###### Abstract  
To date, no universal modelling technique is available to mitigate the effect of site-specific multipaths in high-precision global navigation satellite system (GNSS) data processing. Multipaths affect both carrier-phase and code/pseudorange measurements, and the errors can propagate and cause position biases. This paper presents the use of an Eccosorb AN-W-79 microwave-absorbing material mounted around a GNSS antenna that reflects less than \(-17\) dB of normal incident energy above a frequency of \(600\)  MHz. To verify the feasibility and effectiveness of the Eccosorb, we installed two close stations by continuously operating multi-GNSS (BeiDou, GLONASS, Galileo and GPS) in a challenging location. One station is equipped with the Eccosorb AN-W-79, covering a square area of \(3.35\) m\({}^{2}\) around the antenna, and the second station operates without it. The standard deviation reductions from single point positioning estimates are significant for all the individual GNSS solutions for the station equipped with microwave-absorbing material. The reductions are as follows: for GPS, between \(15\%\) and \(23\%\); for Galileo, between \(22\%\) and \(45\%\); for GLONASS, \(22\%\); and for BeiDou, \(4\%\). Furthermore, we assess the influence of multipaths by analysing the linear combinations of code and carrier phase measurements for various GNSS frequencies. The Galileo code multipath shows a reduction of more than \(60\%\) for the station with microwave-absorbing material. For GLONASS, particularly for the GLOM3X and GLOM1P code multipath combinations, the reduction reaches \(50\%\), depending on the observation code types. For BeiDou, the reduction is more than \(30\%\), and for GPS, it reaches between \(20\%\) and \(40\%\). The Eccosorb AN-W-79 microwave-absorbing material shows convincing results in reducing the code multipath noise level. Again, using microwave-absorbing material leads to an improvement between \(15\%\) and \(60\%\) in carrier phase cycle slips. The carrier-phase multipath contents on the post-fit residuals from the processed GNSS solutions show a relative RMS reduction of \(13\%\) for Galileo and \(9\%\) for GLONASS and GPS when using the microwave-absorbing material. This study also presents power spectral contents from residual signal-to-noise ratio time series using Morlet wavelet transformation. The power spectra from the antenna with the Eccosorb AN-W-79 have the smallest magnitude, demonstrating the capacity of microwave-absorbing materials to lessen the multipath influence while not eliminating it. global navigation satellite system (GNSS); multipath; site-specific effects; microwave-absorbing material (MAM); GNSS reference station +
Footnote †: journal: Sensors  
doi  
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site position solutions: tropospheric and multipath sources [7; 8]. Geodesists estimate site position, troposphere and ionospheric delays assuming that there is only a direct signal as received by the GNSS receiver, but this is not attainable due to the basic design of the GNSS antenna, which receives an electromagnetic wave from multiple directions simultaneously and cannot discriminate direct from reflected directions. The multipath typically manifests as interference from the near- and far-field (Fraunhofer diffraction) reflection of the GNSS signal superimposed on the direct electromagnetic signal transmitted by the satellites. The multipath will introduce errors in the carrier phase and pseudorange measurements, and it will then propagate to other GNSS products that rely on the pseudorange and carrier phase measurements [9]. Many studies have been devoted to mitigating the effects of multipaths on site-position estimates, e.g., [8; 9; 10; 11]. These studies found that the scattering environment within the near-field region of the antenna can introduce errors of a centimetre or more in the estimated vertical coordinate but have no discernible effect on the horizontal coordinates.