Compact microstrip lowpass filter with very sharp roll-off using meandered line resonators
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Compact microstrip lowpass filter with very sharp roll-off using meandered line resonators Mohsen Hayati1
•
Sepehr Zarghami1 • Farzin Shama2
Accepted: 18 November 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, a new compact size microstrip lowpass filter (LPF) with a very sharp roll-off is presented to apply in the modern wireless networks. The proposed LPF is designed using the series main resonators with meandered lines based on inductor-capacitor (LC) equivalent circuit analysis. The main goal is to achieve maximum-sharp roll-off by maintaining a wide stopband bandwidth and high return loss (RL). The main resonator of the proposed filter is consisted of two meandered line hairpin resonators (MLHR), and a meandered line T-shaped resonator (MLTR). The designed suppressor is composed of two coupled radial stubs to create a wide stopband. Low return loss in the passband, which has been created by the main resonator, is resolved by the suppressor structure with high return loss. The measured results show a - 3 dB cut-off frequency of 1.93 GHz. The very sharp transition band starts at 1.93 to 1.97 GHz (from - 3 to - 20 dB). The stopband is from 1.97 to 19.9 GHz (with the suppression level of - 20 dB). Also, the total size of the proposed LPF is only 13.3 9 10.1 mm2. Keywords Coupling effect Microstrip lowpass filter Sharp roll-off Ultra-wide stopband
1 Introduction The development of communications systems are overgrowing. So, update designs have been increased in all of the parts of these systems. One of these critical parts is the various types of filters. Lowpass filters (LPFs) can be used to suppress unwanted harmonics, etc. In the design of advanced communication systems, several filters are used in a diplexer circuit [1] and [2]. The most essential characteristics, for designing an LPF, can be summarized as sharp roll-off, wide stopband, and high return loss (low insertion loss) in the passband. Many methods and topologies have been introduced to design high-performance LPFs in recent years [3–27]. In this regard, filters [3–27] are classified into three categories: extended & Mohsen Hayati [email protected] 1
Department of Electrical Engineering, Faculty of Engineering, Razi University, Tagh-E-Bostan, Kermanshah 67149, Iran
2
Department of Electrical Engineering, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran
stopband, sharp roll-off, and sharp roll-off with extended stopband LPFs. The extended stopband LPFs, which are concentrated on stopband improvement, are divided into three sub-categories: wide stopband [3–7], ultra-wide stopband [8–13], high suppression levels stopband LPFs [14–17]. Obvious disadvantages in LPFs with wide stopband include a gradual response (low roll-off) and low suppression level. In ultra-wide stopband LPFs and to the gradual response, design complexity and large implemented size are common disadvantages. For instance, the presented filter in [8] has a cons
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