Semnan University Press Journal of Modeling and Simulation in Electrical and Electronics Engineering 2821-0786 6 3 2026 09 01 Compact Wide-Band and Narrow-Band Microstrip Bandpass Filters Using the LC Equivalent Model 1 8 10588 10.22075/mseee.2026.40492.1251 EN Morteza Khajavi Department of Electrical Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Khuzestan, Iran. Ebrahim Farshidi Department of Electrical Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Khuzestan, Iran. Mohammad Soroosh Department of Electrical Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Khuzestan, Iran. Shahrzad Ajabi Department of Electrical Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Khuzestan, Iran. Journal Article 2026 02 05 This paper presents an improved design methodology for developing two types of microstrip bandpass filters, a narrowband filter and a wideband filter, employing stepped-impedance resonators (SIRs) and parallel stubs. The fundamental resonator integrates two parallel stubs and a centrally located air gap within a stepped-impedance structure. The corresponding even- and odd-mode capacitances are evaluated, and an additional SIR is coupled to the primary resonator to achieve the desired bandpass response through dimensional optimization. To verify the electromagnetic simulation results, an equivalent LC circuit model is extracted and analyzed, demonstrating strong agreement with the full-wave response. Owing to its compact geometry and structurally efficient configuration, the proposed filter is well suited for integrated microwave systems. The wideband implementation is designed to operate at a center frequency of 10.02 GHz, exhibiting an insertion loss of 1.03 dB, a return loss of 30.1 dB, and 1.33 GHz bandwidth. In contrast, the narrowband design achieves a center frequency of 2.4 GHz with an insertion loss of 0.15 dB, a return loss of 26.26 dB, and 102 MHz bandwidth. https://mseee.semnan.ac.ir/article_10588_7d1cc20770b846877028bc421252dad2.pdf