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Abstract—Identification and separation of electromagnetic mixed sources within a narrow bandwidth are required in various applications. The Independent component analysis (ICA) is here applied in the separation of three independents electromagnetic sources. An efficient algorithm and a measurement setup are proposed for capturing and separating mixed signals. Three uncorrelated microwave signal generators are used to provide multiple independent wireless sources (transmitters). The receivers are high gain broadband antenna placed in the azimuthal plane and randomly positioned. Here the signals are CW waves with a very small frequency difference (.F = 0.1%). In the present analysis the environment noise is also taken into account as an additional source. The estimated signals by ICA and original measured ones have good agreement. Considering the complexity of the measurement setup and the proximity between the frequencies of signal sources the proposed algorithm is suitable for applications in Jamming treatment and Direction of Arrival.
Compensated compact ranges offer accurate testing techniques for large devices under test. The quiet zone field performance is affected by diffracted field components from the sub and main reflector edges even though they are equipped with serrations in order to reduce this effect. The size, shape, and alignment of the serrations have a strong influence on the range performance and are important design parameters. For performance estimation and optimization, detailed EM simulation models are required. Integral equation methods like the Method of Moments (MoM) with Multilevel Fast Multipole (MLFMM) acceleration promise accurate simulation results. However, the memory requirements limit simulations nowadays to lower frequencies due to the electrical size of the compact range reflectors. For example, the main reflector of Astrium's Compensated Compact Range CCR 120/100 including serrations is 1860 ? by 1600 ? in size at 40 GHz. Asymptotic methods are suitable for objects of this size, however, the accuracy has to be investigated and is related to the degree of detail in the model. A detailed simulation model based on the Physical Optics (PO) / Physical Theory of Diffraction (PTD) method is developed in GRASP. Each serration is realized as an individual scatterer and can thus be modeled with arbitrary shape and orientation. Different modeling techniques have been applied in order to realize an accurate simulation model with acceptable runtime. In this paper, the simulation model will be described in detail and a comparison of the quiet zone fields will be drawn with the MoM / MLFMM tool Feko as well as with quiet zone probing measurements.
The ground based, Automatic Identification System (AIS) is a coastal tracking and messaging system used by vessels for maritime traffic monitoring purposes. The European SAT-AIS initiative aims at providing a space-based complementary system to extend the range of the existing AIS system to high seas via a satellite constellation in VHF band. In the course of the AISMAN development activity a miniaturized five element antenna array at 156/162 MHz, has been designed, manufactured and tested on a representative satellite mock-up [1]. The verification testing at satellite mock-up level has been performed in a hemispherical spherical near field antenna test range of Renault in Aubevoye, France [2]-[3]. Due to the scan truncation and the room scattering at VHF frequencies, advanced post processing based on the Equivalent Current expansion technique has been applied in the testing. This paper discuss the post processing issues and the findings of the verification testing.
In this communication, the experimental verification of a probe compensated near-field - far-field (NF-FF) transformation with spherical spiral scanning particularly suitable for elongated antennas is provided. It is based on a nonredundant sampling representation of the voltage measured by the probe, obtained by using the unified theory of spiral scans for nonspherical antennas and adopting a cylinder ended in two half-spheres for modelling long antennas. Its main characteristic is to allow a remarkable reduction of the measurement time due to the use of continuous and synchronized movements of the positioning systems and to the reduced number of required NF measurements. In fact, the NF data needed by the classical NF-FF transformation with spherical scanning are efficiently and accurately reconstructed from those acquired along the spiral, by employing an optimal sampling interpolation formula. Some experimental results, obtained at the Antenna Characterization Lab of the University of Salerno and assessing the effectiveness of such a NF-FF transformation technique, are presented.
