Optically Controlled Reconifgurable Antennas For Cognitive Radio Applications

As an effective solution to the lack of spectrum resources, the cognitive radio technologyhas been predicted to be the most popular wireless technology. Cognitive radio,thefuture radio system, is challenging the design of reconfigurable antennas. The basicarchitecture of a cognitive radio system is composed of a “UWB sensing antenna” thatcontinuously monitors the wireless channels and searches unused frequency channels, and a“reconfigurable transmit/receive antenna” that conducts the required wireless communicationthrough those unused frequency channels.The main content of this thesis includes the following aspects. A brief introduction of thecognitive radio and a discussion to the status of the art of optically controlled reconfigurableantennas for cognitive radio applications are presented in Chapter1. The theoreticalfoundations are introduced in Chapter2for the research work in this thesis, such as theradiation principle of antennas, the basic parameters, the design theory for ultra-widebandantennas, and photoconductive effect. In the Chapter3, we introduce an optically controlledreconfigurable antenna which is the initial realization of the concept of cognitive radio. In thisdesign, the UWB monopole antenna and the microstrip narrow-band antenna are integrated inthe same structure. By controlling four photoconductive switches with the laser anda four-way splitter, the antenna can be tuned to cover a ultra-wideband (2.65-10.3GHz) and three narrower operating bands (7.10-8.01GHZ,3.55-5.18GHz and5.12-6.59GHz). The measured results show good agreement with the simulation results. Inaddition, the effect of optical power on the S-parameters of the antenna has been investigatedby measurement. Finally a new antenna is designed to improve the antenna proposed inChapter3. The improvement includes the modification of the ultra-wideband monopoleantenna structure to reduce the number of the switches required to be illuminatedsimultaneously, and the simplification of the switch control. The three operating bands cancover some practical wireless communication applications, such as WiFi, WLAN and3.5Gnetworks. The measured results show good agreement with the simulation results, validatingthe purpose of improvement for cognitive radio applications.