Structural Design And Application Research Of Lattice Network-based Composite Right/Left-handed Transmission Lines

Nowadays,the wireless communication technology is undergoing rapid developments,and the emergence of the new artificial electromagnetic materials has also brought a new research boom.As a type of new artificial electromagnetic materials,composite right / left-handed(CRLH)transmission lines not only have the peculiar electromagnetic characteristics of left-handed transmission lines,but also have the advantages of small circuit size and wide passband.By employing the CRLH transmission lines into RF/microwave devices,a component with wide bandwidth,dualband,or compacted size can be realized,which has important research significance in the field of RF/microwave circuits.This thesis focuses on the analysis and design of lattice network-based(or X-type)CRLH transmission lines based on the existing theory of CRLH transmission lines.A method of using X-type CRLH transmission lines with the coplanar waveguide(CPW)transmission lines is presented to achieve dual-band or frequency-tunable power dividers.The main work is as follows:1.Implementation of X-type CRLH transmission lines.Based on the theory of the X-type CRLH transmission lines,the implementation with CPW is considered here as its specific structure,that is,the central conductor of the CPW transmission line is on the same plane with the ground conductors.By loading interdigital capacitors,meandered lines,defected ground structures on the CPW transmission line,the 70.7 Ω X-type CRLH transmission line with-90° and +90° phase shift at two different frequencies respectively is achieved.2.Implementation of dual-band power dividers.In order to realize the dual-band power divider,the X-type CRLH transmission line mentioned above is utilized to replace the conventional quarter-wavelength transmission lines in the power divider.The dualband T-type power divider operating at 0.9 GHz and 3.5 GHz is designed firstly.Obviously,the ground conductor is between the two output ports,it is difficult to add an isolation resistor due to the two apart signal output ports.Then,the structure of T-type power divider is optimized to improve the isolation,a dual-band Wilkinson power divider is realized.Furthermore,the overall size of both dual-band power dividers is about 36.6% area of the conventional case,which realizes the miniaturization of the power divider.3.Implementation of frequency-tunable power dividers.By loading varactor diodes in X-type CRLH transmission lines,frequency-tunable transmission lines are realized.Just the same as the above design steps,the X-type CRLH transmission lines with varactor diodes are utilized to replace the conventional quarter-wavelength transmission lines in the power divider.When the bias voltage changes from 4 V to 10 V,both the T-type and Wilkinson power divider realize the feature of frequency-tunable in dual bands.