A Reconfigurable Defected Microstrip Structure Phase Shifter For Low-Cost Beamforming

Beamforming and its most common variant,i.e.,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,phase shifter is one of the most critical devices.Usually,a large number of phase shifters are employed,which contribtes to a large ratio of the cost of the entire system.Therefore,reducing the cost of the 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 dissertation,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 intergrated 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.In addition,this dissertation also presents two reconfugrable antenna designs.The first antenna is a high gain pattern reconfigurable antenna based on a quasi-Yagi antenna.This is an alternative approach to realize low cost beamforming.By inserting PIN diodes in the balun and the director of the quasi-Yagi antenna,the current distribution on the antenna is changed,resulting three different working states with different beam directions.The second antenna is a dual-band polarization reconfigurable antenna based on microtrip patch antennas.The two operation bands are designed to meet the WLAN standards.By controlling the states of the inserted PIN diodes,the antenna is able to switch between three working states with different polarizations.Both the proposed pattern reconfigurable antenna and the polarization reconfigurable antenna are able to endow one antenna with multifuctions,which makes them be able to replace a complicated antenna system employing multiple antennas,thus reduces the cost.