Single-antenna direction finding system for multi-rotor platforms
The single-antenna radio frequency (RF), direction finding (DF) system includes a single-element directional antenna, which is mounted on a multi-rotor UAV (Unmanned Aerial Vehicle) and integrates with a DF algorithm for tracking an RF source in the 2.45 GHz ISM band (or any other frequency band). The algorithm will depend on the rotating nature of the platform to scan the azimuth, as well as several elevation angles with respect to the platform axis of rotation, and thus be able to accurately locate the coordinates of the RF transmitter based on the recorded power levels. The RF source determination step is performed during the search mode of the algorithm. The RF transmitter location is saved, and the UAV takes actions accordingly by commencing movement towards that location in the action mode of the algorithm. After some time, the UAV enters the search mode again in case the RF source has moved.
1. A single-antenna direction finding system for multi-rotor platforms, comprising:
a UAV having multiple rotors, the multiple rotors changing attitude, speed, and direction of the UAV;
a direction finding antenna fixed to the UAV;
control circuitry operably connected to the multiple rotors, the control circuitry maintaining a desired pitch roll and yaw of the UAV;
a direction finding (DF) processor onboard the UAV, the DF processor being operably connected to the control circuitry, the DF processor including:
a DF receiver connected to the DF antenna;
means for controlling the UAV to determine an azimuth of maximum signal strength of a signal received by the DF receiver;
means for controlling the UAV to determine an elevation of maximum signal strength of a signal received by the DF receiver; and
means for controlling propulsion of the UAV along the azimuth and elevation of maximum signal strength towards the signal received by the DF receiver.
2. The single-antenna direction finding system according to claim 1 , wherein said direction finding antenna is a four-element, planar microstrip having a high planar gain and a substantially narrow half power bandwidth.
3. The single-antenna direction finding system according to claim 2 , wherein said direction finding antenna further comprises:
a printed circuit board having a top layer, a middle layer, and a bottom layer;
a dielectric substrate disposed on the top layer of the printed circuit board;
printed patch elements forming said four element, planar microstrip, the printed patch elements being disposed on the dielectric substrate;
a metal ground plane disposed on the middle layer of the printed circuit board;
a feed network placed on the bottom layer of the printed circuit board;
conductive elements extending from the bottom layer to the top layer to feed the patch elements in a probe-feed mechanism; and
a four-port RF combiner circuit, the four ports being connected to conductive elements, the four-port combiner circuit having an output signal feeding said DF receiver.
4. The single-antenna direction finding system according to claim 3 , wherein said patch elements are configured to provide a 3D gain pattern having an XZ plane half-power bandwidth of about 55° at an azimuth of 0°, and an XZ plane half-power bandwidth of about 60° at an azimuth of 90°.
5. The single-antenna direction finding system according to claim 4 , wherein said means for controlling the UAV further comprises PID controllers having:
means for accepting commands from a ground station;
means for accepting feedback states from sensors onboard the UAV; and
wherein the PID controllers output roll, pitch, yaw, and altitude correction signals to adjust speeds of said multiple rotors.
6. The single-antenna direction finding system according to claim 5 , further comprising:
a navigation processor;
a GPS receiver operably connected to the navigation processor; and
a switch operably connecting first pitch and roll angle commands from the ground station to said control circuitry, and, alternatively, second pitch and roll angle commands from the navigation processor to said control circuitry based on a signal searching mode of said DF processor.
7. The single-antenna direction finding system according to claim 6 , wherein said DF processor further comprises:
means for completing a first signal scan in the azimuth direction at 0° pitch;
means for completing a second signal scan in the azimuth direction at −10° pitch;
means for completing a third signal scan in the azimuth direction at −20° pitch; and
means for computing a relative location of a signal based on logged power level data from the first, second and third signal scans.
8. The single-antenna direction finding system according to claim 7 , wherein said DF processor further comprises:
means for automatically entering the search mode after the UAV is initialized;
means for entering action mode when a clear maximum signal strength is found during the signal scans, the UAV being commanded to change its direction and move towards the location of the maximum strength signal;
means for performing an intended mission task when the UAV is a predetermined range from the maximum strength signal; and
means for periodically re-entering the search mode to make path adjustments of the UAV based on changes in the strength of the signal.