Compact Dual-Port Circularly Polarized Wideband MIMO Antenna with an Effective Boresight Polarization Characteristics

A compact dual-port Circularly polarized (CP) multi-input-multi-output (MIMO) antenna is proposed for asserting effective polarization at the boresight radiation. The dominant right-hand-circular-polarization (RHCP) is generated by providing a simple monopole stepped stub wideband resonator (MSSWR) to generate wideband impedance matching and CP characteristics. The dual-port antennas are placed face-to-face with an inter-elemental distance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(d)s$</tex> with satisfactory isolation > -15 dB. When either port is excited, the monopole antenna acts like an quarter-wave transformer with the influence of quarter-wave circular slot in the ground to mimic CP radiated waves. A prototype antenna of dimension <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20\text{mm}\times 20\text{mm}\times 1.6\text{mm}$</tex> has been fabricated and experimented to operate from (5.48 - 10.56) GHz with 63.34% 10-dB impedance bandwidth (IBW), 3-dB axial ratio bandwidth ≈ 40% from (7.23 - 10.81) GHz. The envelope channel coefficient (ECC) for isotropic environment is well below 0.1 in the operating band, showing its potential for indoor and outdoor high frequency wireless applications.