| Graphene has excellent conductivity and is getting more and more attention in recent years. What's more, the interest on researching this new material is also continuing to rise. The terahertz waves has unique performance compared to micro-millimeter wave. Because of these excellent properties, it was believed that terahertz technology has great research value and a good future in many fields, such as radar, wireless communication, imaging technology, biology medicine, security inspection, electronic countermeasures and nondestructive testing while bring a profound influence on them. Compared to metal, graphene has many unique advantages in the terahertz band, such as the advantage in impedance matching, tunable electric conductivity. Thus, it would be a great process in realizing dynamically controlling radiation of antenna, reducing the size of antenna and improving the performance of antenna.In this dissertation, we investigate the radiation characteristics of various forms of graphene based terahertz antenna. The detailed work includes:1. A brief introduction of the properties of terahertz wave and the research progress on graphene-based terahertz antenna was given. And also basic knowledge of antenna and the conductivity model of graphene were described.2. Patch antennas, dipole antenna and bowtie-shaped antenna whose radiator was made of graphene or graphene-copper composite were designed and studied. Comparing to metal antenna, antennas using graphene radiator has advantages in impedance matching and reconfiguration, but will also has loss on radiation efficiency and gain. Simulation results showed that antennas with graphene-copper radiator can be frequency dynamically tunable while achieving a high gain at terahertz band. The fact that graphene plays a role of switch on dipole antenna and bowtie antenna when putting it under the radiators was illustrated.Graphene will change from a non-conductor to a conductor when the voltage applied on it increase, so graphene can be used as a ground plane of a bowtie antenna and changes its working state. We arrange the single antenna reasonably to form antenna array, the simulation results shows that we can change the applied voltage on each graphene patch to realize the reconfiguration of the beam.3. The application of the graphene-semiconductor interfaces known to behave as a diode is studied in terahertz antennas. The design of graphene-silicon diode loaded patch terahertz antenna, graphene-semiconductor diode loaded bowtie-shaped terahertz antenna and graphene-semiconductor diode array loaded dipole terahertz antenna are presented. The results showed that the impedance and resonant frequency are changing neither one-way nor continuous while adjusting the capacity of the equivalent graphene-semiconductor diode. But they will be just in a small range and soon jump to another value much different from the old one if you change the capacity too much. A four graphene-semiconductor diode array loaded dipole photoconductive terahertz antenna is also designed and so is the study of the effects on the radiation properties of the antenna and its array while using different ways of adjusting the capacities.4. The design of monolayer graphene patch antenna operating at THz band with reconfigurable capability is presented. In such Yagi-Uda type of antenna, one graphene patch, threes graphene patches as a array and three arrays of graphene patches are employed for achieving our desired radiation performance, which is based on tunable electrical conductivity of graphene by changing its biasing DC voltage. The adjustable range of its radiation beam at designated terahertz frequency is 160°. Further, we also studied the effects of the angle and distance of the graphene patches array on the radiation direction. And, a beam-scanning antenna based on graphene reflector is designed, which we can achieve a broader tunable range of radiation direction when we use dipole antenna rather than bowtie antenna. |
PDF Full Text Request