Capsule Endoscopic MIMO Antenna With Radiation Pattern and Polarization Diversity

This article presents a novel compact dual-element capsule endoscopic multiple-input-multiple-output (MIMO) antenna at a 915 MHz industrial, scientific, and medical (ISM) band. Both radiating elements of the MIMO antenna system are circularly polarized (CP) at the desired frequency band (915 MHz). In fact, Antenna-1 operates at left-handed CP (LHCP) and Antenna-2 operates at right-handed CP (RHCP), enabling polarization diversity at 915 MHz. Moreover, the radiating elements radiate in two opposite directions; thus, they enable pattern diversity. The performance of the proposed antenna system is analyzed in a realistic human phantom. Reactive slots in the patch antennas are incorporated to achieve compactness (pi x (4.7)(2) x 0.13 = 9.01 mm(3)) and CP characteristics. Furthermore, a rectangular slot on the ground plane is introduced to reduce the mutual coupling between the radiating elements. The proposed antenna has compact dimensions of 9.01 mm(3), a peak realized gain of -24.6 dBiC, and a high isolation level of 29.7 dB within the whole band. The specific absorption rate (SAR), link margin (LM) and main MIMO channel parameters are investigated which show good results. The key features of this antenna are its compact size, high isolation level between the antennas, and polarization and pattern diversity.