The electromagnetic spectrum is becoming increasingly congested due to the rapid development of wireless and mobile communication in recent decades. New, compact and efficient passband filters with multi-functions and good performance are highly demanded in current and future wireless systems. This has also driven considerable technological advances in reconfigurable/tunable filter and filtering antenna designs. In light of this scenario, the objectives of this thesis are to design, fabricate and measure efficient, compact, multi-standard, and reconfigurable/tunable microstrip resonator filters and study the integration of the resonators with patch antennas. As a passive design, a compact dual-band filter is implemented to cover 2.5 to 2.6 GHz and 3.4 to 3.7 GHz for 4G and 5G, respectively. Another design is also presented with the advantages of a wide passband of more than 1 GHz. Conversely, new and compact reconfigurable filters are designed using varactor and PIN diodes for 4G and 5G. The proposed filters are tunable in the range from 2.5 to 3.8 GHz. The bandwidth is adjustable between 40 and 140 MHz with return losses between 17 to 30 dB and insertion loss of around 1 dB. Also, the thesis investigates the design of cascaded and differentially-fed filtering antenna structures. The cascaded designs operate at 2.4 and 6.5 GHz and have a relatively wide-band bandwidth of more than 1.2 GHz and a fractional bandwidth of more than 40%. For the differentially-fed structures, good performance is achieved at the 3.5 GHz with a high realized gain of more than 7.5 dBi is observed. / European Union Horizon 2020 Research and Innovation Programme (Marie Skłodowska-Curie Actions) under grant agreement H2020-MSCA-ITN-2016 SECRET-722424.

Yes / Unmanned Aerial Vehicles (UAVs) are considered, nowadays, as a futuristic and robust paradigm for 5G wireless networks, in terms of providing Internet connectivity services onto infrastructure cellular networks. In this paper, the interference regime caused by multiple downlink aerial wireless transmission beams has been highlighted. This has been introduced by estimating the UAVs coverage area that is analytically derived in a tractable closed-form expression. The rationale of the analysed coverage approach relies on observing and adapting the joint aerial distance between the aerial base stations. This can minimize the intra-overlapped coverage and ultimately maximize the overall coverage performance for a better quality of service demands. The novelty of our approach brings useful design insights for UAVs system-level performance that technically helps in aerial coverage computations without the need of performing an aerial deployment setup. To the end, the performance effectiveness of our methodology has been tested under an urban propagation environment conditions, in which the original probabilistic channel model approximation has been taken into account. Moreover, this paper identifies the interference issue of such an aerial network as a shrinkage or distortion phenomenon.

High efficiency is an essential requirement for any system, where the energy can be saved with full retention of system performance. The power amplifier in modern mobile communications system consumes most of the supplied power through the dissipated power and the required cooling systems. However, as new services were added as features for the developed mobile generations, the required data rate has increased to fulfil the new requirements. In this case, the data should be sent with the allocated bandwidth, so complex modulation schemes are used to utilise the available bandwidth efficiently. Nevertheless, the modulated signal will have a Peak to Average Power Ratio (PAPR) which increases as the modulation complexity is increasing. In this case, the power amplifier should be backed off and designed to provide good linearity and efficiency over high PAPR. Among the efficiency enhancement techniques, the Doherty technique (Load modulation technique) is the simplest one, where no additional circuity nor signal processing is required. In this work, the theory of load modulation amplifiers is investigated through two asymmetrical Doherty Power Amplifiers (DPA) targeting 3.3-3.5 GHz were designed and fabricated using two transistors (25 W and 45 W). In addition, more compact load modulation amplifiers targeting sub 6-GHz bandwidth of 5G specifically 3.4-3.8 GHz is discussed including the theory of implementing these amplifiers, where different amplifier capabilities are explored. Each amplifier design was discussed in detail, in which the input and output matching networks were designed and tested in addition to the design of the stability circuit to make sure that the amplifier is stable and working according to the specified requirements. The fabricated circuits were evaluated practically using the available instrument test, whereas Microwave Office software was used for the simulation purpose, each amplifier was designed separately, where all the designed amplifiers were able to provide the targeted efficiency at different back-off power points. Besides, some additional factors that affect the designed load modulation amplifiers such as the effect of the harmonics at the back-off and mismatching the amplifier is discussed. / European Union’s Horizon 2020 research and innovation programme (SECRET)