Design of a Novel Circularly Polarized MIMO Antenna with Enhanced Isolation for Ultra-wideband Communication

Abstract

In this paper, we propose a circularly polarized (CP) ultra-wideband (UWB) MIMO antenna. Compared with common linearly polarized (LP) UWB antenna, the proposed antenna can excite circular polarization (CP) mode for WLAN communication and its impedance bandwidth can also fully cover UWB spectrum. It consists of identical circularly polarized antennas. Each unit adopts circular monopole with extended orthogonal rectangle patch to realize broadband and symmetrical rectangular ground with slot in the diagonal of each antenna unit to achieve circular polarization for WLAN band. It has a very compact size and the dimension is 25 × 51 × 0.8 mm3. The impedance bandwidth of the proposed antenna is from 3.1 GHz to 13.5 GHz, with average gain of 4 dBi, fully covering UWB bandwidth and enhanced by 38%. At the same time, circular polarization is achieved by embedding two symmetrical rectangular slot structures in the two opposite corners of every antenna unit. The extended orthogonal rectangle patch is introduced to enhance impedance bandwidth and broaden axial ratio (AR) bandwidth. The measured 3 dB axial ratio (AR) bandwidth is 1.8 GHz (4.7-6.5 GHz), fully covering WLAN band. Meanwhile, the slit slot between antenna units and rectangular openings are introduced to achieve high isolation. The proposed antenna keeps ECC (envelope correlation coefficient) below 0.01, which showing good isolation and diversity characteristics. The proposed antenna can simultaneously operate in the UWB spectrum and exhibit circularly polarized (CP) radiation characteristic in WLAN.