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An effort to ascertain the accuracy of the rectangular waveguide measurement technique for permittivity and permeability characterization of materials, has led to the development and application of a waveguide notch filter as a scattering parameter (S-parameter) reference standard. The S-parameters of this reference can be determined accurately using simulations that implement a full wave model of the waveguide measurement technique. The notch frequency response characteristic allows testing over the dynamic range of the measurement system. When fabricated in metal, the filter provides a predictable frequency response, has mechanical and temporal stability, and is reproducible using standard machining techniques. However, manufacturing errors introduce uncertainty in the measured S-parameters. Determining the sensitivity of S-parameter uncertainty as a function of manufacturing errors is important in assessing the appropriateness of the notch filter as a metallic standard for use throughout the material measurements community. This paper presents the characteristics of the filter, showing both calculated and measured S-parameter values, and provides an analysis that demonstrates the relationship between dimensional manufacturing tolerances and the resulting S-parameter uncertainty.
We propose a novel method for measuring the total radiated power (TRP) of small radio terminals, such as mobile phones, active RFID tags, and UWB devices, using a spheroidal cavity coupler in which an EUT and a receiving antenna are displaced symmetrically around the focal points of the spheroid. The proposed method provides a compact, low-cost TRP measurement system with high sensitivity and high speed, supporting TRP measurement for both in-band signals and higher-order spurious radiation. Although the behavior of electromagnetic waves in the coupler is complex due to multiple reflections, we can evaluate the maximum TRP from the EUT by using the displacement technique and comparison with a reference system using a reference transmitting antenna and signal generator. Computer simulation verifies that the method measures TRP with high accuracy.
An error simulator based on virtual cylindrical near-field acquisitions has been implemented in order to evaluate how mechanical or electrical inaccuracies may affect the antenna parameters. In outdoor ranges, where the uncertainty could be rather important due to the weather conditions, an uncertainty analysis a priori based on simulations is an effective way to characterize measurement accuracy. The tool implemented includes the modelling of the Antenna Under Test (AUT) and the probe and the cylindrical near-to-far-field transformation. Thus, by comparing the results achieved considering an infinite far-field and the ones obtained while adding mechanical and electrical errors, the deviations produced can be estimated. As a result, through virtual simulations, it is possible to determine if the measurement accuracy requirements can be satisfied or not and the effect of the errors on the measurement outcomes can be checked. Several types of results were evaluated for different antenna sizes, which allowed determining the effect of the errors and uncertainties in the measurement for the antennas under study.
Electromagnetic Anechoic Chamber has recently been built by Alenia Aeronautica at Caselle South Plant: The Anechoic Chamber is a full anechoic chamber, and it has been designed to carry out electromagnetic vulnerability tests mainly on fighter and unmanned aircraft. In addition measurement can be carried out on many different vehicles that can be brought into the chamber through the main access door. A system to extract exhaust gas was installed in order to carry out tests on a wide variety of vehicles. The Anechoic Chamber has been designed to carry out both HIRF/EMC test and High Sensitivity RF measurement: in particular HIRF/EMC tests in the frequency range 30MHz ÷ 18GHz with the capability of radiating a very high intensity electromagnetic field and High Sensitivity RF measurement, including antenna pattern measurements on antennas installed on aircraft in the frequency range 500MHz ÷ 18GHz. During the design phase a 1/12th scale model of the chamber had been fabricated to assess the desired electromagnetic performance. In this phase of design the model was tested at the scale frequencies for Filed Uniformity, Site Attenuation and Free Space VSWR results. This study was published at the AMTA 2004 meeting. In addition to the physical model, during the construction phase, various computer simulations were performed to further define the detailed internal absorber layout and to define test acceptance methods for procedures not covered by the standards. The computer model analysis was conducted to identify areas of scattering that could be treated with higher performance absorbers to improve the chambers quiet zone performance. The identified “Fresnel Zones." have been treated with high performance absorbers optimized to provide improved performance at microwave frequencies. The absorber optimization was reported at the AMTA 2006 meeting. This optimization has allowed validation of the chamber according to the requirements of CIRSP 16-1-4 2007-02 in the range of frequency 30 MHz - 18GHz. The size (shield to shield) of chamber is 30m wide, 30m long and 20m high, and the 18m wide by 8.5m high main door allows the SUT access. The shielded structure is a welded structure of 3mm-thick steel panels which guarantees shielding effectiveness of more than 100 dB in the frequency range 100 kHz to 20GHz. The chamber includes a 10 meter diameter turntable to rotate a 30 ton SUT with an angular accuracy of ± 0.02° and a pathway to allow SUT access. Both the pathway and the turntable are permanently covered by ferrite tiles. A hoist system permits lifting of the SUT (max 25 tons) up to 10 meters from the turntable centre enabling EMC testing on aircraft with the landing gear retracted.
