Near-field Scan Research Articles

A Prescan Method to Accelerate Near-Field Scan Immunity Tests

A Prescan Method to Accelerate Near-Field Scan Immunity Tests

A Simple and Economical System for Automatic Near-Field Scanning for Power Electronics Converters

Electromagnetic compatibility issues must be considered from the early steps in the design of electronic devices. A specific topic is the near-field emission generated by the device due to the traces on a printed circuit board and the specific routing. The analysis of near-field emission is essential to detect potential electromagnetic interference with nearby devices. This problem is crucial in high power density applications. Therefore, especially in these applications, it is necessary to optimize the circuit and the layout to minimize the generated noise. The design and construction of systems able to scan volumes to determine the spatial distribution of electrical E and/or magnetic B fields in the near-field region of a device under test is a very complex process. The realization of equipment that explores a given surface at a given distance from the device is easier. The main purpose of this paper is to show how it is possible to build a cheap two-dimensional scanner, starting from simple hardware not explicitly designed for near-field scan operations. The presented firmware and software solution can map, with good accuracy, the spatial distribution of fields B and E on a fixed plan close to the board. Finally, the developed system has been used in a GaN-based bi-directional DC/DC Converter.

A Methodology for Predicting Improved Dipole Source Configurations From Near-Field Scan Data

Equivalent sources found from near-electric and magnetic field scans are often used to predict and solve interference problems. While there are many ways to represent the source, the user lacks the ability to determine which of the many possible source configurations is more likely to represent the “true” source, and thus accurately represent field data outside the measurement area and in the presence of typical measurement errors. A methodology is proposed for estimating which of many possible dipole source representations of near-field scan data are likely to give better estimates of fields outside the measurement scan plane when utilizing imperfect measurement data. A quality metric for determining better configurations is proposed, which utilizes the statistical variation of the global difference measure (GDM) in the predicted and measured fields. Equivalent sources are estimated when adding noise to measurement data, and prediction statistics are generated for multiple instantiations of measured noise. Results demonstrate that the better configurations minimize the average plus standard deviation of the GDM. The ability of the technique to identify robust source configurations was tested when measurements were subject to additive measurement noise, cross-field coupling, and systematic errors in probe position, and was evaluated based on its ability to predict fields at points above and to the side of the measurement plane. The method consistently identified better source configurations using both simulated and measured data.

Dipole-Moment-Based Reciprocity for Practical Desensitization Identification and Mitigation

Radio frequency interference can degrade the receiving sensitivity of antennas. The interference is usually caused by certain coupling structures, such as layouts without adequate grounding for the radio frequency signal return path. Those structures can be modeled as a set of equivalent dipole moments when they are electrically small. Herein, the dipole moment model-based coupling framework is applied to a practical cellphone design case to devise an engineering solution. The coupling framework incorporates dipole moments as radiation sources and a coupling model based on the reciprocity theorem. Unfortunately, near-field scan probes often lack access to all locations, owing to the complex phone platform structure. A combined measurement-simulation method is used to obtain the field quantities lacking direct access to measurements. The dipole-moment-based coupling framework helps estimate the couplings from different noise sources individually. Thus, the priority of solving for better layout designs can be determined according to the coupling estimations. Furthermore, the physics associated with the reconstructed dipole moment can provide insights and suggest possible mitigation methods. Several practical mitigation methods are discussed, including the suppression of the dominant noise source (reducing/cancelling the radiation or suppressing the specific noise spectrum) and the coupling path to the victim antenna.

Near-Field Angular Scan Enhancement of Antenna Arrays Using Metasurfaces

In this publication, we continue our previous work on extending the angular scan range of phased arrays using metasurfaces. We consider in detail scan enhancement using a single metasurface lens in the near-field of a source and provide analytical expressions for source excitation to obtain a desired beam. We show that such a device suffers from the same directivity degradation as in the case of far-field lens placement. Moreover, we discuss in detail that this approach has limitations, and one cannot place the lens arbitrarily close to the source array. We then propose a two-lens near-field scan enhancer which is not subject to the same limitations, although still subject to the same directivity degradation. Finally, we propose a binary metasurface concept which theoretically achieves desired scan enhancement without directivity degradation. Some theoretical claims are then verified via full-field simulations.

