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Detection of liquid level in large tanks is presented in this paper. The liquid level is detected using a transmitter and RFID tag antennas as a receiver. The transmitter antenna is a Vivaldi with wide bandwidth from 0.5 GHz to 3 GHz. The Vivaldi antenna is fabricated on FR4 with 𝜀𝑟 = 4.3 and thickness of 0.8 mm. Two conformal RFID tag antennas are used as receiver antennas. The conformal antenna is placed on Rogers Ultram 3850 flexible substrates with 𝜀𝑟 = 2.9 and a thickness of 0.1016 mm. The conformal antenna is designed to set on a cylindrical tank made from PVC material. The first tag works at 0.9 GHz and the second tag works at 2.45 GHz. Water and Oil are used as liquids for testing. The antennas are simulated using CST microwave studio simulator Ver.14. The system is also fabricated and measured. Good agreement is achieved between simulated and measured results.

This paper presents a novel conformal monopole antenna used for liquid level identification in tanks. Designing RFID tag antenna on a liquid detection is challenging due to the relative permittivity, high conductivity and the diversity of liquids. A comparison between planar and conformal designs has been done using a CST microwave studio simulator. The antenna has been fabricated on Roger 3850 flexible substrate material. The conformal Antenna has been designed to work on a cylindrical tanks made of PVC material. The proposed antenna resonance frequency is shifted forward from the planar antenna at 0.9 GHz to 0.8 GHz in conformal design. The impedance bandwidth is 0.29 GHz where a planar antenna gives bandwidth 0.35 GHz. The antenna gain is 2 dB in case of conformal antenna while is 2.28 dB in case of planar design.