**Andreas Krietemeyer \*, Hans van der Marel, Nick van de Giesen and Marie-Claire ten Veldhuis**

Faculty of Civil Engineering, Delft University of Technology, 2628CN Delft, The Netherlands; H.vanderMarel@tudelft.nl (H.v.d.M.); N.C.vandeGiesen@tudelft.nl (N.v.d.G.); j.a.e.tenveldhuis@tudelft.nl (M.-C.t.V.)

**\*** Correspondence: A.Krietemeyer@tudelft.nl

Received: 4 April 2020; Accepted: 25 April 2020; Published: 28 April 2020

**Abstract:** The recent release of consumer-grade dual-frequency receivers sparked scientific interest into use of these cost-efficient devices for high precision positioning and tropospheric delay estimations. Previous analyses with low-cost single-frequency receivers showed promising results for the estimation of Zenith Tropospheric Delays (ZTDs). However, their application is limited by the need to account for the ionospheric delay. In this paper we investigate the potential of a low-cost dual-frequency receiver (U-blox ZED-F9P) in combination with a range of different quality antennas. We show that the receiver itself is very well capable of achieving high-quality ZTD estimations. The limiting factor is the quality of the receiving antenna. To improve the applicability of mass-market antennas, a relative antenna calibration is performed, and new absolute Antenna Exchange Format (ANTEX) entries are created using a geodetic antenna as base. The performance of ZTD estimation with the tested antennas is evaluated, with and without antenna Phase Center Variation (PCV) corrections, using Precise Point Positioning (PPP). Without applying PCVs for the low-cost antennas, the Root Mean Square Errors (RMSE) of the estimated ZTDs are between 15 mm and 24 mm. Using the newly generated PCVs, the RMSE is reduced significantly to about 4 mm, a level that is excellent for meteorological applications. The standard U-blox ANN-MB-00 patch antenna, with a circular ground plane, after correcting the phase pattern yields comparable results (0.47 mm bias and 4.02 mm RMSE) to those from geodetic quality antennas, providing an all-round low-cost solution. The relative antenna calibration method presented in this paper opens the way for wide-spread application of low-cost receiver and antennas.

**Keywords:** GNSS; GNSS antenna; receiver antenna calibration; relative calibration; Phase Center Variation; U-blox; goGPS; Zenith Tropospheric Delay; ZED-F9P