A device and algorithm of measuring of microwave airborne radar antenna impedance and input power level are presented. A compact five-port microwave reflectometer, p-i-n diodes switch, single microwave detector are used. The output detector signal is processed. All of that results in decreasing of the cost of equipment, elimination of instrument components non-ideality and reaching of high equipment accuracy.
Planar near-field probing is used in the optimisation of the quiet-zone of a hologram-based compact antenna test range (CATR). In this paper, the measurement instrumentation for 650 GHz operation is introduced and the potential measurement errors in the quiet-zone measurements are identified. Applicable error correction and compensation methods are discussed and the total measurement accuracy is calculated.
This paper presents a novel method to evaluate very small stray signals in compact range. The ripples of signals probed by an omni-directional antenna along the orthogonal direction of the bore sight could be treated as signals in time domain. Transforming the probed data with fast Fourier transform (FFT), the direction and amplitude (relative to the test signal) of each stray signal could be obtained. To improve the accuracy, time domain software gating should also be used in calibrating the measurement error of amplitude and phase. The presented method has the ability to measure very small stray signals with good angle resolution. The method has been tested by both simulation using MATLAB and experiment in the compensated compact range CCR120/100 in CAST using a monopole antenna centered on a circular ground plane as a probe. Good results were obtained.
This paper describes the Rectangular Coaxial 40’ long measurement system recently designed and installed at AEMI with the primary purpose of measuring the reflectivity of its high performance VHF/UHF absorbing materials in the frequency range 30 – 510 MHz. The basic principles of the system are described in detail in [1] and are based on S11 – measurements of absorbing material reflectivity by a Vector Network Analyzer (VNA). In order to improve the system productivity and measurement accuracy it was enhanced by the time-gating software option – the standard option of ORBIT/FR Spectrum 959 automated measurement software package [2].The measurement system performance was thoroughly evaluated and validated by a number of tests performed in the “empty” coaxial line, and in the line loaded by absorbing materials. The list of RF uncertainties – various measurement error sources - was generated, the main measurement error contributors were identified, the corresponding errors – estimated and the overall RSS measurement errors were calculated for the absorber reflectivity varying in the range of -30dB to – 40dB.
ABSTRACT A new probe compensated near-field – far-field transformation technique with planar spiral scanning is here proposed. It is tailored for quasi planar antennas, since an oblate ellipsoid instead of a sphere is considered as surface enclosing the antenna under test. Such an ellipsoidal modelling is quite general (containing the spherical one as particular case) and allows one to consider measurement planes at a distance smaller than one half the maximum source size, thus reducing the error related to the truncation of the scanning surface. Moreover, it reduces significantly the number of the needed near-field data when dealing with quasi planar antennas. 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.
The 2004 AMTA paper entitled “The “Cam” RCS Dual-Cal Standard” introduced the theoretical concept of the “cam,” a new calibration standard geometry for use in a static RCS measurement system that could simultaneously offer multiple “exact” RCS values based on simple azimuth rotation of the object. Since that publication, we have constructed a “cam” to further explore its utility. The device was fabricated to strict tolerances and its as-built physical geometry meticulously measured. Utilizing these characteristics and moment-method analysis, a high-accuracy computational electromagnetic (CEM) “exact” file required for calibration was produced. Finally, the “cam” was evaluated for its efficacy as a single device that could be utilized as a dual-cal standard. This development was conducted with a particular focus on the hypothesized improvements offered by the new standard, such as the elimination of frequency nulls exhibited by other resonant-sized calibration devices, and improved operational efficiency. In this follow-on paper, we present the advantages to and challenges involved in making the “cam” a viable RCS dual-cal standard by describing the fabrication, modeling and performance characterization.
