Slotted series Iteration log periodic fractal koch antenna with stub-loaded for UHF TVWS applications

Abstract

The research works in this thesis mainly focusses on the development of slotted series iteration log periodic fractal Koch antenna (S-LPFKA) for ultra high frequency (UHF) television white space (TVWS) spectrum applications. Log periodic, fractal Koch structure and stub technique facilitates the achievement of wide operating frequency band and size miniaturization, besides enhancing directivity and gain. Three different structure of antennas; S-LPFKA, S-LPFKA with rectangular stub-loaded and S-LPFKA with Cshaped stub-loaded have been designed by using 3D simulator software Computer Simulation Technology (CST) to study and verify the effect of each techniques on the performances of the antenna. All the proposed antennas consist of 10 radiating elements of series iteration fractal Koch technique with 30° flare angle on both sides of the substrate in a criss-cross arrangement. All antennas are fabricated on FR-4 substrate with dielectric constant of 𝜀𝑟=4.7 and loss tangent of tan δ=0.019. Both measured and simulated results show an enhancement in bandwidth for all S-LPFKA which covering 100% of the required frequencies from 0.47 GHz to 0.79 GHz when fractal Koch structure and stub technique are employed to the log periodic dipole array (LPDA) antenna. Furthermore, 30.23%, 43% and 48.8% size reduction are achieved for SLPFKA, S-LPFKA with rectangular stub-loaded and S-LPFKA with C-shaped stubloaded, respectively. The proposed antennas recorded linear polarization and unidirectional patterns. The antennas maintain input impedance approximately 50 Ω over UHF TVWS frequencies. The measured results agree well with the simulated results. Those antennas exhibits high gains of between 4 dBi to 7.8 dBi and stable radiation patterns within 0.47 GHz to 0.79 GHz frequency range.The research works in this thesis mainly focusses on the development of slotted series iteration log periodic fractal Koch antenna (S-LPFKA) for ultra high frequency (UHF) television white space (TVWS) spectrum applications. Log periodic, fractal Koch structure and stub technique facilitates the achievement of wide operating frequency band and size miniaturization, besides enhancing directivity and gain. Three different structure of antennas; S-LPFKA, S-LPFKA with rectangular stub-loaded and S-LPFKA with Cshaped stub-loaded have been designed by using 3D simulator software Computer Simulation Technology (CST) to study and verify the effect of each techniques on the performances of the antenna. All the proposed antennas consist of 10 radiating elements of series iteration fractal Koch technique with 30° flare angle on both sides of the substrate in a criss-cross arrangement. All antennas are fabricated on FR-4 substrate with dielectric constant of 𝜀𝑟=4.7 and loss tangent of tan δ=0.019. Both measured and simulated results show an enhancement in bandwidth for all S-LPFKA which covering 100% of the required frequencies from 0.47 GHz to 0.79 GHz when fractal Koch structure and stub technique are employed to the log periodic dipole array (LPDA) antenna. Furthermore, 30.23%, 43% and 48.8% size reduction are achieved for SLPFKA, S-LPFKA with rectangular stub-loaded and S-LPFKA with C-shaped stubloaded, respectively. The proposed antennas recorded linear polarization and unidirectional patterns. The antennas maintain input impedance approximately 50 Ω over UHF TVWS frequencies. The measured results agree well with the simulated results. Those antennas exhibits high gains of between 4 dBi to 7.8 dBi and stable radiation patterns within 0.47 GHz to 0.79 GHz frequency range.