The purpose of this study was to automatically track an Unmanned Aerial Vehicle (UAV), with an electronically steered antenna. To make it possible to track the UAV during flights, a 2.4 GHz transmitter was mounted on the aircraft.
Due to the regulations of transmitted signal power and the fact that a very powerful transmitter would consume to much power, a 10 mW transmitter was used during development. With such a weak transmitter a high gain antenna (a reflector antenna in this case) is required, in the receiver, to detect the transmitted signal at far distances.
To be able to detect movement of the UAV, four small Yagi-antennas are mounted around the focal point of the reflector disc antenna. The received signal strength in the four Yagi-antennas will vary depending on where the transmitter (UAV) is located relative to the tracking device. By comparing the strength of these signals using a microcontroller, the direction of the UAV can be computed and in turn the antenna can be
made to track the UAV.
To detect the strength of the signals, four Linear Technology® 5534 power detector chips were used. These chips produce a linear DC voltage output corresponding to the received RF signal strength. The DC outputs of the power detectors are connected to the A/D inputs of the microcontroller (in this case a Microchip PIC16F877). The levels are evaluated, and the antenna motors are driven in the necessary direction.
A great deal of time was also spent on the mechanical design, as it had to be very strong but also collapsible to fit into a car trunk. All details were drafted in IronCAD before production in the ECSE mechanical workshop.
The project was very successful; test flights were made on distances up to ~1km with good results. With minor adjustments in the power detectors, tracking of the UAV would be possible at even greater distances.
Source: Luleå University of Technology
Authors: Jonas Gustafsson | Fredrik Henriksson
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