Bandpass Hairpin Filters Harmonics Suppression by Using the Combination of Open Circuit Stub and Spur-line

This paper proposes a microstrip bandpass filter which uses a variety of structures to suppress harmonics. By connecting two open-circuit stub lines in parallel in the resonator and introducing spur line into the coupling section, it can further suppress harmonics while ensuring good performance of passband. The center frequency of the hairpin filter designed in this paper is 2.5GHz and bandwidth is 200 MHz, which covers the blue-tooth communication band. And extend stopband with a rejection level of 37.5 dB up to 2f
0
, the harmonic suppression effect of the combination of the two structures is much better than that of the single one which can further ensure the performance of the passband.