The compact band-pass filter using L slot lines and enhanced air-bridge for the spurious responses suppression

In microwave communication systems, filters with wide stopband are required to enhance the system performance. The presence of undesired spurious response is a problem for microwave filters. Many papers have proposed the second harmonic suppression method for the band-pass filters by adding additional structures, such as DGS. However, those structures are at the sacrifice of large size and higher order harmonics could not be suppressed efficiently. In this paper, we present a new method to suppress high harmonics. Through introducing the enhanced air-bridge and L slot lines, the stopband of the bandpass filter in [1] can be extended to 30GHz so that the harmonics in 5f0, 7f0 and 11f0 are all eliminated while the passband selectivity still keeps excellent. Moreover, those extra-structures do not increase the size of the filter.