Design of Field Decorrelating Frequency Selective Surface (FSS) Radome for MIMO Antenna Systems in Wireless Terminals

The fifth generation (5G) of wireless standard will be deployed on or before the year 2020 with a targeted improved capacity of 100-1000 times that of 4G. This huge increase in the capacity will be accomplished via the use of several technologies such as multiple-input-multiple-output (MIMO), massive MIMO, millimeter-wave (mm-wave) enabled radios and advanced coding techniques with the deployment of very dense cells for more coverage at higher bands. This puts a major burden on the design of sophisticated mobile terminals with advanced radio frequency (RF) front-ends. A major part in the RF front-end is the antenna system. In 5G enabled user terminals, it is expected that at least 4-antenna elements will be operating in the same band to provide higher channel capacity via MIMO technology. In addition, one or more mm-wave based antenna array will be integrated to provide higher bandwidth and ultra-high data rates for short distances between the user terminal and the base station. A challenge in the sub-6 GHz bands that will be utilized in 5G user terminals is the field correlation between adjacent antenna elements. To be able to take advantage of MIMO systems, the channels should be as isolated in space as possible. Since multiple antennas are placed within a small form factor device, this necessitates careful antenna design with low correlated radiation patterns that can be achieved via tilting the patterns away from one another. In this work, we propose to design a radome cover for smart phone size devices with multiple antenna elements in a MIMO configuration that are closely spaced, and within this radome, we will integrate a frequency selective surface (FSS) that will have dual functions, first, act as a spatial filter that will tilt the beams of adjacent antenna from one another in space (elevation angles) by at least 40 degrees yielding very low field correlation values, and second, it will act as a bandpass filter allowing certain frequencies to pass and others will be reflected back. The FSS-based radome should not exceed 70 x 130 mm2 in area (i.e. for a typical smart phone), and should operate with antennas resonating at 5.8 GHz or below. An important requirement of this cover is that it will be placed above the main antenna board within a distance not exceeding 3 mm, meaning it will be placed at a distance shorter than the conventional distance of half a wavelength. Several superstrate loading techniques will be investigated to be able to achieve spatial separation with such a small distance. The targeted bandwidth is at least 100 MHz, and two antenna element types are to be investigated within a 2-element MIMO antenna configuration; a patch and a printed monopole. The FSS enabled radome will be optimized and tested above the two MIMO antenna configurations. Then the model will be prototyped and measured in the Antennas and Microwave Structure Design Laboratory (AMSDL) at KFUPM. The duration of this project is not to exceed 18 months, and with a budget of 99,800 S.R.