The directional antenna tracker for enhancing range communication between UAVs and Ground Control Station

This paper discusses the development of an antenna tracker project focused on evaluating a 2.4 GHz Yagi Uda directional antenna connected to an NRF24L01 transceiver. It employs a gear reduction system for precise yaw and pitch control using two servo motors. The tracker calculates rotation angles using the Haversine formula for coordinates and inverse tangent trigonometry for elevation. Experiments took place in an open area with a stationary Ground Control Station (GCS) and a moving Unmanned Aerial Vehicle (UAV) to assess performance. The experiments comprised three tests: first, GCS without the Yagi Uda antenna or tracker; second, GCS with the Yagi Uda antenna but without the tracker, positioned along a 30-degree angle away from the transmitter; and third, GCS with both the Yagi Uda antenna and the tracker. The UAV gradually moved away from the tracker in 5-meter intervals until data loss occurred. The test results are based on received coordinates, distance, temperature, humidity, and data loss. Among the three tests, Test 3 demonstrates the best outcome, where the Yagi Uda antenna successfully receives data up to 180 meters before experiencing data loss.


Introduction
In the last decade, Unmanned Aerial Vehicles (UAVs) have revolutionized various sectors, particularly in surveillance and monitoring [1][2].Despite their versatility, a persistent challenge is the susceptibility of UAVs to communication losses, which can lead to critical failures [3][4][5].To address this, researchers have explored antenna enhancements and positioning techniques [6][7][8].This study focuses on developing and evaluating an automatic pointing antenna tracker paired with a directional Yagi Uda antenna to extend UAV-Ground Control Station (GCS) communication range.Previous research has highlighted the significance of communication robustness for UAVs [9], and various approaches have been examined, such as omnidirectional antennas and advanced positioning methods [10][11].However, a gap exists in addressing non-line-of-sight (NLOS) propagation challenges using directional antennas 2 [12].The primary objective is to enhance communication reliability for UAVs by creating an automatic pointing antenna tracker alongside a 2.4 GHz Yagi Uda antenna.This research simulates UAVs equipped with essential sensor modules, transmitting data to a GCS.Parameters such as data transfer rates, distance coverage, and environmental factors are rigorously evaluated.In the broader context, with UAVs finding increasing applications, uninterrupted communication gains paramount importance in disaster relief, agriculture, and environmental monitoring.Our study contributes to this discourse by developing a system that bridges the gap in UAV-GCS communication.The following sections delve into the mechanics of the antenna tracker, gear reduction systems, mathematical formulations for precise tracking, the experimental setup, and the results.By exploring uncharted territory, this research aims to enhance the communication range between UAVs and GCS within the realm of UAV communication methods.

Methodology
This section will delve into the principle of motion employed in the antenna tracker, utilizing a gear reduction system.Furthermore, the utilization of the Haversine formula and the arctangent twoargument function with the required parameters will be explained.The design of the antenna tracker will be thoroughly reviewed, and the experimental setup will be described in detail.

3D Design
Figure 1 presents a 3D model of the developed antenna tracker.The upper part of the tracker shows the Yagi Uda antenna, firmly affixed using the stall torque provided by the SPT5325LV-360 servo motor.This section is designed to facilitate yaw movement, allowing for motion along the z-axis.The lower part of the tracker consists of the control box, housing the necessary circuitry and serving as the mounting location for the MG996R servo motor, specifically designed for the yaw movement.

Circuit Design
Figure 2 illustrates the circuit design, featuring the Raspberry Pi Pico as the main microcontroller.The circuit includes two servo motors responsible for controlling the yaw and pitch movements.Additionally, a 2.8-inch TFT Display is incorporated to showcase the data transmitted from the transmitter to the receiver.

Gear Reduction
According to Equation 1, the number of teeth required for the drive gear and the driven gear can be calculated.This formula is used to determine the output torque of the servo motor, ensuring that it can handle the weight of the antenna and the rotating part for both the yaw and pitch movements.
In Figure 3, Gear 1 is the drive gear with 15 teeth, connected to the yaw servo motor, while Gear 2 is the driven gear.The gear reduction system implemented for the pitch axis movement follows a 2:1 ratio, where the drive gear has 15 teeth, and the driven gear has 60 teeth.The drive gear has a diameter of 15 mm, while the driven gear has a diameter of 48 mm.This configuration allows for effective gear reduction in the pitch movement of the antenna.The drive gear is mounted on a servo motor MG996R with a torque of 9.4 kg/cm.According to Equation 1, the maximum output torque from the driven gear is 4.7 kg/cm.Considering the weight of the Yagi Uda antenna and its rotating gear part, which is approximately 1.4 kg, the output torque is more than sufficient to support the weight and provide enough force to rotate the upper part of the antenna tracker.
Figure 4 demonstrates a gear configuration where the drive gear has 15 teeth, and the driven gear has 30 teeth.The drive gear has a diameter of 15 mm, while the driven gear has a diameter of 23 mm.This gear reduction system is employed to enable the rotation of the Yagi Uda antenna in pitch angle motion.The drive gear is mounted on a Servo motor SPT5325LV-360 with a torque of 25 kg/cm.Utilizing Equation 1, the maximum output torque from the driven gear is calculated to be 14.29 kg/cm.With the weight of the Yagi Uda antenna and its rotating gear, part is approximately 1 kg, this configuration can handle the antenna at any rotating position.Additionally, it can support the antenna at a stall position at any angle if encountered during testing.2illustrates the Haversine formula, which is employed to calculate the differences in distance and angle between the antenna tracker and the transmitter box on the UAV, based on their respective coordinates.This formula enables an accurate estimation of the variations in both distance and angle between the two points.
Where,  & refers to the latitude of the UAV,  ' refers to the latitude of the antenna tracker,  & refers to the longitude of the UAV,  ' refers to the longitude of the antenna tracker and  represents the radius of the earth, approximately 6371 kilometres.

