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The Mathematical Absorber Reflection Suppression (MARS) technique is a method to reduce scattering errors in near-field and far-field antenna measurement systems. Previous tests by the authors had indicated that NSI's MARS technique was not as effective for directive antennas. A recent development of a scattering reduction technique for cylindrical near-field measurements has demonstrated that it can also work well for directive antennas. These measurements showed that the AUT shouldbeoffsetfromtheorigin byadistanceatleastequal to the largest dimension of the AUT rather than only 1-3 wavelengthswhich hadbeenusedfor smallerantennasin the earlier MARS measurements. Spherical near-field measurementshaverecently beenconcludedwhich confirm that with the larger offsets, the MARS technique can be applied to directive antennaswith excellent results. The MARS processing has recently been modified to produce significantly improved results. This improvement isespeciallyusefulfor antennaswherethephasecenterof the horns is located inside the horn and varies with frequency like pyramidal Standard Gain Horns (SGH). Fewermodesarerequired for thetranslatedpatternandthe filtering is more effective at reducing the effect of scattering. The improvement is very apparent for pyramidal horns.
Modern vehicle telematics subsystems often employ wireless interfaces. The design and evaluation of these subsystems involves measurement of antenna characteristics or Over-The-Air (OTA) performance of the subsystem as installed in a vehicle. Several subsystems servicing multiple user applications may be installed in a single vehicle, with antenna structures located anywhere on or within the vehicle. In general, the radiation characteristics of each subsystem must be measured over a partial spherical surface surrounding the vehicle and of sufficient radius to be outside the reactive near-field of the Device Under Test (DUT). This paper describes a distributed axis spherical scanning system designed for vehicle applications. The elevation axis which supports the probe antenna has a measurement radius of 25 ft (7.62m). The elevation positioner is supported on a hydraulic vertical lift axis to permit the adjustment of the measurement coordinate origin to be in the same horizontal plane as the DUT phase center. The measurement instrumentation system supports VNA based antenna pattern measurements or active OTA testing of telematics subsystems. The system is suitable for outdoor or indoor measurement facilities. An outdoor installation is described.
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.
The electromagnetic field within a test volume can be determined by use of spherical scanning techniques. Characterization of the field within the sphere requires compensation for probe-pattern effects. We provide a simple analysis to estimate uncertainties associated with this deconvolution.
The probe correction of near-field measured data can be considered as being composed of two parts. The first part is a pattern correction that corrects for the effects of the aperture size and shape of the probe and can be analyzed in terms of the far-field main component pattern of the probe. The second part is due to the non-ideal polarization properties of the probe. If the probe responded to only one vector component of the incident field in all directions, this correction would be unnecessary. But since all probes have some response to each of two orthogonal components, the polarization correction must be included. The polarization correction will be the focus of the following discussion. Previous studies have derived and tested general equations to analyze polarization uncertainty12. This paper simplifies these equations for easier application. The results of analysis and measurements for Planar, Cylindrical and Spherical near-field measurements will be summarized in a form that is general, easily applied and useful. Equations and graphs will be presented that can be used to estimate the uncertainty in the polarization correction for different AUT/Probe polarization combinations and measurement geometries. The planar case will be considered first where the concepts are derived from the probe correction theory and computer simulation and then extended to the other measurement geometries.
Dual polarized probes for modern high precision measurement systems have strict requirements in terms of pattern shape, polarization purity, return loss and port-to-port isolation. A desired feature of a good probe is that the useable bandwidth should exceed that of the antenna under test so that probe mounting and alignment is performed only once during a measurement campaign. As a consequence, the probe design is a trade-off between performance requirements and the usable bandwidth of the probe. For measurement applications in circular polarization the choice is between measuring the linear polarization components separately and derive the resulting circular polarized by computation or to measure directly with a circular polarized probe. Dual polarized probes in circular polarization with high polarization purity is difficult to achieve on a wide bandwidth. Dual linear polarized probe technology has recently been developed capable of achieving as much as 1:4 bandwidth while maintaining the high performance of traditional probe designs [1–7]. This paper describes the development, manufacturing and test of dual circular polarized probes with as much as 1:2 bandwidth as shown in Figure 1.
