Microstrip cross-coupled interdigital hairpin bandpass filter

Miniaturized interdigital hairpin resonator is proposed. A four-pole cross-coupled bandpass filter is also implemented. The validity of the proposed method was confirmed through the design, fabrication and measurement of compact hairpin bandpass filter at 1.8 GHz on FR4 substrate. The insertion loss of the filter with using FR4 substrate is about 1.26 dB, however, the attenuation values out of the band was below 16.7 dB on the lower frequency region, and approximately 20.6 dB in the higher frequency region. The compactness in the circuit size make the design of cross-coupled filters using the microstrip miniaturized hairpin resonators attractive for further developments and applications in modern communication systems.