Antennas for 5G and 4G/LTE mobile devices

Increasing demand for high data throughput and reliable service for mobile traffi chave motivated the development of 5G mobile communication systems, which are currently in the planning stage. Proposed 28 GHz millimeter-wave bands have much potential for forthcoming 5G mobile communication because of the available massive bandwidth and relatively low atmospheric absorption compared with 60GHz Wi-Gig and other short-range systems. Although the standards for 5G mobile devices have not been finalized as yet, this thesis focuses on the designand development of single-beam antennas and pattern reconfigurable antennas,which are potentially suitable for forthcoming 5G mobile devices. This thesis initially develops three highly efficient antennas radiating boresight at 28 GHz. Firstly, a narrow-band compact planar inverted-F antenna (PIFA) is developed. Then, a method is presented to convert this narrow-band PIFA to a wideband PIFA while maintaining the same size of the antennas (i.e. 4 mm x 4 mm). Also, a wideband leaky-wave antenna (LWA) array is presented and investigated. Methods to enhance the efficiency and impedance bandwidth of the antennas are proposed. All the antennas have stable boresight radiation in both the x-z and y-z planes. The impact of the mobile device battery on antenna performance is investigated using one of the PIFAs. A novel 1-D and 2-D pattern reconfigurable antenna has been developed and investigated for 28 GHz band. Firstly, a basic LWA radiating off-boresight was designed for mobile devices. Then, a wideband LWA radiating boresight was developed and investigated. This was followed by a novel multi-feed antenna being developed, prototyped and verified experimentally, for 1-D beam switching.The antenna is able to switch beam in three different directions along the antenna axis such as boresight, forward and backward directions using three feeds at three different positions. Because of the wide beamwidth, the antenna radiationpatterns can fill 128º of space (3-dB coverage), i.e. θ = -64º to +6º at the azimuth angle of Φ = 0º. Then two antennas are placed at right angles to eachother to achieve 2-D beam switching. The 2-D beam switching antenna pair was prototyped and tested after integrating them in to the ground plane of a mobile device. The antenna is able to point the beam in five different directions, and infact its beam covers 167º (θ = -89º to 78º) at Φ = 0º, and 154º (θ = -72º to 82º)at Φ = 90º. For 5G mobile communications, a new technology of cognitive radio named licensed shared access (LSA) has been demonstrated and two bands (1452-1492 and 2300-2400 MHz) have been allocated by the European Commission. More bands are expected to be allocated for LSA operation from the bands 698-960,1427-2690 and 3400-3800 MHz. Hence, the future mobile device antenna require to cover all the LSA and LTE bands while having no null in the radiation patterns.To cover these frequency bands, initially a planar antenna was developed for the said LSA bands and the performance of the antenna was investigated with and without a battery of a mobile device. Secondly, another planar antennawas developed to reduce the number of nulls in the radiation patterns. These antennas cover the LSA (1452-1492 and 2300-2400 MHz), mid-LTE (1427-2690MHz), GSM1800, GSM1900, UMTS and 2.4 GHz WLAN bands. Thirdly, a dual-band antenna loaded with a small vertical plate was developed and investigated. This antenna covers the LSA, mid-LTE and high-LTE (3400-3800 MHz) bands. In the lower LSA band radiation patterns there is no null but a null is present in the higher LSA band and two nulls are evident in the high-LTE band. Fourthly, a novel wideband antenna having a planar structure, loaded with an L-shaped vertical plate was developed and prototyped; thus the concept was validated experimentally. The antenna radiation patterns have no nulls and cover the above-mentioned bands. All the antennas were designed without requiring an active or passive component for input impedance matching. The dual-band and wideband antennas cover the aforementioned bands even when the size of the substrate and ground plane is varied between 120 mm x 70 mm and 240 mm x 170 mm. This makes them suitable for mobile devices of different sizes, for instance smart phones and tablet computers. The final contribution this thesis makes in the development of a highly efficient inverted-L-feed capacitive-coupled inverted-L antenna for the low-LTE (698-960MHz) band. Similar to the previous antennas this antenna does not require any lumped components for input impedance matching. The antenna is presented for future mobile devices utilizing LSA/spectrum reallocation within the low-LTE band. The measured reflection coefficient bandwidths are 684-732, 714-774, 748-823, 788-882, and 820-965 MHz for the tuning inductor values of 9, 7, 5, 3, and1 nH, respectively. Therefore, this antenna concept is suitable for conversion to a frequency reconfigurable antenna, with switchable inductors. The prototype's radiation performance was measured with the 1 nH inductor to verify the concept. Although some modern commercial mobile phone handsets use very thin antennas with relatively poor performance due to their low cost and high emphasis on handset aesthetics, high-performance antennas such as those developed in this thesis are required for some multiband (4G/5G/LSA) applications. One of them is a defense application where a handset - carried by many military personnel - detects, intercepts and jams mobile phone signals used by the enemy to trigger explosive devices such as land mines. Such handsets for improvised threat detection and neutralization require high-performance antennas with high efficiencyand gain and their thickness and cost are not critical.