The Beam-scanning Antenna Based On The Composite Right/left Handed Transmission Line

With the development of science and technology,wireless communication plays an important role in the whole system.The device with wide band,multi-band and multi-mode has been greatly needed.The antenna,which transmits and receives the electromagnetic waves,has been requested for a higher performance.The phased array is typically used for the beam-scanning antenna,but the use of the high-precision T/R components,the phase shifters and the attenuators inevitably bring the problems of high cost and heavy volume.Therefore,leaky-wave antenna(LWA)has received great interests in recent years due to its significant advantages such as low cost and beam-steering capability.As the composite right/left handed(CRLH)transmission line(TL)with low loss and wide bandwidth emerged,the research progress of the LWA has been accelerated and numerous studies of LWA based on the CRLH has been presented.The combination of the metamaterial and the leaky wave antenna has greatly improved the shortcomings of the traditional LWA.Meanwhile,compared with the phased array,the LWA based on the CRLH also has low cost and low power consumption.This paper focus on this topic and has achieved remarkable results.The main work of the paper can be summarized as follows:(1)The theory of the CRLH TL is studied.Its electromagnetic characteristics,including balanced states,unbalanced states,LC network,transmission matrice,dispersion curve and bloch impedance have been analyzed and deduced.Furthermore,the principle of the traditional LWA and the LWA based on the CRLH TL have been researched methodically.(2)This paper has proposed two kinds of electrically controlled beam-scanning leaky wave antennas operating at a fixed frequency.The continuously beam scanning can be achieved by controlling the bias voltage of the varactors which determine the phase constant.The simulation results given by Ansoft HFSS and the measured results has been compared and analyzed.The first design based on substrate integrated waveguide exhibits a good scanning capability from-49° to 22° at 8.4GHz.The second design is based on a coplanar waveguide.When the varactors operate from0.38 pF to 1.9pF at 3GHz,beam scanning from-65° to +60° can be achieved.This antenna shows a better performance than the existing achievements of the studies.The second design can shift the dispersion curve properly by using the suitable equivalent circuit,so the scanning range of the existing study is extended.The method of parameter fitting is adopted to verify the equivalent circuit.By optimizing the parameters,the unbalanced state in the broadside is eliminated.So the gain decline in this direction is solved.The use of the CPWG in this design also makes it easy and feasible to load the varactors.(3)In this paper,the principle of multi-band CRLH transmission line has also been studied.A novel dual-band CRLH TL leaky-wave antenna based on the coplanar waveguide which has a much simplified equivalent circuit is presented.The main lobe of the radiation pattern can be steered from-34° to 68° in the first frequency band from4 to 10.3GHz,while a beam scanning range of-64° to-32° is achieved in the second frequency band from 10.4 to 12.7GHz.This antenna shows some desirable merits,such as low cost and easy integration with planar circuits,which has a good prospect for practical applications.