In this paper, the design of a multiband multiple-input multiple-output (MIMO) antenna with frequency and radiation pattern reconfiguration capability in the 5G sub-6 GHz band is presented. Frequency and radiation pattern reconfiguration are enabled on the antenna consisting of two planar inverted-F antenna (PIFA) elements using PIN diodes and DC biasing circuits. At the reflection coefficients of less than -6 dB, both PIFA element 1 and PIFA element 2 achieves triband with bandwidth from 220 MHz to 2330 MHz, ranging from 0.8 GHz to 6 GHz, covering cellular bands for GSM, UMTS, LTE and 5G-NR bands. Moreover, high isolation of at least -10 dB and envelope correlation coefficient with less than 0.3 between ports ensures satisfactory MIMO diversity performance. PIFA elements 1 and 2 have achieved main lobe gain ranging from 1.06 dB to 2.97 dB at their respective resonant frequencies with total efficiencies ranging from 46.2% to 74.5% achieved within the operating bandwidth. This enables a calculated channel capacity of 9.45 to 10.5 bit/s/Hz for PIFA element 1 and 9.56 to 10.23 bit/s/Hz for PIFA element 2, respectively. The percentage of channel capacity achieved over IID capacity for both PIFA elements ranges from 73.71% to 92.8%. Simulated antenna performance parameters agreed well with measurements, and potentially enables reliable and consistent data throughput for 5G mobile terminals.
