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Abstract—The 3D reconstruction algorithm of DIATOOL is applied to the prototype feed array of the BIOMASS synthetic aperture radar, recently measured at the DTU-ESA Spherical Near-Field Antenna Test Facility in Denmark. Careful analysis of the measured feed array data had shown that the test support frame of the array had a significant influence on the measured feed pattern. The 3D reconstruction and further post-processing is therefore applied both to the feed array measured data, and a set of simulated data generated by the GRASP software which replicate the series of measurements. The results of the diagnostics and the corresponding improvement of the feed array field obtained by removal of the undesired effect of the frame are presented and discussed.
Abstract—This paper describes the approach of solving the electromagnetic scattered field of semicircular array using numerical method (MoM). Considering the variable number of elements, uniform radius of element, element spacing, azimuth plane as inputs of the numerical model and distributed complex current coefficients, scattered E-field are extracted as the outputs. The desired input and output to the artificial neural network are pattern values and number of elements respectively. The purpose of applying neural network is to change from lengthy analysis and design cycles required to develop high performance systems to very short product development times. The work allows the designer to achieve any desired values of pattern without requiring the usage of more elements. The generated data is divided in to training and test sets, for observing the error behavior with the progress of training. It is proved that the network gives a high success rate.
Abstract—Mutual coupling is a major issue in phased array antennas, especially when steering the beam to low angles, causing bandwidth and gain reduction. Such coupling arises from the presence of adjacent elements that produce scattering and absorption effects during low-angle beam steering. The scattering effect comprises of structure-mode scattering and antenna-mode scattering. The absorption effect happens when the EM energy received by an adjacent element is dissipated into the system. In addition, lattice scattering from the periodic structures of antenna elements and feed lines in phased arrays also produces undesired scattering modes that limit the frequency upper bound and maximum scan angles.
Abstract— A non-destructive method for the characterization of sheet material in the VHF/UHF range using a 3 inch square device is presented. The device is a linearly polarized open resonating probe that measures sheet admittance. The probe can be tuned to a given resonant frequency and the sensitivity can be adjusted for measuring ranges of sheet admittance.
Abstract—this paper will cover the key design attributes of a high-speed frequency switching synthesizer. It will highlight the importance of a stable reference and then go on to examine the different types of commercial high speed synthesis approaches, including advantages and disadvantages in terms of speed, frequency range, phase noise and part count. We will then explore a new hybrid approach to synthesis utilizing a lower part count commercial approach.
Abstract— Attempts to produce robust, objective, and quantitative measures of similarity between antenna pattern data sets using statistical methods have been widely reported in the open literature [1, 2]. Hitherto, such techniques have primarily been restricted to the purposes of comparing two or more images as a means in itself. However, no measurement can be considered to be completely free from error, and as such each data set inevitably contains an associated uncertainty. Therefore, in contrast to previous work, this paper discusses and extends some commonly used comparison techniques to take account of the finite, non-zero, measurement uncertainties that complicate the comparison process. Results are presented that illustrate the effectiveness of the comparison method and conclusions drawn.
Abstract—High absorption rate due to the field enhancement at the terminals of a bowtie nanoantenna is utilized to develop a nano-meter thick and highly efficient thermophotovoltaic (TPV) system. A nano-meter size block of Indium Gallium Arsenide Antimonide (InGaAsSb), a low bandgap semiconductor (Eg = 0.52 eV) is used for infrared (IR) energy absorption and also used as an antenna load. At the desired frequency (180THz) where the maximum quantum efficiency of the dispersive InGaAsSb material is observed, InGaAsSb load presents a high resistance and capacitance. For conjugate impedance matching, a high impedance plasmonic bowtie nanoantenna operated at its anti-resonance mode is developed and an inductive nano transmission line stub is used to compensate for the high capacitance of InGaAsSb load. The bowtie nanoantenna loaded with 30 cubic nanometer InGaAsSb block shows 23.5 of the field enhancement which is the ratio between field intensity at the antenna’s terminals and the incident field intensity. The infinite array of the bowtie nanoantenna backed by a metallic reflector is shown to absorb ~ 95% of the incident power at the desired band. A nano-meter thin TPV system using the bowtie nanoantenna array can show 1.5 times higher efficient than the bulk InGaAsSb TPV cell.
Abstract — Nearfield Systems Inc. (NSI) has been contracted by the Department of Electrical and Computer Engineering of the University of Waterloo to install a unique antenna test system with multiple configurations allowing it to characterize a wide variety of antenna types over a very wide bandwidth. The system employs a total of 10 positional axes to allow near-field and far-field testing in various modes of operation with great flexibility. A 4 m x 4 m planar near-field (PNF) scanner is used for testing directive antennas operating at frequencies up to 110 GHz with laser interferometer position feedback providing dynamic probe position correction. The PNF’s Y-axis can also be used for cylindrical near-field (CNF) testing applications when paired with a floor mounted azimuth rotation stage. A single phi-over-theta positioner permits both spherical near-field (SNF) testing from L-band to W-band and far-field testing down to 0.2 GHz. This positioner is installed on a translation stage allowing 1.8 m of Z-axis travel to adjust the probe-to-AUT separation. In addition, a theta-over-phi swing arm SNF system is available for testing large, gravitationally sensitive antennas that may be easily installed on a floor mounted rotation stage. In order to ensure system and personnel safety, a complex interlock system was designed to reduce the risk of mechanical interference and ease the transition from one configuration to another. The system installation and validation was completed in March 2013. We believe that this facility is unique in that it encompasses all commonly used near-field configurations within one chamber. It therefore provides a perfect environment for the training of young engineers and could potentially form the baseline of future academic test facilities. This paper will outline the technical specifications of the scanner and discuss the recommended applications for each configuration. It will also describe the details of the safety interlock system.
Abstract— Several gain measurement techniques exist for near-field antenna ranges. These include Comparison-gain, Direct-gain and Three-antenna gain methods. Each technique has its own unique advantages and disadvantages in terms of accuracy, cost and measurement time. Range operators must understand the differences between these techniques in order to properly configure their test system to best suit their requirements. This paper surveys each of the gain techniques and identifies the relative advantages of each. As part of the survey, all three techniques were performed on three types of near-field antenna measurement systems: Planar, Cylindrical and Spherical. The results of this paper provide the reader with a practical understanding of each technique, the formulas required, and real-world examples for the trade-offs needed to outfit a range for fast and accurate gain measurements while balancing cost and schedule.
Abstract -We propose a method of utilizing near-field spherical measurements so as to obtain the back lobes of high gain antennas without sacrificing the accuracy of the far-field, high-gain main lobe prediction. While a spherical scan is perfectly adequate to gauge the relatively broad back lobes, it is in general inadequate to capture the required details of a sharp forward peak. We overcome this difficulty through recourse to our Field Mapping Algorithm (FMA), which latter allows us to assemble planar near-field data based upon the spherical measurements actually acquired. In particular, planar data of this sort on the forward, main-lobe side offers the standard route to predicting the desired, high-gain, far-field pattern. Our spherical-to-planar FMA near-field data manufacture showed excellent agreement with direct planar near-field measurements for a slot array antenna, each one of them, naturally, underlying a common, far-field, high-gain pattern.
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.