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Reference stations are a critical element of the GNSS infrastructure and provide valuable measurements for constellation monitoring [1]. It is however important to obtain high-quality measurements from these stations and therefore any kind of local error source shall be minimized or properly accounted for. When choosing the site for a new reference station or when analyzing the performance of a current one, particular attention shall be devoted to multipath. The multipath (and a poor suppression of it) is one of the major error sources and can lead, in an extreme case, to non-usability of measurements of the reference stations’ network and/or to the need of expensive countermeasures to be put in place after installation [2]. Currently, however, there is, to the authors’ best knowledge, no scientific way to assess the multipath conditions of a given site before installation of a new antenna. It was demonstrated in previous work from the authors [3] that the amount of multipath available at the receiver in a given installation site strongly depends on the so-called antenna “multipath suppression capability indicators” (MPSI). Antennas with similar MPSIs placed in the same position are expected to deliver similar amount of multipath error to the receiver. It is therefore feasible to perform a generic characterization of the site by using a reconfigurable “probe” antenna, capable of assuming different levels of MPSI. The results obtained by this set of measurements will then form a sort of “database of multipath” for the site for each MPSI level. Such technique will then allow to foresee beforehand the performance obtainable with any other antenna, just by comparing its MPSI values with the multipath obtained with a corresponding MPSI of the “probe antenna”. This paper will show the design of the reconfigurable antenna. The results of the electromagnetic measurement of the antenna will also be shown together with the different values of MPSI achievable by reconfiguring the antenna. Moreover, MPSI values from different commercial antennas will be derived for comparison. An experimental validation of the method will be reported, in which the multipath probe antenna will be used to estimate the multipath environment in a given site.

This paper presents a new approach to interference mitigation. We propose to equip a Global Navigation Satellite System (GNSS) receiver with a diversely polarized antenna array in order to combine signal processing in the spatial and polarization domains in a novel way. The new algorithm is evaluated using measurement data, and results show significant improvement in receiver robustness against interferences when the dual-polarization approach is used. Two specific benefits come to light. First, the carrier-to-noise-density ratios of the line-of-sight components are improved since the receiver can make use of the power present on the left-hand circularly polarized (LHCP) channels because of non-ideal polarization purity of the antenna, resulting in better receiver computed position, velocity, and time (PVT) solutions. Second, interference mitigation becomes more effective because of the possibility of filtering in the polarization domain and the additional number of available degrees of freedom, increasing receiver robustness and enabling tracking and PVT in severe interference scenarios.

Satellite navigation is a fundamental asset in today’s mobile platforms to determine position, velocity and time. In mobile applications, however, the available footprint to place the navigation antenna is often chosen a priori, taking into consideration mechanical/esthetic reasons. This leads often to not-optimal placement, causing multipath and hence impacting on the achievable performance of the antenna and therefore on the achievable navigation accuracy. Proper knowledge of the antenna performance once installed on the platform is therefore of paramount importance to achieve high-precision navigation: methods and tools to assess such performance will be discussed in this work. It will be shown how to characterize the performance in a fully simulative way and then also in a hybrid way, combining anechoic chamber measurement of the antenna with simulation of the platform. It will be shown that, through installed performance analysis, information about the multipath-induced pseudorange error can be obtained.

This paper proposes DFMC airborne multipath models and antenna error models derived from measurement and supported by simulations. Based on the data evaluated, new multipath models (including the contribution from the antenna) for Galileo E1 and GPS L1 and Galileo E5a and GPS L5 are discussed. Furthermore, a model for the Ionosphere-Free combination of the signals is proposed.

Nowadays, an increasing trend to use autonomous Unmanned Aerial Vehicles (UAV) for applications like logistics as well as security and surveillance can be recorded. Autonomic UAVs require robust and precise navigation to ensure efficient and safe operation even in strong multipath environments and (intended) interference. The need for robust navigation on UAVs implies the necessary integration of low-cost, lightweight, and compact array antennas as well as structures for multipath mitigation into the UAV platform. This article investigates a miniaturized antenna array mounted on top of vertical choke rings for robust navigation purposes. The array employs four 3D printed elements based on dielectric resonators capable of operating in all GNSS bands while compact enough for mobile applications such as UAV.

Two miniaturized antenna arrays for GNSS receivers are presented. The effects of the miniaturization on the performance of an interference mitigation STAP algorithm are analyzed. The performance degradation imposed by the miniaturization on the spatial gain is showed and a potential compensation is proposed.

