# C Band 360\({}^{\circ}\) Triangular Phase Shift Detector for Precise Vertical Landing RF System
## 5 Discussions  
In this paper, a design methodology has been developed for a circuit that can function as a phase shift measurement instrument and assist in the vertical landing maneuver of a drone. The methodology has been applied to a prototype manufactured in the C band and microstrip technology. The circuit consists of three RF inputs that are combined two by two to obtain the phase shifts from the output voltages of the detectors. The transmitter is located at the landing point. The main virtue of the designed circuit is the ability to obtain high ODR values for a given computational capacity, compared to those of imaging [5; 6; 7; 8; 9; 10; 11; 12; 13] or UWB [18; 19; 20; 21; 22; 23; 24; 26]. The ODR will be determined mainly by the speed in obtaining the phase shifts between the input signals. The designed circuit is not as fast as that of [25] because that circuit can operate directly with voltages proportional to the \(\pm 90^{\circ}\) phase shift. In contrast, it has a lower tracking area. However, the tracking range and ODR could be maintained using digital detectors with \(\pm 180^{\circ}\) reaching 8 GHz, as used in the frequency synthesizer of [30]. The topology used in this paper needs to acquire two voltages to calculate the phase shift by software as in [24 pablo, 25 pablo, 41; 42; 43; 49; 50]]. Microstrip technology has been used, and by switching the input signals (Q and I) to the phase detector, line crossover has  
Figure 16: Three-dimensional and top view of several landing maneuvers at 5.4 GHz and \(D=4\) cm. Trajectories when the drone is oriented along the positive \(Y\) axis and starts from the position \(\{0,0^{\circ},500\}\). The landing points are located at \(\{490,(-35+n60)^{\circ},0\}\). The original (\(\times\)mark) and final (dot mark) LP have been highlighted in green when the drone has left the unambiguous zone (Figure 17). Figure 17: Input phase shifts and distance to LP when the drone reaches the LP (dashed lines and LPI in Figure 16) and when it does not (solid line and LP6 in Figure 16). The green circle highlights the moment of the abrupt phase change, from \(180^{\circ}\) to \(-180^{\circ}\), to the drone leaving the tracking area. been avoided. This will mean dividing the ODR of [25] by at least a factor of two, while maintaining the tracking area of \(\pm 180^{\circ}\). However, compared to a solution using \(\pm 180^{\circ}\) digital detectors, it allows one to extend the frequency range in an almost unlimited way, since it uses devices (Figure 7) that are commercially available in different technologies: integrated circuits, waveguides, coaxial, etc. The topology with the three reception points on the drone allows the correction information to be available directly, saving time compared to those who obtain it on the ground and subsequently must transmit it to the drone [10; 23]. In addition, the reference signal is at a single point (as are the imaging points [5; 6; 7; 8; 9; 10; 11; 12; 13]), avoiding the visibility problems that can be presented by the dispersion of several anchors in a forest area. However, the latter are able to correct large drone displacements when close to the LP, while the inverted cone shape reduces the correction surface (unambiguous phase) as it descends towards the LP. In practice, the drone receiver system should be at a certain distance from the LP. However, considering that the diameter of the surface is approximately twice the height of the tri-receiver (Figure 5), 25 cm drone legs would provide a surface of half a meter in diameter. On the other hand, our design has the advantage that the base can be moved in pitch and roll without varying the phases on the drone inputs since the transmitter is on the LP. On the other hand, the paper design has the advantage that the base can be pitch and roll without varying the phases on the drone inputs, since the transmitter is on the LP.