Mobile Phone Antennas for MIMO and 5G Millimetre Wave Communications

Cellular Communication Technology has evolved over the past 3 decades with each phase bringing with it new and exciting capabilities and services to the end user. Evolution in 4G wireless mobile communications has shown that by employing multiple inputs and multiple outputs (MIMO) technology at both the transmitter and receiver, the wireless system capacity and reliability can be enhanced without the need for increasing the power transmitted or using more spectrum by utilising the multipath diversity. Despite a considerable amount of research has already been done on the design of MIMO and diversity handset antennas, the design of low profile, small footprint and multi-standard (wideband or multi-band) diversity antennas for handset devices still remains a challenging issue. In the final stages of 4G deployment, there was a wave of developments of new 5G technology. The focus will be on mm-wave communication above 24 GHz using antenna arrays capable of providing higher bandwidth. It is a challenging task for an antenna array design to achieve a wide bandwidth, high gain, small size, good coverage and simple fabrication technique all at the same time. The latter part of this thesis focuses on developing several different novel compact, high gain and wide bandwidth 5G antenna arrays capable of providing wide coverage. There are five main contributions from this PhD work: • In the first part of this thesis, the author propose a new wide-band reconfigurable antenna design for handset MIMO and diversity applications. The proposed reconfigurable open slot antenna operates on the lower band as well as higher band and offers excellent isolation and diversity performance over 698-960 MHz and 1710-2690 MHz. The new MIMO antenna configuration outperforms the state of the art designs in terms of the bandwidth of operation and the isolation performance. • A novel capacitive coupled patch antenna array capable of providing a wide bandwidth, high gain and 3600 coverage is designed and presented. The antenna elements are positioned in the mobile phone chassis as a set of 4 subarrays each with 12 antenna elements to provide high realised gain around 16.5 dBi with each of the sub-array providing 900 coverage. The antenna array covers the frequency range of 24-28 GHz, which is a promising band for future 5G based smartphone services. • A hybrid capacitive coupled patch-Yagi-Uda antenna array configuration, which is capable of providing wide coverage, and a wide bandwidth for future mm-wave 5G communication is presented. The wide coverage is obtained by combining broadside radiation from a dual polarised capacitive coupled patch antenna array and end-fire radiation from a modified Yagi-Uda antenna array. The proposed antenna array consists of 16 antenna elements located at the bottom edge of the mobile phone chassis of which 8 antenna elements are dual polarised broadband broadside capacitive loaded patch antennas and 8 elements are broadband end fire modified Yagi-Uda antennas placed alternately. The proposed antenna array exhibits a wide bandwidth from 24-28 GHz, uniform radiation patterns and uses a low-cost fabrication technique. The antenna array achieves a peak realised gain of 13.6 dBi. • A transparent antenna array in which the radiating elements are made visually transparent and integrated on a device display panel is proposed as a solution for saving enormous PCB area giving an additional degree of freedom for mobile phone system design engineers. The new antenna array configuration consists of dual polarised meshed capacitive fed patch antennas with feed section on device PCB and radiating patch antenna array on device display panel. Indium tin oxide is used as the transparent conducting oxide. The antenna array has a 10 dB return loss over 27-37 GHz and achieves a peak realised gain of 11.2 dBi. The antenna array is then tested on the mobile phone and the smartwatch display panel for various practical user scenarios. • A dual-band dual-polarised stacked capacitive coupled patch antenna element is proposed to provide a 10 dB return loss over 25.75-30.25 GHz and 36.5-41.5 GHz. A worst-case isolation of 17 dB and 15 dB is seen between the two feeds of the dual polarised patch antenna in the lower band and higher band, respectively. A 2×2 antenna array using this antenna element has a peak gain of 12.6 dBi in the lower band and higher band. The design outperforms the existing dual-band, dual-polarised antenna designs and is a suitable candidate for 5G deployment for multi-band operation