2.4/5.2 GHz dual-band bandpass filter using open-loop square-ring and insert coupling structure

A novel 2.4/5.2 GHz dual-band bandpass filter is proposed for WLAN (IEEE-802.11a/b/g) applications. The filter is cascaded by three open-loop square-ring resonators and two modified input/output transmission lines. The open-loop squarering with novel insert coupling structure is used to replace the typical hairpin structure for minimization. The filter is fabricated on the Al₂O₃ substrate with high quality factor by the printing method. The substrate is 0.6 mm in thickness and has a relative dielectric constant of 9.4. By combining the high dielectric constant substrate and modified structure, the proposed filter shows the advantages of low insertion loss, high out-of-band rejection, wide bandwidth and tiny size. The measured frequency responses reveal excellent agreement with the simulated ones.