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Accuracy

A Novel Phaseless Spherical Near-Field Antenna Measurement Including the Issue of Robustness
Carsten Schmidt,Thomas Eibert, Yahya Rahmat-Samii, November 2009

The radiation characteristics of antennas can be deter-mined by measuring amplitude and phase data in the ra-diating near-field followed by a transformation to the far-field. Accurate phase measurements especially at high frequencies are very demanding in terms of the required measurement equipment and tolerances. Phaseless mea-surement techniques have been proposed, which often deal with a second set of amplitude only measurement data in order to compensate the lack of phase information. In this paper the concept of phaseless spherical near-field measurements will be addressed by presenting a phaseless near-field transformation algorithm for spherical antenna measurements, working with amplitude only data on two spheres. In particular the measurement of a patch antenna is considered to demonstrate the utility of the technique for low gain antennas. To address the issue of robustness, inaccurate measurement distances as well as spherical rotation angles are considered in order to evaluate the accuracy of the method against probe positioning errors. Furthermore noise contributions are introduced to emu-late measurement inaccuracies in general.

Single Antenna Method for Determining the Gain of Near-Field Waveguide Probes
Russell Soerens, November 2009

Accurate calibration of near-field measurements requires the probe used for the measurement be well characterized. The determination of the absolute gain of rectangular open-ended waveguide probes is difficult due to the broad beamwidth in both the E-plane and H-plane which increase the likelihood of multi-path affecting the accuracy of the measurement. Multi-path may be minimized by reducing the separation distance, but at the price that far-field conditions may no longer apply. A variation of the two matched antenna method is to use a large reflecting plate to form an image of the probe. Use of the entire bandwidth of the probe, and time-gating the results to isolate the signal reflected from the plate allows the gain to be determined. The procedure also allows the determination of the aperture reflection coefficient used by theoretical probe models used for pattern compensation in the near-to-far-field transformation.

HIGH PERFORMANCE BROADBAND FEEDS FOR ECONOMICAL RF TESTING IN COMPACT RANGES
Juergen Hartmann,Christian Hartwanger, Christian Hunscher, Ralf Gehring, Un-Pyo Hong, November 2009

Compact test ranges are worldwide used for real-time measurements of antenna and payload systems. The Compensated Compact Range CCR 75/60 and 120/100 of Astrium represent a standard for measurement of satellite antenna pattern and gain as well as payload parameter due to its extremely outstanding cross-polar behavior and excellent plane wave field quality in the test zone. The plane wave performance in the test zone of a compact test range is mainly dependent on the facilities reflector system and applied edge treatment as well as on the RF performance of the range feed. To provide efficient and economic testing and maintaining the needed measurement accuracy the existing standard set of high performance single linear feeds covering the frequency range from 1 - 40 GHz had been extended to operate simultaneously in dual linear polarization. In addition several customer specific range feeds had been developed and manufactured and validated. More detailed information and achieved test results for the new high performance range feeds will be presented.

An accurate and efficient error predictor tool for CATR measurements
Cecilia Cappellin,Allan Ostergaard, Maurice Paquay, Stig Busk Sørensen, November 2009

An accurate and efficient numerical model is developed to simulate the far field of an antenna under test (AUT) measured in a Compact Antenna Test Range (CATR), on the basis of the known quiet zone field and the theoretical aperture field distribution of the AUT. The comparison with the theoretical far-field pattern of the AUT shows the expected measurement accuracy. The numerical model takes into account the relative movement of the AUT within the quiet zone and is valid for any CATR and AUT of which the quiet zone and aperture field, respectively, are known. The antenna under test is the Validation Standard Antenna (VAST12), especially designed in the past for antenna test ranges validations. Simulated results as well as real measurements data are provided.

A NONREDUNDANT NF–FF TRANSFORMATION WITH SPHERICAL SPIRAL SCANNING USING A FLEXIBLE AUT MODEL
Francesco D'Agostino, November 2009

ABSTRACT In this work, a probe compensated near-field – far-field transformation technique with spherical spiral scanning suitable to deal with elongated antennas is developed by properly applying the unified theory of spiral scans for nonspherical antennas. A very flexible source modelling, formed by a cylinder ended in two half-spheres, is considered as surface enclosing the an­tenna under test. It is so possible to obtain a remark­able reduction of the number of data to be acquired, thus significantly reducing the required measurement time. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported.

