###### Abstract
Another technique to characterize multipath effects is by repetitively observing the same satellite, looking for patterns in the carrier-phase measurements that are shifted by approximately 247 s in the case of a GPS satellite constellation, which is linked to its intrinsic one-day sidereal orbital period [25]. However, the shift between two consecutive sidereal days varies even among GPS satellites [25], and it can be even more complex for multiple GNSS constellations. In the time domain, the methods of sidereal filtering as first reported by [26] and subsequently improved by [27; 28; 29], or advanced sidereal filtering [30; 31], have been developed to alleviate the effects of multipath errors capitalising on such repeating orbits. In addition, a slew of a new generation of GNSS signals, formed by modulation through multiplexing a wideband signal with a narrow-band signal, can improve the multipath effect [32]. Another approach is to use the signal-to-noise ratio (SNR) observations caused by the interference due to the multipath effects superimposed on the direct signal [33; 34; 35], isolating the multipath frequency by performing the wavelet analysis method [34; 35]. Furthermore, [36] applied an advanced homomorphic (or cepstrum) filtering technique on the SNR signal to remove multipath influences and improved stochastic modelling by giving different weights to the carrier phase observations depending on their corresponding SNR values [37]. Creating multipath stacking maps is one option from long-term observation by allocating the carrier phase post-fit residuals to azimuth and elevation grid cells to mitigate unmodelled site-specific errors [38; 39; 40; 41; 42] and with further improvement in multipath stacking maps using congruent cells [43; 44] and multipath hemispheric mapping [45]. [PERSON] [46] investigated multipath mitigation using the ray-tracing technique. [PERSON] et al. [47] developed an antenna and multipath calibration system to provide _in situ_ corrections, but the technique calls for a reoccupation of the site if the multipath varies. Another _in situ_ technique is to place microwave-absorbing materials around the GNSS antenna; as a result, which reduces the amplitude of the reflected/scattered signals [8; 10; 48]. This study limits the area covered by the microwave-absorbing material around the antenna's direct vicinity and uses GPS-only data. In spite of the multitude of studies devoted to understanding site-specific multipaths, the multipath error remains elusive, and researchers haven not yet found a \"silver bullet\". Additionally, each multipath mitigation technique has its own set of weaknesses, such as implementation difficulty or incompatibility with either static or real-time navigation applications. One strategy for minimizing multipath effects is to employ a larger-sized microwave-absorbing material that is appropriately placed in an antenna's vicinity in an _in situ_ method that avoids the need for sophisticated mitigation techniques. This paper explores how the influence of multipath on the GNSS carrier phase and code/pseudorange measurements can be reduced by using micro-absorbing materials covering a larger area than previous studies have attempted and further including other GNSS, i.e., BeiDou, GLONASS and Galileo. For this, we have established two continuously operating GNSS stations, one with microwave-absorbing materials and the other station without the Eccosorb materials. Section 2 presents the general theory on multipath detection techniques. Section 3 presents a brief theory on Fresnel zones. Section 4 outlines the experimental setup and GNSS data processing. Sections 5 and 6 present the effect of the Eccosorb An-W-79 microwave-absorbing material on the post-fit carrier phase residual, impacts on single-point positioning, linear multipath combinations from multi-GNSS code observables, and measure the multipath frequency manifested in the SNR time series by performing a wavelet transform. A conclusion is offered in Section 7.