# C Band 360\({}^{\circ}\) Triangular Phase Shift Detector for Precise Vertical Landing RF System
## 5 Discussions
In any case, the key to being able to cope with a wide variety of turbulences or movements is to have circuits that can provide a high ODR, such as the one proposed in this article. Including an AGC in the design reduces to four curves the number of minimum functions needed to characterize the circuit response. In addition, it provides a dynamic range in excess of 50 dB, without having to handle interpolation matrices as in [42] or being limited to a single power as in [41; 43]. However, it will have to operate within the linear ranges of the devices, mainly the mixer (product phase detector), in order to use simple sinusoidal modeling, unlike the matrix model used in [42], which can model any type of response and operate the circuit outside the linear ranges. Despite the introduction of the AGC, calibration is necessary for each frequency to be used. First, the phase shift of each branch depends on the frequency. Second, between the AGC reference point and the detector output are the power divider and the multiplier (Figure 7), which have a different amplitude and phase response at each frequency. However, the calibration procedure is identical at all frequencies and it is sufficient to include the parameters of the sinusoidal model (Table 3). Despite the parameters to be included in memory (Table 3) and the calculations to switch from voltages to phases, it is still a solution that can be easily integrated into piloting platforms such as Ardupilot or Pixhawk, without the need for specific processing units. This is unthinkable when using image processing [5; 6; 7; 8; 9; 10; 11; 12; 13] or UWB [18; 19; 20; 21; 22; 23; 24], where powerful processing platforms, communication ports, and memory must be used. The proposed system presents a 1.7% reduction in phase detection over a range of \(\pm 180^{\circ}\) (Figure 13). The percentage affects equally the tracking area for each drone height. However, it is not considered a significant loss of range that could compromise the landing maneuver. This loss is much lower than in [25; 27], when the loss was 11% over \(\pm 90^{\circ}\). In both cases, multipliers have been used as phase detectors. However, a displacement due to unbalance between paths is transformed into a loss of the same value when a single multiplier is used (unambiguous range \(\pm 90^{\circ}\)), while the double multiplication procedure compensates this displacement and reduces it to \(0^{\circ}\), i.e., the all range \(\pm 180^{\circ}\) is available. In the article circuit, the loss of range is confined to the lack of precision in the curve modeling the detector response (Equation (4) and Figure 12), i.e., it derives from the fact that the multiplier does not have a purely sinusoidal phase response. A simple program has been developed to show the drone guidance algorithm and the phasing behavior in the drone descent. The system with phase range \(\pm\)90\({}^{\circ}\) must detect the proximity to the ends to determine that it is not in ambiguous area [25; 27]. This is an effective reduction in the useful range. However, the topology used allows detecting the instant at which it leaves the unambiguous zone from an abrupt change in any of the phase shifts (Figure 17). If this situation occurs, the drone must undo the maneuver and return to the unambiguous zone, unlike systems based on image processing [5; 6; 7; 8; 9; 10; 11; 12; 13] or UWB [18; 19; 20; 21; 22; 23; 24; 26], where there is no concept of ambiguous zone and they do not have this limitation.