ACC has developed for the ESA-ESTEC CATR a compact but highly versatile 5-axis positioner. It is composed of a roll axis, upper azimuth, elevation, translation and lower azimuth axis. The clearance between the floor and the translation stage is designed to pass over a 12” walkway absorber while the roll axis height is only 155 cm (~5 feet). The standard configuration for medium or high gain antennas is the roll-over-azimuth or elevation-overazimuth configuration with a vertical interface for the AUT. For omni-directional antennas and RCS measurements, the positioner can be configured as a low profile azimuth positioner with a horizontal interface without a blocking structure behind the AUT. The positioner can also be configured for bistatic RCS measurements and Spherical Near Field. With the addition of a linear scanner, the Quiet Zone can be scanned in a polar way but also planar scanning is possible. Other key parameters are: angular accuracy: 0.01°, accuracy of the translation axis: 0.01 mm, load capacity 100 kg.
Current means to improve position accuracy in antenna ranges are often expensive, consume important CPU time, and/or limit data acquisition speed. By taking advantage of axes with good repeatability, higher multi-dimensional positioning accuracy can be achieved directly by a controller to ease complexity and achieve real-time position correction. A product family of controllers brings this capability to fruition. Comparison analysis of field data demonstrates improved accuracy with no measurement speed degradation. Results indicated a considerable accuracy improvement limited by axis repeatability. Existing and new antenna ranges can benefit from this simple cost-effective approach to improved position accuracy.
Boumans [1] has introduced an alternative to the classical (Advanced) Antenna Pattern Correction (A)APC method by moving the range feed in the focal plane of a Compact Antenna Test Range (CATR) instead of moving the Device Under Test (DUT) around in the Quiet Zone (QZ). The advantages are clear: it is easier (cost and accuracy wise) to implement a feed scanner than a DUT scanner; the method can be used for azimuth and elevation patterns and it can even be implemented using multiple feed horns to get to the same measurement time as with a single range feed. The capabilities of defocused measurements in the Compact Payload Test Range (CPTR) at ESA/ESTEC have been previously assessed [2] and they revealed a triply reflected ray [2] and a QZ ripple induced by periodic surface inaccuracies [3]. This paper focuses on verifying the performance of the Focal Plane AAPC method for these effects. Use has been made of the well known DTU-ESA VAST-12 antenna [3].
The Microwaves and Radar Institute regularly performs calibration campaigns for spaceborne synthetic aperture radar (SAR) systems, among which have been X-SAR, SRTM, and ASAR. Tight performance specifications for future spaceborne SAR systems like TerraSAR-X and TanDEM-X demand an absolute radiometric accuracy of better than 1 dB. The relative and absolute radiometric calibration of SAR systems depends on reference point targets (i. e. passive corner reflectors and active transponders), which are deployed on ground, with precisely known radar cross section (RCS). An outdoor far-field RCS measurement facility has been designed and an experimental test range has been implemented in Oberpfaffenhofen to precisely measure the RCS of reference targets used in future X-band SAR calibration campaigns. Special attention has been given to the fact that the active calibration targets should be measured under the most realistic conditions, i. e. utilizing chirp impulses (bandwidth up to 500 MHz, pulse duration of 2 µs for a 300 m test range). Tests have been performed to characterize the test range parameters. They include transmit/receive decoupling, background estimation, and two different amplitude calibrations: both direct (calibration with accurately known reference target) and indirect (based on the radar range equation and individual characteristics). Based on an uncertainty analysis, a good agreement between both methods could be found. In this paper, the design details of the RCS measurement facility and the characterizing tests including amplitude calibration will be presented.
A new antenna diagnostics technique has been developed for the DTU-ESA Spherical Near-Field Antenna Test Facility at the Technical University of Denmark. The technique is based on the transformation of the Spherical Wave Expansion (SWE) of the radiated field, obtained from a spherical near-field measurement, to the Plane Wave Expansion (PWE), and it allows an accurate reconstruction of the field in the extreme near-field region of the antenna under test (AUT), including the aperture field. While the fundamental properties of the SWE-to-PWE transformation, as well as the influence of finite measurement accuracy, have been reported previously, we validate here the new antenna diagnostics technique through an experimental investigation of a commercially available offset reflector antenna, where a tilt of the feed and surface distortions are intentionally introduced. The effects of these errors will be detected in the antenna far-field pattern, and the accuracy and ability of the diagnostics technique to subsequently identify them will be investigated. Real measurement data will be employed for each test case.
