Ultrawideband MIMO Circularly Polarized Cube Antenna With Characteristic Mode Analysis for Wireless Communication and Sensing

An ultrawideband multiple-input-multiple-output (MIMO) circularly polarized (CP) cube antenna is proposed for wireless communication and sensing of Internet of Things. This antenna comprises an ultrawideband grounded criss-cross radiator, four square parasitic patches, and a four-port feeding network. Following the inverted-F radiation principle, a criss-cross patch is incorporated with its center grounded. Surrounding it, four small exciting patches are strategically positioned to drive via electromagnetic couplings. The ultrawideband radiation characteristics are analyzed based on the mode behaviors predicted by characteristic mode analysis (CMA). The introduction of four square parasitic patches between the radiator and the ground plane leads to an improvement in impedance matching. To create a single-port CP antenna element, a four-port feeding network with equal magnitude, but spaced 90° apart in phase, is connected to the radiator. The MIMO diversity performance is assessed through metrics like envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), and channel capacity loss (CCL). To validate the design concept, a prototype of the cube antenna is fabricated and assembled, demonstrating the ability to radiate right-hand circularly polarized (RHCP) waves. The measured results indicate impressive performance metrics: a −10-dB impedance bandwidth of 2.2–7.8 GHz (112%), a 3-dB axial ratio bandwidth of 2.1–7.3 GHz (110.6%), a realized gain ranging from 5.6 to 9.5 dBic, and a radiation efficiency between 65% and 88.5%. Additionally, the port isolation exceeds 30 dB, and the ECCs are below 0.009.