Impact of the voltage and frequency of a pulse signal applied to a toroidal coil on near magnetic field measurements

In power electronic systems, electromagnetic radiation of the near field is detrimental because it generates electromagnetic interference in static converters ultimately leading to the degradation of the EMC filter performance. This paper presents an experimental investigation into magnetic radiation generated by magnetic components, specifically toroidal inductors, in the time domain (TD) using an oscilloscope and in the frequency domain (FD) via a spectrum analyzer. The method employed to quantify the magnetic field is the near field scan (NFS) using magnetic probes. This approach enables us to identify the areas with the highest magnetic field emissions from the toroidal inductance across its three components (HX, HY, HZ). Initially, our investigation focused on two key parameters of the pulse signal. First, we examined the impact of varying the pulse signal?s frequency while keeping the voltage constant. Next, we analyzed the effect of variations in the amplitude of the pulse signal while keeping a constant frequency. Following these experiments, we generated magnetic field maps in the frequency domain (FD) above the surface of the inductor, specifically focusing on the HZ component. The scanning step is equal to 0,5 cm. The scanning area is equal to (x, y) = (4 cm, 4 cm).

Investigation of active phased arrays performance deficiency due to array planarity and misalignment

ABSTRACT This paper investigates the degradation in the electromagnetic performance of an active phased array antenna and establishes the coupling relationship between the antenna array alignment/planarity to the near-field scanner probe. An analytical framework is presented to evaluate the sensitivity of radiation parameters of active phased arrays antenna due to the deviation of complex excitation vector. A laser-based positioning metrology equipment measures the near-field scanner plane to the antenna under test (AUT) plane in a global coordinate system. The antenna array surface is adjusted and aligned to the near-field scanner probe measurement plane within 1 mm (in S-band) by employing the mechanical mechanism within the positioning accuracies of 50–100 µ. The collimation of a perfectly aligned antenna array results in the alignment of electrical and mechanical boresight of the active phased array radar. The theoretical evidence and experimental results presented powerful tools and guidelines to set a reasonable tolerance for array alignment in the near-field test range (NFTR) to achieve high performances of the active phased array antenna.

High-Speed Antenna Measurement System Using Multi-Probe Array Technique for 5G Applications

In this article, a high-speed antenna measurement system using multi-probe array technique for 5G application is suggested. The spherical near-field scan measurement system for millimeter wave frequency band (3 GHz–40 GHz) and the multi-probe array rotation method is adopted to improve the antenna measurement speed. The proposed measurement RF system consists of the 14 multi-probe array (28 channel with dual-polarization), switch matrix, downconverters, amplifiers/attenuators, digitizers, and signal generators, and is compared to the conventional planar near-field scan antenna measurement system. The measurement speed performance can be improved significantly and the 3D beam pattern of the AUT can be achieved. The designed system was verified through comparison with a verified far-field measurement system. In addition, to increase the measurement efficiency, an effective sampling technique was proposed and verified.

On the Correlation Between Near-Field Scan Immunity and Radiated Immunity at Printed Circuit Board Level – Part II

The work presented in this two-part paper focuses on a prediction method of the radiated susceptibility of integrated circuit and printed circuit board from near-field scan injection, in order to anticipate risks of noncompliance due to design weakness. In Part I, a worst-case estimator of the far-field induced voltage on a PCB trace was proposed. Based on it, an estimator of the radiated susceptibility of a printed circuit board based on near-field scan results is derived and validated through two validation case studies.

Study of the impact of the power dimming and lighting modes of LED lamps on the near magnetic field

The LED represents the hot topic has many traditional lighting systems because of their high energy efficiency and lifetime. Nevertheless, if the emissions of harmonic currents are relatively present in the literature because presenting problems on the grid, the measurements of emissions radiated by LED lamps have rarely been carried out. This work studies the magnetic field above LED Lamp Spot Type with different probes, for the three directions (HX, HY, HZ), in the frequency domain (FD) using a spectrum analyzer by the technique of near-field scan (NFS). The scan step is 0.5 cm, the LED lamps are powered directly by the electrical network 220 V/ 50 Hz, then quantify the magnetic field above the center of the inductor depending on the variation of the mode of lighting for each lamp. We used two lamps of power P = 6 W and P = 12 W, the lighting modes for each lamp are: mode 1 (white), mode 2 (colored), mode 3 (white + colored), to understand the impact of variation power and mode of lighting on the magnetic field.

On the Correlation Between Near-Field Scan Immunity and Radiated Immunity at Printed Circuit Board Level – Part I

Near-field (NF) scan immunity is a powerful technique to identify the root-cause of failures produced during radiated immunity (RI) tests at the integrated circuit and printed circuit board (PCB) levels. However, a prediction method of the RI level from NF scan immunity results is still lacking. This type of method would help board designers to anticipate risks of RI noncompliance related to PCB directly after an NF scan campaign. This two-part article addresses this issue. In the first part, the equivalence between far-field (FF) and NF coupling on a microstrip line is discussed in order to derive an estimator of the FF induced voltage from NF scan results.