Accurate antenna measurements at sub-millimeter frequencies are very challenging. Especially the phase measurement accuracy is usually limited by the mechanical accuracy of the measurement equipment. The measurement techniques used, and the measurement results of a dual reflector feed system (DRFS) at 650 GHz are presented in this paper. Planarity error compensation technique was used that enabled accurate correction to the measured phase pattern without accurate pre-existing information of the planarity error of the planar near-field scanner. The measured DRFS beam agrees well with the simulated and the achieved measurement accuracy is good.
Now-a-days, far-field ranges are being used to measure antenna radiation patterns. Two main types of ranges used are used for these measurements: direct and indirect illumination. In either case, the accuracy of the measurement is dependent upon the quality of the range quiet-zone fields. In direct illumination, phase and amplitude taper cause discrepancies in the fields. For indirect illumination, only amplitude taper must be accounted for. Additionally, stray signals and cross-polarization will further distort the quiet-zone fields and lead to measurement errors. This new methodology starts with the measured antenna data and a priori knowledge of the incident fields and estimates an Effective Aperture Distribution (EAD). The EAD compensates for these sources of error and can be used to predict the far-field radiation pattern of the antenna under test. Analytical results are presented for taper and stray signal analysis.
As new antenna designs reach higher frequencies and smaller sizes, traditional large scale antenna chamber systems become ill-suited for measurement. External mixing, room-sized chambers, and expensive test equipment add large costs and burden to antenna measurement systems. A smaller, more cost effective system is proposed. Using the bipolar planar scanning technique developed at UCLA, a portable and movable millimeter-wave antenna chamber is currently under development. The chamber is being designed to fit on the end of a standard optical table and enjoys the space-saving and accuracy inherent to the bipolar planar configuration. Simple construction of the chamber will allow relatively easy assembly and disassembly and allow movement of the chamber from one table to another, if needed. Antenna of diameters up to 40cm can be accommodated and scan planes of up to ~160cm can be measured. Millimeter-wave frequencies from around 30GHz to 67GHz can be measured. Antennas measured will use planar near-field to far-field techniques. In particular, the post-process will follow the OSI/FFT method and will incorporate the phase retrieval techniques developed for the bipolar configuration. These phase-less measurements will allow the use of scalar millimeter-wave test equipment with much lower cost than comparable vector test equipment.
This paper discusses design aspects related to a tiltable lightweight near-field scanning system for use at sub-millimeter frequencies. It addresses design issues as they relate to accuracy and scanner distortions from multiple causes. Calibration methods to measure and correct for anticipated and unanticipated errors are briefly addressed. Actual test results are presented. The tiltable scanner being discussed was designed for the Atacama Large Millimeter/submillimeter Array (ALMA) [1] and is being used by the National Radio Astronomy Observatory (NRAO) [2]. It has many other applications by virtue of its light weight (approx. 120 lbs) and ability to be oriented at different angles. These include flight-line testing and other in-situ antenna test applications.
The CTIA (The Wireless Association – www.ctia.org) were the first to publish a widely accepted test plan for antenna performance testing of “live” mobile phones[1]. The test plan describes the use of phantom heads and involves recording transmitted power and receiver sensitivity information over a full sphere to derive parameters such as Total Radiated Power (TRP) and Total Integrated Sensitivity (TIS). The test plan, has until now, assumed that testing is performed in the far-field at test distances greater than 2D2/.. For typical mobile phone frequency and device test diameters (assumed 300mm in the CTIA test plan), this has not been a constraint. However, as such testing evolves to include the various versions of IEEE 802.11 combined with new devices such as larger laptops and other consumer electronics, a far-field test requirement would lead to very large test facilities. Using experiments and rigorous simulations, this paper will show that for the commonly accepted performance criteria, the far-field requirement is unnecessarily strict. A minimum distance requirement based on the geometry and probe pattern is proposed which will ensure that the performance parameters (TRP, TIS, and others) are obtained with insignificant loss of accuracy.