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Accuracy
Simplified Spherical Near-field Accuracy Assessment
G. Hindman, November 2006
Spherical near-field measurements have become a common way to assess performance of a wide variety of antennas. Published reports on range error assessments for spherical near-field ranges however are not very common. This is likely due to the perceived additional complexity of the spherical near-field measurement process as compared to planar or cylindrical measurement techniques. This paper will establish and demonstrate a simple procedure for characterizing the performance of a spherical near-field range. The measurement steps and reporting can be largely automated with careful attention to the test process. We will summarize the process and document the accuracy of a spherical near-field test range at NSI using the same NIST 18 terms commonly used for planar near-field measurements.
Characterization of the PLANCK Radio Frequency Qualification Model and Preparations for Flight Model Tests
H. Garcia,C. Nardini, D. Dubruel, G. Forma, J. Marti-Canales, M. Paquay, November 2006
The measurement of the radiation patterns of the PLANCK Radio Frequency Qualification Model (RFQM) is one of the most important elements of the verification of the PLANCK telescope. PLANCK is one of the scientific missions of the European Space Agency and is devoted to observe the Cosmic Microwave Background radiation, with unprecedented accuracy. The satellite payload consists of two state-of-the-art, cryogenically cooled instruments sharing a dual reflector telescope with 1.5 m aperture and covering the frequency range from 27 GHz to 1000 GHz. As a key part of the telescope verification logic, the radiation patterns of the RFQM has been measured in the Alcatel Alenia Space Compact Antenna Test Range (CATR) at four frequencies (30, 70, 100 and 320 GHz) using representative flight feed horns of the focal plane unit. This paper presents the test logic, the measured radiation patterns, the custom-made instrumentation set-up, the correction techniques used and the final link to the Flight Model verification.
Adaptive Array Based Antenna Pattern Correction Technique
V. Viikari,A. Räisänen, J. Salo, V-M. Kolmonen, November 2006
Adaptive array based antenna pattern comparison technique is presented in this paper. In the method, the antenna pattern of the antenna under test (AUT) is measured several times at different positions in the quiet-zone. The corrected antenna pattern is obtained by taking a weighted average of the measured patterns. An array synthesis algorithm is used to obtain averaging weights at the different rotation angles of the AUT. In addition, the weights are adapted specifically for the AUT. The adaptive array correction technique is demonstrated in a hologram based compact antenna test range (CATR) at 310 GHz. The demonstration is based partly on the measurements and partly on the simulations. For verification, the accuracy provided by the method is compared to the accuracy provided by the uniform weighting.
Complex Antenna Transfer Function Measurements with Emphasis on High Positional Resolution
J. McLean,A. Medina, H. Foltz, R. Sutton, November 2006
Position uncertainty in antenna measurements is unavoidable. This is due in part to mechanical inaccuracy in the fixturing and positioning equipment. For many classes of antenna, there is also not an obvious choice of reference point, due to lack of a well-defined phase center. It has been shown [1] that a UWB transfer function measurement, taken either in the time or frequency domain, is highly sensitive indicator of antenna displacement. Extraction of the linear phase from the transfer function data results in a uniquely defined distance for any given pair of antennas in a given orientation. When a two- or three-antenna measurement using identical antennas is performed, the result is a unique reference plane for the antenna. Unlike the phase center, is not tied to a particular frequency. Here, using frequency domain measurements of monopoles, ridged horns, and an end-fed biconical antenna, we show that distances can be extracted with a high degree of repeatability. Resolution on the order of 1 part in 5,000 can be obtained in a 4-meter chamber with measurements extending to 20 GHz. Thus, variation in the extracted distance should be a highly sensitive indicator of positional inaccuracy.
