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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.

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.

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.

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).

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.