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A variety of measurement applications in conjunction with the spherical near-field antenna test range at National Taiwan University of Science and Technology (Taiwan Tech) using an NSI (Nearfield Systems Inc.) made 700S-90 spherical near-field scanner built in a shielded anechoic test chamber environment has been implemented beyond the typical application scope for spherical near-field antenna test ranges. Thanks to the low RF perturbation nature of NSI-700S-90 spherical scanner hardware architecture in mobile wireless communication frequency ranges, not only for being a proven solution used in certified CTIA OTA test range for lowdirectional wireless mobile devices OTA and antenna performance evaluation, the system while incorporated with the special chamber configuration at Taiwan Tech is enhanced to be also capable of performing measurement scenarios associated with evaluating radio frequency identification (RFID) 3D readable range performance. This paper will present the abovementioned test range at Taiwan Tech for performing RFID static testing scenarios. Some measurement parameters in realistic DUT packaged modes will be demonstrated and analyzed with 3D graphical outputs of tag readable range. Various tests using commercial RFID tags for system validation purpose through measuring the tag readable range characteristics of the associated scenarios will be presented along with discussions and results on the method for testing tags with either the forward or reverse links dominated being included as additional supports of system applicability.
Stray signals/scattering suppression techniques will be deployed to enhance measurements quality of a combined compact antenna test range (CATR) and spherical near-field (SNF) measurement facility. Spherical mode filtering and softgating techniques will be the focus of this paper. Using soft-gating the mutual effects between the CATR and SNF facilities will be shown and mitigated. The use of SNF decomposition to enhance the far-field measurements will be also shown. This contributes to a reduction of the costs arising from the need of absorbers to shield both facilities and cover the antenna's support structure.
This paper presents V-band radiation pattern characterization of both low- and high-directivity antennas. A fourarm micro-machined spiral antenna with monolithically integrated mode-forming network designed for dual circularlypolarized radiation represents the low-directivity antenna, while a standard gain horn is used for the highly directive antenna. All measurements were performed using an in-house NSI-700S- 30 system capable of spherical near-field measurements from 1-50 GHz and direct far-field measurements from 50-110 GHz. Complete comparisons of simulated, near- and far-field patterns show the feasibility of near-field measurements in V-band. Based on pattern comparison and measurement statistics conclusions are drawn about V-band near-field measurements.
The 3D reconstruction algorithm is applied to a slotted waveguide array measured at the DTU-ESA Spherical Near-Field Antenna Test Facility. One slot of the array is covered by conductive tape and an error is present in the array excitation. Results show the accuracy obtainable by the 3D reconstruction algorithm. Considerations on the measurement sampling, the obtainable spatial resolution, and the possibility of taking full advantage of the reconstruction geometry are provided.
Ideally, a spherical-scanning probe should be uniformly sensitive to the spherical-wave modes that are superimposed to represent the transmitted .elds of a test antenna. We consider several actual and simulated probes, calculate their sensitivities, and discuss their best use in spherical-scanning measurements. We recommend evaluating probe sensitivity prior to measuring a test antenna.
ABSTRACT When the mechanical requirements are established for a spherical near-field scanner, it is desirable to estimate what effects the expected mechanical errors will have on the determination of the far field of potential antennas that will be measured on the proposed range. The National Institute of Standards and Technology (NIST) has investigated the effects of mechanical errors for a proposed outdoor spherical near-field range to be located at Ft. Huachuca, AZ. This investigation was performed by use of theoretical far-field patterns and introducing position errors into simulated spherical near-field measurements using software developed at NIST. Periodic and random radial and angular position errors were investigated. Far-field patterns were then calculated with and without probe-position correction to determine the effects of mechanical position errors. Periodic errors were found to have a larger effect than random errors. This paper reports the results of these investigations.
ABSTRACT Northrop Grumman Aerospace Systems (NGAS), working with Nearfield Systems Inc. (NSI) and others, has installed a state-of-the-art near-field antenna measurement system to test various payload antenna systems. This horizontal planar near-field system was designed to measure antennas with up to 30’ diameter apertures. In addition, a second bridge was included in the design so that the range can operate either as one very large scanner or as two autonomous ranges and double the testing throughput of the range. This near-field system features a large scan plane of nearly 40 ft. x 47 ft. with two smaller scan planes of 17’ x 47’ each. This horizontal near-field measurement system has the capability to operate from 500 MHz to 75 GHz using NSI’s high speed Panther receiver and high speed microwave synthesizers. The system is capable of performing conventional raster scans, as well as directed plane-polar scans tilted to the plane of a specific Antenna Under Test (AUT). The range was completed in December 2011. This paper will describe this near-field range’s design and installation, present test data and plots from its acceptance test including results of a NIST 18term error assessment.