Current satellite navigation systems are providing more and more dual frequency capabilities, enabling an improved navigation accuracy and reduction of residual errors (e.g. from ionosphere)[1,2]. Recently, the aviation community has started an effort to achieve new standardized minimum operational performance specifications (MOPS) for GNSS equipment, in order to allow for use of dual frequency multi constellation (DFMC) systems in the future, with clear benefits in terms of obtainable navigation performance. In such conditions, residual errors due to the GNSS antenna become more and more relevant and actually need to be properly identified and bounded, both in the antenna specifications and, for instance, in the models for aircraft multipath. Previous work from the authors [3] has shown the methodology developed in order to accurately simulate the installed performance (both in terms of antenna pattern distortion and multipath) of commercial antennas mounted on commercial aircraft. The antennas are measured in an anechoic chamber and then the data are imported into electromagnetic simulation software. Combining these measurements with a proper CAD model of an airplane, they are then used to simulate the real-life installation on the airplane. In this work, an analysis of the multipath performance obtainable by different antennas mounted on different aircraft (single aisle and wide body) will be shown: such results will provide a good indication for the performance to be expected in real-life scenarios and will also be used to further validate (and ensure the general applicability of) the new proposed model for multipath, obtained from flight data and shown in a concurrent paper at the conference. Moreover, the multipath suppression indicator (MPSI) will be introduced which is able to quantify the multipath suppression capability of the antennas: its applicability in the avionic context will be validated against the data obtained by the installed performance analysis and a proposal for its use in future antenna MOPS will be given.

The current increase in the number of available satellites from different constellations as well as in the number of satellites emitting signals at multiple frequency bands is promising to strongly increase the positioning performance of satellite navigation receivers. Such improvement is for instance due to the possibility to use dual frequency corrections for the ionospheric effects. Dual frequency multi constellation (DFMC) systems are hence currently being deployed worldwide for different applications. In the aeronautical field, a standardization effort for DFMC navigation systems is currently being coordinated by RTCA, with the aim to define the minimum operational performance specifications (MOPS) of future avionic systems. In such framework, antennas assume a central role: on the one hand, the impact of antenna imperfections on the overall pseudorange error will become more relevant with DFMC systems. This is due to the minimization of other error terms, such as the ionospheric one, thanks to multifrequency processing. Such contribution needs therefore to be properly characterized. On the other hand, antenna characteristics impact the multipath error at the receiver, which is due to the multipath susceptibility of the antenna itself: such contribution also needs to be further investigated and when possible, modelled. This paper aims at addressing both these antenna-related error terms, focusing on airborne applications. A method for a precise antenna characterization will be shown, also considering, through electromagnetic measurements and simulations, the (multipath-generating) installation on the aircraft. An initial comparison of the results obtained through this method with data collected from flight tests will be shown, validating the correctness of the method. Moreover, a further insight will be given regarding the different performance levels achievable by different commercial antennas.

Nowadays GNSS receivers are required to operate in miniaturized system and platforms, such as UAV. Two miniaturized GNSS antenna arrays -formed of four L1 band capable elements and one tetra-band capable element- are presented. The antenna arrays not only deliver good positioning estimations but also provide robustness against interference signals. Real measurement positioning performance results are shown. In addition, the interference mitigation performance of the two arrays is investigated and assessed using Spatial Temporal Adaptive Performance (STAP) algorithm simulations.

Current standardization activities in the aeronautical community are paving the way to using multifrequency multiconstellation GNSS as a primary means of aircraft navigation. The increase in the number of satellites from different constellations as well as the increasing use of multiple frequency GNSS receivers promise improvements in the achievable accuracy in GNSS positioning. The effects of receiver antennas shall be investigated because of the stronger impact of possible imperfections on the overall error budget for multifrequency combinations. The scope of this paper is to show the possibility of properly modeling and indeed characterizing the antenna-induced GNSS pseudorange errors, through simulations and electromagnetic measurement. An insight into antenna characteristics giving rise to such errors will be given, by analyzing the impact of the feeding technique on the achievable pattern uniformity and hence on antenna-related pseudorange errors. The technique is then validated through GNSS field measurement.