Accurate radar distance measurements in dispersive circular waveguides considering multimode propagation effects
Eckhard Denicke,Gunnar Armbrecht, Ilona Rolfes, November 2009

This contribution deals with guided radar distance measure­ments in the .eld of industrial tank level control. The aim is to achieve a submillimeter gauging accuracy even when conduc­ting the measurement within thehighlydispersive environment of large and thus overmoded cylindrical waveguides. In this case normally multimode propagation causes a decrease in measurement precision. Therefore, the effects of intermodal dispersion are fundamentally reviewed and based on these re­sults, two different approaches for overcoming the drawbacks of this measurement scenario are derived. On the one hand a prototype of a novel concept for compact mode-preserving waveguide transitions is presented, ef.ciently avoiding the excitation of higher order modes. By applying this concept, free-space optimized signalprocessing algorithms canbe used advantageously. On the other hand, an alternative correlation-based signal processing method is presented. The method is able to exploit the otherwise parasitic dispersion effects to enhance the measurement precision even in constellation with a simple waveguide transition. Finally, the trade-off between the signal processing’s and waveguide transition’s complexity is highlighted and discussed. Measurement results in a frequency range of 8.5 to 10.5 GHz are provided for different kinds of waveguide transitions proving the capability of both approaches.

Numerical Calibration of Standard Gain Horns
Don Bodnar, November 2009

The gain-transfer technique is the most commonly used antenna gain measurement method and involves the comparison of the AUT gain to that of another antenna with known gain. At microwave frequencies and above, special pyramidal horn antennas known as standard-gain horns are universally accepted as the gain standard of choice. A design method and gain curves for these horns were developed by the US Naval Research Laboratory in 1954. This paper examines the ability of modern numerical electromagnetic modeling to predict the gain of these horns and possibly achieve greater accuracy than with the NRL approach. Similar computational electromagnetic modeling is applied to predict the gain and pattern of open-ended waveguide probes which are used in near-field antenna measurements. This approach provides data for probes that are not available in the literature.

Identifying Pointing Errors for the NIST 18 Term Error Technique
Zachary Newbold,Allen Newell, Bruce Williams, November 2009

The NIST 18 Term Error Analysis Technique uses a combination of mathematical analysis, computer simulation and near-field measurements to estimate the uncertainty for near-field range results on a given antenna and frequency range. A subset of these error terms is considered for alignment accuracy of an antenna’s RF main beam. Of the 18 terms, several have no applicable influence on determining the beam pointing or the terms have a minor effect and when an RSS estimate is performed they are rendered inconsequential. The remainder become the dominant terms for identifying the alignment accuracy. There are six terms that can be evaluated to determine the main beam pointing uncertainty of an antenna with respect to dual band performance. Analysis of the near-field measurements is performed to identify the alignment uncertainty of the main beam with respect to a specified mechanical position as well as to the main beam of the second band.

ACCURATE INFINITE GROUNDPLANE ANTENNA MEASUREMENTS
Lars Foged, November 2009

The accurate measurement of the infinite ground plane antenna patterns are needed in different applications as discussed in [1–12]. The comprehensive performance of a general antenna in a complex environment including interaction can be evaluated fast and accurately using ray tracing techniques [1,2]. This approach requires a reliable representation of the local source behaviour either through measurements or simulation. A good source approximation for this method is the infinite ground plane pattern assuming a perfectly conducting plane. The infinite ground plane condition can be achieved easily in simulation using full-wave computational tools but is very difficult to measure on a general antenna due to the finite dimensions of the measurement systems. Different measurements and post processing approaches have been investigated in the past to determine the infinite ground plane pattern of a general antenna. Spherical mode truncation/filtering have been used as means to eliminate edge diffraction from finite ground plane measurements. This method suffers from the dependence on the selection of filtering parameters as discussed in [3]. Time-gating can give some information about the isolated antenna pattern in most directions as discussed in [4-6] but is not completely general and require special equipment and setup for the measurement. Other approaches to eliminate the edge diffraction by special design of the ground plane shape have also been pursued as discussed in [7-10]. This paper introduces a simple formulation to accurately determine the infinite ground plane pattern of any antenna from measurements on a small finite ground plane. The theory of the method is presented and its accuracy and suitability demonstrated with measured examples.

