Investigations on fractal based microstrip bandpass filters for wireless applications

Abstract

Microstrip Bandpass Filters (BPFs) are the key components in wireless communication systems. Due to light weight and easy fabrication, microstrip filters play an essential role in many wireless applications. However, the design of BPFs with smaller size and better performance is always challenging. In recent years, the enormous development in wireless communication technologies demands the design of high-performance, lowcost, and miniaturized microwave filters. The application of such filters in wireless systems extends from the traditional AM/FM to GSM, GPS, Wi-Fi, Bluetooth, WLAN, Wi-Max and so on. Recently, there has been widespread attention in the design of planar structures such as antennas, filters, and so on by deploying fractal geometry due to its properties of space-filling and selfsimilarity. Miniaturization of the planar circuit is possible because of the space-filling property of fractals; whereas, the multiband operation of the planar structure is attributed to its self-similarity property. Moreover, compared to the research works on fractal antenna design, very limited research has been carried out in the design of BPFs employing fractal geometry. To cater to the various applications of wireless systems in narrowband, dual-band and wideband, such fractal geometries can be integrated with the design of microstrip filters for better performance. Therefore, the requirement for the compact design of microstrip fractal BPFs suitable for use in narrowband, dual-band as well as wideband wireless applications is highly demanded and thereby, attracts much attention among the filter research community. The major objective of this thesis is to investigate the design of fractalbased microstrip BPFs for narrowband, dual-band and wideband wireless applications. The presented filter designs exhibit smaller footprint, high selectivity and better performance in terms of low insertion loss and better return loss. Besides, a flat group delay has also been obtained in the design of fractal BPFs which indicates minimum phase distortion and good linearity in signal transmission. The first part of this thesis discusses the design of single-band dualmode BPFs utilizing the fractal geometry with a narrow bandwidth (BW) for 2.4 GHz WLAN applications. By embedding a square perturbation at the diagonal corner of the patch resonator, the configuration of dual-mode BPFs is realized. First, the design of modified Sierpinski fractal-based dual-mode BPF has been analyzed on various microwave laminates such as FR-4, RT/duroid 5880 and 6010. As compared to the other two laminates, the simulation results show better characteristics for the dual-mode filter designed on RT/duroid 6010. newline