## 5 Conclusions and Future Work  
In this work, a GNSS adaptive antenna array with digital beamforming was reported. The array was developed with COTS GNSS antennas. The performance of these antennas was validated via simulation in CST. The array geometry was studied resorting to Matlab, and the final array simulations were performed in CST. It was demonstrated that the proposed array can improve the gain comparatively to the traditional GNSS antenna in all directions, even close to the horizon. It was also possible to observe that the array maintains reasonable circular polarization in the directions to which the main beam points.  
A digital beamforming solution was developed in Xilinx's ZCU216, with each of the array's 16 antennas being connected to an ADC channel. The GNSS signals, after being sampled by the ADCs, were weighed according to a beamforming algorithm that received as inputs the direction towards which the main beam was to be pointed. The full system was tested in an anechoic chamber, where good results were obtained in both single- and multibeam scenarios, with a great agreement between the simulated and measured data.  
Nevertheless, desirable improvements in the system have been identified, namely the use of custom GNSS antennas with better AR over the range of interest. Furthermore, it was verified that in the multibeam approach, the results could be improved by developing an array with an improved HPBW, either by using more directive antenna elements or by geometry redesign.  
The results presented in this paper validate the FPGA-based array and beamforming development platform, paving the way for the seamless and rapid design and test of numerous antenna array geometries with up to 16 channels and beamforming algorithms, including adaptive ones. This powerful and versatile tool will accelerate research on the performance improvement of GNSS reception.  
Figure 17: Measured and simulated multibeam azimuth radiation pattern with beams pointing towards \(\theta=0^{\circ}\), \(\theta=45^{\circ}\), and \(\theta=330^{\circ}\). The blue dashed lines indicate the targeted main beam directions.  
**Author Contributions:** Conceptualization, G.D., H.D., D.B. and P.M.M.; methodology, G.D., H.D., D.B. and P.M.M.; software, G.D. and D.B.; validation, H.D. and P.M.M.; formal analysis, G.D., H.D. and D.B.; investigation, G.D., H.D. and D.B.; resources, D.B. and P.M.M.; data curation, H.D. and D.B.; writing--original draft preparation, G.D., H.D. and D.B.; writing--review and editing, G.D., H.D., D.B. and P.M.M.; supervision, H.D. and P.M.M.; project administration, H.D., D.B. and P.M.M.; funding acquisition, P.M.M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work is supported by national funds through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project n\({}^{\circ}\) 179491; Funding Reference: SIFN-01 999-FN-179491].  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Bosch Car Multimedia Portugal, S.A. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.