An Integrated Slot-Based Frequency-Agile and UWB Multifunction MIMO Antenna System

This letter presents an integrated multiple-input–multiple-output (MIMO) antenna solution for cognitive radio (CR) front ends. The antenna consists of the four-element slot-line-based frequency-reconfigurable (FR) MIMO antenna integrated with a four-element half-annular slot-based ultrawideband (UWB) multifunction MIMO antenna system, printed on the same substrate. Each FR antenna element is loaded with a unique split-ring resonator to achieve multiband operation. A wide frequency sweep over multibands is achieved using one varactor diode per antenna element, thus covering 1.495–2.18, 3.35–4.08, and 4.15–4.49 GHz. The proposed multipurpose UWB antenna senses the spectrum from 1.48 to 4.56 GHz, as well as it can be utilized to serve as an UWB MIMO antenna system. The proposed antenna has planar and compact structure with total size of 200 <inline-formula><tex-math notation="LaTeX">$\times\; \text{150}\;\times$</tex-math></inline-formula> 0.76 mm<inline-formula><tex-math notation="LaTeX">$^3$</tex-math></inline-formula>, thus is suitable to be used for tablet PC applications in second-generation CR platforms.