The GNSS antenna is an interface between the GNSS satellites and GNSS receivers. With the rapid increase in demand of Location Based Services, GNSS is becoming a must have feature in the smartphones these days. With a quick test of smartphone equipped with GNSS, it is evident that although GNSS chip are more efficient as compared to the old generation chips, the integrated end results still suffer from a performance limitation. With the latest advancements like dual frequency chipsets from Broadcom BCM45577 (Shade & Madhani 2018), the positioning performance of the smartphones have significantly improved from several meter to decimeter meter level (Banville & Van Diggelen 2016). But, with the increasing precise positioning applications, the current smartphones still offer a limited accuracy (decimeter level) results. Multiple challenges faced by the smartphones designers are key factor in the performance glitch, with the main two being the antenna performance and the crosstalk within the smartphone platform itself (Moernaut & Orban 2009). Most of the handset designers are not GNSS or even RF experts, and rely on catalog components to provide GNSS and antenna hardware. Often unsuitable, cheap antenna are chosen or they are placed in the most unseemly positioning within the Smartphone casing. The handset designer faces several problems when incorporating a GNSS antenna. Cost efficient, omnidirectional radiation pattern are only few of those. As a GNSS engineer, we would prefer GNSS antenna to be far as possible from the transmitting devices like Bluetooth, Wi-Fi, FM etc. (Haddrell et al. 2010). Secondly, the performance of GNSS antenna itself is unacceptable. The point at which GNSS signal is received is called APC (Antenna Phase Center). The APC does not coincide with the physical phase center and keeps on changing with signal frequency, elevation, azimuth and intensity of the satellites (El-Hattab 2013). Hence, the mean positon of the varying electrical center must be determined for the calibration purpose. Additionally, the multipath is a second major problem in terms of GNSS positioning quality in smartphones. Cheap antenna in smartphones offers no or minimal multipath rejection capabilities (Haddrell et al. 2010). Waves suffering longer diffraction and reflection can be separated from the original signal due to the delay in arrival time. But, the waves which have minor reflection and diffraction distort the correlator function, thus degrading pseudoranges and carrier phase (Granger & Simpson 2008). In this paper, we propose a GNSS smartphone multipath mitigation (rejection) using state of the art choke ring platform. In this setup, the smartphone is mounted on geodetic pillars with choke ring platform underneath. Grooves likes structure is choke ring platform is well known from blocking or decaying the waves travelling parallel to the surface. The idea behind this technique is to decay the waves travelling from below or parallel to the ground plane. The GNSS raw measurements logged with the smartphone are used to perform RTK with another reference receiver within the small baseline.

Keywords: RTK, GNSS, carrier phase, choke ring platform, duty cycle, cycle slips