An Innovative Alignment System in Near-Field Measurements
amedeo capozzoli,Angelo Liseno, Claudio Curcio, Gennaro Strazzullo, Giuseppe D'Elia, Pietro Vinetti, November 2009

The paper presents a new system, to be used in near-field antenna characterization, which (in its simplest implementation) automatically assists the alignment of the Antenna Under Test (AUT) and the definition of the uniform/non-uniform sampling and filtering procedures. The system, based on a very cheap hardware (3D, coded structured-light, digitalization device), is able to provide a complete description of the geometry of the measurement set-up and of the movements of its parts, probe included. In this paper the simplest case, the alignment of the AUT, is considered. In this case, the system determines the coordinates of the surface points of the AUT in the Laboratory Reference System (LRS), providing the position and the orientation of the AUT in the LRS. The acquisition of the geometrical data on the AUT requires only few seconds, with a negligible human intervention. The acquired data are then processed to provide the desired setting of the AUT either manually or by means of computer controlled actuators, ensuring the accuracy suited to millimetre-wave band. The geometrical information can be exploited also to make possible the correction via software, when movements of the AUT should be avoided. The accurate information on the AUT geometry can be fruitfully exploited in advanced, high-performance filtering and sampling approaches, again drastically reducing any human interaction with the system. The performance of the system is discussed by referring to a prototype working in the millimetre-wave band.

Rapid Continuous Linear Spiral Planar Measurements for Millimeter-Wages
Timothy Brockett,Yahya Rahmat-Samii, November 2009

Bipolar planar antenna measurements have been used as an alternative to other planar scanning techniques such as plane-rectangular or plane-polar scanning. Bipolar scanning features important advantages such as the elimination of linear motion in measurement, increased stability, compact footprint, and a variety of data acquisition modes. The most rapid data acquisition mode for planar measurements overall, depending on range implementation, is the linear spiral sampling mode. This technique involves simultaneous incrementation of both the radial and azimuthal positioners to create a data grid in a spiral configuration. Data sampling and interpolation for linear spiral sampling has been obtained previously through rigorous development and modification of bipolar sampling requirements and interpolation techniques [1]. Implementation of the continuous linear spiral technique is not a trivial task. Positional program requirements require non-uniform acceleration and velocity for each axis. Data acquisition requires precise synchronization of both positional and RF equipment. Finally, post-processing is complicated by the inherent nature of a linear spiral data grid. This paper will describe, in detail, the implementation of the linear spiral technique with our portable millimeter-wave bipolar planar measurement system with emphasis on the issues mention here. In addition, measurements of a 31GHz rectangular patch array using both the conventional bipolar and linear spiral techniques are compared for both measurement time requirements and pattern accuracy. The continuous linear spiral technique has shown a significant measurement time reduction and has shown excellent agreement with results obtained in comparison to previously implemented stepped spiral measurements.

Polarimetric calibration of indoor and outdoor polarimetric radar cross section systems
L.A. Muth (National Institute of Standards and Technology), November 2008

We used a set of dihedrals to perform polarimetric calibrations on an indoor RCS measurement range. We obtain simultaneously hh, hv, vh, and vv polarimetric data as the calibration dihedrals rotate about the line-of-sight to the radar. We applied Fourier analysis to the data to determine the polarimetric system parameters, which are expected to be very small. We also obtained polarimetric measurements on two cylinders to verify the accuracy of the system parameters. We developed simple criteria to assess the data consistency over the very large dynamic range demanded by the dihedrals. We examined data contamination by system drift, dynamic range nonlinearities, and the presence of background and noise. We propose improved measurement procedures to enhance consistency between the dihedral and cylinder measurements and to minimize the uncertainty in the polarimetric system parameters. The final recommened procedure can be used to calibrate polarimetrically both indoor and outdoor ranges.

