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The polarization extraction in the phaseless near-field measurement is investigated. Sensing the antenna polarization based on the implementation of phase-retrieval methods like IFT (Iterative Fourier Technique) will not result to a unique solution. It is shown how a single extra point measurement can provide the complete vectorial representation of the field in a two-component representation. This means for the first time by the application of phaseless methods, one not only can get an understanding of the dominant polarization of the antenna in terms of linearity, ellipticity or circularity but also the true representation of the co- and cross polarized components in the far-field based on any definition (like Ludwig’s definitions). The applicability of the method is shown through a near-field measurement of a right-hand elliptically polarized antenna array in UCLA bi-polar near-field facility.
A full time domain characterization bench is realized in the CEA-LETI-Minatec anechoic chamber, to automatically derivate UWB antennas transfer function from waveform acquired by a fast sampling oscilloscope. Time domain measurement technique brings several advantages: faster and simpler measurements, out of band antenna behavior, intrinsic time windowing… Several time domain performance criteria are processed. A comparative method takes into account distortion due to the pulse generator and the test bench. Two different bands 0.3-2 GHz and 2-12 GHz are available. The comparison between frequency and time domain measurements shows excellent results (less than 0.3 dB on gain and 1° on phase) on the 2-12 GHz frequency band. Limitations of the proposed method are also addressed. The dynamic range is better than 35 dB thanks to averaging. Minimum bandwidth limit is evaluated to measure wideband and narrow band antennas.
The next generation of antennas will benefit from advanced instrumentation receivers capable of providing simultaneous analog and digital IF inputs, better TR pulse synchronization and high resolution pulse profiling. One such receiver uses a synergistic combination of a tightly coupled FPGA based beam controller, high performance analog digitizers, multiple FPGA based digital signal processors and a new mathematical programming environment. The FPGA signal processor provides direct digital downconversion, high resolution pulse processing and dynamically reconfigurable time and frequency gated matched filter signal integration. The signal processing functions are fully scriptable, providing spectral analysis, various other types of transform analysis, instantaneous demodulation, pulse characterization, noise estimation and more. Advanced mathematical tools combined with novel user interface technologies provide multiple intuitive views into the test setup, error analysis and measurement environment.
Space qualification of antennas imposes stringent RF testing to assure on-orbit reliability and environmental testing to assure the antennas can withstand launch and on-orbit conditions. The qualification testing requirements are reviewed for antenna systems. Specialized RF tests specific to satellite applications are described. Development recommendations for future testing are also described.
The dynamic range of a measurement system is typically evaluated in the frequency domain. However, for radar-cross-section (RCS) measurements, time processing of the frequency-domain data is often utilized to determine the temporal or spatial (down-range) location of responses. Dynamic range in the time domain is thus of considerable importance in determining what range of responses can be resolved and identified. While the coherent integration inherent in the pulse-compression process can increase the time-domain dynamic range beyond that of the frequency-domain, non-linearity in the measurement system leads to signal-dependent noise which, in turn, limits the time-domain dynamic range to a much smaller value. Thus, specification and characterization of time-domain dynamic range is critical for understanding the linearity requirements and the time-domain capability of the measurement system. This paper reviews design considerations, error sources, and measurement methods relevant to optimizing dynamic range in the time domain. Examples of time-domain measurements are included.
Conventional compact ranges use a reflector antenna’s near field to produce the plane wave illumination needed to measure a second antenna under test (AUT). The quasi-compact range described here uses a conventional reflector antenna at a greater range separation than conventional compact ranges, but still within the reflector’s near field. Its illumination allows the antenna evaluations at smaller range separations than the AUT’s far-field distance and allows modification of a current far-field range with a reflector range antenna to measure larger test articles than normally acceptable. This approach preserves many advantages of a standard compact range including reduced multipath and high measurement sensitivity that result from the collimated near field of the illuminating reflector antenna. Additionally, a conventional reflector antenna is used without requiring edge treatments. Experience with a four-foot prime focus parabola operating at 18 GHz illustrates this technique. The measured quiet zone fields compare favorably with calculated values using the GRASP codes. Likewise, measurements of a 20”-diameter offset reflector antenna compare favorably with GRASP results.
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.
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.
Method of moments (MoM) codes have become have become increasingly capable and accurate for predicting the radiation and scattering from structures with dimensions up to several tens of wavelengths. In particular, for simple structures like canonical shapes or antenna / RCS test fixtures, especially those with material treatments, the primary source of disagreement between measurements and predictions is often due to differences between the “as-designed” and “as-built” material parameters rather than to the underlying MoM code itself. This paper describes an algorithm that uses a MoM model combined with backscatter measurements to estimate the “as-built” materials parameters for the case where the treatments can be modeled using an equivalent boundary condition. The algorithm is a variant of the network model technique described in [1]-[3]. The paper presents a brief formulation of the network model materials characterization algorithm, along with numerical simulations of its performance for a simple canonical RCS shape using the CARLOS-3D™ MoM code [4]. The convergence properties of the algorithm are also discussed.
The use of characteristic modes or eigenmodes in arbi-trary electromagnetic geometries for a variety of ap-plications has a long history ([7], [8], [9]). This work introduces a means for numerically computing these modes over frequency in a Finite Element Boundary Integral (FE-BI) prediction code framework for arbi-trary patch antenna geometries. Manipulation of modes using material texturing is demonstrated as an effective means for adjusting lossless patch antenna performance. Mode visualization aids in understand-ing material texture requirements for a particular wideband optimization condition.
