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Over-the-Air (OTA) measurements of modern mmWave User Equipment (UE) should be performed under plane-wave conditions which require sufficiently large measurement distances. Alternatively, shorter distances can be considered but special plane-wave generator devices should be used instead of conventional probes/range antennas. The use of probes/range antennas at reduced distances would offer advantages in terms of cost effectiveness and improved dynamic range but in general, they would not provide the proper plane-wave condition. To set the proper measurement distance the electrical size of the whole UE is usually considered. However, in most cases only a smaller portion of the UE actively contributes to the radiation. Reduced distances can thus be considered without significant loss of accuracy, unless the source of radiation is offset from the center of the measurement system. This latter scenario is called parallax and often causes distortions of the pattern if the distance is not sufficiently large. In this paper parallax compensations techniques applicable to amplitude-only measurements will be investigated considering realistic OTA measurement emulations of modern devices equipped with mmWave phased arrays placed in different positions. The investigation is performed focusing both on the measurement of the single beams and on the overall spherical coverage provided by the antennas.
The ESA HERA-JUVENTAS mission relies on 50-100 MHz dipole antennas mounted on a CubeSat. The mission requires an accurate verification of the 3D co-polar and cross-polar directivity, gain, and matching. The performance verification of low gain antennas installed on space platforms at frequencies below 400MHz is a challenging task. The use of spherical near-field measurement technique is the most suitable and accurate approach for low gain antennas. However, a well-designed conventional anechoic chamber, for indoor testing, equipped with suitable absorbers at the desired test frequencies would be large and thus expensive. In this paper, the so-called synthetic probe array technique to suitably shape the probe pattern for minimum illumination of the chamber walls will be presented. Its applicability to spherical near field measurements in the existing HERTZ testing facility at ESA/ESTEC will be discussed. A comprehensive theoretical study has been performed using full-wave simulation of the chamber and the spacecraft. Moreover, scaled measurements considering a 10:1 scaled model of the final scenario are currently under investigation to better verify the performance of the proposed measurement technique. Preliminary results obtained from the simulation analysis and the scaled tests are reported in this paper.
A Novel Microstrip patch antenna have been designed for satellite communication, to be used in satellite simulator system for transmitter and receiver antenna, at X and Ku frequency band, integrated as transceiver antenna. The transmitter antenna is designed for the uplink at 14.25 GHz and receiver antenna is designed for the downlink at 11.45 GHz. The transmitter and receiver antennas are integrated into a microstrip patch with microstrip transmission feedline on two sides for each frequency band. Quarter-wavelength structure is used for matching. Simulation results reveal a broadband structure for reflection, with a gain of 6.5 dB and high efficiency.
Near-field far-field transformations (NFFFTs) are usually performed for time-harmonic fields. In cases where insitu antenna measurements are required and the antenna under test (AUT) is not accessible for specifically tailored test signals, the need for handling time-modulated fields arises. The shorttime measurement (STM) approach offers a way to deal with continuously modulated fields while a time-harmonic NFFFT can be employed. We present results of numerical simulations to demonstrate and characterize the STM approach for the case of a cylindrical measurement geometry as found in UAV-based antenna measurements. We further derive guidelines from the simulation results that describe the applicability of the STM for different measurement situations.
This paper presents a wide incident angle metasurface unit cell element applied to a reconfigurable intelligent surface (RIS) for beamforming and beam-steering applications in the 26 GHz frequency band from the fifth generation of mobile communications (5G) frequency range 2 (FR2). Each metasurface unit cell is based on a printed frequency selective surface (FSS) loaded with a varactor diode. The FSS-based structure is based on a circular loop at the top and a slot-based ground plane at the bottom resulting in a 0.25x0.25λ0 total area. The complete unit cell element encompasses four conducting layers, in which the first two ones form the FSS. RF chokes are printed at the middle layer to isolate the DC circuit, and the bias lines are routed at the fourth layer. The unit cell has been conceived using the full-wave electromagnetic solver ANSYS HFSS. Its numerical results demonstrate a reflection phase shift up to 180º and reflection magnitude higher than 0.4 at the 26 GHz frequency band for incident wave angle from 0 to 50º. The proposed reconfigurable intelligent surface might be applied to future wireless communication systems, planar antenna reflectors, and vortex beam generation.