The Antenna Metrology Lab at the National Institute of Standards and Technology in Boulder Colorado has developed a robotically controlled near-field pattern range for measuring antennas and quasi-optical components from 50 GHz to 500 GHz. This range is intended to address the need for highly accurate antenna pattern measurements above 100 GHz for a variety of applications including remote sensing, communications and imaging. A new concept in near-field range systems, this system incorporates the positioning repeatability of a precision industrial six-axes robot, six-axes parallel kinematic hexapod, and high precision rotation stage, integrated with a highly accurate laser tracking system. Programmable robot positioning allows the system geometry to be configured for spherical, planar, and cylindrical scans, as well as gain extrapolation measurements. Variable scan volume accommodates different test antenna sizes. Positioning accuracy better than 10 µm is predicted. Specifics of the system design, operating specifications and configurability will be presented.
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed in 2007 at CEA for indoor near field monostatic RCS assessment. This experimental layout was composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target was located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allowed full 3D near field monostatic RCS characterization. A new study was conducted in 2011 in order to achieve a more accurate positioning of the measurement antenna. The main objective is to enhance the RCS measurement performances, especially the environment subtraction directly related to the positioning repeatability of the measurement antenna. This new mechanical design has therefore been optimized to allow a +/-100° azimuth range with an angular positioning repeatability of less than 1/1000°. To achieve this level of accuracy, several keys design elements were considered: robust mechanical design, position control system… This paper describes the new experimental layout and the results of a positioning accuracy assessment campaign conducted using a laser tracker.
A novel holographic near-field phaseless technique is presented. The measurement system is composed of the antenna under test, the reference antenna, the amplitude scanning measurement system and the holographic reconstructed algorithm. The interference amplitude of the antenna under test with the reference antenna is measured by the amplitude scanning system. The complex near field of the antenna under test is reconstructed by computer, where the measured interference is corrected by the multiplication with the virtual spherical reference wave and then filtered in Fourier Transformation domain (e.g. Plane Wave Angular Spectrum) or the back-projected image space. The reconstruction method is rigorous without traditional Fresnel Approximation. The novel technique requires the amplitude on one measurement surface and the computer reconstructed algorithm, while the previous phaseless technique depends on two measurement surfaces or extra hardware to provide SynthesizedReference-Wave. The novel holographic measurement method and reconstruction algorithm could be used in many applications as for planar near field measurements for example. Simulated results are presented to demonstrate the complex field retrieval method and near-field to far field transformation.
A novel holographic near-field phaseless technique is presented. The measurement system is composed of the antenna under test, the reference antenna, the amplitude scanning measurement system and the holographic reconstructed algorithm. The interference amplitude of the antenna under test with the reference antenna is measured by the amplitude scanning system. The complex near field of the antenna under test is reconstructed by computer, where the measured interference is corrected by the multiplication with the virtual spherical reference wave and then filtered in Fourier Transformation domain (e.g. Plane Wave Angular Spectrum) or the back-projected image space. The reconstruction method is rigorous without traditional Fresnel Approximation. The novel technique requires the amplitude on one measurement surface and the computer reconstructed algorithm, while the previous phaseless technique depends on two measurement surfaces or extra hardware to provide SynthesizedReference-Wave. The novel holographic measurement method and reconstruction algorithm could be used in many applications as for planar near field measurements for example. Simulated results are presented to demonstrate the complex field retrieval method and near-field to far field transformation.
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed in 2007 at CEA for indoor near field monostatic RCS assessment. This experimental layout was composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target was located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allowed full 3D near field monostatic RCS characterization. A new study was conducted in 2011 in order to achieve a more accurate positioning of the measurement antenna. The main objective is to enhance the RCS measurement performances, especially the environment subtraction directly related to the positioning repeatability of the measurement antenna. This new mechanical design has therefore been optimized to allow a +/-100° azimuth range with an angular positioning repeatability of less than 1/1000°. To achieve this level of accuracy, several keys design elements were considered: robust mechanical design, position control system… This paper describes the new experimental layout and the results of a positioning accuracy assessment campaign conducted using a laser tracker.
Some antenna measurement applications require the precise positioning of an antenna along a prescribed path which may be realized by a combination of several, independent physical axes. Coordinated motion allows for emulation of a more complex and/or precise positioning system by utilizing axes which are mechanically less complex or precise and are correspondingly more easily realizable. An ideal coordinated motion system should 1) Allow for the description of coordinated paths as parametric mathematical functions and/or interpolated look-up tables 2) Support control variable parameters which affect the trajectory 3) Compute a feasible trajectory within given kinematical constraints 4) Generate measurement trigger signals along the trajectory 5) Minimize control-induced vibration 6) Compensate for multivariate positioning errors. This paper will describe a novel approach to virtual-axis coordinated motion which offers significant improvements over existing motion control systems. This advancement can be applied to many antenna measurement problems such as Helicoidal Near-Field Scanning and Radome Characterization.
