| Summary: | This paper presents a <inline-formula> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> sub-array design with elements having parasitic patches (PPs) for massive MIMO applications. The frequency chosen for the design is 3.5 GHz, one of the 5G frequency allocations. A coaxial feeding probe is employed. For each sub-array element, multiple PPs are placed on the top layer to enhance the bandwidth. We show that with a greater number of PPs, the bandwidth of an element can be increased considerably with respect to previous designs. Two types of single element antenna with 5 and 10 PPs exhibit a bandwidth of more than 600 MHz and 700 MHz or a fractional bandwidth of about 17% and 20%, respectively. The increase in element dimension and, consequently, element spacings reduces the mutual coupling in the sub-array. Simulation results and measurements of the <inline-formula> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> sub-arrays with the 5-PP and the 10-PP elements show that the sub-arrays meet the desired performance with return loss less than −10 dB and bandwidth of 567 MHz and 730 MHz, respectively. Mutual coupling effects can be suppressed to less than −20 dB in the frequency range of 3.202 GHz − 3.934 GHz.
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