Abstract
UAV assisted wireless sensor networks play a key role in the detection of toxic gases and aerosols. UAVs can be used to remotely deploy sensor nodes and then collect gas concentration readings and GPS positioning from them to delimit an affected area. For such purpose, a dual-band communication system is required, supporting GPS reception, and sensor reading data transfer, which is chosen to be at 2.4 GHz using LoRa physical layer. In this work we propose a switched-beam antenna subsystem for the sensor nodes capable not only of satisfying the dual band requirements but also of maximizing communication range or energy consumption through a good antenna polarization match and improved antenna gain. This antenna subsystem is built using dual-port, dual-band, circularly polarized antenna elements, whose design and experimental validation is carefully detailed. A low profile microstrip stacked structure has been used to obtain return loss in both bands better than 15 dB, axial ratios below 1.5 dB, and wide −3 dB beamwidths around 90° and 75° for GPS and 2.4 GHz bands, respectively, thus limiting the gain reduction of the switched-beam system in critical sensor orientations. Special attention has been paid to reduce the coupling between both ports through the optimization of the relative placement of both patches and their feeding points. The measured coupling is below −30 dB.
Highlights
The use of toxic chemical warfare agents—e.g., sarin, mustard gas, or novichok—in both military conflicts and terrorist attacks [1,2] during the late 20th and early 21st centuries, revealed that such toxic chemical compounds represent a serious threat to life, in the context of chemical warfare and for the civilian population
There is an urgent need for sensing systems capable of detecting the presence and concentration of the toxic chemical compounds to delimit an exclusion area, which must be first evacuated and monitored or decontaminated
The operation of the SensorQ system considers that after an attack, sensor nodes are deployed on ground with the UAV and once positioned, they start reporting gas concentrations and GPS coordinates to the UAV using LoRa modulation at 2.4 GHz
Summary
The use of toxic chemical warfare agents—e.g., sarin, mustard gas, or novichok—in both military conflicts and terrorist attacks [1,2] during the late 20th and early 21st centuries, revealed that such toxic chemical compounds represent a serious threat to life, in the context of chemical warfare and for the civilian population. Focusing on the antenna elements forming the switched-beam system, the requireity reduction can be achieved performing a discrete ments include compactness for easy integrationby with the sensor electronics, moderatescanning gain, dual-band operation We propose a design based on dual-band circularly polarized elements instead of the single-band linearly polarized solution used in [9] Under this configuration, the antennas can be perfectly integrated with the sensor node electronics as part of its housing.
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