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Experimental Verification of the Focal Plane APC Method with the VAST-12 Antenna
Boumans  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  and they revealed a triply reflected ray  and a QZ ripple induced by periodic surface inaccuracies . 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 .
Application of the SWE-To-PWE Antenna Diagnostics Technique to an Offset Reflector Antenna
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.
Antenna Measurement at 650 GHZ With A Planar Near-Field Scanner
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.
Evaluation of the Telia Scattered Field Measurement Method for Estimation of In-Network Performance of Mobile Terminal Antennas
In this paper we present and evaluate a method for estimation of in-network performance of mobile terminal antennas developed by the Swedish telecom operator Telia. The Telia Scattered Field Measurement (TSFM) Method is intended to give a better estimate of the performance of the mobile terminal antenna as in an in-network fading scenario. The parameter measured from the TSFM method is referred to as the Scattered Field Measurement Gain, SFMG, i.e. the Mean Effective Gain, MEG, measured relative to a half wave dipole antenna. MEG includes the radiation pattern of the mobile terminal antenna as well as an estimate of polarization and directional losses that occur due to the propagation environment. In this study it is found that the TSFM method provides a good measure of the in-network performance of the mobile terminal antenna. Furthermore, it is shown that the SFMG measured with this method is found to be well correlated with the Total Radiated Power Gain, TRPG, or radiation efficiency. This suggests that the Total Radiated Power, TRP, may be a good measure of the in-network performance of mobile terminal antennas if measured with proper adjustment to the antenna and propagation channel mismatch.
Compact Wideband Antenna Array for GNSS Receivers
This paper presents a miniature conformal GNSS (Global Navigation Satellite Systems) antenna array with integrated low-profile feed that provides continuous upper hemisphere coverage with good axial ratio. The four element array is comprised of two-arm wire spirals with substrate dielectric loading and termination resistors. The array has a total size of 3.5” x 3.5” and is approximately 0.8” thick. The antenna array can be used to receive signals from all GNSS satellites in various bands. The antenna has a similar footprint as a FRPA-3 (Fixed Reception Pattern Antenna – 3), and thus can easily replace the existing FRPA-3. One can obtain improved performance with the new antenna in that the signals from any GNSS satellite can be received. In addition, the array can be used to null interfering signals by adaptively weighting the signals received by various antenna elements. We have analyzed the performance of the antenna using HFSS, and are in the process of building the antenna. Next, the performance of the antenna will be verified experimentally.
Planar/Spherical Near-Field Range Comparison with -60 dB Residual Error Level
Comparisons of the far-field results from two different ranges are a useful complement to the detailed 18 term uncertainty analysis procedure. Such comparisons can verify that the individual estimates of uncertainty for each range are reliable or indicate whether they are either too conservative or too optimistic. Such a comparison has recently been completed using planar and spherical near-field ranges at Nearfield Systems Inc. The test antenna was a mechanically and electrically stable slotted waveguide array with relatively low side lobes and cross polarization and a gain of approximately 35 dBi. The accuracies of both ranges were improved by testing for, and where appropriate, applying small corrections to the measured data for some of the individual 18 terms. The corrections reduce, but do not eliminate the errors for the selected terms and do not change the basic near-to-far field transformations or probe correction processes. The corrections considered were for bias error leakage, multiple reflections, rotary joint variations and spherical range alignment. Room scattering for the spherical measurements was evaluated using the MARS processing developed by NSI. The final results showed a peak equivalent error signal level in the side lobe region of approximately -60 dB for both main and cross component patterns for angles of up to 80 degrees off-axis.
A Method to Correct Measurement Errors in Far-Field Antenna Ranges
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.
RECONFIGURABLE ANTENNA ARRAYS USING PIXEL ELEMENTS
The goal of this research is to develop an unconstrained reconfigurable programmable array antenna. The concept is to build patch arrays using individual controllable pixels. The aperture of the system is made up of a large array of small (1/10 .min) pixels. Each pixel is a small piston made up of a metal top, a dielectric shaft, and a metal base. The pistons can be moved up and down under computer control. When all pistons are in the down position, a ground plane is created. When a line of pixels is raised into the up position, a microstrip transmission line (a metal line over a dielectric substrate) is created. A patch antenna is created when multiple pixels are raised into the up position to form a larger rectangle or other shape. In the final design, a set of feed lines and antennas can be created in any pattern within 1 millisecond. Under computer control, it is possible to change the beam direction, the beamwidth, the polarization, and the frequency of operation of the array. Design details, theoretical models, and the behavior of test fixtures and configurations will be discussed during this presentation.
