A New Approach to Design Microstrip Low Pass Filter

Abstract

With the emergence of novel wireless technologies, the demands for larger bandwidth, high efficiency and high capacity RF and microwave devices have been growing tremendously. The recent implementations in solid state and semiconductor materials give us hope for future applications. It should be remarked that although many of the ideas could have been proposed much earlier, it is only recently that they were identified or demonstrated due to various technological advances. The electromagnetic bandgap (EBG) is introduced to improve the performances of existing RF active and passive devices. Electromagnetic Band Gap (EBG) structures produced a wide variety of design alternatives for researchers working in the area of microwave and photonics. The focus is now towards on finding real applications combined with detailed modeling. Due to the incredible potential of EBGs, there are huge applications in which they can be used. New companies have also started to exploit the commercial potential of this technology. This thesis describes the planar EBG structures in the forms of conventional circular and rectangular photonic bandgaps (PBGs) and dumbbell shaped defected ground structures (DGSs). Novel PBGs in the form of non-uniform Binomial and Chebyshev distributions of unit PBG cells have been proposed. This novel PBGSs contains fewer ripples with lesser height or ripple free passband and wide stopband properties, which are very useful to suppress higher order harmonics in the lowpass filters (LPF). The dumbbell shaped DGSs study has been described with the gap width and length and the size of dumbbell slots. Some novel designs have been proposed such as; non-uniform dumbbell shaped DGSs with Binomial and Chebyshev distribution, hybrid dumbbell shaped DGS and PBGS and modified hybrid dumbbell shaped DGS and PBGS configurations. The novel designs perform better than the conventional DGSs reported in the literature. The DGSs yield perfect LPF responses with negligible passband ripples and extremely wide stopband. In this thesis, we have investigated on uniform circular, rectangular and dumbbell shaped DGS structures with different filling factor (FF). Therefore, FF is not a single valued parameter. In our study, we have defined the FF as the ratio of central dumbbell shaped DGS element and inter-element spacing. And then for the better performance, we have focused on different Binomially and Chebyshev distributed dumbbell shaped DGSs. This research conveys the performance of low pass filter using those distributions at about 4 GHz cutoff frequency. These distributions remove the unwanted insertion loss in the band rejection region. Sufficient explanations have been provided to validate the total research works in the thesis. Finally, comparing the insertion loss (IL) and return loss (RL) performances of the LPFs with binomially and Chebyshev distributed dumbbell shaped DGSs and hybrid DGSs. Binomially distributed DGSs and hybrid DGSs provide improved performance than conventional PBGSs and Chebyshev distributed dumbbell shaped DGSs in terms of suppression of the ripple in the passband and return and insertion-loss bandwidths.