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.
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.
In this paper a method to identify faulty elements in a planar array using Artificial Neural Networks (ANN) is presented. The input to the neural network is amplitude of deviation pattern and output of neural network is the location of faulty elements. A planar array of 5×5 number of isotropic elements with uniform excitation and spacing ?/2 is considered. Either one faulty element or two faulty elements can exist in the array. The network is trained with some of the possible faulty deviation patterns and tested with various measurement errors. ANN is implemented with Radial Basis Function neural network (RBF) and Probabilistic neural network and their performance is compared.
Paper discusses the design, optimization and implementation of a Circularly Polarized (CP) microstrip 2 x 2 sequentially rotated phased antenna array for an X-band onboard satellite transceiver. In the final design, CP radiation is constructed by using CP elements, having unique sequential rotation along with sequential phase shift feeding–giving wider 3dB Axial Ratio (AR) Bandwidth. CP in each patch element is achieved by a perturbation segment, in this case a pair of truncated corners and with a single point feed–reducing complexity, weight and RF loss of the array feed. First analysis based on cavity model approach for the single CP patch is carried out, which is used to determine the normalized perturbation parameter. The initial dimensions are calculated using perturbation analysis. Optimization initially for individual patch and then for the array is performed using full wave analysis tools based on Method of Moments (MoM), and verified using Finite Difference Time Domain (FDTD). Finally, the measured input impedance and radiation patterns are correlated with the calculated results. It is observed that the measured Gain and 3db Beamwidth agrees well with the simulated results of the array optimized using MoM, while the measured results of Axial Ratio, VSWR and reflection coefficients Sxx follows closely the results from the simulations based on FDTD.
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.
In this paper, three possible approaches for definition of a highly accurate reference pattern of a reference antenna are described and their pros and contras are discussed. Following the most reliable approach, a dedicated measurement campaign was planned and carried out in 2007-2008 for definition of the highly accurate reference pattern of the VAST12 antenna. In planning the campaign, conclusions from the first comparison campaign with the VAST12 carried out within the ACE network in 2004-2005 were taken into account and these are also presented and discussed. Some typical measurement errors and uncertainties are listed and briefly discussed.
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.
The IsoFilterTM technique was originally demonstrated to operate by rejecting secondary signals that derive from reflections off of a nearby metallic object – namely, the ground plane surface supporting a small pyramidal horn.[1,2] The aperture of the horn was located several wavelengths above the ground plane and the sidelobes and backlobes of the horn illuminated the ground plane itself. The success of this demonstration has been sufficient to encourage us to pursue further the question of how well the IsoFilterTM technique will work to suppress other types of secondary signals– such as signals coming from other elements of an array antenna or another individual first-order primary radiator nearby. Here we report on some of the results of that investigation. We have calculated the far-field patterns of a sparsely populated array and applied the IsoFilterTM technique. The goodness of the suppression is judged by how well the “IsoFiltered” result agrees with the calculated pattern of the individual radiator.
A near-field measurement technique for the prediction of asymptotic far-field antenna patterns from data obtained from a modified cylindrical, or plane-polar, near-field measurement system is presented. This technique utilises a simple change in facility alignment to enable near-field data to be taken over the surface of a conceptual right cone [1, 2], or right conic frustum [3, 4] thereby allowing existing facilities to characterise wide-angle antenna performance in situations where hitherto they would perhaps have been limited by truncation. This paper aims to introduce the measurement technique, describe the novel probe-corrected near-field to far-field transform algorithm which is based upon a cylindrical mode expansion of the measured fields before presenting preliminary results of both computational electromagnetic simulations and actual range measurements. As this paper recounts the progress of ongoing research, it concludes with a discussion of the remaining outstanding issues and presents an overview of the planned future work.
