Date

2017

Author

Karadağ, Serkan

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This study proposes three microstrip line fed circular monopole antennas with ultra-wideband (UWB) characteristics, improved omnidirectional radiation pattern and WLAN (5 GHz-6 GHz) band notched characteristics for wireless and mobile communication systems. In this thesis, first, a microstrip line fed ultra-wideband ring monopole antenna with improved omnidirectional radiation pattern is designed, fabricated and measured. Two corners are tapered on the ground plane for increasing impedance bandwidth. In order to obtain low cross polarization level on the H plane, two symmetrical rectangular notches are cut on lower side of the ground plane. Moreover, in the center of the circular patch, a slot is opened to improve impedance matching at lower frequencies. The proposed antenna has measured bandwidth from 2.6 GHz to 20 GHz. The antenna has omnidirectional radiation pattern on the H-plane. The measured cross polarization level is low up to 9 GHz on the H plane. Moreover, it has near-omnidirectional radiation pattern on the Eplane. The measured cross polarization is low at all frequencies on the E-plane. Secondly, an UWB antenna (4.3 GHz-11.2 GHz) with symmetrically located open-circuited stubs is designed, fabricated and measured. The aim of this design is to distribute some part of the current in the symmetrical open circuited stubs to vi improve the radiation patterns of the antenna at high frequencies. The cross polarization level is less than -20 dB up to 6 GHz. However, cross polarization level increases at high frequencies. Finally, an UWB with band-notched characteristics (WLAN 5 GHz-6.1 GHz) is designed, fabricated and measured. U shaped slot is etched on feedline to obtain band-notched characteristics. Antenna shows omnidirectional pattern on the H plane up to 7 GHz. The cross polarization level is below -20 dB up to 7 GHz. The proposed antenna has measured bandwidth from 2.5 GHz to 16.5 GHz. The antenna has wide bandwidth and large peak gain when compared to the previous studies. For all antennas developed, the effect of different parameters such as the gap between monopole patch and ground plane, width of ground plane, length of the ground plane, dielectric constant, thickness, and patch radius is studied. Measured return loss characteristics and radiation patterns agree well with the simulated ones.

Subject Keywords

Antennas (Electronics)., Ultra-wideband antennas

URI

http://etd.lib.metu.edu.tr/upload/12621706/index.pdf
https://hdl.handle.net/11511/27034

Collections

Graduate School of Natural and Applied Sciences, Thesis