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In Multi-Probe (MP) based measurement systems, the standard procedure is to calibrate the probe array with a well-known reference antenna [1]. This procedure equalizes amplitude, phase, and polarization characteristics of each probe array element. In Planar Near Field (PNF) systems, the probe pattern impact is usually more pronounced than in other near field scan geometries, such as spherical. Thus, the probe pattern must be compensated during post-processing for more accurate measurements at wider angles. While the probe array calibration ensures the on-axis equalization, the probe array elements still have individual pattern difference due to finite manufacturing accuracy and absorber interaction. Probe compensation using an equivalent probe pattern of the array has been shown to be very effective and accurate for MP PNF systems [2]. In this paper we compare two methods to determine the equivalent probe pattern for a given MP PNF system. We also discuss the acceptable limits of pattern variation within the array versus measurement accuracy as a design parameter for MP PNF systems.
Radar sensors are an essential component in the automotive sector and take over safety-relevant functions in the field of autonomous driving. Therefore, the need for validation of automotive radar systems is increasing. Within this paper, a measurement setup for automated static and dynamic tests of integrated radar sensors is set up in the robot-based measurement chamber available at the Institute of High Frequency Technology, RWTH Aachen University. The system parameters two-way pattern, range and speed resolution as well as angular resolution and separation capability are measured and analyzed for an integrated automotive radar sensor. The measured results show the expected performance of the radar system and point out the high variability of the built setup.
Robot-based measurement systems typically have a larger tolerance with respect to their positioning accuracy than conventional systems, e.g. roll-over-azimuth positioners. However, for spherical near-field measurements, the positioning accuracy of the probe is an important uncertainty in the required near-field-to-far-field transformation. One way to account for those non-idealities is to use the higher-order pointwise probe correction (PPC). It allows to consider the actual position and orientation of the probe by additional rotations and translations of the probe receive coefficients. To evaluate the PPC, the occurring position tolerances and the differences in the transformed farfield patterns of a standard gain horn are investigated at 60GHz. Using an onset measurement as reference, it is shown that the PPC provides improvements of 41dB and 65dB for the co- and cross-polarized measurements, respectively. In addition, an offset measurement is shown where the measurement sphere is shifted relatively to the AUT. The pointwise implementation of the correction method allows to reproduce the far-field pattern without additional measurement points, while the transformation without PPC fails. Thus, the implementation of the PPC not only enables the processing of irregular sampling grids, but also increases the measurement accuracy by including the actual position and orientation of the probp>
Accurate characterization of locomotive antennas is key to safe and robust railway signaling and control communication. With the introduction of new technologies and the foreseeable migration from the GSM-R standard towards FRMCS, new wireless applications and specifications arise, and suitable antenna solutions need to be developed and tested. Moreover, the rooftops of modern locomotives present a dense and harsh environment; therefore, potential antenna mounting spaces should be carefully evaluated to avoid undesirable degradations of the antenna radiation patterns. Due to the electrically large and complex structure of locomotives, full-scale testing is challenging to perform, especially under laboratory conditions. Antenna measurements with geometrically scaled models present a powerful alternative to address this issue. In this paper, we present and discuss antenna measurement results of a scaled locomotive mockup. The mockup incorporates two different cabin geometries, one with a step-like rooftop contour, and one with a smooth slightly tilted geometry. First, the optimum scaling factor was identified and validated through numerical simulations. Afterwards, antenna measurements with a scaled locomotive mockup were carried out in our automotive antenna measurement facility VISTA. The measured results were compared with the numerical simulations, where a good correlation above 80% was found. Secondly, the impact of the rooftop geometries, and superstructures on the roof has been investigated for a range of operational frequencies between 700 and 2600 MHz. The results reveal that the parasitic impact of the antenna environment becomes more pronounced at higher frequencies.
In this paper, a design of a linear-to-circular polarization converter based on a 3D printed anisotropic metamaterial substrate (AMS) is presented. The AMS is a stack of thin sheets of acrylonitrile butadiene styrene (ABS) material, with air gaps in between, placed over a ground plane. This produces a metamaterial structure composed of periodic anisotropic unit cells, enabling the conversion of a linearly polarised (LP) incident wave to a circular polarised (CP) reflected wave. Results demonstrate that the proposed 3D printed AMS provides good angular stability. Using the AMS as a substrate, a CP antenna application is proposed operating within the L1 GPS reducing the complexity of designing/feeding and fabricating of the primary antenna.
Antenna measurement Intercomparison Campaigns represent a successful activity within the working group on antenna measurement of the European Association on Antennas and Propagation [1] since the group foundation in 2005. These campaigns, constitute an important resource for participating facilities to demonstrate their measurement proficiency, useful internally but also towards obtaining or maintaining official accreditations. In this paper we present the completion of a campaign involving a high gain X/Ku/Ka-band reflector, MVG SR40 fed by an MVG SH4000 Dual Ridge Horn. Preliminary results were shown in [2]. Results from seven facilities are compared through plots of gain/directivity patterns. The data is used to generate reference patterns and establish accurate gain performance data based on the uncertainty estimates provided by each facility. Statistical analysis of the measured data such as Equivalent Noise Level and Birge ratio of each measurement with respect to the established reference will also be shown.
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.
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.
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.
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.