Earlier works have shown the benefits of imaging stray signals in a range with planar-scanner data. This paper discusses some additional tools that can be employed for stray-signal identification. Related range diagnostics are presented that employ Fourier spectral and holographic processing of 1D linear scans through the quiet zone. For the special case of a compact range, the interpretation of arrival angles from the paraboloidal reflector surface is explored. Measured data from multiple facilities are presented that were used to locate, quantify, and remedy the unwanted signals.
The Two Scans phase retrieval technique is based on magnitude measurements of the antenna under test (AUT) in two different configurations and the analytical relation between these two measurements. For spherical near-field measurements this relation is given by the spherical transmission formula and the best-known implementation of this method makes use of nearfield measurements over two measurement spheres. In this paper we propose a novel method where the two sets of near-field measurements are measured over a single sphere, with the AUT in two different positions wrt. the origin of the measurement coordinate system. The two positions are known in the measurement coordination system, and the relationship between the AUT transmission coefficients for the two positions is given by the transmission formula, or by a far-field phase translation. The phase is then retrieved through an iterative process between the two measurements. The principles of this approach will be presented and the performance will be evaluated based on simulated data. Particularly, the impact of the extent of the translation on the accuracy of the phase retrieval will be studied, and the viability of the method for real applications will be discussed. Additionally, the possibilities of an error metric in the complex domain is explored by performing two simultaneous retrievals, starting from two different initial phase guesses, and tracking the complex difference between the two to determine whether the algorithm has converged correctly.
This paper experimentally investigates the ping pong channels resulting from a narrow but divergent beam of the horn antenna as witnessed in non-line-of-sight (NLoS) scenario for the 240−300 GHz frequency range. A THz vector network analyzer (THz−VNA) extender measurement setup equipped with a ∼ 25 dBi horn antenna as transceiver (TRX) is employed to retrieve and evaluate the reflections prompting a ping pong influence on THz wireless channels. This ping pong effect being uncommon at lower frequencies is studied from extensive measurement campaigns for monostatic measurement setups in the frequency range of interest. Corner reflector (CR) as well as metal plate reflectors (MRs) are employed to analyze the resultant ping pong channels in the manifold scenario setups. This ping pong effect may lead to an irreversible ambiguity in the channel transfer functions (CTFs) and certainly demands understanding of such sub-harmonics.
Full Probe Compensation (PC) techniques for Spherical Near Field (SNF) antenna measurements have recently been proposed and validated with success [1]-[4]. Such techniques allow the use of antennas with more than a decade of bandwidth as near field probes in most systems. The clear advantage is that multi-service/frequency measurements campaigns can be performed dramatically reducing the number of probes hence decreasing the downtime between two measurements. This is a highly desirable feature for modern antenna measurement applications such as automotive. The use of a dual-polarized probes further improves the measurement efficiency as two orthogonal field components are measured at the same time. The possible differences between the pattern radiated by the two ports of the probe should sometimes be considered to keep the overall measurement accuracy. The full PC technique objective of this paper accounts for generic dual-polarized probes and is validated for the first time. For this purpose, measurements of three monocone antennas from 450 to 6000 MHz performed with only one wideband (15:1) dual-polarized probe will be considered.
In anechoic chambers, the level of spurious reflections is determined by the reflectivity of the installed absorbers and is usually estimated using ray-tracing methods. But since the basic assumption of a purely specular reflection in most of these ray-tracing methods can lead to insufficient results, the reflectivity of the absorbers must be analyzed for oblique incidence and over a broad range of observation angles. In this paper, a bi-static measurement setup is proposed, which overcomes angular limits of the NRL-arch method and allows to analyze the scattering behavior of absorbers in an extended angular range. Using this setup, and applying the radar cross-section method, the reflectivity of two types of pyramidal absorbers was analyzed with respect to different illumination and observation angles for parallel and perpendicular polarization between 2 and 18 GHz. While the measurement results for normal incidence agree well with the specifications, additional non-specular reflections of similar strength were detected in the time-domain at different observation angles. Especially for the case of oblique wave incidence, it becomes apparent that the highest reflectivity does not necessarily occur for specular reflection. These findings help to improve the understanding of the scattering behavior of absorbers in general, as more comprehensive analyses become possible with this method. Index Terms—bi-static scattering, electromagnetic wave absorption, reflectivity, RF absorber, time-domain analysis.