Plasma antennas use partially or fully ionized gas as a conductor instead of metal. Plasma antennas can perform as metal antennas do but with reconfiguration, lower thermal noise at the higher frequencies, and lower side lobes in some experiments. At the higher frequencies, plasma antennas have lower thermal noise than metal antennas and the thermal noise of plasma antennas decreases with the operating frequency of the plasma antenna making them ideal for satellite antennas. Plasma feeds such as plasma waveguides and plasma co-axial cables have been built by Haleakala Research and Development, Inc., Inc. A satellite plasma antenna pointed at the sky with plasma feeds and a low noise receiver can create a low noise plasma antenna system with a consequence of higher data rates. Some experiments show that plasma antennas have smaller side lobes than metal antennas. Plasma satellite antennas can be made conformal with a surface and give the performance of a parabolic dish antenna. This is true because beam steering and focusing can be done by varying the plasma density from one tube of plasma compared to the next. With this design, plasma satellite antennas can be operated in the reflective or refractive mode. Once computerized, the plasma antenna becomes a versatile smart antenna. High powered plasma antennas have been built as a possible directed energy weapon. Plasma reflector antennas, plasma FM/AM radio antennas, various plasma transmitting antennas, and smart plasma antenna has been built. Alexeff and Anderson and [1]-[2] Anderson and Alexeff [3] have done theory, experiments, and have built prototype plasma antennas. Anderson
This communication deals with the experimental validation of an efficient near-field - far-field (NF-FF) transformation using the planar wide-mesh scanning. Such a scanning technique is so named, since the sample grid is characterized by meshes wider and wider when going away from the center, and makes possible to lower the number of needed measurements, as well as the time required for the data acquisition when dealing with quasi-planar antennas. It relies on the use of the nonredundant sampling representation of electromagnetic fields based on the use of a very flexible modelling of the antenna under test, formed by two circular "bowls" with the same aperture diameter but eventually different bending radii. A two-dimensional optimal sampling interpolation formula allows the reconstruction of the NF data at any point on the measurement plane and, in particular, at those required by the classical NF-FF transformation with the conventional plane-rectangular scanning. The measurements, performed at the planar NF facility of the antenna characterization laboratories of Selex ES, have confirmed the effectiveness of this nonconventional scanning, also from the experimental viewpoint.
In this study, a novel and compact microstrip-fed slot antenna, which has a dual-band resonance characteristic, is proposed for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The proposed antenna has a simple geometry. It has a microstrip feed line on one side and a ground plane having simple slots on the other side of the substrate. The prototype is fabricated by using mechanical mill-etching technique on a 1.27 mm thick RT/duroid 6006 substrate with the relative permittivity of 6.15, and a loss tangent of 0.0027. The return loss (dB) characteristics of the proposed antennas are measured. The results show that the antenna can provide dual impedance bandwidths of 180 MHz centered at 2.44 GHz, 200 MHz centered at 5.56 GHz, which covers the 2.4 GHz (2400-2484 MHz) WLAN band, 2.3 GHz (2300-2500 MHz) and 5.5 GHz (5250-5850 MHz) WiMAX bands. A good agreement between the results of the numerical and experimental studies has been observed. Consequently, the proposed antenna with simple structure and dual-band frequency response can be suitable for WLAN/WiMAX applications.
A variety of measurement applications in conjunction with the spherical near-field antenna test range at National Taiwan University of Science and Technology (Taiwan Tech) using an NSI (Nearfield Systems Inc.) made 700S-90 spherical near-field scanner built in a shielded anechoic test chamber environment has been implemented beyond the typical application scope for spherical near-field antenna test ranges. Thanks to the low RF perturbation nature of NSI-700S-90 spherical scanner hardware architecture in mobile wireless communication frequency ranges, not only for being a proven solution used in certified CTIA OTA test range for lowdirectional wireless mobile devices OTA and antenna performance evaluation, the system while incorporated with the special chamber configuration at Taiwan Tech is enhanced to be also capable of performing measurement scenarios associated with evaluating radio frequency identification (RFID) 3D readable range performance. This paper will present the abovementioned test range at Taiwan Tech for performing RFID static testing scenarios. Some measurement parameters in realistic DUT packaged modes will be demonstrated and analyzed with 3D graphical outputs of tag readable range. Various tests using commercial RFID tags for system validation purpose through measuring the tag readable range characteristics of the associated scenarios will be presented along with discussions and results on the method for testing tags with either the forward or reverse links dominated being included as additional supports of system applicability.
High performance materials are often used in extreme temperature environments to enable advanced microwave frequency designs in both commercial and military applications. Accurate knowledge of microwave material properties as a function of temperature is key to ensure product or mission success. Robust designs must accommodate intrinsic material property changes with temperature or else the design may become unstable or fail. Researchers at the Georgia Tech Research Institute have recently developed a refined methodology suitable for high temperature testing of microwave materials based on the ASTM D2520 perturbation measurement technique. This paper presents the system design and examines the measured system response as a function of temperature to study the relationship of system dynamics and measurement uncertainty. Lessons learned from laboratory experiments are provided and measured data for several commonly available materials is presented to illustrate typical system performance for medium and low loss materials. The paper concludes with suggestions for further system improvements.
