Abstract
A novel design methodology for an improved hairpinline microstrip narrowband bandpass filter is presented in this paper. The new proposed methodology incorporates use of via ground holes and a capacitive gap to improve the performance and dimensions of a conventional hairpinline bandpass filter. This design approach incorporates use of /4 resonators thus reducing the overall size of the filter by 15.5 % as compared to the conventional design. A capacitive gap is also introduced in the center of the center resonator. The proposed design achieves 3 dB fractional bandwidth less than 4 %, insertion loss less than 0.8 dB and return loss better than 40 dB at the center frequency of 1 GHz. The effects of tap point height, characteristic impedance and gap width are analyzed in detail and subsequent relationships are developed with the fundamental design parameters. Based on the proposed design, a bandpass filter is designed and fabricated on FR4 substrate, and good agreement is observed between measured and simulated results.