Design of two-stage fish spear-shaped UWB bandpass filter with sharp selectivity and good out-of-band performances

(ProQuest: ... denotes formulae and/or non-US-ASCII text omitted; see image)

Research Papers

I.

INTRODUCTION

Since the release of 3.1-10.6 GHz spectrum for unlicensed use by the Federal Communication Commission (FCC) in [1], the researches in the design of ultrawideband (UWB) components had received major attention from both the industries and academia. UWB filters are one of the necessary components of the UWB communication systems [2]. So, UWB filters that have compact dimensions, low insertion loss, sharp selectivity, and good out-of-band performance are required for UWB systems. Several works on the design of UWB filters have been reported in the literature [3, 4], which utilizes different design methodologies. Multimode resonator (MMR)-based UWB bandpass filters (BPFs) are presented in [5-7]. In these designs, three/four/five resonant modes are excited to form passband of the filter, which covers the entire UWB spectrum. In [8-11], stub-loaded MMRs are used in the design of UWB BPFs in order to improve the selectivity and out-of-band performance. These stub-loaded MMRs generate two transmission zeros in the lower and upper sides of the passbands. An electromagnetic bandgap-embedded MMR-based [12] UWB BPF is implemented in order to achieve the wide upper stopband. However, it is a true challenge is to design UWB BPF with the following characteristics: compact dimensions, low insertion loss, good return loss, sharp selectivity, and good out-of-band performance.

In this paper, a novel UWB BPF prototype is designed. This prototype consists of two stages of fish spear-shaped MMR, which are cascaded together to improve the skirt selectivity of UWB BPF. Each stage of fish spear-shaped MMR has five resonant modes: two odd modes and three even modes. In order to improve the out-of-band performance, a stepped impedance resonator (SIR) is loaded at the center of fish spear-shaped MMR. This SIR creates an additional transmission zeros at higher frequencies. Finally, the two-stage fish spear-shaped MMR-based UWB BPF is fabricated and measured.

II.

SINGLE-STAGE UWB BPF

Figure 1 shows the single-stage stub-loaded fish spear-shaped MMR-based BPF. This fish spear-shaped MMR has two open stubs of length L ₄ and width W ₄ along each side of the symmetrical central plane. This MMR generates fives resonant modes: two odd and three even modes, which lie in the passband of the UWB spectrum as shown...