Radar sensor working at 76-77GHz band, because of its long detection range, high resolution and excellent performance in different weather and illumination conditions, has been used to develop on-road pedestrian collision avoidance system. Therefore, studying the pedestrian radar scattering features is important to develop reliable on-road pedestrian detection algorithm. In this paper, we first discuss the measurement setup requirement at 76-77GHz to obtain reliable radar cross section (RCS) data of human subjects. Then the RCS pattern of human subjects with different postures and different body features are measured and studied. The observed radar features could be further developed into stable radar signatures to improve the pedestrian identification algorithm.
The Fast Irregular Antenna Field Transformation Algorithm (FIAFTA) determines the equivalent sources of an antenna under test (AUT) from arbitrarily located sampling points of the antenna field. The application of Fast Multipole Method (FMM) principles to the formulation of the forward operator shows that the influence of the measurement probe is fully corrected based on its far-field radiation pattern. For antenna diagnostic purposes, equivalent surface current densities represent the unknown equivalent AUT sources. However, the FMM gives the possibility to settle the unknowns of the inverse problem in the ^k-space domain. The expansion of the appearing plane wave spectra in spherical harmonics leads to a compact representation of the equivalent plane wave sources. The forward operator is evaluated in a multilevel fashion similar to the Multilevel Fast Multipole Method (MLFMM). This enables to incorporate a priori knowledge about the geometry of the AUT in the antenna model by placing nonempty FMM boxes where sources are assumed.
Two filtering applications using the Fourier Transform of frequency diverse (chirp) data into the range/time domain are demonstrated. First, a Zero Doppler Clutter (ZDC) estimate acquired by averaging in the frequency domain is optimized by pre-filtering in the range domain. By suppressing information based on location and/or return value prior to inverse transforming back to the frequency domain, non-zero Doppler scatterer information can be omitted from the ZDC estimate prior to averaging. Second, by considering the phase difference between range bins of adjacent samples, high-doppler artifacts can be identified and removed in the range domain. Additional rules based on range domain information are used to further refine the filtering. The test case for high-doppler removal is an ISAR scenario with flying insects moving much faster than the rotating speculars of the target scene.
A diagnostic technique was published over 20 years ago on imaging compact-range reflectors by focusing plane-polar field-probe data. At that time, only synthesized data had been evaluated. Since then, a few reflectors have exhibited performance lower than expected, and this technique has been successfully employed to improve that performance based on their measured data. This paper reviews the technique and discusses the results of processing those measured data sets. The technique produces an image of the estimated field amplitudes at the reflector surface that do not contribute to the desired quiet-zone plane wave. Point sources, line sources, and deformations over an area have all been successfully identified, often outside the projected circular boundary of the field-probe data. All measurements to date have used very coarse angular spacing with acceptable degradation in image quality.
There are several applications in which knowledge of the location of the phase center of an antenna, and its twodimensional variation, is an important feature of its use. A simple example occurs when a broad-beam antenna is used as a feed for a reflector, where the center of the spherical phase fronts should always lie at the focal point of the paraboloidal surface. Here, the ability to determine the phase center of the feed from knowledge of its far-field phase/amplitude pattern is critical to the reflector's design. Previously published methods process a single cut of data at a time, yielding 2D lateral and longitudinal phase-center offsets. Eand H-plane cuts are thus processed separately, and will, in general, yield different answers for the longitudinal offset. The technique presented here can process either one line cut at a time or a full Theta-Phi raster. In addition, multiple frequencies can be processed to determine the average 3D phase-center offset. The technique can merely report the phase-center location, or it can also adjust the measured phases to relocate the origin to the computed phase center. Example results from measured data on multiple antenna types are presented.