DATA REDUCTION IN THE NF-FF TRANSFORMATION TECHNIQUE WITH SPHERICAL SPIRAL SCANNING
Francesco D'Agostino (University of Salerno),Claudio Gennarelli (University of Salerno), Flaminio Ferrara (University of Salerno), Giovanni Riccio (University of Salerno), Massimo Migliozzi (University of Salerno), Rocco Guerriero (University of Salerno), November 2008

An effective near-field – far-field transformation technique with spherical spiral scanning tailored for antennas having two dimensions very different from the third one is here proposed. To this end, an antenna with one or two predominant dimensions (as, e.g., an elongated or quasi-planar antenna) is no longer considered as enclosed in a sphere, but in a prolate or oblate ellipsoid, respectively, thus allowing one to remarkably reduce the number of required data. Moreover these source modellings remain quite general and contain the spherical one as particular case. Numerical tests are reported for demonstrating the accuracy of the far-field reconstruction process and its stability with respect to random errors affecting the data.

Advanced Computational Tools for Antenna Placement Studies
Rensheng Sun (EM Software & Systems (USA) Inc.),Gopinath Gampala (EM Software & Systems (USA) Inc.), C. J. Reddy (EM Software & Systems (USA) Inc.), November 2008

Recent advances in computational electromagnetic tools have made antenna design possible along with integration of antennas on various ground, sea and air platforms. Numerical computations can be performed to evaluate the effects of antenna placement, radiation hazard, EMC/EMI, etc. The typical numerical approaches include full wave techniques such as Method of Moments (MoM), Multilevel Fast Multipole Method (MLFMM) and asymptotic techniques such as Physical Optics (PO) and Uniform Theory of Diffraction (UTD). For many practical applications, sometimes it is necessary to study the electromagnetic behavior on a specific structure over a broad frequency band, and therefore it is important to have some benchmark data on computational resources needed for some commonly used numerical techniques. In this study, representative full-size air, ground and sea platforms are considered and the frequency limit is pushed at different bands using several numerical techniques. The accuracy and computational resources are compared.

MODELING ANTENNA PATTERN DISTORTION CAUSED BY SUPPORTING STRUCTURES
Pablo A. Vicharelli (Equilateral Technologies Inc.),Donna Fagen (Equilateral Technologies Inc.), November 2008

This paper presents a technique for calculating the antenna pattern distortion caused by supporting structures such as buildings, towers, etc. The technique is based on ray tracing and the uniform theory of diffraction. The resulting distorted pattern can then be added to antenna databases and used as input to, for example, wireless network planning tools. The present method is fast and can considerably improve the accuracy of propagation calculations of radio frequency signals. A representative example from the application of this technique to an antenna mounted on the top of a building is presented.

Radiation Pattern Measurements and Predictions of the PLANCK RF Qualification Model
Gilbert Forma (Thales Alenia Space),Denis Dubruel (Thales Alenia Space), Fabrizio Villa (°INAF-IASF), Gerald Crone (ESA-ESTEC), Isabelle Ristorcelli (CESR), Jan Tauber (ESA-ESTEC), Javier Marti-Canales (ESA-ESTEC), Maura Sandri (°INAF-IASF ), Maurice Paquay (ESA-ESTEC), November 2008

PLANCK is one of the scientific missions of the European Space Agency, devoted to observe the Cosmic Microwave Background radiation with unprecedented accuracy. One of the key factors for the performance is the radiation pattern of the telescope, especially the sidelobe performance in the direction of hot celestial bodies like Sun, Earth and Moon. The satellite will operate around the L2 Lagrangian point in deep space under cryogenic conditions. These conditions can not be realized in an antenna test range for a payload of this size. Therefore, the predictions for the performance under flight conditions depend highly on numerical simulations. The model to be used had never before been verified to this level of confidentiality. The challenge was to conduct a test campaign at frequencies up to 320 GHz (far beyond the normal range of the used CATR) with a very large object (the PLANCK RF Qualification Model with an aperture size of 1.5 m, i.e. more than 1500 wavelength at 320 GHz) to demonstrate Sidelobe Levels down to -90 dB. A selection of the measurement results and comparison with predictions will be presented.

FIELD ESTIMATION AND ASSESSING ACCURACY IN COMPLEX RF ENVIRONMENTS
Ivor L. Morrow (Cranfield University),A. W. Wraight (QinetiQ), November 2008

A novel technique for estimating the spatial electromagnetic field distribution and its covariance error is presented based on variogram analysis and the statistical interpolation technique known as Kriging. The spatial structure of some field measurements are characterized by variogram analyses and their propagation properties identified. The physical implications of the Kriging interpolator functional fit to measured data is considered and illustrated. It is concluded that with specialist interpretation this new technique can be used as a valuable checking tool, or to reduce the number of field measurement, in a measurement programme, particularly when the costs of the latter are considered.