Multipath is recognized as a limiting factor for precise GNSS positioning. Therefore, a strong interest in identifying and mitigating it both at antenna and receiver side has led to much research in this topic and solutions being developed and commercialized. However, from the antenna point of view, a clear analysis of the actual antenna multipath susceptibility (or in an opposite way, its rejection capability) for multiple and more complicated cases than single bounce from ground has, to the best knowledge of the authors, not been extensively performed. Scope of this work is therefore to analyze the multipath rejection capability of different GNSS antennas (both at L1/E1 and L5/E5a band) in different situations, such as in tripod-like scenarios (hence being affected by multipath from horizontal surfaces) or in scenarios with multipath coming from slanted obstacles or in the vicinity of buildings (hence in cases with multipath coming from vertical surfaces). Such results will then be correlated with the antenna characteristics, in terms for instance of cross polarization discrimination and down-to-up ratio (DUR) and an optimal performance indicator for the different cases will be sought for. It will be shown that the antenna electromagnetic characteristics deterministically determine the rejection capabilities, but also that different parameters shall be taken into account for each category of multipath.

Important signal processing techniques require that the response of the di�fferent elements of the array have specifi�c characteristics, which are often not achievable for real systems due, for instance, to the fact that the responses of the array elements are a�ffected and distorted by mutual coupling. In such cases, in order to allow the application of ESPRIT, FBA, and SPS, it is necessary to apply array interpolation. Array interpolation provides a model or transformation between the real and a desired array with the necessary characteristics. As the real response becomes more distorted with respect to the desired one and the region of the fi�eld of view to be considered increases a nonlinear approach becomes necessary. In this work, two di�fferent methods for sector discretization are presented. An Unscented Transform (UT) based method and a principal component (PC) based method are discussed in detail. Two nonlinear interpolation methods are also presented, Multivariate Adaptive Regression Splines (MARS) and Generalized Regression Neural Networks (GRNNs). They are extended and applied to the problem of array interpolation. The performance of the proposed methods is examined using simulated and measured array responses of a specially designed physical system for research on mutual coupling in antenna arrays

All mechanical structures are subjected to deformation and cracks, due to fatigue, stress, and/or environmental factors. It is, therefore, of uttermost importance to monitor the mechanical condition of critical structures, in order to prevent catastrophic failures, but also to minimize maintenance costs, i.e., avoid unnecessary inspections. A number of technologies and systems can be used for this purpose: among them, the ones proposing the use of wireless passive crackmeters have a strong impact potential, in terms of simplicity of installation and measurement and low cost. This paper, hence, shows a crack width wireless radio-frequency identification sensor, developed for applications on various materials (such as concrete and metal) and able to detect submillimeter deformations occurring on the object, on which it is placed. A design method based on high-sensitivity phase detection is shown.

Array processing algorithms such as direction of arrival (DOA) estimation, deterministic beamforming and null-steering as well as spoofer detection and mitigation are known to be sensitive to errors in the model for the antenna array spatial response. In particular, unknown gain and phase mismatches between antenna channels, mutual coupling between antenna elements, crosstalk-effects in the RF-Frontend and in the case of using ephemeris data as auxiliary spatial information unknown antenna array attitude can seriously degrade the performances of array-processing algorithms. This paper proposes a novel algorithm to estimate gain, phase and mutual coupling / crosstalk coefficients as well as the attitude of the antenna array by exploiting the ephemeris from each GNSS satellite that is sent along with the navigation data. The estimation of the various parameters is based on a maximum likelihood approach. Numerical results are shown to illustrate the potential usefulness of the proposed calibration algorithm toward better accuracy and resolution in deterministic array-processing algorithms

The quest for compact antenna arrays able to perform robust beamforming and high resolution direction of arrival (DOA) estimation is pushing the antenna array dimensions to progressively shrink, with effects in terms of reduced performance not only for the antenna but also for beamforming and DOA estimation algorithms, for which their assumptions about the antenna properties do not hold anymore. This work shows the design and development of an antenna array with adjustable mutual distance between the single elements: such setup will allow to scientifically analyse the effects that progressive miniaturization, i.e. progressively smaller mutual distances between the antennas, have on the DOA estimation algorithms, as well as show the improvements obtained by using array interpolation methods, i.e. techniques able to create a virtual array response out of the actual array one, such as to comply with the algorithms' requirements on the antenna response.

