A Package-Cognizant CMOS On-Chip Antenna for 2.4 GHz Free-Space and Implantable Applications

A 2.4 GHz industrial, scientific, and medical band on-chip antenna (OCA) is integrated into an on-chip broadband balun in $0.18~\mu \text{m}$ CMOS technology on a die of size 4 mm². Antenna miniaturization is achieved from the capacitive loading of meandered dipole arms. A back-to-back configuration of the balun on a separate die is characterized with in-band insertion and return loss of better than 0.9 dB and 20 dB, respectively. A commercial low-cost package is used to provide a decoupling effect to the OCA when immersed in tissue, enabling it to maintain stable impedance matching as in the air. A detailed explanation of the decoupling mechanism is provided using field plots and equivalent circuit analysis. The OCA is characterized in air and different tissue phantoms with a gain of −23.8 dBi in air and −25.9 dBi inside skin mimicking gel. The maximum simulated uplink specific absorption rate is obtained as 160 $\mu \text{W}$ /kg for an input power of $25~\mu \text{W}$ to the OCA in the transmitting mode. As the antenna has a small footprint and is analytically estimated to be capable of communicating at a high uplink bit rate of 1 Mb/s over a distance of 5.2 m with a 3 dB link margin, it is most suited as a minimally invasive implantable medical device.