Pattern Reconstruction of 3-D Modular Antennas by Means of a Non-Redundant Near-Field Spherical Scan

A very flexible source model is proposed here to reduce the volumetric redundancy when considering the pattern reconstruction of three-dimensional modular antennas by means of a near-field spherical scan using a non-redundant sampling representation. Since this last facet is based on the appropriate choice of antenna model for the evaluation of the optimal parameters to be used, the proposed geometry guaranteed the minimum number of needed samples and then a significant time saved for data acquisition on the near-field spherical grid. Then, an optimal interpolation algorithm used these non-redundant samples for an accurate evaluation of the near-field data that were usable in the classical near-field to far-field transformation. The reliability and accuracy of the reconstruction process were proven by means of numerical tests. These last showed a remarkable reduction (about 53%) in needed near-field samples as compared to those required by the classical near-field to far-field transformation and this was achieved without any loss in accuracy.

Power-Dependent Metasurface With Self-Induced Bandgap

A metallic ring-based, diode-integrated, low-profile, power-dependent metasurface working from 3 to 3.6 GHz is proposed in this letter. Unlike the previous study which shifts a band up and down to change the impedance of the surface, the triggering of the diodes directly transforms the structure from a surface wave supportive state to a self-induced bandgap topology if exposed to high-power radio-frequency (RF) illumination. We demonstrate the concept by conducting the electromagnetic (EM)-circuit co-simulation and measurements for a 6-by-8 unit 2-D prototype. Near-field scan experiments verify that the proposed topology works in two distinct states, the <small>on</small> and <small>off</small> states, and high-power measurements prove that the reflection varies with the incident signal power. The highest 10 dB decrement in transmission occurs at 3.3 GHz with 52 dBm illumination. This structure can be used to protect sensitive devices from large signals while otherwise supporting a communication channel for small signals.

Two-Dimensional Beam Pattern Synthesis for Phased Arrays With Arbitrary Element Geometry via Magnitude Least Squares Optimization

In this paper, an optimization procedure for synthesizing shaped beams with an arbitrary geometry phased array system with real-time capability is presented. The algorithm involves a combination of an arbitrary extension of the Woodward-Lawson synthesis procedure with the magnitude least-squares optimization method. This simple combination significantly reduces the optimization time, enabling real-time beam shaping in response to changing requirements on beam shape or evolving geometry in distributed arrays. The technique places no restrictions on element positioning in all three spatial dimensions and is demonstrated to accurately reproduce the desired beam shape in both angular dimensions. The algorithm is demonstrated for multiple beam cases with a large, randomly generated array in computational simulation. The applicability of the algorithm to practical phased array hardware is also demonstrated using full-wave electromagnetic simulations and measurements of a realized arbitrary phased array system using a near-field scanner in an anechoic chamber.

Near-Field Orthogonal Beam Scan by Phased Arrays of Antennas With Active Analog Beamformer for Maximum NF-RCS in Target Detection

Near-field radar cross section (NF-RCS) of a target depends on antennas’ radiation and can be maximized by adjusting the radiation patterns. It is justified by the power return ratio and can be computed by a comparison method. A theoretical foundation of operational mechanism for phased arrays of antennas is presented to produce conformal radiations for NF-RCS enhancement. The target’s scattering coefficients are extracted from operating the antenna array’s digital phase shifters (DPSs) to steer the resulting beams in this work. The scattering matrix is then analyzed by the singular value decomposition (SVD) to determine the antennas’ excitations for maximum NF-RCS with estimation stability. It results in orthogonal beams for the two-way radiations of antenna arrays to interpret the scattering mechanisms. The feasibility is validated by HFSS full-wave simulations and experimental measurement data.

Large Horizontal Near-Field Scanner Based on a Non-Tethered Unmanned Aerial Vehicle

A horizontal planar scanner with an approximate size of 40 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times40$ </tex-math></inline-formula> m has been implemented using the Unmanned Aerial Vehicle (UAV) technology. The UAV is not wired to the ground to maintain the flexibility and short setup time of a non-tethered flight. In this configuration, the UAV-mounted continuous-wave source is not phase-locked to the on-the-ground receiver. A dual-polarized reference antenna placed on the ground is hence used to retrieve the relevant phase information. The presented approach has been applied on the Pre - Aperture Array Verification System (Pre -AAVS1) of the Square Kilometre Array, which is a digital beamformed array with 16 active elements. An inverse source technique has been applied on measured Near-Field (NF) data acquired on two different sets of points (one for each electric field component) from all the receiver channels. In this way, Embedded Element Patterns (EEPs), array calibration coefficients and pattern have been determined from NF data only. The achieved results have been validated using a complementary set of Far-Field (FF) measurements and simulations.

