Mitigation of Mutual Coupling In Dual Polarized Mimo Antennas With Wave Propagation Models For 5g Base Station Applications

Abstract

Fifth Generation or 5G, is the contemporary new release of cellular generation, engineered to drastically increase the speed and approachability of wireless net- works. 5G performance objectives high data rate, increased capacity, low latency and large device connectivity. 5G enables massive increase in amount of data han- dling capacity due to its broad spectrum allocation covering both sub 6GHz range and mm-wave frequency bands. Massive MIMO (additionally referred to as huge- Scale Antenna structures, Very large MIMO, and Hyper MIMO) is an electrifying concept in wireless communications studies that promises to deal with the huge capacity requirement demanded by means of 5G systems. Massive multiple-input multiple-output (MIMO) technology, where a base station is installed with huge number of antennas serves large number of users by utilizing time-frequency re- source will meet the requirements for 5G. Hence, MIMO is selected as promising candidate technology for upcoming generations of wireless systems. The selec- tion of antenna and building the MIMO base stations which address both spatial and polarization diversity is one of the major task. The thesis focuses on design and implementation of dual polarized MIMO an- tennas with both spatial and polarization diversity. The designed dual polarized MIMO antennas are implemented with different MIMO configurations to address the high data rate with massive connectivity for 5G requirements. Novel dual po- larized MIMO antenna element with complete planar printed balun feed network is designed, fabricated and tested. In extension, a compact 2×2 dual slant 450 po- larized MIMO antenna for 4G LTE band 40 is designed. The stringent parameter while developing MIMO antennas is mutual coupling associated with the adjacent antenna elements in both azimuth and elevation planes. By considering array of split ring resonators(SRRs) embedded with transmission line low mutual coupling and high isolation are achieved for 2×2 MIMO antenna. The selected configura- tion is also extended for massive 8×8 MIMO antenna by addressing both spatial and polarization diversity for C-RAN applications. Here, mutual coupling miti- gation is carried out by inserting U shaped aluminium strips in both azimuth and elevation planes. As there is also need for wide band antennas with low profile for quick instal- lation in compact base stations. So here, a wide band, low profile dual polarized bow-tie antennas for band 42 covering sub 6 GHz range for 5G communication is implemented. Wide band dual polarized bow-tie antenna is designed with both polarization and spatial diversity. Low profile miniaturized dual polarized 1×2 MIMO antenna backed with chessboard configured artificial magnetic conductor (AMC) surface is designed for compact base station applications. To mitigate the mutual coupling between two low profile dual polarized antennas a novel ap- proach with frequency selective surface (FSS) wall is constructed. The FSS cell is properly designed for wideband operation which indirectly suppress the near fields for entire band of operation. The other parameters like isolation, impact on with and without FSS wall, radiation patterns, front to back ratio, co-cross po- larization levels are also discussed. MIMO performance related parameters like envelope correlation coefficient, diversity gain and total active reflection coeffi- cient are also discussed. The thesis also focuses of practical deployment of base station antennas with various wave propagation models and network planning. For practical deploy- ment, dual polarized antenna covering the sub 6 GHz range is considered along with 2×2,4×4 and 8×8 MIMO configurations. The study of propagation models, modulation schemes, data rates and throughput over the selected geographical ter- rain that is NITK campus are reported. The maximum data rate with 8×8 massive MIMO antenna configuration is achieved to meet the 5G requirements. Also, the radome analysis with dual band microstrip patch antenna operating at both 4G and 5G frequencies also discussed. Metamaterial based radome is considered to enhance the gain for the designed dual band patch antenna. Proposed designs are fabricated using LPKF protomat machine S103 and ex- perimentally verified using far field and anechoic chamber radiation pattern mea- surement set-up. Impedance bandwidth, peak gain, isolation, mutual coupling, front to back ratio, cross-polarization level, envelope correlation coefficient, di- versity gain and total active reflection coefficient are various metrics considered for the performance measures of the proposed MIMO antenna.