Compact Ultrawideband MIMO Antenna With Half-Slot Structure

In this letter, a multiple-input–multiple-output (MIMO) antenna with very compact size of only
$\text{23}\times \text{18}\; \text{mm}^{2}$
is proposed for ultrawideband (UWB) applications. The proposed MIMO antenna consists of two symmetrical half-slot antenna elements with coplanar waveguide-fed structures and a Y-shaped slot that is cut at the bottom center of the common ground plane. The slot efficiently prevents the current from directly flowing between two ports at low UWB frequency. For such a compact-size antenna, the ground plane works as a radiator as well as a reflector that reflects the radiation from radiators at high frequency. The measured impedance bandwidth for
$S_{11}, S_{22}$
< −10 dB is from 3 to 12.4 GHz. The measured mutual coupling for
$S_{12}, S_{21}$
< −15 dB is from 3 to 4 GHz and for
$S_{12}, S_{21}$
< −20 dB is from 4 to 12.4 GHz. The proposed antenna also contains relatively stable radiation patterns and gains. These performances indicate that the proposed antenna is one competitive candidate for UWB applications.