Single‐ and dual‐band bandstop filters with U‐shaped resonators are proposed. First, short and open U‐shaped resonators are coupled to a main transmission line to obtain second‐order stopband performance with two transmission zeros in the stop band and two reflection zeros in the passband. In contrast to traditional second‐order bandstop filters, the two different resonators are coupled to both sides of the microstrip line so that the commonly used quarter wavelength distance between resonators is eliminated. Secondly, open and short U‐shaped stepped impedance resonators are employed to obtain dual‐band bandstop filters in a compact size. Both filters are prototyped and measured. Good agreement between simulated and measured results demonstrates the reliability of the design method. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1362–1365, 2017