Circularly Polarized Dual-Frequency MIMO Antenna With Cosecant-Squared Radiation Pattern for Ku-Band Applications

In this letter, the realization of a circularly polarized multiple-input-multiple-output (MIMO) array antenna with a cosecant-squared pattern is presented. The proposed antenna structure consists of microstrip patches with rectangular slots etched from the top. The desired radiation pattern is generated using amplitude tapering obtained by modifying patch widths and slot lengths, based upon the amplitude coefficients of the Woodward-Lawson method for pattern synthesis. A MIMO arrangement with circular polarization is formed by connecting two such arrays excited by two ports. A Z-shaped slot is used to minimize the mutual coupling. Using two shorting pins, the isolation is enhanced and kept above 30 dB. This arrangement offers a small size (52 x 24 x 0.8 mm(3)), wide bandwidth, and high-gain antenna operating at 13.2 and 16.6 GHz. The antenna operates in a wide bandwidth, from 12.6 to 14.25 GHz, and from 16 to 17.61 GHz, with admirable directional characteristics. The achieved gain is 16.9 and 16.6 dB with a cosecant pattern and low sidelobe level. The analysis of the VSWR, gain, axial ratio, group delay, efficiency, and MIMO performance metrics are also investigated, both in simulation and in experiment.