RF Front End Design for Cognitive Radios with Reduced Out of Band Emission

Abstract

In the recent years, wireless communication systems have developed rapidly. By the newlineobservation of communication traffic, the expectation is that the traffic doubles every year, newlinewhich may result into scarcity of communication spectrum. On the other hand, the spectrum newlineallocated to the primary users is not utilized fully. This results into wastage of bandwidth. newlineCognitive Radio (CR) system addresses these issues, for better utilization of spectrum, by newlinesensing the spectrum for unused frequencies with a wide band sensing antenna, and then newlineallocating the free channels to the secondary users for communication with a frequency and newlinepattern reconfigurable communication antenna. This thesis presents the design of RF front newlineend antenna for applications in CRs. newlineIn the first part of the thesis, focus is on investigation of front end antennas. First, a newlinefrequency reconfigurable patch antenna is designed at 5.8 GHz resonant frequency. Then two newlineslots oriented at an angle of 45 degrees are made and are loaded with varactor diodes for newlinefrequency reconfiguration characteristics. The radiation characteristics and S-parameters newlineresults are analyzed. A continuous frequency reconfiguration is achieved in four different newlinebands. Later, this single element antenna is extended in a 4 × 4 array antenna consisting of 16 newlinepatch elements loaded with varactors. This array antenna is designed to provide frequency newlinereconfigurable characteristics with high gain. Thereby interference to other CR users can be newlineavoided. Therefore it is possible to transmit signals to only the intended user receiver. Next, newlinea wide band antenna to operate in sub-6 GHz band for scanning the wireless spectrum in the newlinenearby environment is designed. The spectrum holes are identified, in terms of frequency newlineand bandwidth. Then the applied voltages to varactor diodes in the communication antenna newlinearray elements are used to tune to a set of or a particular frequency identified by the sensing newlineantenna. newlineThe omni-directional antenna and array antenna are placed on the same substrate FR4 newlinewith