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Abstract — A technique for near-field measurements over a digital PCB is presented. Phase measurement with a vectorial network analyzer (VNA) is possible with antennas but it is in principle not possible when the DUT has its own free-running oscillator. In order to get around this problem, a two-probe approach is proposed. While one of the probes is mobile the other one is fixed and collect the reference signal. An analogue circuit must be used to obtain the specifications in power and phase of the reference signal of the VNA. The collected near field above the test circuit allows us to clearly identify the hot spots and the constant phase areas. These results could be used to find problematic spots on a board or to extrapolate the far-field. This is of practical interest in EMC testing of digital devices.
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.
Spherical near-field measurements require an increased level of sophistication and care to achieve accurate results. This paper will demonstrate an automated set of self-comparison tests, which can be used for establishing and optimizing a spherical system's performance. An over-determined set of measurements can help to qualify positioner alignment, range reflection levels, truncation effects, and additional parameters of interest. These results will help in optimizing the test configuration to achieve accurate near-field measurement results.
We propose a simple method for estimating uncertainties due to multiple reflections between the test antenna and probe in near- field spherical-scanning measurements. To estimate uncertainties in far-field parameters, we measure the test antenna by scanning the probe over two spheres whose radii differ by a quarter wavelength (?/4). We compare this estimate to that obtained with a reduced data set (containing all values of ? but only a few values of f). In our example, we find that measuring only two f cuts suffices to obtain RMS uncertainties within 1 dB of those obtained using full-sphere data.
The gain patterns of VHF/UHF antennas on ground structures and vehicles are influenced by the characteristics of the ground. The measurement of the performance of such antennas is more accurate with a test chamber that incorporates a realistic ground surface. This paper will discuss the near field to far field transformation process for the case where there are reflections from a ground surface outside the probing hemisphere. We will show that the ground reflection term in the transformation must be based on the characterization of the ground outside the probe region.
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.
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
A general approach is introduced for estimating uncertainties in far-field parameters obtained from spherical near-field measurements. Although the analysis is incomplete at present, we expect that as the measurement radius increases, our results will transform smoothly into the far-field case, where uncertainties depend on the on-axis gain and polarization of the probe and on the measurements in the far-field direction of interest.
A prototype design of the dielectric rod antenna is discussed. This novel design is suitable for nearfield probing application in that it provides broad bandwidth, dual-polarization and low RCS. The design details are provided in this document along with measurement data associated with important antenna characteristics such as VSWR and far-field radiation pattern
This paper will compare and evaluate the results of two imaging techniques on near-field ISAR data. The two techniques are polar reformat and back propagation. The back propagation technique is a wave number technique that accounts for wave front curvature. The techniques are evaluated on simple targets at various image distances and aperture extents. Finally a suggestion is made to when the more computationally complex back propagation technique should be used.
As satellite communication systems grow increasingly complex, so has the need for spacebased phased array antennas. After these antennas have been designed and assembled, they need to be tested. This paper describes the new antenna measurement facility that NGST (Northrop Grumman Space Technology) has installed to that end. This includes descriptions of near-field and compact ranges that are integral parts of the Phased Array Assembly, Integration and Test Area.
A measurement technique for Effective Isotropic Radiated Power (EIRP) using planar near-field scanning has been demonstrated earlier. In this paper I show how we at MI Technologies have implemented using the spherical near-field method the measurement of EIRP and a vector phasor quantity analogous to Effective Area that we call Antenna Receive Response. This technique is applicable to all antennas, including active antennas.
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.
In this paper, we describe the process used to align a large spherical near-field test system. The probe positioner consists of a cantilevered arc design with a probe path radius of five meters and a scan angle of 180°. The AUT positioner consists of an MI Technologies Model 51230 azimuth positioner with a high-precision encoder. The system is aligned using an SMX Tracker 4000 tracking laser interferometer. Alignment into a spherical system is achieved by initially defining two cylindrical systems; a primary probe positioner based system and a secondary, AUT positioner based system. Sources of mechanical error in each of these systems are identified and techniques used to control these error sources are described.
This paper describes a family of new measurement systems, termed “test cells”, designed to satisfy the certification requirements of the Cellular Telephone & Internet Association’s (CTIA) “Method of Measurement for Radiated RF Power and Receiver Performance” test plan for wireless subscriber stations. These test cells employ simultaneous dual-axis mechanical scanning and operate in both far-field and near-field modes over the 750MHz to 6 GHz frequency range. Operation can be extended to higher frequencies through the use of suitable sampling antennas. Test cell facility configuration is detailed. Scanner layout and RF sampling antenna designs are discussed. Anechoic chamber characterization data is presented along with typical measured pattern and efficiency data for both broadbeam and directive AUT’s. Measurement test times for various test scenarios are discussed.
Specific Absorption Rate (SAR) constitutes a key issue for mobile phones. Indeed, SAR which represents the power per unit mass delivered in biological tissues must comply with existing standards. The averaged SAR required by standards can be deduced from the measurement of E-field distribution in a volume of biological phantoms, filled with a tissue equivalent liquid. Such a standard procedure is time consuming and rather incompatible with the rapidity required for developing new mobile phone models. This paper describes a new rapid SAR measurement approach based on near-field techniques. The use of a plane wave decomposition of the measured field in a plane allows the reconstruction of the electric field in the phantom from which the averaged SAR can be deduced. The combination of this approach a with probe array technology should bring real-time SAR measurements possibilities.