An Improvised Four-Port Multifunctional MIMO Antenna for Integrated Cognitive Radio System

This article presents a four-port multiple input multiple output (MIMO) antenna designed and demonstrated for cognitive radio (CR) applications. The proposed geometry is made of a single-layer dielectric substrate, where metallic patterns and electronic components are articulately used to exhibit both types of CR techniques (interweave and underlay) through three different working states. In the first state, the antenna radiates over a wide bandwidth from 2.26 to 7.00 GHz for sensing applications, while in the second mode, the geometry has a frequency tunability between 4.80 to 6.20 GHz to be used for interweave CR communication. In the third mode, a fixed band-notch response is obtained at 4.20 GHz (which can also be made tunable from 3.10 to 4.80 GHz), thereby fulfilling the underlay operation. The novelties of the proposed work are the realization of an innovative antenna topology exhibiting all types of CR operations (102.38% in the wideband state, 14.4% in the tunable narrowband state, and 27.21% in the tunable bandnotch state), at the expense of using the lowest number of diodes components (2 p-i-n diodes and 1 varactor or 1 p-i-n diode and 2 varactors). Further, each of the design steps in the single antenna as well as MIMO geometry is in-depth analyzed by simulation, fabrication, and measurement responses.