# C Band 360\({}^{\circ}\) Triangular Phase Shift Detector for Precise Vertical Landing RF System
## 6 Conclusions  
In this paper, a novel circuit for accurate vertical landing of drones based on a triple phase detection in the range of \(\pm\)180\({}^{\circ}\) has been presented. * The design has been realized with a double multiplication phase detector, in phase and phase-shifted, which facilitates the design because it allows an unbalancing of the different branches without loss of detection range. The increase in the phase detection range up to \(\pm\)180\({}^{\circ}\) transforms into a directly proportional increase in the tracking area. An analysis of the tracking volumes (inverted cones) has been performed comparing different frequencies, distances between RF inputs, and phase detection ranges (\(\pm\)180\({}^{\circ}\) and \(\pm\)90\({}^{\circ}\)). * The results with \(\pm\)180\({}^{\circ}\) show the possibility of increasing the working frequency and reducing the size of the antennas, while maintaining the tracking area of systems operating at \(\pm\)90\({}^{\circ}\). Compared to previous designs that have used this technique, an AGC has been included that substantially simplifies the calibration and modeling of the curves of this type of detector and, therefore, the algorithm to determine the phase shift from the voltages measured at the output of the multiplier. This makes possible its integration in a simple control circuit board or as part of the flight control system. * A simple program is proposed that implements the guidance instructions from the calculated phase shifts, which could be integrated into the same flight control platform, thus avoiding the need to add additional processing and memory components. * A prototype has been manufactured with commercial circuits and microstrip technology that operates in the C frequency band, avoiding the crossing of lines by means of switches. In this work, the calibration and characterization process has been performed at 5.3 GHz. The measurements show a dynamic range of more than 50 dB and an unambiguous detection range of \(\pm\)177\({}^{\circ}\), taking into account the uncertainty produced by the phase error of \(\pm\)3\({}^{\circ}\). The tracking area shows a considerable increase with respect to previous developments that have a theoretical phase shift of \(\pm\)90\({}^{\circ}\). As shown, it changes from an area of approximately 1 m radius to 3.3 m radius when the inputs are at \(D\) = 7 cm, the frequency is 2.5 GHz, and the drone is at 2 m height (Figure 4). * Finally, a simulation program has been developed to visualize the drone trajectories and phase evolution. Different situations have been analyzed in which the drone stays inside the tracking zone (phase shifts lower than \(\pm\)180\({}^{\circ}\)) and achieves a successful landing or goes out of it (phase shifts higher than \(\pm\)180\({}^{\circ}\)) and lands at any wrong location. Conceptualization, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Methodology, B.P.D.-N. and E.J.-Y. ; Software, V.A.-P. and F.C.-A. ; Validation, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. Formal analysis, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. Investigation, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Resources, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Writing--original draft, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Writing--review and editing, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Visualization, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Supervision, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. ; Project administration, V.A.-P.; Funding acquisition, V.A.-P., B.P.D.-N., F.C.-A. and E.J.-Y. All authors have read and agreed to the published version of the manuscript. This work was supported by the project grant PID2020-116569 RB-C32, funded by the Spanish Ministry of Science and Innovation. Not applicable. The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author. The authors would like to thank [PERSON] for his enormous contribution during this research. The authors declare no conflicts of interest.