Close-Packed Quad-Element Triple-Band-Notched UWB MIMO Antenna With Upgrading Capability

A close-packed 4-port multiple-input multiple-output (MIMO) antenna with three notched bands (NBs) is designed for ultra-wideband (UWB) applications. The presented antenna contains four monopole antenna elements (AEs) with rectangular radiators, each fed by an L-shaped microstrip line. The compact size of
$35.9\times 35.9\times0.8$
mm is attained by cropping the lower axis of the antenna and optimization. The isolation greater than 19 dB is accomplished by the orthogonal direction of AEs and cross-shaped decoupling structure (CSDS). The designed antenna can realize wireless local area network (WLAN) and X-band NBs by etching two C-shaped slits from each radiator and Worldwide Interoperability for Microwave Access (WiMAX) NB by introducing an L-shaped slit in the ground. By placing these NBs in appropriate positions, their efficiencies are decreased for their better rejection. The value of
$\vert \text{S}_{\mathrm {ii}}\vert < -10$
dB is from 3.2 to 10.8 GHz (except for three NBs). Also, the 4-port MIMO antenna is upgraded to a 16-port MIMO antenna by arranging the four identical 4-port MIMO antennas side by side with a small gap of 8 mm. The upgraded antenna gives bandwidths from 3.38 to 10.56 GHz with three NBs, isolation >20.9 dB, and size
$79.8\times79.8$
mm2, which is appropriate for future wireless communications.