By processing the phase of the backscattered field from a radio frequency identification ultrahigh-frequency tag antenna, physical information can be derived about the change of the materials and boundary conditions around a sensor-less tag. The phase-based sensing, however, is strongly dependent on the specific setup arrangement, and huge artifacts would arise in successive independent measurements involving temporary (handheld) readers at different distances. This letter introduces a multiport tag arrangement suitable to achieve distance-independent measurements. The method exploits the use of sensitive and reference tags. Their phase responses are combined within a double phase difference metric suitable for robust data inversion. The method is demonstrated through an experiment with a displacement-sensing system.

This paper discusses the design and manufacturing of a miniaturized 2x2 stacked patch antenna array, operating at E5a and E1 Galileo bands (i.e. respectively at central frequencies of 1176 and 1575 MHz), for robust navigation applications. The 2x2 array configuration has a total dimension of 100 mm x 100 mm, hence enabling its use in mobile applications. Due to the tight placement of nearby elements, mutual coupling problems arise. The reduction of the electromagnetic interaction among the elements is pursued by means of a metallic fence.

The increase in global navigation satellite systems (GNSS) availability and services is fostering a new wave of applications related to satellite navigation. Such increase is also followed by more and more threats, aiming at signal disruption. In order to fully exploit the potentialities of precise and reliable navigation, being able at the same time to counteract threats such as interference, jamming, and spoofing, smart antenna systems are being investigated worldwide, with the requirements of multiband operation and compactness. In order to answer such need, the present work proposes a miniaturized dielectric resonator antenna (DRA) 2 × 2 array able to operate at E5/L5, L2, and E6 bands, with an overall footprint of only 3.5′′ (89 mm).

A specific procedure is implemented for the optimization of passive part of multichip RFID tag antenna, based on the performance parameter in terms of newly developed concepts. Examples are given and significant improvements have been observed comparing with previous results, which verifies the approach.

The communication performance of Passive RFTD tags mounted inside tires for application to automotive logistics are investigated at the purpose to evaluate the achievable reading ranges. The maximum performance, reaching up to 8 meters for tags integrating low power ICs, are estimated by simulations of a benchmark dipole tag in different positions inside the tire. The realistic performance are retrieved by simulating and measuring COTS helical tags whose characteristics of flexibility and durability make them suitable to overcome the stresses of tire applications. Computer simulations and then laboratory experimentations in real conditions allowed evaluating the influence of metal and the position inside the tire. It was also demonstrated that, once the tag position inside tire is established, there is an optimal length of the antenna maximizing the realized gain and consequently the tag read range.

UHF passive radio-frequency identification technology is rapidly evolving from simple labeling of things to wireless pervasive sensing. A remarkable number of scientific papers demonstrate that objects in principle can have their physical properties be remotely tracked and monitored all along their life cycle. The key background is a new paradigm of antenna design that merges together the conventional communication issues with more-specific requirements about sensitivity to time-varying boundary conditions. This paper presents a unified review of the state of the art of the tag-as-sensor problem. Particular care is taken to formalize the measurement indicators and the communication and sensing tradeoff, with the purpose to provide a first knowledge base for facing a large variety of emerging sensing applications.

RFID systems are growing in use also for sensing purposes. In the last years, there has been quite a lot of effort in identifying RFID parameters most suited to sensing and at the same time wirelessly recordable: there are however still some open issues to solve. The use of wirelessly recordable parameters being independent from the measurement setup is surely one of the most interesting open questions and promises, if solved, significant improvements to the state of the art of RFID sensing. This work shows hence two such parameters and analyzes their performance in terms of setup independence.

—The possibility to wirelessly monitor the state and the evolution of cracks is of increasing interest in emerging Structural Health Monitoring Systems. A simple and effective measurement method considers the placement of two passive RFID antennas on top of the crack, so that the crack’s evolution will produce a change of the inter-antenna coupling and in turn of the phase of the backscattered field. An ad-hoc design technique, based onto the coupled-mode physics, permits to maximize the sensor’s sensitivity avoiding, or at least mitigating, the read range reduction during the evolution of the displacement that is instead typical of amplitude-oriented RFID displacement sensors. The proposed idea is demonstrated by numerical and experimental examples showing the possibility of sub-millimeter resolution with low-cost devices.

This contribution presents investigation and development of a miniaturized antenna on a PTFE/ceramic substrate for GNSS high-performance applications. Due to the use of such a high-DK substrate, the performance of the antenna is very sensitive to variations in substrate and ground-plane dimensions. It may also severely degrade when the antenna is used in array configurations, due to the excitation of surface waves, producing spurious radiation and a high coupling between adjacent elements. A soft surface is employed to deal with this limitation, resulting in an antenna that exhibits lower coupling with adjacent elements and low sensitivity to changes of the substrate outer dimensions.

