Design and band coalition of dual band microstrip filter using DGS, coupled line structures and series inductive metallic vias Sourav Moitra 1 • Ranjan Dey 1 • Partha Sarathee Bhowmik 2 Received: 14 August 2018 / Revised: 24 November 2018 / Accepted: 18 January 2019 Ó Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract An approach to design compact dual band BPF and technique to unite the two bands into a single wide band is presented in this paper. The novelty of the filter stands on the application of series of metallic vias which are used to merge the bands obtained using coupled line circuits and DGS structure. The coupled line filter and the coupled line filter integrated with DGS shows passband resonance at 4.5 GHz and 5.1 GHz within the microwave frequency of operation. Series metallic vias are used to merge the passbands into a single wider passband of bandwidth 1.6 GHz (3.5–5.1 GHz). The filter configurations are fed using stepped-impedance open stub technique to reduce cross coupling between adjacent structures. Moreover effects of several salient filter parameters like gap between edge of the microstrip coupled line resonator and via series G V and gap between mid- point of the open ended feed line and via row G M are studied to achieve greater isolation at higher frequencies. All simulated designs are fabricated and experimentally studied to vindicate the practical performance of all filter configurations. Keywords Stepped impedance open stub (SIOS)  Defected ground structure (DGS)  Microstrip coupled line  Inductive posts  Band pass filter (BPF) 1 Introduction Band pass filters that are based on parallel-coupled microstrip-lines are widely used in microwave systems due to their simple structure, low cost, and easy integration with other devices. Thus multi-band and wideband band- pass filters (BPF) are considered to be one of the main components in modern wireless communication systems. This enables them to be a lucrative area for research due to their vast scope application in several compact communi- cation systems. However, their use in many wideband applications is hindered by two factors. The first one is the presence of the harmonic responses. The undesired second harmonic appears due to the difference in the odd- and even-mode phase velocities of the microstrip coupled structures. That difference becomes larger, and thus, the second-harmonic problem becomes more dominant when a substrate with high dielectric constant is used. The second factor that limits the use of microstrip bandpass filters in wideband systems is the need for a very narrow spacing between the coupled lines which increases design com- plexity. In recent date, several approaches have been introduced to design multi band BPFs which presents several method to eliminate these limitations and enhance filter performance. Cascaded multiband resonators, tri- section stepped impedance resonators (SIRs) are used to obtain multi-band filters [1–3]. Coupled complementary split ring resonators (CSRRs) into a balanced stepped- impedance microstrip slot line structures are also analyzed to obtain multiple frequencies pass bands [4]. Dual-band microstrip bandstop filter with multiple poles using open/ shorted coupled lines is presented where the two stopbands are realized by conventional coupled lines and transmission lines [5]. High impedance short circuited stubs and stepped couple line structures are also effectively used to obtain wideband microstrip filters [6, 7]. Inter digital edge & Sourav Moitra souravmoitra25@yahoo.in Partha Sarathee Bhowmik psbhowmick@gmail.com 1 Department of Electronics and Communication Engineering, Dr. B C Roy Engineering College, Durgapur, Durgapur, West Bengal, India 2 Department of Electrical Engineering, National Institute of Technology, Durgapur, Durgapur, West Bengal, India 123 Analog Integrated Circuits and Signal Processing https://doi.org/10.1007/s10470-019-01412-2