Measurement of Circular Polarized Antennas
I. Jupta,T-H. Lee, November 2006
In antenna measurements, the orientation of the antenna under test (AUT) is very important. The orientation here refers to the antenna placement in a plane perpendicular to the incident wavefront. For a linear polarized antenna, the antenna should be oriented parallel to the co-polarized component of the incident fields. A small error in the orientation can lead to a drop in the measured gain and an increase in the measured cross-polarization level. In the case of a circularly polarized antenna, it is not obvious how the antenna should be oriented. If the quiet zone fields (incident wavefront) have no cross-polarized component, then the orientation does not affect the measured data. However, when the quiet zone fields have a cross-polarized component, which is true for almost all test ranges, the measured gain and cross-polarized level can vary significantly with the antenna orientation. In this paper, the measured data is used to show the effects of antenna orientation on a circularly polarized antenna. The reason for the variations in the measured data with antenna orientation is discussed. A simple method to improve the measurement accuracy is presented.
An Extended Method for Measuring Time Delay Behavior of Small Antennas
H. Adel,A. Eidloth, R. Wansch, November 2006
The time delay behavior of antennas is of high importance for high accuracy localization and navigation systems. Next to the investigation of the receiving antennas, the transmitting antennas are of substantial interest, too. In the application envisioned these antennas are small dipoles integrated in a battery powered miniaturized transmitter system. The method described in this paper is based on the measurement of the time difference of arrival of a broadband signal in a synchronized setup. This setup consists of the transmitter under test which transmits a bursted sequence of the localisation waveform. The receiving side of the measurement system consists of two antennas, where one works as a reference antenna (with fixed position in relation to the transmitter) and the other works as “classical” probe antenna. Two synchronized tuners and data acquisition systems determine the time difference of arrival of the signal. Detailed measurements of different transmitters have been performed in the 2.45 GHz ISM band and will be presented.
Measurements of the CloudSat Collimating Antenna Assembly Experiences at 94 GHz on Two Antenna Ranges
J. Harrell,A. Prata, C. Lee-Yow, C. Stubenrauch, L.R. Amaro, R. Beckon, T.A. Cariveau, November 2005
This paper presents measurements of the CloudSat Collimating Antenna (CA) as fabricated for the 94.05 GHz CloudSat radar, which is to be used to measure moisture profiles in the atmosphere. The CloudSat CA is a 3 reflector system consisting of the 3 "final" (relative to the transmitted energy) reflecting surfaces of the CloudSat instrument. This assembly was fed by a horn designed to approximate the illumination from a Quasi-Optical Transmission Line (QOTL). This same horn was employed as a "standard" for measurement of the CA gain via substitution, and its patterns were also measured (this substitution represents a departure from the standard insertion loss technique in the near field range). The CloudSat CA presented a substantial measurement challenge because of the frequency and the electrical size of the aperture is approximately 600 wavelengths in diameter, with a nominal beamwidth of 0.11 degrees. In addition, very high accuracy was needed to characterize the lower sidelobe levels of this antenna. The CA measurements were performed on a 3122-ft outdoor range (this distance was 41% of the far field requirement), which were immediately followed by measurements in an indoor cylindrical Near Field (NF) range. The instrumentation challenges, electrical, mechanical, and environmental are described. Comparison of the outdoor vs. indoor pattern data is presented, as well as the effect of the application of tie-scans to the near field data.
Low Cost Satellite Payload Measurement System
J. Migl,W. Lindemer, W. Wogurek, November 2005
The performance of modern Satellites Antennas and Payloads is characterized by physical parameters like e.g. Antenna Pattern and Gain; EIRP, Flux Density, G/T and the overall PIM-performance. The available time frame for measurement of these parameters is getting constantly shorter. The EADS Astrium GmbH Compensated Compact Range (CCR) allows a time efficient measurement of all payload parameters with high accuracy under controlled environmental conditions. In addition to an efficient measurement facility high-performance measurement equipment is required. The economical budgets of most space programs demand the application of well-known measurement techniques in a cost efficient way. EADS Astrium GmbH supported by Agilent Technologies GmbH has developed an easy to handle and therefore cost optimized measurement platform for Satellite Payload Measurements. This platform consists mainly of a generic Agilent switch matrix operating up to 40GHz which can be connected to a wide range of measurement equipment. The matrix allows a highly flexible routing of the RF uplink and downlink signals including reference paths. Integrated and/or external RF components, like amplifiers, attenuators, and hybrids can be added to the paths, depending on the required test configuration. Starting from a minimum configuration the system can be modularly upgraded to satisfy any further test requirements. The software interface utilizes standard protocols and can be therefore easily addressed by any user specific measurement software. The EADS Astrium GmbH Advanced Antenna Measurement System (AAMS) includes an optional payload toolbox which provides a modular concept expandable for additional test functions.
