This paper introduces a novel design for a miniaturized wide-stopband hairpin filter that aims to overcome the challenges of parasitic passbands at the harmonic frequencies encountered in traditional microstrip hairpin filters. By incorporating three 1/4-wavelength open-circuit microstrip lines at the input and output of the conventional hairpin filter, the design effectively suppres-ses parasitic passbands. Additionally, the application of cross-coupling techniques facilitates the miniaturization of the device. The design, fabrication, and testing phases culminated in the development of a bandpass filter with a 400 MHz bandwidth and a center frequency of 3 GHz. The filter demonstrates an insertion loss of 2.5 dB and achieves effective suppression of parasitic passbands below 13 GHz, with an out-of-band suppression of 24 dB. The new filter design is characterized by its simplicity and low complexity, with dimensions of just 23 mm by 27.7 mm, meeting the current demands in the communications field for high-performance, miniaturized filters, and demonstrating significant potential for future applications.