Slot-loading based compact wideband monopole antenna design and isolation improvement of MIMO for Wi-Fi sensing application

The dense establishment of the Wi-Fi devices creates an opportunity to map the surrounding environment using Wi-Fi signals as sounding waveforms. Recently, the Channel State Information (CSI) measurement analysis from Wi-Fi networks has been widely used for detecting and possibly tracking the presence of obstacles between a transmitter and a receiver. According to the IEEE 802.11bf Task Group, Wi-Fi sensing will utilize a band between 5.925 and 7.125 GHz, making the CSI measurement finer-grained with the additional large bandwidth. In this paper, a wideband compact antenna is designed targeting the 5.9-7.1 GHz band based on the slot-loading technique. Later, a wideband multiple-input multiple-output (MIMO) antenna is designed using defected ground structures, protruded ground, and electromagnetic band gap structures for isolation improvement, and the measured isolation shows 30-45 dB between the elements in the operating frequency range. The envelope correlation coefficient is less than 0.001 with the diversity gain being nearly 10. The fabricated single antenna has a compactness of 0.3 & lambda;0 ${\lambda }_{0}$ in both dimensions (14 mm x $\times $ 14 mm), measured bandwidth of 1.55 GHz (5.95-7.5 GHz) with a peak gain of 2.2 dBi at 6.8 GHz, and 90% efficiency in the operating frequency range whereas the wideband MIMO antenna has a size of 14 mm x $\times $ 37 mm with 0.5 & lambda;0 ${\lambda }_{0}$ spacing between the elements.