The increased complexity of an active array's transmit beams by itself elevates the need for an interface between the array and the acquisition system. With the embedded receivers of a DBF, however, standard antenna testing of a DBF becomes nearly impossible without such an interface. MI Technologies has developed a reasonably general interface between its acquisition system and active arrays with digital beamformers. MI has produced minor variations of this interface for multiple customers, and these customers will each use the interface to test multiple types of DBF active arrays. This paper discusses the challenges, capabilities, and architecture of this interface.
The feasibility of using adaptive acquisition techniques to reduce the overall testing time in spherical near-field (SNF) antenna measurements is investigated. The adaptive approach is based on the premise that near-field to far-field (NF-FF) transformation time is small compared to data acquisition time, so that such computations can be done repeatedly while data is being acquired. This allows us to use the transformed FF data to continuously compute and monitor pre-defined decision functions (formed from the antenna specifications most important to the particular AUT) while data is being acquired. We do not proceed with a complete scan of the measurement sphere but effectively allow the probe to follow a directed path under control of an acquisition rule, so that the sampled NF datapoints constitute an acquisition map on the sphere (the geographical allusion being purposeful). SNF data acquisition can be terminated based on decision function values, allowing the smallest amount of data needed to ensure accurate determination of the AUT performance measures. We demonstrate the approach using actual NF data for several decision functions and acquisition rules.
The improved calibration model proposed in this paper is based on the traditional capacitance model which suffers from errors caused by the assumption that the capacitance is independent of frequency and the permittivity of the ambient medium under test. By analyzing the near-zone field of the coaxial opening, we introduce the new near-field capacitance to account for the dependency on the external permittivity. Simulation results show that the calibration error is significant reduced for low and moderate loss medium. And the calibration of the unknown coefficients simply requires the premeasurement of three known material including air, which provides convenience for the real field measurement. Measurement results obtained by a novel wideband in-situ coaxial probe are included to prove the accuracy improvement improved calibration model. by using this
This paper describes the measurement campaigns carried out at P-band (435 MHz) for selection of optimum on-ground verification approach for a large deployable reflector antenna (LDA). The feed array of the LDA was measured in several configurations with spherical, cylindrical, and planar near-field techniques at near-field facilities in Denmark and in the Netherlands. The measured results for the feed array were then used in calculation of the radiation pattern and gain of the entire LDA. The primary goals for the campaigns were to obtain realistic measurement uncertainty estimates and to investigate possible problems related to characterization of the feed array at P-band. The measurement results obtained in the campaigns are compared and discussed.
A wideband scalable dual-polarized probe designed by the Electromagnetic Systems group at the Technical University of Denmark is presented. The design was scaled and two probes were manufactured for the frequency bands 1-3 GHz and 0.4-1.2 GHz. The results of the acceptance tests of the 0.4-1.2 GHz probe are briefly discussed. Since these probes represent so-called higher-order antennas, applicability of the recently developed higher-order probe correction technique [3] for these probes was investigated. Extensive tests were carried out for two representative antennas under test using the manufactured probes; the results of these tests are presented and discussed in details.
The speed of spherical near-field scanning is increased significantly when measurements are not restricted to standard measurement locations, i.e., the locations that are equidistant in theta and in phi. Measurement positions can be chosen so that mechanical positioners perform scans with a continuous motion; this will decrease the time it takes to acquire data for near-field measurements. The issue then becomes transforming the data acquired with non-uniform spacing. This paper describes the development of a spherical near-field to far-field transform that can efficiently process data acquired on a non-uniform grid.
A desired feature of modern field probes is that the useable bandwidth should exceed that of the Antenna Under Test (AUT) [1]. Recent developments in probe and orthomode junctions (OMJ) technology has shown that bandwidths of up to 4:1 are achievable [2-5]. The probes are based on inverted ridge technology capable of maintaining the same high performance standards of traditional probes However, in typical Spherical Near Field (SNF) measurement scenarios, the applicable frequency range of the single probe can also be limited by the content of µ.1 spherical modes in the probe pattern [6-7]. This is because the traditional NFtoFF software applies probe correction under the assumption that the probe pattern is fully specified from knowledge of the E-and H-plane patterns only [8]. While this condition is guaranteed for virtually any type of probe for small illumination angles of the AUT and/or a long probe/AUT distance this assumption may lead to unacceptable errors in special cases. This paper describes the design and experimental verification of a Ka-band probe based on the inverted ridge technology. The probe is intended for high precision SNF measurements in special conditions that require less than -45dB higher order spherical mode content. This performance level has been accomplished through careful design of the probe and meticulous selection of the components used in the external balanced feeding scheme. The paper reports on the electrical and mechanical design considerations and the experimental verification of the modal content.