Print parallel coupling wideband filters on Al2O3 ceramic substrate

In this paper, low loss wideband 3 order parallel-coupled microstrip line filters are fabricated, and the influences of the designed parameters are well developed in this study. As the displacement parameter A increases, the insertion loss and ripple decrease and the bandwidth increases; As the displacement parameter B increases, the bandwidth decreases and the insertion loss and ripple increase. On the other word, for the purpose of low ripple and wideband, the best choice is to increase A and decrease B. For the interval parameters C and D, increasing of them will decrease bandwidth, for the reason of wideband, decrease the interval parameters (C and D) will be a good choice, however, the decrease of interval will also increase the coupling of each resonators. Due to the higher the dielectric constant and the high quality factor of the Al₂O₃ ceramic substrate, the wideband filters have the advantages of small size (about 25 mm x 6.2 mm), good insertion loss and the ripple characteristics in the passband, wide bandwidth and large left-transmission zero. From above results, the fabricated filters are suitable for the wideband microwave applications of WLAN system.