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Abstract— This paper presents a two-layer mushroom-like reactive impedance surface (RIS) and patch antenna miniaturization with potential application in matel-backed antennas. RIS, known as meta-substrate, has shown the ability to miniaturize printed antennas with omni-directional radiation pattern, when served as the substrate for the antenna [11]. However, the area of conventional RIS substrate usually has to much larger than that of miniaturized antenna, since the cell’s dimension is comparable with the antenna, even using a high dielectric constant. Here an RIS with very small unit cell dimensions (cell area reduction by 95% compared to traditional RIS) is proposed and utilized to design a miniaturized antenna over the RIS substrate with the same size as the antenna itself. A microstrip transmission line over the RIS substrate model is studied and shown to have a high propagation constant near the resonant frequencies of the RIS. This model is used to predict the much reduced resonant frequency of patch antennas over the RIS. Applying the two-layer RIS substrate and an optimized miniaturized patch antenna topology, several UHF band patch antennas working around 400MHz have been designed and fabricated. Using this approach a miniaturized antenna with dimensions .0/11.4× .0/11.4 × .0/74, including the RIS substrate is developed.
Abstract— The extrapolation measurement technique has been used with the three antenna method for more than 40 years, to determine absolute antenna gain and polarization. The critical part of the extrapolation technique is an insertion loss measurement that is done repeatedly as two antennas are physically separated. When the two antennas are close together, they may unintentionally interact and reflect signals between the antennas. Part of the data processing procedure requires a subjective determination about the distance at which the antennas are far enough apart that they are no longer interacting with each other. In this paper, we present an alternative method with the goal of providing a more objective way to determine when the antennas are no longer interacting with each other. The proposed method relies on using the phase data obtained from the insertion loss measurement.
Abstract— Any radiating system consisting of a small radiating device positioned somewhere on a larger scattering structure can be completely characterized by different antenna measurement technologies [1]. A practical limit to the full characterization, by means of antenna measurements, is imposed by the available measurement equipment on the maximum allowable physical dimensions and/or mass of the radiating system. A viable solution to characterize arbitrarily large systems is to apply a domain decomposition technique in which only the part of the system containing the actual antenna is determined by measurements. The remaining part of the entire system can then be determined by numerical modeling [2]-[9]. A well-known approach, based on a spherical wave expansion technique, is considered a highly efficient domain decomposition technique [10]. However, this method is only valid when all of the scattering objects are located outside the minimum sphere surrounding the source. A new domain decomposition technique has been presented based on an equivalent current expansion (EQC) [11]-[12]. The advantage of this approach is the freedom to have the source mounted more freely in any position wrt the large scattering structure. This paper presents the EQC technique including the results of a validation campaign in which a small source antennas is mounted on an electrically large satellite breadboard. The EQC approach is compared with a direct measurement of the full system.
This paper will describe newly developed mechanical and electrical alignment techniques for use with plane-polar near-field test systems. A simulation of common plane-polar alignment errors will illustrate, and quantify, the alignment accuracy tolerances required to yield high quality far-field data, as well as bounding the impact of highly repeatable systematic alignment errors. The new plane-polar electrical alignment technique comprises an adaptation of the existing, widely used, spherical near-field electrical alignment procedure [8] and can be used on small, and large, plane-polar near-field antenna test systems.
This paper will discuss a highly customizable and integrated waveform generator (WFG) subsystem used to coordinate the phased array test process. The WFG subsystem is an automated digital pattern generator that orchestrates the command and triggering interface between the NSI measurement system and a phased array beam steering computer. The WFG subsystem is controlled directly by the NSI 2000 software and allows the test designer to select and generate a sequence of up to sixteen unique synchronized timing waveforms. Test scenarios, results and data for the WFG subsystem will be presented along with plots showing the key timing characteristics of the system.
Abstract—In this paper, a bespoke, fully automated anechoic chamber is discussed and the positioner effects on measurements of antennas are investigated. Antenna measurements performed in this robust anechoic chamber are undertaken in two parts namely; acquisition and analysis, with the aid of low cost positioner hardware and low level software language. In order to get a measure of validation of our measuring system only the important parts of the chamber have been modelled and measurements carried out using a balanced sleeved dipole and a microstrip patch antenna, which have well-known characteristics. It was noticed from the results that the positioner, exaggerates the performance of some antennas particularly small antennas without a ground plane at certain distances and frequencies. The positioner has a tendency to reflect energy, and distort radiation patterns; hence, it was important to ensure that such antennas are placed at an appropriate distance away from the positioner. The comparison between the simulated and measured efficiency of a balanced sleeved dipole is good. The predicted and measured peak efficiency at 2.49 GHz was 95% and 94% respectively. It was also observed that the variability in efficiency measurements was less than 3% for measurements with different angular resolutions on different days.
Abstract— Electromagnetic properties of aircraft and missile skins have a large effect on radar cross sections and determine the level of stealth that is achieved over the various RF bands currently in use. RF absorption, reflection, and propagation along the skin surface all serve as important measures of the electromagnetic performance of the coated surfaces. Non-invasive probing of the electromagnetic field just above the propagating wave at multiple spots along the propagation direction can be used to determine and measure wave propagation parameters, including effective RF index, loss per length, wave impedance, and frequency dependent material properties of the coatings. Wide-band photonic electric field sensors have been demonstrated for probing of dielectric layers by measuring the traveling waves along the coated aircraft surface. The photonic E-field sensors are extremely linear and produce an exact real time analog RF representation of the electric field, including phase information. These ultra-wideband (UWB) photonic RF sensors are very small and contain negligible metal content, allowing them to be placed at close proximity without perturbing the RF surface waves. This is very important in accurately characterizing highly damped surface waves on absorber layers. This paper discusses the linearity, bandwidth, polarization, and sensitivity of the unique UWB photonic E-field sensor design. Experimental results are presented on surface-wave characterization measurements using these sensors.
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.
Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction
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.