HIGH ACCURACY COMPACT RANGE ANTENNA MEASUREMENT FACILITY
G.Pinchuk (Orbit/FR-Eng),Y. Bitton (Orbit/FR-Eng), Bernhard Priemer (Orbit/FR-Europe), Marcel Boumans (Orbit/FR-Europe), Seong-Soo Kim (ACE Antenna), November 2008

Orbit/FR has installed a new compact range for antenna measurements at ACE Antenna Corp. The measurement facility covers a frequency range from 0.8 to 40GHz with a Quiet Zone size of 3 m diameter x 3 m length. The design of the compact range is similar to the one already installed by Orbit/FR at Ericsson (Sweden) with some improvements in the mechanical design and in the system parameters. An intensive simulation of the reflector serrations had allowed for finding its optimal profile, thus improving the quiet zone parameters at entire frequency range, especially at low frequencies, at which a number of base-station and mobile antennas are expected for testing by ACE Antenna Corp. A new design of a feed positioner and a baffle house added more convenience for the compact range alignment and operation. The system was installed and qualified in March 2008. The field probing has been performed within the entire operating frequency range, which then allows for evaluation of the antenna measurement accuracy. A system description as well as results of simulation and excerpt of the qualification data is presented in the paper.

PROCEDURE AND PROCESS OPTIMIZATION FOR REDUCTION OF MEASUREMENT UNCERTAINTIES IN RF TEST FACILITIES
Juergen Habersack (Astrium GmbH – Satellites, Measurement Technology), November 2008

The measurement accuracy of state-of-the-art RF test facilities like near-field or compact test ranges is influenced due to applied system hardware as well as operational facts which are influenced by human errors. The measurement errors of near-field test facilities were analyzed and published in the past times and are based on the 18-term error model of Newell [1]. For compact test ranges and especially for the cross-polar free compensated compact range a similar error model was established at Astrium GmbH within a study for the satellite service provider INTELSAT [2] in order to define possible facility performance improvements and maximum achievable values for the measurement accuracy. It has to be remarked, that test programs for space applications require very stringent adherence to procedures and documentation of process steps during a test campaign. Within this paper, recommendations for process optimizations and procedures will be presented to guarantee the adherence to the valid error budgets and to minimize the Human Factor. A description of main error contributions in the Compensated Compact Range (CCR) of Astrium GmbH will be performed. Furthermore, the error budgets for pattern and gain measurements and achievable performance improvements will be given.

Characterization of measurement systems through extensive measurement campaigns
Sara Burgos (Universidad Politécnica de Madrid.),Manuel Sierra-Castañer (Universidad Politécnica de Madrid), H. Eriksson (SAAB Microwave Systems), O. Breinbjerg (Technical University of Denmark), S. Pivnenko (Technical University of Denmark), November 2008

Within the European Union network "Antenna Center of Excellence" – ACE (2004-2007), a first intercomparison campaign among different European measurement systems, using the 12 GHz Validation Standard (VAST12) antenna, were carried out during 2004 and 2005. One of the challenges of that campaign was the definition of the accurate reference pattern. This was the reason why a dedicated measurement campaign for definition of the accurate reference pattern was hold during 2007 and beginning of 2008. This second campaign is described in the companion paper “Dedicated measurement campaign for definition of accurate reference pattern of the VAST12 antenna”. This dedicated measurement campaign was performed by Technical University of Denmark (DTU) in Denmark, SAAB Microwave Systems (SAAB) in Sweden and Technical University of Madrid (UPM) in Spain. This campaign consisted of a large number of measurements with slightly different configurations in each of the three institutions (2 spherical near field systems and one compact range). The purpose of this paper is to show the process to achieve the reference pattern from each institution and the evaluation of the accuracy. The acquisitions were performed systematically varying in applied scanning scheme, measurement distances, signal level and so on. The results are analyzed by each institution combining the measurement results in near or far field and extracting from these measurements: a “best” pattern, an evaluation of possible sources of errors (i.e. reflections, mechanical and electrical uncertainties) and an estimation of the items of the uncertainty budget.







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