Design and Analysis of CPW Fed Ultrathin Flexible MIMO Antenna for UWB and X-Band Applications

Abstract

This work describes a compact Co-planar Waveguide (CPW) fed flexible 4-port Multiple Input Multiple Output (MIMO) antenna for Ultra-Wideband (UWB) and X-band applications. The MIMO antenna occupies an overall volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5\lambda \times 0.5\lambda \times 0.00063\lambda $ </tex-math></inline-formula> where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> is the free space wavelength at 3.82 GHz. A single CPW fed monopole antenna is developed with a hexagonal shaped patch, and symmetrical inverted L-shaped grounded strips along with symmetrical hexagonal shaped stubs. The antenna is designed on Polyimide substrate of dielectric constant <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon _{\mathrm {r}} = 3.5$ </tex-math></inline-formula> , thickness of 0.05 mm, and loss tangent (tan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> ) = 0.0027. The proposed MIMO antenna consists of 4 identical antenna elements arranged in orthogonal pattern to achieve polarization diversity. Its performance is evaluated at three different resonance frequencies at 5 GHz, 8 GHz and 12 GHz. The proposed MIMO antenna operates at a frequency from 3.82 to 15.9 GHz, a wide impedance bandwidth of 122.52% is attained which is suitable for UWB, and X-band applications. The inter-element isolation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gt -17$ </tex-math></inline-formula> dB, between antenna elements is obtained, and other diversity parameters such as the envelope correlation coefficient (ECC) of < 0.005 and diversity gain (DG) of > 9.999 dB are obtained. Other parameters like channel capacity loss (CCL) are < 0.2 bps/Hz, channel capacity, total active reflection coefficient (TARC), mean effective gain (MEG) MEG1 and MEG2 values are below -3 dB and the difference between two MEG1 and MEG2 is zero are studied. The achieved peak gain and efficiency of proposed MIMO antenna are 6.33 dBi and 93% respectively. The proposed 4-port flexible MIMO antenna is tested under bending conditions and similar impedance bandwidth as well as isolation <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gt -15$ </tex-math></inline-formula> dB are observed.