A High Performance Combined NF-FF Antenna Test Facility
U. Shemer,C.T. Tong, November 2005
DSO National Laboratories (DSO) has commissioned a state-of-the-art combined near-field and far-field antenna test facility in 2004. This facility supports highly accurate measurement of a wide range of antenna types over 1–18 GHz. The overall system accuracy allows for future extensions to 40GHz and higher. The 11.0m x 5.5m x 4.0m (L x W x H) shielded facility houses the anechoic chamber and the control room. As the proffered location for this indoor facility is on top of an existing complex instead of the ground floor, antenna pick­up is facilitated by a specialized loading platform accompanied by a heavy-duty state of the art fully automated 2.0m x 3.0m (W x H) sliding door, as well as an overhead crane that spans the entire chamber width. Absorber layout comprises 8-inch, 12-inch, 18-inch and 24-inch pyramidal absorbers. The positioning system is a heavy-duty high precision 3.6m x 2.9m (W x H) T-type planar scanner and AUT positioner. The AUT positioner system is configured as roll over upper slide over azimuth over lower slide system. This positioning system configuration allows for planar, cylindrical and spherical near-field measurements. A rapidly rotating roll positioner is mounted on a specialized alignment fixture behind the scanner to facilitate far-field measurements. Instrumentation is based on an Agilent PNA E8362B. Software is based on the MiDAS 4.0 package. A Real-Time Controller (RTC), accompanied by an 8-port RF switch, facilitates multi-port antenna measurements, with the possibility of interfacing to an active antenna.
Low Cost and High Accuracy Alignment Methods for Cylindrical and Spherical Near-Field Measurement Systems
J. Demas, November 2005
Precise mechanical alignment of motion axes of both cylindrical and spherical near-field systems is critical to producing accurate data. Until recently the only way to align these types of systems was to employ traditional optical tooling (i.e. jig transits, theodolites). Alignment by these methods is difficult, time consuming, and requires specialized training. More recently, laser trackers have been used for this type of alignment. Unfortunately, these devices are expensive and demand an even higher level of operator training. This paper describes the use of low cost alignment tools and techniques that have been developed by Nearfield Systems, Inc. (NSI) that greatly simplify the alignment process. Setup and alignment can be performed in a very short period of time by technicians that have been given minimal training. Suitable optical alignment procedures when followed by the use of electrical alignment techniques [7] yield sufficient alignment accuracy to permit testing up to Ku-band.
Antenna Pattern Correction for the Circular Near Field-to-Far Field Transformation (CNFFFT)
I. LaHaie,C. Coleman, S. Rice, November 2005
In previous work [1], we presented an antenna pattern compensation technique for linearly-scanned near field measurements. In this paper, we present a similar tech­nique to mitigate the errors from uncompensated azi­muthal antenna pattern effects in circular near-field monostatic radar measurements. The antenna pattern co mpensation is implemented as part of an improved algorithm for transforming the near-field measurements to the far-field RCS. A description of this improved circular near field-to-far field transformation CNFFFT technique for isotropic antennas is presented in a com­panion paper [2]. In this paper, we formulate the near-field signal model in the presence of an azimuthal an­tenna pattern under the same scattering approximation used in the isotropic CNFFFT. Using this model, we derive a modified version of the CNFFFT that includes antenna pattern compensation. Numerical simulations are presented that demonstrate the ability of the tech­nique to remove antenna pattern errors and improve the accuracy of the far field RCS patterns and sector statistics.
