Developing planar printed technologies for 5G wireless frontends

This thesis studies and examines the effectiveness of various polanar interfacing methods to replace conventional waveguide-based interfacing approaches used in state-of-the-art directional antennas. The interests and demands towards the fifth generation (5G) of wireless communication networks regarding wireless frontends have been growing constantly. 5G is considered as the next generation of wireless technology, which claims to be 20 or more times the speed of the LTE (4G) network. As far as operating spectrum in 5G networks, it defines the frequency bands which are much higher than standard 4G networks. Particularly, the frequency band beyons 30 GHz ( millimeter wavebands) attracts various researchers due to its merits, such as unlicensed band, high capacity, uncrowded channels and potential for multi-points networks. At millimeter-wave (mm-wave) bands, atmospheric attenuation and propagation loss increase significantly and become a burden on the the link budget of wireless systems. These drawbacks are considered as the main obstacle to the realisation of energy-efficient mm-wave wireless transceivers. To overcome the obstacle, the directional antenna is suggested for use in in the transceivers at mm-wave frequency bands, since it provides more abilioty to satify the requirements of link budgets. In the last decade, the electromagnetic band gap (EBG) resonator antennas (ERA) became a popular choi9ce for achieving this goal due to its merits, such as simple, compact and high potential in mm-wave applications. This thesis focuses on the significant challenge in the practical use of ERAs at high-frquency bands, which is the interfacing approach with the transceiver, often termed as the feed. The hollow metal waveguide is a feeding technique that has been popularly applied to feed ERAs. However, it suffers from some disadvantages, including bulky size, heavy weight and expensive cost, as compared with the rest of the assembly. In this thesis, I examine various planar methods based on printed circuit technology to feed the ERAs. These approaches contain microstrip-based feed, substrate integrated waveguide (SIW) based feed and hybrid SIW-cavity based microstrip feed. Each feeding method is studies and simulated by using time-domain full-wave electromagnetic solver of CST microwave studio. The optimised result of each ERA has been presented and analysed in this thesis. Owing to the scalability of ERA models at various frequency bands, they have been investigated around 12 GHz for the purpose of simplicity and due to the availability of test equipment. It turned out that the SIW-based tapered slot antenna has a good overall performance as compared with the other two planar antennas. Quantitative as well as qualitative comparisons between different approaches are presented in this thesis. Note that a compromise of bandwidth performance for the planar antenna is made. A typical advantage of a conventional waveguide-based antenna identified in the studies is that it can reach a fractional bandwidth of 30 to 45%. The planar feeding methods are limited by the bandwidth. However, these planar approaches are capable of obtaining efficient fractional bandwidth as required in most of the planned 5G mm-wave spectra, like at 30GHz, 45 GHz and 60GHz.