The close displacement of UHF RFID tags can be considered as an electromagnetic interconnected system having specific properties. The so denoted RFID Grid includes single-chip tags in close mutual proximity or a single tag with a multiplicity of embedded microchips. A multi-port scattering framework is used to derive the macroscopic parameters governing the system response which could be optimized for the specific application. Moreover, unique features are introduced, such as the possibility to improve the power scavenging and the generation of analog identifiers and fingerprint. The last ones are electromagnetic responses independent on the position and orientation of the reader and on the nearby environment, with great relevance for Sensing and Security.

The automatic optimization is proposed of the passive RF part of RFID, with special attention to multi-chip tags, and to the novel concept of RFID grids. Performance metrics follows a recent all-comprehensive approach. The proposed approach employs a Genetic Algorithm-based optimization, and an efficient electromagnetic problem parameterization and solution strategy. Resulting structures, while non-intuitive in shape, exhibit enhanced performance.

Satellite ground testing is nowadays suffering from long and complicated measurement procedures, where cabled sensors are involved: as such, it could strongly benefit from wireless sensing capabilities, enabling simplified measurement setup procedures and substantial cost reduction. Passive RFID wireless sensors are improving in maturity and robustness for Earth use and could be optimal candidates also for Spacerelated applications. The present work shows a first attempt to evaluate the performance of newly developed temperaturemonitoring RFID sensor tags for satellite ground testing, both from a sensor point of view and from a EMC/EMI perspective.

The UHF passive Radio Frequency Identification technology generally enables an asymmetric interaction between the reader and the tag, the latter only being able to respond to the query of the reader through backscattering modulation. Very recently some experiments put into evidence the possibility to set up a tag to tag communication by using a simple illuminator. The key issues and the physical limitation of such a cross-link are here investigated both theoretically and numerically by fully accounting for the mutual coupling among the tags, their radiation properties and the impedance modulation.

This work presents an analytical analysis of the thermal noise in widely used correlated double-sampling (CDS) circuits. The objective is to provide designers with simplified noise formulas essential for the design and optimization of such blocks. The obtained analytical results are confirmed with SpectreRF noise, SpectreRF transient noise and ELDO transient noise simulations.

In this paper we present a novel approach to interference mitigation. We propose to equip a GNSS receiver with a diversely polarized antenna array in order to combine signal processing in the spatial and in the polarization domain in a novel way. The new algorithm is evaluated by means of measurement data obtained during a measurement campaign which has been carried out in the Automotive Testing Center in Aldenhoven, Germany. The results of the measurement campaign show a significant improvement in receiver robustness against interferences when the dual-polarization approach is used when compared with the general single-polarization case. The benefits that come to light using dual-polarization are of a dual nature. First the carrier-to-noise-density ratios of the line-of-sight components are improved since the receiver can make use of the RHCP power present on the left-hand circularly polarized (LHCP) channels due to non-ideal polarization purity of the antenna, in particular for satellites with low elevation, resulting in better receiver computed position, velocity and time (PVT) solutions. Secondly, the interference mitigation becomes more effective due to the possibility of filtering in the polarization domain and the additional number of available degrees of freedom, increasing the receiver robustness and enabling tracking and PVT also in severe interference scenario

This work shows the design and manufacturing of a compact antenna array for use as controlled radiation pattern array (CRPA) in satellite navigation applications. The array has dual band capability for the Galileo Global Navigation Satellite System (GNSS) at E5a and E1 bands. The overall size of the array is only 10 cm × 10 cm and this enables it to be used in applications where compactness is a key factor. The small dimension of the array implies a close arrangement of the antennas, thus producing mutual interaction between the elements, with potential performance degradation. A solution to such problem is proposed in the paper, making use of a metallic wall, managing to reduce the coupling.

This work shows the design and test of a dielectric resonator antenna (DRA) able to cover all GNSS bands with good polarization purity and minimal group delay variations, thus enabling minimal antenna-related contributions to the GNSS pseudorange error. Both electromagnetic simulations and measurements in DLR’s near field chamber are shown, proving the excellent performance of the antenna. Moreover, the antenna related GNSS error is shown by means of a GNSS software receiver.