Yaw Formula
To facilitate the yaw movement or vertical rotation of the antenna, the inverse tangent function is employed to calculate the angle between the altitude of the antenna tracker and the altitude of the transmitter box.Equation 3 presents the formula utilized in the programming for this purpose.
& refer to angle for yaw motion,  & refer to altitude of the UAV,  ' refer to altitude of the antenna tracker and  is the distance from antenna tracker and UAV unit is in meter.

Gear Reduction Formula
The Gear Reduction method involves reducing the rotational speed of the output gear by meshing its teeth with the driven gear.Equation 4 represents a Gear Reduction formula, which typically refers to the ratio between the number of teeth on the driven gear (output gear) and the drive gear (input gear).
where,  ' is the number of driven gear teeth and  & is the number of drive gear teeth.

Result and Discussion
The movement of the antenna for yaw and pitch is dictated by variations in coordinates and elevation values.Precise location information is obtained from the NEO 6M GPS module, while the MS5611 pressure and altitude sensor provides elevation data.These measurements collectively enable the yaw rotation of the antenna.To gauge the accuracy of distance measurements, the Haversine formula is employed to calculate the distance between the antenna tracker and the transmitter.This serves as a valuable metric for assessing distance precision.Furthermore, the system captures temperature and humidity values using the AHT10 temperature and humidity sensor located on the transmitter of the UAV.This data is transmitted to the ground control station, enabling an evaluation of data transmission and communication range in real-world weather conditions.

Result
The performance evaluation of the Yagi Uda antenna is based on the parameter of data loss time in seconds.The results of Test 1 show that when the Yagi Uda antenna is not connected to the NRF24L01 receiver, data transmission is possible in an open area without obstacles up to 20 meters between the GCS and the UAV.The outcome of Test 2 demonstrates that data can be effectively transmitted to the Yagi Uda antenna for distance of up to 45 meters.However, at 40 meters, signs of momentary data loss started to emerge.This lasted for 3 seconds, after which the data was successfully retrieved and received by the Yagi Uda antenna.The result from Test 3, focused on dynamic movement of the Yagi Uda antenna tracker, that tracking the movement of the UAV's motion through the transmitter box, are detailed in Table 1.The data can be transmitted over long distances, reaching the end of the designated area.The table shows that the maximum distance achieved was 180 meters, limited by the experimental setup area.Starting from 130 meters, there were consistent occurrences of data loss, with the data loss time progressively increasing until it became unreachable at the maximum distance of 180 meters.

Conclusion
Throughout this project and testing, the developed antenna tracker has demonstrated good performance in accurately pointing toward the transmitter box on the UAV, with minimal pointing tolerances.However, it should be noted that the data obtained from the GPS module exhibited some instability and tolerance due to the sensitivity and precision limitations of the module itself.Since the GPS module has a maximum precision of 2.5 meters, the antenna tracker is best suited for long-range applications to ensure more precise coordinates and movement.As the calculated distances increased, there were slight tolerances observed within an acceptable range.Despite minor fluctuations in the pressure values affecting the elevation measurements, the Yaw movement displayed minimal errors.However, when the value changes were small, the pointing direction showed slight deviations.The utilization of the SPT5325LV servo motor as the actuator for Yaw rotation allowed for a minimal rotation angle of 15 degrees.The results suggest that the application of the Yagi Uda 2.4Ghz antenna can enhance the distance capabilities of the NRF24L01 as an antenna tracker.In conclusion, this antenna tracker design can be implemented in various applications, as it offers improved antenna performance for communication.However, it is important to consider the limitations and tolerances associated with the GPS module's precision for accurate operation.

Figure 3 .
Figure 3. Gear reduction for yaw movement.Figure 4. Gear reduction for pitch movement.

Figure 4 .
Figure 3. Gear reduction for yaw movement.Figure 4. Gear reduction for pitch movement.

3. 1 .
Experimental SetupThe antenna tracker underwent testing in the open field of the Faculty of Electrical Engineering at UniMAP.The initial setup involved preparing the transmitter box, which consisted of a GPS module, altitude sensor, and humidity and temperature sensor.The GPS module was allowed to receive signals for a minimum of 5 minutes to ensure signal stability.Next, the antenna tracker was set up by placing the receiver box on it to determine the position of the antenna.The experiment proceeded with three tests: Test 1: Without the Yagi Uda antenna and without the tracker, Test 2: With the Yagi Uda antenna but without the tracker, positioned along a 30-degree angle away from the transmitter and Test 3: With both the Yagi Uda antenna and the tracker as depicted in Figure5.To ensure the stability of transmitted coordinates, a 10-second delay was implemented.After the delay, the data was displayed on the antenna tracker.The experiment was conducted by gradually increasing the distance between the antenna tracker and the transmitter box.The distance intervals started from 0 meters and were incremented by 5 meters until data loss was observed.

Figure 5 .
Figure 5. Testing site and setup.

Table 1 .
Data received by using Yagi Uda antenna with tracker.