This paper shall discuss antenna range measurements performed upon a prototype Ultra Wide Band communication system. The measurements required the evaluation of both wideband RF pulses (5 MHz) and an active transmit antenna at the NUWC Fishers Island facility including the Mile Site Overwater Range. The measurement technique employed will be discussed along with choice of equipment, approach used for data collection and test results. Funding is provided by the Office of Naval Research.
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.
In the framework of the Antenna Centre of Excellence (ACE) of the European Union, a specific action is devoted to the development of a mapping database of international antenna measurement facilities, with the aim to share them for performing accurate antenna validations. During the ACE-2 activity (2006-2007), two kinds of measurement services have been developed and included in the mapping database. They are intended to give the opportunity for registered users to contact a list of selected institutes (Unified Request Form service) and to perform the benchmarking of their own measurement facilities (Benchmarking service). Both services are accessible through the Virtual Centre of Excellence (VCE) homepage (www.antennasvce.org) at the Measurement Facilities link.
Focused-beam measurement systems are commonly employed in material characterization measurements due to their inherent broadband capability. Calibration of this system is typically performed using a simple response calibration in conjunction with gating techniques to eliminate unwanted reflections. An undesirable artifact of this calibration technique is the extracted permittivity and permeability measurements can be highly dependent on the width and shape of the gate. This paper explores a three-short full two-port calibration technique which eliminates the need for gating. The two-port calibration consists of three independent short measurements in both the forward and reverse directions (i.e., S11 and S22), two isolation measurements (S21 and S12) and four empty measurements (S11, S21, S12, S22). Material parameter extraction measurements based upon this calibration technique were performed using both a low-frequency (0.5 - 2 GHz) and high-frequency (4 - 18 GHz) focused-beam system. Initial results show the technique’s viability and the dependency on accurate positioning of the shorts used in the calibration process and possible interaction between the sample and the sample holder.
Most measurement instruments being terminated by unbalanced ports, the measurement of a balanced antenna’s radiation characteristics is generally done using balanced to unbalanced transformers (baluns). These circuits are lossy, cumbersome and generally narrowband thus introducing added measurement imprecision. In this paper, we present a novel method for measuring differential antennas’ radiation characteristics by using traditional RF instrumentation, without the use of baluns. By regarding the differential antenna as a two port device, we can obtain the radiation characteristics of the differential mode from the measurement of the radiation characteristics and the scattering parameters of the single access fed two-port antenna. A theoretical study, based on the superposition principle, establishes equations that allow the passage from the single access feed mode to the differential mode. This method is validated by comparing the measurement results with the simulation results of a canonical differential antenna, a half-wave dipole antenna printed on a dielectric substrate.
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.
Electromagnetic compatibility is a critical concern in the automotive industry, as customer safety depends on the reliability of vehicle electronics systems. The proximity of high current switching loads to sensitive vehicle electronics within the typical automobile results in serious EMC problems. Currently, passive EMI filters are used extensively as a means to reduce the conducted (and resulting radiated) emissions from interference-causing automotive devices. However, existing high current EMI filters incorporate expensive passive components. This paper investigates the application of active EMI filtering to high current switched loads typical of automobile applications. Several active EMI filtering topologies are discussed, and an active capacitance filter design is introduced. The measured noise reduction performance of two active EMI filter implementations presented, along with notes on measurement techniques, active filter viability, and motor drive design.
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.
An important aspect of antenna measurements and numerical modeling, both for research activities and for industrial use, is the possibility to exchange and compare data from different measurements systems or modeling tools. The primary approach is the exchange of data in files. The need for a common way to describe physical objects and quantities involved in measurements and electromagnetic modeling of antennas has been discussed by many in the recent years [1]. This paper reports on the development of the Electromagnetic Data eXchange language (EDX). This joint Antenna Center of Excellence (ACE) and European Space Agency (ESA) activity on a common language for data exchange has yielded data dictionaries covering most essential types of data that are communicated among electromagnetic software tools. Although the joint activity is focusing on numerical modeling tools the field dictionary is a subset of this activity and of particular interest also to the antenna measurements community. The concept of Data Domain modeling and Data Dictionaries are first discussed. Then, the language developed to describe and record data is introduced, followed by a short illustration of the Electromagnetic Data Interface library and of the Translator, a utility that automatically translates Data Dictionaries definitions into program code to access the data. Finally the application of EDX as common data format in an international facility comparison campaign is discussed.
OTA performance testing of active wireless devices has become an important part of evaluation and certification criteria. Existing test methodologies are extensions of traditional antenna pattern measurement techniques. A critical assumption of these methods is that the device under test utilizes a single active antenna. Advances in wireless technology continue to incorporate more complex antenna systems, starting with simple switching diversity and progressing to more advanced concepts such as adaptive arrays (smart antennas) and multiple-input multiple-output (MIMO) technologies. These technologies combine multiple antennas with various software algorithms that can dynamically change the behavior of the antennas during the test, negating the assumption that each position and polarization of an antenna pattern measurement represents a single component of the same complex field vector. In addition, MIMO technologies rely on the multipath interaction and spatial relationship between multiple sets of antennas. An anechoic chamber with a single measurement antenna cannot simulate the environment necessary to evaluate the performance of a MIMO system. New measurement methods and system technologies are needed to properly evaluate these technologies. This presentation will discuss the issues and evaluate possible solutions.