Producing uncertainty estimates is an integral part of every measurement procedure. This is a time consuming process in spherical near-field antenna measurements, because for a few factors in the uncertainty list it is necessary to perform additional full-sphere measurements. In this paper we propose an original method to simulate in a computer the effect of two important items in the uncertainty list, namely θ-zero and axes intersection errors, by taking advantage of the fact that after a measurement the antenna under test is completely characterized. These sources of errors are associated with the rotating positioner of the anechoic chamber and, therefore, are more prone to change between campaigns. Consequently, they need to be checked and assessed for every antenna under test, which can be inefficient if the measurement time is excessive due to the test antenna’s size. With the techniques presented in this work, the time spent estimating the impact of these errors in the measurands is greatly reduced, since additional full-sphere measurements are not needed. Furthermore, the errors can be isolated from each other and the degree of linearity between measurand and error source can be assessed. Finally, it is no longer necessary to occupy the antenna under test in order to perform the uncertainty estimation.
The Plane Wave Generator (PWG) concept has recently been presented for millimeter wave applications [1-2]. The PWG has attracted interest, also because of its unique application in direct testing of 5G/6G enabled devices while in use by life people or mounted on suitable phantoms. This test feature is important to evaluate the shadowing effect by the user and the effectiveness of distributed array system on devices to overcome the shadowing. In this paper, we investigate the feasibility and achievable measurement accuracy in such scenarios. Using the measured performance of the PWG reported in [1-2], the measurement scenario is emulated accurately and compared to the reference case.
This paper presents antenna design and packaging consideration for near field communication (NFC) system that is being used in automotive security systems, and, more specifically, to an NFC reader for obtaining access to, and controlling activation of, a transportation vehicle such as a motor vehicle. Various important studies for automotive applications were performed in this work such as a magnetic wall method. This magnetic wall method can prevent the reduction in NFC reading range caused by proximity to body sheet metal. It provides a unique and superior magnetic shielding effect as compared to ferrite sheets because it is not temperature dependent and can be implemented with minimal cost and complexity. The proposed design can be easily fabricated on the back face of the NFC reader antenna PCB using conventional PCB techniques.
In this work, a simulation-based study is presented exploring the effect of surface roughness of 3D printed plastics on the accuracy of material parameter extraction. A homogenous sample material is placed inside the W-band waveguide and the S-Parameters are simulated. Two different methods for estimating the dielectric properties of the sample using the simulated S-Parameters are presented (i) NRW (Nicolson-Ross-Weir) technique-based estimation method, and (ii) Feko optimization-based estimation method. An error analysis study is presented to understand the percentage of error due to the surface roughness of the 3D printed plastics. For N7 grade surface roughness, NRW predicts 14% error in material parameters due to surface roughness, whereas Feko optimization method predicts 10% error compared to estimation without any surface roughness. Process outlined in the paper can be used to estimate effect of surface roughness of waveguides on material property measurements at mm wavebands such as W-band.
We tackle the problem of recovering 2-D complex fields starting from the spectral amplitude data, the support of the source, and a few additional information. In particular, we further elaborate on our ‘crosswords-solution like’ approach where the solution is found by solving 1D problems and congruence arguments. Its argued that intersecating lines and circles (rather than just lines) is more effective, and we show how the resulting approach, initially developed for the case of continuos (aperture) sources, is also effective in determining the excitations of discrete (array) sources.
