Design Of Band Notched UWB Antennas Based On SRR

UWB technologies were approved to be used in commercial systems by American Federal Communications Commission (FCC) in February 2002.In the technical standard of FCC, the ultrawide band of 3.1-10.6GHz can be used for short-distance high-speed wireless communication.Because UWB wireless communication has many distinct advantages such as high concealment, high multipath discernibility, high transmission speed and strong penetrability,UWB technology has become one of the most attractive technology fields of modern wireless communication.Antenna is one of the critical components of a wireless communication system.In order to achieve a high-performance system,UWB antennas should have enough efficiency,no dispersion and a big bandwidth.As the working bands of Worldwide Interoperability for Microwave Access (WiMAX,3.3-3.7 GHz),Wireless Local Area Network (WLAN,5.15-5.35GHz/5.725-5.825GHz) and other narrow band systems located in UWB band,if we have not separated these bands from the UWB band, there will be interference between systems.Interference reduces the quality of communication.So UWB antennas should be designed to be insensitive in these bands,that means in these bands the antennas can not radiate and receive electromagnetic waves efficiently and possess a band notch function.The main work of this thesis can be concluded as follows:(1) A brief history of UWB antennas’development and a fundamental theory of UWB antennas are introduced.We also expound the research status of band notched UWB antennas around the world.Then the resonant characteristics of SRR(Split Ring Resonators) and its improved structures have been analyzed.The analysis indicates that high-Q small-size narrow band resonant structures have the advantages in band rejection of band-notched UWB antennas.(2)Two single band-notched UWB antennas with sharp selectivity in the band ofWiMAX(3.3-3.7GHz) are proposed.By etching a pair of complementary interdigital capacitance loading loop resonators and a pair of L-shaped slots with one end open in the ground plane of the first antenna,and by etching a pair of complementary interdigital capacitance loading loop resonators(CICLLR) in the ground plane of the second antenna and etching a C-shaped slot on its radiating patch, notched bands with sharp selectivity covering WiMAX(3.3-3.7GHz) are obtained.(3)A triple band-notched UWB antenna with sharp selectivity is proposed.We respectively add a pair of narrow band resonant structures near the feedline and in the radiating patch of the first antenna,so the two notched bands with sharp selectivity of WLAN lower band (5.15-5.35GHz) and WLAN higher band (5.725-5.825GHz) are achieved.The three designed antennas are all fabricated and tested.The measured and simulated results show good agreement.Measured reflection coefficients show that the proposed antennas can cover entire UWB band and have band notches with sharp selectivity in the notched bands.Measured radiation patterns and peak gains demonstrate that in the working band the antennas have a omni-directional radiating characteristic and in the notched bands they are insensitive in radiating.