| The application of intelligent systems has increased dramatically in industrial and agricultural fields recently.Some tasks such as high-definition monitoring and remote sensing telemetry have gradually been finished by UAV(unmanned aerial vehicle)systems to improve the work efficiency in some complex environmental conditions.The UAVs used in industrial and agricultural fields impose stringent requirements on the cost and the volume of airborne systems.As a result,the data link system,which is one of the key systems of UAVs,is developing in the direction of miniaturization,low cost,multi-function,and high reliability.The UAV data link system consists of the airborne communication system and the ground communication system.The airborne communication system includes an antenna unit,a RF(radio frequency)unit(or RF front-end),a baseband processing unit(including an image and video compression circuit),and a power supply unit.The ground communication system includes functional units such as an antenna unit,a RF front-end unit,a servo tracking unit,a baseband processing unit,a power supply unit,and some interface units.As an important part of the UAV data link system,the RF front-end unit with features of small size,low power consumption,and high reliability plays an important role in the realization of miniaturization and generalization of the UAV data link system.The design and optimization of the RF front-end system are very critical tasks in the design of UAV data link systems.A design scheme of UAV data link integrated with S-band data transmission link and C-band image transmission link is presented to meet the application requirements of UAVs used in industrial field with a flight range of 10 km ~ 100 km.The data transmission link is implemented by using the S-band data transmission link with the bit rate of 150 kbps.And the image transmission link is implemented by using the C-band data transmission link with the bit rate of 10 Mbps.With the development of microwave integrated circuit,the performance and the integration of RF chips are gradually increasing.A small-scale and low-cost RF front-end is implemented by using high-integrity and low-cost industrial-grade RFchips to meet the design requirements of UAV data link RF front-end.The transmission unit of the RF front-end is implemented by using direct-conversion transmitter architecture.The industrial-grade RF quadrature modulator chips are used to implement the quadrature modulating unit which can implement direct modulating of baseband signal to S-band and C-band carrier frequency.In order to reduce the system cost and shorten the development cycle,the S-band and C-band power amplifiers for the UAV data link are implemented by using the same broadband power amplifier design scheme.The output power of the S-band and C-band power amplifiers of the UAV data link communication system is to about 7W respectively,and the output EVM(error vector magnitude)of the RF modulation signal is less than6%.The receiving unit of the RF front-end is implemented by selecting the industrial-grade low noise amplifier,one mixer and some filters to achieve a wide dynamic range.The sensitivity of the S-band receiving unit is better than-110 d Bm,and the sensitivity of the C-band receiving unit is better than-85 d Bm.A testing platform for the miniaturized RF front-end performance of the UAV data link was built in the laboratory,and the tests of the RF front-end circuit modules and the entire UAV data link system were completed.The RF front-end of the UAV data link were used to support the flight missions of the UAV.Finally,based on the problems in the flight tests,some ideas for the next step work in the optimization of the functions and performance of UAV data link communication systems are proposed. |
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