Spherical wave function expansions involving a TM- R and TE-R field decomposition are widely used. Here we examine a spherical wavefunction expansion based on a TM- z and TE-z field decomposition. The impetus is the straightforward relationship between the TM-z and TE-z spherical wavefunctions and the cartesian multipoles which, in turn, have contemporary application in wireless power transfer. However, there are potentially other useful features of such a TM-z and TE- z spherical wavefunction expansion. For example, the TE/TM-z decomposition results in the ????-polarized far electric field being associated exclusively with the TM-z wavefunctions while the ????-polarized far electric field is associated exclusively with the TE-z spherical wavefunctions. Unfortunately, from the analysis given here, it appears that it is not possible to represent a generalized finite source in TE/TM-z spherical wavefunctions exclusively. One succinct way to show this is by attempting to expand the far field of an x or y directed electric or magnetic dipole in TE/TM- z spherical wavefunctions. The dipole can be represented by a single TE/TM-R spherical wavefunction, but the expansion in TE/TM-z wavefunctions is problematic.
Owing to the increasing interest in high frequencies, as the millimeter wave range, wherein accurate phase measurements are increasingly difficult and expensive, phaseless near-field techniques are prime candidates for antenna characterization. In this paper, an experimental validation of a phaseless near-fieldfar- field (NF-FF) transformation with plane-polar scanning for antenna characterization is presented. A proper representation of problem unknowns and data, using the available information on the antenna under test (AUT) and on the scanning geometry, is adopted in order to improve the reliability and the accuracy of the proposed characterization algorithm. By exploiting the nonredundant sampling representations of electromagnetic fields and by using an oblate spheroid to model the AUT, a remarkable reduction (about 90%) of the required NF samples is achieved. Experimental results on data acquired at the University of Salerno Antenna Characterization Lab are reported to validate experimentally the effectiveness of the proposed characterization technique.
There has been much discussion in the last few decades regarding redundancy in conventional near-field sampling, and that redundancy is most pronounced in the planar geometry. There has also been much discussion regarding modal filtering of near-field data to attenuate the effects of stray signals. Both discussions revolve around the limited local spatial bandwidth that can be produced at each probe location when the antenna under test’s (AUT’s) radiating sources are all contained within a known geometric boundary. This paper discusses a novel filtering technique that exploits the inherent sampling redundancy in conventional planar near-field acquisitions. The filtering is based solely on the known location and shape in the scanner’s coordinate system of a closed 3D boundary around the radiators of interest. The paper describes the algorithm and presents results from both measured and synthesized input. The new filter is also compared to other available filters in terms of speed, attenuation of stray signals, and preservation of AUT signals.
Cellular LTE MIMO downlink performance, for 4x4, 4x2, and 2x2 LTE MIMO architectures, in terms of average data throughput and availability, were investigated in an urban canyon environment of Frankfurt, Germany at 2110 MHz on a Sport Utility Vehicle (SUV) with metal and glass roofs for a virtual route. This study utilized the following measured antenna radiation patterns for total polarization on the SUV at 2110 MHz for the mobile station: 1) roof-mounted antenna on metal roof; 2) roof-mounted antenna on glass roof; 3) interior-mounted planarinverted F antenna; and 4) interior-mounted planar-inverted F antenna rotated 90 degrees. This research was carried out using a three-dimensional simulation software suite that enabled users to simulate electromagnetic wave propagation and wireless network planning. The following observations were obtained from this research. First, the MIMO architectures for the SUV with metal roof exhibited approximately 5% higher average data throughput levels compared to the same MIMO architectures on the SUV with glass roof. Second, the throughput availability for the 4x4 and 4x2 MIMO systems were comparable. Lastly, the average throughput for the 4x4 MIMO system was higher than the 4x2 and 2x2 MIMO systems for the SUV regardless of roof material.
Performing End-to-End testing of satellite payloads on planar near-field test ranges can greatly reduce the cost and real estate required compared to conventional far-field systems. Previous work has shown that this is theoretically possible, with limited test data showing viability. This paper provides additional validation of the technique’s ability to characterize various system-level parameters, including the equivalent isotropically radiated power , group delay, saturating flux density, system noise temperature and the gain vs. frequency response. Details of a new software satellite payload test suite is presented, along with the accompanying simulated payload that was developed for system verification and facility-to-facility comparison.