Implementation Issues of Planar Adaptive Antenna Array with Mutual Coupling
Adaptive antenna has both the amplitude and phase (as weights) which can be adapted optimally to get required multi path arrival estimation or directed beam forming. We had earlier tried to find out errors in adaptive arrays (ULA) and further try to investigate mutual coupling effect in closely spaced antenna elements in rectangular / planar arrangement. It is always desired to place antenna elements closer in order to reduce grating lobes when the main lobe is electrically tilted. In real life when an adaptive array is subjected to multi path and mutual coupling it is necessary to counteract with suitable modeling so as to make it usable for wireless communication. We attempt to study / investigate the mechanism for mutual coupling between antenna elements. In adaptive antenna arrays, mutual coupling can deteriorate the algorithms which try to deal with the direction of arrival (DOA) and beam forming. There is also a need to reduce the size of the antenna aperture and element itself, without degrading the performance and bandwidth of the element. We have simulated in Matlab our planar adaptive array algorithm which mitigates errors and reduces effects of mutual coupling. It was found that Tschebyscheff polynomial distribution was one of the optimum arrangements for antenna synthesis. When aperture length has to be fixed and new antenna elements are introduced we try to find way to deal with this by spacing nulls on unit circle according to Tschebyscheff pattern. We also try to touch issues in implementing the array on FPGA. Key words: ULA, DBF, Tschebyscheff, FPGA.
Unique Application of Chebyshev Absorbers
The purpose of this paper is to report on the application of Chebyshev absorbers in the design of a multi use anechoic chamber. The requirement was for a chamber which allowed for evaluation of various wireless devices to be evaluated in a multi use chamber. The purpose of the chamber is to support multiple programs and allow for the evaluation of both complete handsets as well as individual components of the wireless devices. Due to the dual purpose applications that were to be evaluated in this chamber neither a standard” antenna range” nor a “classic wireless” chamber fit the bill. In order to optimize the use of this chamber a unique design was developed which incorporates the best of both classical chamber designs. To improve the low frequency response of the chamber a Chebyshev pattern was designed for chamber termination wall. Due to the short length of the chamber in comparison to the target length a Chebyshev pattern was designed for the specular patches on the sidewalls, floor and ceiling to improve the “off angle” performance of the chamber.
Coordinate System Plotting For Antenna Measurements
Antenna measurement data is collected over a surface as a function of position relative to the antenna. The data collection coordinate system directly affects how data is mapped to the surface: planar, cylindrical, spherical or other types. Far-field measurements are usually mapped or converted to spherical surfaces from which directivity, polarization and patterns are calculated and projected. Often the collected coordinate system is not the same as the final-mapped system, requiring special formulas for proper conversion. In addition, projecting this data in two and three-dimensional polar or rectangular plots presents other problems in interpreting data. This paper presents many of the most commonly encountered coordinate system formulas and shows how their mapping directly affects the interpretation of pattern and polarization data in an easily recognizable way.
Mission to MARS - In Search of Antenna Pattern Craters
Reflections in anechoic chambers can limit the performance and can often dominate all other error sources. NSI’s MARS technique (Mathematical Absorber Reflection Suppression) has been demonstrated to be a useful tool in the fight against unwanted reflections. MARS is a post-processing technique that involves analysis of the measured data and a special mode filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near field or far-field range. It has also been applied to extend the useful frequency range of microwave absorber down to lower frequencies. This paper will show typical improvements in pattern performance, and will show results of the MARS technique using data measured on numerous antennas.
Near-Field Spherical Scanning: Uncertainties In Test-Zone Field 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.
Free Space VSWR Method for Anechoic Chamber Electromagnetic Performance Evaluation
This paper gives a detailed account of free space Voltage Standing Wave Ratio (VSWR) method. We first review the formulations and terms commonly used in this method. We then discuss errors involved in its direction determination of extraneous signals, contrasting them among plane wave, spherical wave and specular reflection. We highlight issues relating to its application in anechoic chamber electromagnetic performance. Also discussed is the practice of data processing through analyzing a measured VSWR pattern.
Cross Polarization Uncertainty in Near-Field Probe Correction
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.
CIRCULAR POLARISED WIDE BAND FIELD PROBES
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.
MODELING ANTENNA PATTERN DISTORTION CAUSED BY SUPPORTING STRUCTURES
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
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.
A NEURAL NETWORK TECHNIQUE FOR FAULT DETECTION IN PLANAR ARRAYS USING RBF AND PNN ARCHITECTURES
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.
ANALYSIS, DESIGN, OPTIMIZATION AND IMPLEMENTATION OF A CIRCULARLY POLARIZED, X-BAND MICROSTRIP 2 X 2 SEQUENTIALLY ROTATED PHASED ANTENNA ARRAY
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.
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