Miniaturized Dual-Band Bandstop Filter with High Attenuation Using Hybrid Capacitive-Loaded Microstrip Resonator

This paper proposes a miniaturized dual-band bandstop filter (BSF) based on a hybrid capacitive-loaded microstrip resonator. Using the two resonant modes of this resonator, distinct stopbands are created, and an equivalent circuit model verifies its operation. Capacitive loading not only reduces the footprint but also enables independent tuning of the stopband frequencies. Additionally, capacitive coupling to the feedlines offers flexible bandwidth control. A fabricated prototype shows strong agreement between simulations and measurements, demonstrating significant attenuation and a compact size.