AbstractTo reduce the size and improve the performance, a miniature microstrip bandpass filter (BPF) is investigated in this article. On the basis of open‐loops, an interdigital capacitive load has been connected. The new design has advantages of a compact size and a large ratio of the first spurious resonant frequency to the fundamental frequency. A fabricated microstrip BPF has been validated design, and experiment results are shown in very good agreement with expectation. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:748–751, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25829