Reconfigurable defected microstrip phase shifter for phased array antennas

Beamforming and its most common variant, phased arrays, offer a number of advantages for wireless communications and radar systems. These include increased range and capacity, immunity against interference, and system flexibility. However, due to the associated high cost, both digital and analogue beamforming systems are primarily employed in defence and space applications where cost is not necessarily an obstacle. This thesis is motivated by a strong need from civilian applications where low-cost beamforming systems are required. In a beamforming system, a phase shifter is one of the most critical devices. Usually, a large number of phase shifters are employed, however they are very costly. Therefore, reducing the cost of phase shifters is an effective way to decrease the total cost of a beamforming system. And so, a phase shifter that is low in cost, compact, has an easy control method, and which can be constructed using a simple fabrication process is in high demand. In this thesis, firstly, some basics of phased arrays and different types of phase shifters used in phased arrays are reviewed. Then, a novel type of phase shifting unit called as reconfigurable defected microstrip structure (RDMS) is proposed. The RDMS is printed on a microstrip line due to its low cost, low complexity, and for its incomparable popularity in antenna and microwave designs. A series of phase shifters employing RDMS are discussed and integrated in phased arrays, to demonstrate their practicability in beamforming systems. Subsequently, a modified RDMS (MRDMS) phase-shifting unit is introduced, which is smaller in size but has comparable or even better performance. Based on the MRDMS unit, a complete phase shifter design scheme consisting of three steps is presented, and each step is elaborated with theory, simulation, and experiment. A significant improvement in performance and a reduction in cost are achieved and illustrated by comparing the performance of the phase shifters employing RDMS and MRDMS units to each other. Finally, the proposed RDMS- and MRDMS-based phase shifters are used to construct a phased array antenna and a reconfigurable PRS antenna, which proves them to be excellent candidates to provide phase shifts in antenna systems. Future work will focus on the realization of large-scale phased array antennas using the proposed phase shifters.