A Four Element Stringray-Shaped MIMO Antenna System for UWB Applications

This paper presents a CoPlanar-Waveguide (CPW)-fed stingray-shaped Ultra-WideBand (UWB) Multiple-Input-Multiple-Output (MIMO) antenna system designed for microwave imaging applications. Featuring a diagonal square with four inner lines and a vertical line at the center from toe to tip with a CPW feed line, the unit antenna element looks like a stingray fish skeleton and is, therefore, named as a stingray-shaped antenna. It offers a bandwidth spanning from 3.8 to 12.7 GHz. Fabricated on a 31mil RO5880 RF teflon substrate with a relative permittivity of 2.2, the proposed antenna has dimensions of 26 × 29 × 0.787 mm3. The maximum realized gain achieved is 3.5 dBi with stable omnidirectional radiation patterns. The antenna element is used in a four-antenna MIMO configuration with an isolation-improving structure at the center. The MIMO system has dimensions of 58 × 58 × 0.787 mm3 with a maximum realized gain of 5.3 dBi. The antenna's performance in terms of MIMO parameters like Envelope Correlation Coefficient (ECC) and Diversity Gain (DG) is within satisfactory limits for medical imaging applications. Time domain analysis also yields positive results, allowing its integration into a breast phantom tumor detection simulation. The simulation and measurement results demonstrate excellent agreement, making this antenna a promising candidate for microwave imaging and biomedical applications.