ENVELOPE CORRELATION COEFFICIENT OF A TWO-PORT MIMO TERMINAL ANTENNA UNDER UNIFORM AND GAUSSIAN ANGULAR POWER SPECTRUM WITH USER'S HAND EFFECT

This paper studies the effects of incident wave angular power spectrum (APS) distribution and user hand effect on the envelope correlation coefficient (ECC) of a two-port MIMO antenna operating in the sub 6GHz LTE-U frequency band. APS of uniform and Gaussian distributions are used with different Gaussian angular spread (AS) values, i.e., 10◦, 30◦, 50◦, and 70◦. A prototype was fabricated, and three-dimensional radiation patterns of the antenna elements were measured in an anechoic chamber from 4 to 6GHz in both cases of free space and when the prototype is held in data mode using a hand phantom. An algorithm to calculate ECC from the complex data of far field radiation pattern with different APS distributions is explained in detail. Results show that user hand presence increases ECC between ports compared with free space, whose increase is more obvious under Gaussian APS. ECC values under uniform APS is practically zero over the entire frequency range except at frequencies close to 6 GHz, where the highest ECC values are 0.13 and 0.16 in free space and with user hand, respectively. However, Gaussian APS with different ASs shows a significant impact of the ECC. With narrow AS of 10◦, ECC at some incident directions can be as high as 0.84 (in free space) and 0.92 (with user hand), and the mean ECC values under this AS are 0.25 (in free space) and 0.37 (with user hand). ECC values keep decreasing as AS gets wider, with the maximum ECC at AS = 70◦ observed to be 0.23 and 0.34 in free space and with user hand, respectively, whereas the mean ECC values are close to uniform APS. Statistical distribution of the ECC showed good agreement with exponential distribution, with a better agreement between measured ECC and exponential distribution observed in free space with wider AS.