Triangular phase-shift detector for drone precise vertical landing RF systems

TL;DR

The paper tackles precise vertical drone landing by introducing a triangular phase-shift detector fed from a landing-point oscillator, leveraging three inputs and 90° hybrid-based analog phase detectors to generate DC voltages proportional to inter-input phase differences. The approach maps phase information to drone position and provides a simple, integrable landing algorithm that operates within a non-ambiguous phase range of about $\pm 80^{\circ}$, demonstrated via a 2.46 GHz prototype using AD8302 detectors and 90° hybrids. Key contributions include a complete design, calibration procedure, a polynomial model to convert detector outputs to phase, and validated flight-like maneuvers showing tracking within an inverted cone of radius roughly half the drone height. The work offers a lightweight, high-rate guidance option for the final landing phase, suitable to augment imaging and GPS-based systems for robust vertical precision in challenging environments.

Abstract

This paper presents a circuit for precise vertical landing of drones based on a three phase-shifts detection of a single frequency transmitted from the landing point. The circuit can be considered as a new navigation sensor that assists in guidance corrections for landing at a specific point. The circuit has three inputs to which the signal transmitted from an oscillator located at the landing point arrives with different delays. The input signals are combined in pairs in each of the three analog phase detectors, after having passed through 3 dB@90 o hybrid couplers that guarantee a theoretical non-ambiguous phase-shift range of +-90 degree. Each output has a voltage that is proportional to the phase-shift between each of the input signals, which in turn depend on the position relative to the landing point. A simple landing algorithm based on phase-shift values is proposed, which could be integrated into the same flight control platform, thus avoiding the need to add additional processing components. To demonstrate the feasibility of the proposed design, a triangular phase-shift detector prototype has been implemented using commercial devices. Calibration and measurements at 2.46 GHz show a dynamic range of 30 dB and a non-ambiguous detection range of +-80 degree in the worst cases. Those specs let us to track the drone during the landing maneuver in an inverted cone formed by a surface with a +-4.19 m radius at 10m high and the landing point.

Figures (15)

• Figure 1: Coordinate reference system and points that define the problem.
• Figure 2: (a) Top view of Fig. \ref{['fig:figura1']}. (b) Phase shift between input and signals when location of the landing point ($L$) is changed around drone.
• Figure 3: (a) Simplified measurement system for phase-shift measurements based of analog multiplier. (b) Ideal phase detector response highlighting the non-ambiguous range ($\pm$90º).
• Figure 4: Drone locations at the limit of the non-ambiguous detector phase range ($\pm$90º) for several drone height ($f$=2.45GHz and $D$=7cm). Curves traced from 1m to 10m in 1m step and from 1m to 0.1m in 0.1m step. (a) 3D view. (b) Top view where the worst case ($r_{L_{WC}}$=486 cm) and best case ($r_{L_{BC}}$=585 cm) are indicated at 10m drone height.
• Figure 5: Polar coordinates of sectors and corresponding angles obtained from phase-shift curves in Fig. \ref{['fig:figura2b']}.