Clutter suppression method for linear scan indoor near-field RCS measurement based on interferometric SAR

Near-field indoor scattering measurement has become an important RCS test and evaluation technique. However, in a closed indoor environment, the test is susceptible to clutter interference. In this paper, a clutter suppression method for indoor near-field linear scan RCS measurement is proposed based on interferometric SAR technology. This method obtains the height information of scattering centers in the 2-D radar image by interferometric process, and removes all clutter scattering centers which have obviously incorrect height value by spatial filtering. Compared with clutter suppression methods such as vector background cancellation and range gate filtering, this method can effectively suppress clutter inside the target area. The practical effect of this method is verified by simulation and experiment.

Stand for measuring the directional characteristics of antennas of satellite communication systems

The development of network based on satellite communication systems is a promising solution for providing telecommunications services in the Arctic. Therefore, the task of developing and creating earth stations for advanced satellite communication systems that have characteristics significantly higher than their world counterparts is actual. Characteristics of such stations depend on antenna’s systems characteristics that determine the energy characteristics of the communication channel. The aim of this work is a stand developing for measuring directional characteristics of antennas of satellite communication systems based on the spherical scanner (TS8991). Spiral scanning is an alternative measurement method aimed at reducing measurement time with saving necessary accuracy. As a result of this work, the spiral scanning algorithm based on the near-field scanner Rohde &amp; Schwarz TS8991 was implemented. Moreover, the stand for monitoring and configuring the parameters of satellite earth station antennas was built. Block diagram of this stand is presented in article. An antenna with 1,2 m diameter of reflector was tested on the developed stand. The measurement results showed deviations of the measured values from the calculated values, which related by design disadvantages of the antenna. The stand using time was 35 minutes for measurements and conversions to the far field, for an antenna with 1,2 m diameter of reflector.

Quasioptical System for Corneal Sensing at 220–330 GHz: Design, Evaluation, and Ex Vivo Cornea Parameter Extraction

The design, simulation, and characterization of a quasioptical system for submillimeter-wave quantification of corneal thickness and water content are presented. The optics operate in the 220-330 GHz band and are comprised of two, custom aspheric, biconvex lenses in a Gaussian beam telescope configuration. The design produces broadband wavefront curvature matching to 7.5 mm radius of curvature target surfaces thus emulating a plane-wave-on-planar-media condition and enabling application of stratified medium theory to data analysis. Aspheric lens coefficients were optimized with geometric ray tracing subject to optical path length penalties and physical-optics simulations showed aspheric designs achieved wavefront coupling to spherical surfaces, superior to equivalent, canonical hyperbolic lenses. The fabricated lens system was characterized in a planar near-field scanner system and demonstrated good agreement to physical-optics simulations. An average central corneal thickness of 652 μm and free water content volume of 47% were extracted from ex vivo sheep corneas via complex s-parameters and agree with literature values. Extracted contact lens thickness and water content agreed with independently validated values. Moreover, the quasioptical system enabled observation of dynamic changes in artificial tear-film, thickness, and water content. This work elucidates two major findings related to submillimeter-wave wavefront matching on spherical surfaces, with wavelength order radii of curvature: 1) An asphere whose sag coefficients are optimized via field phase variation on a spherical surface produces coupling superior to a plano-hyperbolic lens. 2) For most feasible apertures, the Gaussian beam waist is located in the aperture near field, suggesting consideration for operating in the beam near field.

Near-field acoustical holography incorporating compressive sampling: Effect of measurement distance and array density

To identify sound source locations and strength by using near-field acoustical holography (NAH), many microphones are generally required in order to span the source region and to ensure a sufficiently high spatial sampling rate. It is often the case that hundreds of microphones are needed, so such measurements are costly, which has limited the application of NAH in industrial settings. Recently, however, it has been shown that it is possible to accurately identify concentrated sound sources with a limited number of microphones based on compressive sampling theory. Here, the theory of the four NAH methods that were studied in the present work, that is, statistically optimized near-field acoustical holography (SONAH), wideband acoustical holography (WBH), l1-norm minimization, and a hybrid compressive sampling method, is briefly reviewed. Note that the latter three procedures incorporate elements of compressive sampling. Then, a simulation with one monopole as the sound source was conducted to illustrate some basic characteristics of these algorithms. In the experimental portion of the work, a multi-element loudspeaker was used as the sound source. A near-field intensity scan was conducted to measure both the true intensity spatial distribution and the sound power generated by the loudspeaker to provide a basis against which the values obtained from the holography reconstructions could be compared. The sound field was reconstructed by using both near- and far-field measurements, and the number of microphone measurements used to reconstruct the sound field was systematically decreased by increasing the spacing between microphones. Both in the simulation and experiment, the sound field was reconstructed by using the four NAH methods mentioned above. Then, the reconstruction results were comparedwith the measured intensity results in terms of spatial localization and sound power, and the benefits of the compressive sampling approach are illustrated.