The Phaseless techniques have gained considerable attention during the past two decades in the antenna measurements community. The removal of the phase measurements has some immediate advantages over the common vectorial measurements. They are cost effective, well-adapted for higher frequencies and insensitive to phase instabilities. The phaseless techniques have been discussed in the antenna measurements community and the theories behind these techniques are well explained in the literature. Unfortunately the issue of the noise and the presence of measurement errors are not investigated in details to provide strong impetus to the importance of phaseless measurements. In this paper the near field of a number of different types of antennas with high, medium and low side lobes is simulated to create as realistic case as possible. The effects of the probe positioning errors are investigated by injecting random errors in the position of the probe samples along x-, y- and z-axis. It is also illustrated how the positioning errors can distort the phase distributions. Through detailed characterizations of the constructed far field patterns, robustness of the Iterative Fourier technique even at the presence of very high probe positioning errors is demonstrated. It is shown how the utilization of the phaseless techniques will significantly reduce the probe positioning error effects when it is compared to the commonly used amplitude and phase near field measurement techniques.
Most traditional antenna measurement techniques presume that the antenna under test (AUT) is accurately aligned to the mechanical axes of the test range. Sometimes, however, it is not possible to achieve such a careful antenna alignment [1]. In these cases, standard post processing techniques can be used to accurately correct antenna-to-range misalignment. Alternatively, similar results may be obtained by approximation in the form of piecewise polynomial interpolation. When carefully employed, this method will result in only a small increase in uncertainty, but with a significant reduction in computational effort. This paper describes this far-field alignment correction method, which is closely related to standard active alignment correction methods [2]. This paper then proceeds to use numerical simulation as well as actual range measurements to demonstrate the effectiveness of this method. Finally, the utility of this technique in the presentation of far-field antenna pattern functions is illustrated.
In this paper, it is shown that using the phase center as distance reference point is equivalent to applying the proximity correction in determining gain of antennas with a SGH at finite distances. Clear guidelines for calculating the phase center location of a SGH, for application to antenna gain determination, are presented and explained. The phase pattern necessary for the calculation can be obtained either from measurement data or from computer simulations of the SGH. The region of validity of this approach is outlined and the residual error is quantified.
This paper describes joint studies of Wroclaw University of Technology and Denmark Technical University on optimizing placement and performance of low-profile antennas on small satellite, such as ESMO Moon orbiter. After comprehensive electromagnetic studies with use of numerical analysis, a spacecraft mockup modeling its conductive surfaces was developed. Two to four antennas were mounted and several placement configurations were investigated. For verification purpose of numerical analysis and formulating design guidelines to an actual Moon probe, precise measurements of combined radiation pattern were performed at the Near-Field Antenna Test Facility, Denmark Technical University.
Lockheed Martin MS2 has a long history of utilizing antenna ranges for calibration, test and characterization of the phased array antennas. Each range contains an integrated RF receiver subsystem for performing antenna measurements, typically on the full array. For solid-state phased array testing, what is often needed, however, is a test station capable of performing complex S-parameter measurements on a subarray or subset of the full antenna system without incurring the expense of a test chamber. To address this requirement, Lockheed Martin, working with Nearfield Systems, has developed a portable standalone RF measurement system. The standalone system consists of an Agilent PNA, automated transmit/receive unit (TRU) and a waveform generation (WFG) subsystem for interfacing to the phased array beam-steering computer. This paper will discuss the capabilities of the Standalone RF System including the TRU and WFG subsystems. The TRU is used to tailor the RF signal by automated switching of amplifiers and programmable step attenuators for various test scenarios. The WFG is an automated pattern generator used to present many digital waveforms in arbitrary sequences to the phased array beam steering computer. The design features of the standalone RF system will be presented along with the COTS hardware utilized in assembling the station.