Ultra-compact dual-band WLAN filter using independent band stop resonators

摘要

In this paper, a highly miniaturized dual-band band pass filter using independent band stop resonators has been newly designed and fabricated by embedding all the passive lumped elements into a low-temperature co-fired ceramic (LTCC) substrate for 2.4 to 2.5 GHz (802.11b) and 5.15 to 5.85 GHz (802.11a/g) wireless LAN system applications. In order to reduce a size/volume of the filter and avoid electromagnetic parasitic couplings between the embedded passive elements, the proposed filter was designed by using 3rd order Chebyshev circuit topology and J-inverter transformation technology. The 3rd order Chebyshev band pass filter was firstly realized for 802.11b frequency band selection and it was transformed by using finite transmission zeros technology to minimize the electromagnetic coupling. Finally a dual-band filter was realized by constructing 802.11a/g WLAN band selection filter by adding independent band stop resonators into the 802.11b filter circuit. The measured maximum insertion losses in the lower and higher pass-bands were better than 2.0 dB and 1.3 dB with minimum return losses of 15 dB and 14 dB, respectively. The overall size/volume of the fabricated filter was 2.7 × 2.3 × 0.68 mm3 which was the smallest one in the previously reported devices.