الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
 |  | from | 121 |  |  |
| | | from | 121 | | |
Abstract
A leap in scientific research has occurred since February 2002, when the federal communications commission (FCC) issued a ruling that UWB could be used for data communications. The FCC allowed the frequency band between 3.1 and 10.6 GHz for Ultra-wideband transmission. Higher data rates, saturation of the frequency spectrum, low power consumption, etc. are some of the reasons why Ultra wideband has been of increased interest over the past years. The planar monopole antenna fed by the coplanar waveguide (CPW) has several advantages over antennas fed by microstrip lines such as low-profile, fabrication cost and ease of integration with feed-networks. UWB system has a great challenge to overcome the electromagnetic interferences due to the existing narrowband wireless communication systems. Recently several UWB antennas with band notch characteristics have been reported, to minimize this interference. The band notch characteristics can be obtained by using split ring resonator (SRR) which one of the new artificial materials that exhibit unusual properties which called metamaterials.
Reconfigurable antenna is an antenna that has the ability to reconfigure its characteristics such as frequency, polarization, bandwidth, and radiation pattern to be suitable for the required system using the same antenna geometry. The frequency reconfigurability has been obtained by adding switches with different types such as PIN diode or micro-electromechanical switches. The notched-band frequency tunability can be also achieved with another method which has been used in this thesis which is a varactor diode and its capacitance can be controlled using applied DC voltage.
In this thesis, the theoretical analysis of different SRRs shape are first examined using Matlab program and its results are compared with the simulated HFSS ones. Elliptical SRR (ESRR) introduce more advantages than these of CSRR such as it has two design parameters which are major radius and ratio. These parameters facilitate the resonant frequency adjustment. Another Priority of ESRR is that the distance between two gaps depends on gap position which
Abstract
III
may affect the resonant frequency so that a geometrical reshaping of circular to elliptical SRR is done. Comparison between both configurations is also introduced. The newest ESRR can be adapted to operate in a multi-range of frequencies. Gap position changing effect in ESRR resonant is also examined. A CPW-Fed UWB planar monopole antenna is designed, examined and fabricated. This antenna provides a directive radiation pattern in E-plane and omnidirectional radiation patterns in the H-plane with the return loss less than -10 dB and linear in phase. By using single hexagonal SRR (HSRR) a notch frequency at 6.2GHz can be obtained. Two HSRRs are loaded on the antenna backside to achieve 6.2 GHz and 8.7 GHz dual band-notched functions (for WLAN and x-band communication application respectively). A single ESRR with specific dimensions is loaded in the proposed antenna backside for single frequency notch instead of using double SRR with the same dimension to stop a single frequency. A CPW-Fed UWB planar monopole antenna loaded by two ESRRs for dual notch frequencies (at 5.2 GHz for WLAN and 6.9 GHz for C-band wireless applications) is introduced, examined and fabricated. The ESRRs are also rotated and the corresponding return loss effect is examined to check the effect that will happen if the ESRR inclined by angle during fabrication. The proposed antenna loaded with double inclined ESRR also fabricated. High radiation efficiency for the antenna is the main required parameter in UWB system, the proposed antenna structure offers high radiation efficiency of more than 95% throughout the working band and decreases over these two band notched frequencies. The proposed antenna gives a peak gain ranges from 1.5 to 5 dB throughout the whole UWB frequency band, except double stopband.
Different SRRs loaded with varactor diodes have been simulated to obtain a tunable resonant frequency. A prototype of band notched coplanar waveguide filter loaded with single reconfigurable ESRR is fabricated and measured to cover the band from 5.2GHz to 5.7GHz. Finally, Reconfigurable band rejection elliptical CPW ultra-wideband antenna loaded with single ESRR has been designed and simulated. The notch frequency of the antenna can be controlled by varying the varactor diodes capacitance using suitable DC voltages, and frequency tunability can
Abstract
IV
be achieved without modifying the basic antenna geometry. The proposed antenna is suitable for notching the frequency band from 5.8 GHz to 6.7 GHz to avoid interference with Wireless Local Area Network (WLAN).