An Effective Antenna Modelling For the NF-FF Transformation with Planar Wide-Mesh Scanning
C. Gennarelli,F. D'Agostino, F. Ferrara, G. Riccio, R. Guerriero, November 2005
ABSTRACT A fast and accurate technique is proposed in this work for the far field evaluation from a nonredundant number of voltage data collected by using the planar wide-mesh scanning (PWMS). It relies on the nonredundant sam­pling representations of the electromagnetic field and on the optimal sampling interpolation expansions of central type. By using a very flexible source modelling, which fits very well a lot of actual antennas, a new sampling technique is developed to recover the plane-rectangular data from the knowledge of the PWMS ones. It must be stressed that the so developed near-field–far-field transfor­mation requires a number of data remarkably lower than that needed by the standard plane-rectangular scanning. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported.
Measurement Sensitivity and Accuracy Verification for an Antenna Measurement System
N. Hui,A.A. Lubiano, C.R. Brito, D. Arakaki, November 2005
An antenna measurement system was developed to complement a new rectangular anechoic chamber (20’L x 10’W x 9’7”H) that has been established at California Polytechnic State University (Cal Poly) through donations and financial support from industry and Cal Poly departments and programs. Software algorithms were written to provide four data acquisition methods: continual sweep and step mode for both single and multiple frequencies. Log magnitude and phase information for an antenna under test is captured over a user-specified angular position range and the antenna's radiation pattern is obtained after post processing. Pattern comparisons against theoretical predictions are performed. Finally an RF link budget is calculated to evaluate the performance of the antenna measurement system.
Theoretical Basis and Applications of Near-Field Spiral Scannings
C. Gennarelli,C. Rizzo, C. Savarese, F. D'Agostino, G. Riccio, November 2005
ABSTRACT A unified theory of near-field spiral scans is proposed in this work by introducing a sampling representation of the radiated electromagnetic field on a rotational surface from the knowledge of a nonredundant number of its samples on a spiral wrapping the surface. The obtained results are general, since they are valid for spirals wrapping on quite arbitrary rotational surfaces, and can be directly applied to the pattern reconstruction via near-field–far-field transfor­mation techniques. Some numerical tests, assessing the accuracy of the technique and its stability with respect to random errors affecting the data, are reported with ref­erence to the case of the helicoidal scan.
SCARA Scanner for Portable Near-Field Antenna Testing
J. Snow,B. Slowey, November 2005
ABSTRACT The article discusses the performance and design of a SCARA type robot with counter balanced arms for portable near-field antenna testing. An X-band 43” by 93” antenna on its’ system trailer was tested. A SCARA robot uses rotating joints with parallel axis on linked arms to achieve straight line (or arbitrary) probe movement in a plane. For a horizontal movement plane counterbalanced arms allow movement without change in stress in the scanner structure or foundation, therefore probe movement stays in a plane and structure and foundations can be lightweight and more portable. Probe movement stayed within .004” of a flat surface. Graphite-epoxy tubular arms were used for lightweight, stiffness, and vibration damping. A clockspring like cable carrier was used for each rotary axis. This design kept the center axis free for a directly connected rotary encoder (providing greater accuracy). The diameter of the cable carrier housing at the rotary joint, between arms, enhanced safety by reducing the hazard of a scissoring effect. A dimension touch probe mounted in place of the RF probe was used to align the scanner to the antenna while on its’ system trailer.
Increasing the Measurement Accuracy of a Hologram-Based CATR by Averaging in Frequency Domain
V. Viikari,A. Raisanen, J. Ala-Laurinaho, J. Hakli, J. Mallat, November 2005
Hologram-based compact antenna test range (CATR) is a promising way to measure submm wave antennas. The hologram quality and the measurement accuracy of the hologram-based CATR is limited by the hologram manufacturing process. The measurement accuracy can be improved using pattern correction techniques. However, at submm wavelengths only the antenna pattern comparison (APC) technique is able to correct the effects of the spurious signals originating from the residual inaccuracies of the hologram pattern. A problem with the APC technique is that it is time consuming. This paper introduces a pattern correction technique for hologram-based CATRs. The technique is based on averaging in the frequency domain, and it is able to correct spurious signals originating from the hologram. Proposed technique is also faster than the APC technique. The proposed method is verified with a combination of measurements and simulations.
