Modelling and developing of microstrip rotman lens based on electric field analysis and defected ground structure.

• Main Author: Ibraheem, Mohammed Khalid
• Format: Thesis
• Language: English; English; English
• Published: 2021
• Subjects: T Technology (General)
• Online Access: http://eprints.uthm.edu.my/8439/1/24p%20MOHAMMAD%20KHALID%20IBRAHEEM.pdf; http://eprints.uthm.edu.my/8439/2/MOHAMMAD%20KHALID%20IBRAHEEM%20COPYRIGHT%20DECLARATION.pdf; http://eprints.uthm.edu.my/8439/3/MOHAMMAD%20KHALID%20IBRAHEEM%20WATERMARK.pdf; http://eprints.uthm.edu.my/8439/
• Institution: Universiti Tun Hussein Onn Malaysia

Allocating multiple beams in desired angles is a cornerstone component in modern wireless systems. Scanning in microwave lens is independent of phase coupler and phase shifter compared to other scanning techniques. A discontinuity between the 50 Ω feeding lines and unknown lens cavity impedance has a direct impact on lens performance in terms of power loss, phase performance, and lens size. A tapered line is used conventionally in microstrip lens. However, taper line modelling required sophisticated computer specifications to optimise its dimensions besides the simulation time factor. Further, taper line length increases lens size. Therefore, two approaches have been introduced in this study to solve this problem. The first contribution is introduced a matching impedance based on determining and analysing the magnitude of the standing wave pattern of an electric field. The impedance matching is achieved effectively using the proposed approach independent of the optimisation process, which saves 3 hours of simulation time compared to the taper line approach. Further, an increase of bandwidth for beam ports two and three by 25.65% and 11.47%, respectively is notified. However, beam port one bandwidth is decreased by 7.17%. While the second work in this study is embedding a defected ground structure for microstrip lens is used for the first time to replace the full ground of the microstrip lens and examined the effect of the defected ground structure on the lens performance. A suggested defect structure is used to modify the inductance and the capacitance of the lens cavity to increase its characteristic impedance and balance the 50 Ω feeder lines. The suggested method successfully increases the impedance of the lens cavity and reduces the discontinuity between input ports and lens internal impedance to achieve an acceptable return loss at design frequency with an enhancement of 22.9% for beam port one and 103% for beam port three. Further, miniaturization of lens size by 11.21% is achieved due to the replacement of the taper line by the proposed approach. The suggested methods are applied to microstrip lens works at ISM band frequency and measurements are led to successful validation.