Integrated Broad-/Narrow-band Optically Controlled Reconfigurable Antennas For Cognitive Radio Systems

The cognitive radio (CR) technology is considered as one promising solution to improvethe management and utilization of the radio spectrum. In the future, the design of antennas,especially of the reconfigurable ones, will being challenged. In a CR system, ultra-wideband(UWB) antennas (i.e.,“sensing antenna”) can broadly scan frequency ranges effectivelyperforming “spectrum sensing”. When such an antenna detects an idle frequency bandavailable, a reconfigurable antenna (namely “communicating antenna”) will switch to thecorresponding unused band for communication. This dissertation was supported in part by theNational Natural Science Foundation of China (60802004), in part by the State KeyLaboratory of Millimeter Waves (K201405), and in part by the Fundamental Research Fundsfor the Central Universities (2014ZZ0031), and three optically controlled reconfigurableantennas for cognitive radio are proposed.Firstly, an integrated broad-/narrow-band optically controlled reconfigurable antenna forcognitive radio systems is presented. The coplanar waveguide (CPW) fed antenna wasemployed dual ports and comprised of two parts. One element is a UWB monopole antennafunctioning as the spectrum sensor, while the other one acts as a reconfigurable narrowbandresonator for communication. With an inherent property of decreased electromagneticinterference, four appropriately placed laser-controlled photoconductive silicon switches areused to achieve reconfigurable frequency characteristics in the four bands of5.8-6.8,6.7-7.3,7.0-8.4, and7.9-9.2GHz with the reflection coefficient below-10dB.Then, in order to improve the performance, the integrated broad-/narrow-band opticallycontrolled reconfigurable antenna has been modified. Four silicon switches were embedded inthe structure symmetrically, and the four reconfigurable bands of2.51-3.64,3.42-4.0,4.78-5.41, and7.66-8.38GHz are achieved, which focus on the lower frequency sub-bands ofthe UWB. The four operating sub-bands can cover some practical wireless communicationapplications, such as WLAN, WiMAX, and ITU8-GHz band for satellite communication.Finally, an ultra-wideband planar monopole antenna with reconfigurable band-notched characteristics is presented. With inserting U-shaped slot，the miniaturization ultra-widebandantenna get the band-notched property. Five optically controlled photoconductive siliconswitches are placed in the UWB antenna and four reconfigurable notch bands (2.2-2.9,3.2-4.7,4.8-6.6, and7.5-8.7GHz) and one wideband (2.5-12GHz) are obtained.How to choose suitable switch plays crucial role in the design of reconfigurable antennas.Different types of electrical devices, such as RF MEMs, varactor and PIN diodes, have beenincorporated in the antenna prototypes. In this paper, photoconductive silicon chips wereemployed as the switching elements. This type of optical switch does not need additionalbiasing lines, simultaneously with the advantages of less electromagnetic influence onantenna radiation, and high frequency transition speed.