Embedded antenna design based on zero and pole resonances for wireless sensor modules for applications in advanced greenhouses

This paper presents an embedded antenna design for wireless sensor modules for application in advanced greenhouses. The wireless sensor modules are realized based on the UHF RFID tag plus low-power MCU chip [1]. In the antenna design, resonator models are used to tailor the input impedance of the antenna to satisfy the condition of complex conjugate matching, and hence the maximum power transfer between the RFID tag chip and the antenna. The proposed embedded antenna possesses an open-ended quarter wavelength strip monopole to generate a zero resonance, lowering the real part of the input impedance of the antenna, and a parallel chip capacitor near the feeding terminal to provide a pole resonance, pulling up the imaginary part of the impedance, to achieve conjugate matching to the highly capacitive RFID tag chip, whose input impedance is 18 - j171 Ω. The simulated realized gain of the antenna is -0.26 dBi, and the associated maximum read range is 8 m based on Friis´ equation with the maximum EIRP of 4 W.