S-Parameter Extraction of a Partially Filled Waveguide by Using the Finite Element Method and the Numerical TRL Calibration Technique
P. Barba,A. Bogle, L. Kempel, November 2005
Inversion of the material parameters for a sample usually requires that the sample fill the waveguide cross-section. Alternative methods require that a non-filling sample be aligned along the center-line of the waveguide. However, it is not known how errors in placement impact the accuracy of the inversion. Hence, a numerical simulation to assess these errors is beneficial to the community. The extraction of the S-parameters from a rectangular­dielectric-filled waveguide is conducted numerically by means of the Finite Element Method (FEM) and the Thru-Reflect-Line (TRL) calibration technique. Three different ratios of dielectric sample width (d) to waveguide width (a) are primarily studied. The results are then validated with experimental data on the X-band. An assessment of error with respect to position will be presented at the meeting.
Sidelobe Accuracy Improvement in a Compact Range by using Multiple Feed Locations
M. Boumans,H. Eriksson, November 2005
A generally practiced way to improve the sidelobe accuracy in antenna measurements is by repeating and averaging the measurements in different positions in the quiet zone (also referred to as APC or AAPC, depending on the application). An alternative new way for improving the accuracy of compact range measurements is by moving the compact range feed in different locations. This can easily be achieved for both horizontal and vertical directions. Although feed scanning causes a boresight shift, this can be easily compensated if the feed positions are selected intelligently. A significant measurement speed improvement can be realized by using multiple feeds in the relevant locations, instead of moving a single feed sequentially into these locations. Feed scanning APC has been successfully tested in the Ericsson Microwave Systems Compact Range, where it is now practiced in high accuracy radar antenna measurements.
The Calibration of Four-Arm Spiral Modal Measurements for Angle-of-Arrival Determination
J. Radcliffe,K. Pasala, November 2005
Direction Finding (DF) systems have long been an area of intense research within the Air Force Research Laboratory. There are presently two types of existing DF systems: wideband multi-mode antennas and interferometers. Wideband multi-mode DF systems allow for a large bandwidth but present a low resolution and high variance. Interferometers provide high accuracy and low variance but are narrow band and require a large number of single aperture antenna elements. An effort has commenced to incorporate a broadband DF system with high resolution using two multi-mode spiral antennas. Using an interferometer of multi-mode elements, we can provide high resolution and wideband operation without using numerous antennas. This paper presents the results of extensive wideband measurements carried out on a four-arm spiral antenna and the associated modeformer. These measurements are used to assess and validate the angle estimation capability of the multi-arm spiral antenna.
An Analysis of The Accuracy of Efficiency Measurements of Handset Antennas Using Far-field Radiation Patterns
I. Kadri,R. Thorpe, T, Palmer, November 2005
Radiation efficiency is an inherent property of an antenna that relates the net power accepted by an antenna to the total radiated power. It is especially useful for handset antennas where the radiation patterns are often of less use for comparing competing antennas. Radiation patterns though not as useful for direct comparisons, still provide one method by which efficiency can be calculated. To accurately calculate the efficiency from patterns, it becomes necessary to obtain multiple pattern measurements (cuts). A larger number of cuts whilst yielding more accurate efficiency results, significantly increase measurement time. Thus an antenna designer is often forced to trade off accuracy against measurement time since both quick and accurate measurements are desired. The focus of this paper is to quantify this trade off, in order to provide guidelines on the number of pattern measurements required for accurate efficiency results. Simulated and measured far-field radiation patterns are used and various numbers of cuts are utilized to quantify the loss in accuracy with a reduced number of cuts. The techniques outlined are geared primarily towards cellular handset antennas.


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