A Conversionless Angular Displacement Antenna Sensor Node Based on Microstrip Cross-Shaped Matching Network With Rotational Stub for RFID Applications

This paper presents a conversionless angular displacement antenna sensor node for chipless RFID applications. The sensor realizes sensing capability by altering the reflection coefficient of a patch antenna through a cross-shaped matching network with a rotatable stub. This cross-shaped network comprises two quarter-wavelength stubs, one vertical and one horizontal, allowing for compact impedance matching and providing a significant variation of an open-ended stub as a rotor. Combining the rotatable cross-shaped network and the antenna’s reference antenna modifies the transmitted signal attenuation level, allowing for simple wireless angular displacement signal transmission. A prototype antenna sensor operated at 2.38 GHz for 90° sensing is designed using the conventional microstrip fed square patch antenna measured by 150 mm
${\times }\,\,150$
mm. When the rotor rotates from 0° to 90°, the corresponding return losses are 6.22 dB to 16.86 dB, with an average gain of 4.93 dB. The angular displacement measurement is intrinsically upconverted to 2.38 GHz without conversion circuitry and is easily detected with a reference receiving patch antenna in 100 cm wirelessly. Compared with the traditional sensor nodes for angular displacement measurement, the proposed sensor node eliminates the conversion circuits, thus making it suitable as a chipless RFID sensor.