Antenna test engineers are faced with testing increasingly complex antenna systems, one of these being the AESA (Active Electronically Steered Array) antennas used for cell communications, jammers, and radars. Often these antennas have integrated electronics and RF components that are an intricate part of the antenna, and as a result must be tested with the waveforms generated by the antenna itself. One cannot simply inject an unmodulated continuous wave signal. These antennas require new measurement techniques which are compatible with their broadband waveforms. The reference channel of a measurement receiver can be used to collapse the spectrum of the modulated signal into a single CW measurement. Done properly all the energy in the signal is captured with noise and interference being dispersed, resulting in no loss of DR (dynamic range) over a CW measurement. A receiver employing this technique can capture all the energy in modulated and pulsed signals wielding wide dynamic range measurements. Phased locked loops (PLL) are not used as they can preclude such measurements. A measurement receiver that uses a digital correlator to collapse the spectrum of modulated and pulsed signals will be presented. This paper will describe the technique used to do this and show measured results on example broadband signals.
More complex antennas with higher transmit power levels are being tested in compact range environments. AESA's and other phased array antennas can transmit significant power levels from a relatively small volume. Without consideration of the impact of the transmitted power levels for a given test article, human and facility safety could be at risk. This paper addresses designing a test chamber in light of these power handling considerations for high power antennas on two fronts: 1) A methodology is presented to determine the power levels seen by surfaces in the chamber that are covered with absorber material and 2) Calculating the power levels seen at the compact range feed due to the focusing effect of the compact range itself. A test case is presented to show the application of the methods.
Compact range measurement facilities have been used successfully for many years to characterize antenna performance as well as radar signature. This paper investigates strategies for improving compact range measurement accuracy by mitigating errors associated with ground reflections inherent in most range designs. A methodology is developed for strategically modifying, or patterning, the surface between the range source antenna and the reflector to reduce error terms, thereby increasing measurement accuracy. Candidate patterns were evaluated using a full-wave computational finite-difference time-domain (FDTD) model at VHF/UHF frequencies to determine baseline performance and develop trade rules for more advanced designs. Physical optics (PO) models were used to analyze the final design at the frequencies of interest.
Multi Input Multi Output (MIMO) antenna systems are needed to meet the increasing demands of users in wireless systems. MIMO technology has been used to improve the capacity of wireless systems; however, designers have faced challenges to reduce antenna-size and increase the isolation between the antennas in MIMO systems. In this paper, a compact MIMO antenna array platform is proposed for LTE MIMO and Handset applications. The proposed array was designed to operate at the 2.6GHz Long-Term Evolution (LTE) band for wireless communication systems. The proposed array consists of four compact patch antennas on a dielectric substrate with total dimension of 12.5x6.25x1.27mm3. Modification of the ground plane along with the systematic placement and orientation of the antenna elements on top of the substrate play a key role to reduce mutual coupling, which normally degrades the performance of MIMO antenna arrays. The performance of this MIMO antenna array has been evaluated through simulations and measurements of the scattering parameters [S] and radiation patterns. The minimum gain of a single antenna with all the other three elements terminated in 50O loads is 1.49dBi, while the isolation is over 25dB between all the MIMO antennas located in the array structure. The measured results suggest that the antenna is well suited for LTE MIMO applications as well as handset antennas.
Measurement of rotating components in cluttered, high-temperature jet engine environments is challenging for conventional wired sensors. We have developed a passive wireless sensing (PaWS) system to measure strain, temperature, and other parameters in high-temperature, harsh environments such as jet engines. PaWS utilizes piezoelectric surface acoustic wave (SAW) devices which are conformal, require no batteries, and can operate at temperatures up to 300 C. PaWS were fabricated to operate at frequencies between 2.4 and 2.5 GHz and installed on test specimens representative of engine components. These specimens underwent strain of over 4000 microstrain at ambient and elevated temperatures. A miniature patch antenna was developed to incorporate a package whose total dimensions are smaller than 25x30x2 mm. An RF interrogation system (RFIS) was developed for simultaneous measurement of multiple sensors. Post-processing software has been developed to convert data from multiple sensors into calibrated strain values. Calibrated measurements were made with the RFIS using both wired and wireless methods in a laboratory and in a jet engine test cell. Sensor measurements
A new material validation and verification standard is designed to imitate the behavior of a lossy dielectric absorber. This standard is constructed from well-characterized, low-loss materials in a manner that ensures manufacturing repeatability. The performance of this standard is verified with S-parameter and permittivity measurements in a free space focused beam system and with finite difference time domain simulations. A sensitivity analysis, based on a series of simulations, is presented to quantify the uncertainty in the measured S-parameters due to dimensional and alignment variations from the ideal design values.