anechoic chamber provides adequate uniform amplitude illumination of the antenna under test, but it minimizes the level of energy reflected from the walls of the chamber. The selection is a function of the range length (R), test aperture (D), source antenna gain (G), and the chamber’s aspect ratio (AR) (range length/width). The latter sets the angle of incidence seen by the absorber on the chamber walls. Adequate phase uniformity is assumed.
An indoor far-field range consists of the appropriate instrumentation and an anechoic chamber. In most of cases, the construction of the anechoic chamber is a laboring task and costs at a great expense. To save the money and labor, efforts for the range design are needed before the chamber been constructed. In this paper, the finite-difference time-domain (FDTD) method is employed to establish the design criteria for the far-field ranges. The commercial package named “FIDELITYTM”, based on FDTD algorithm released by Zeland Software, Inc., is used for the numerical calculations. To emulate the test procedure of the free-space VSWR technique, the electric fields of the points on the scanning axis are recorded during the simulation. And then, by plotting the amplitude ripples calculated from the recorded data, the range performance can be evaluated. The criteria of chamber layout, absorber arrangement, and source antenna selection and placement will be presented and discussed.