Compact Trible-band Microstrip BPF Utilizing Interdigital-coupled Lines Feeding Structure

This paper presents a new compact band-pass filter (BPF) with three band operates at 1.2 GHz, 3.3 GHz, and 5.6 GHz for GSM, WiMAX and WLAN applications respectively. The proposed filter is designed based on three-coupled resonators; two of them are identical, folded like L-shape and placed back to back to generate one passband, while the third is constructed to couple with other two resonators in order to generate dual bands. The feeding of the proposed BPF is accomplished employing an interdigital-coupled lines structure connected to 50 Ω microstrip line. This feeding topology is utilized to control the coupling at the feeding points and hence controls the IL, the pass bands location. Moreover, The proposed BPF is 31.5 × 8.9 mm
²
, which is very compact compared to the literature work. This filter is designed on Rogers 3210 substrate with a thickness of 1.5 mm, permittivity of 10.8, and a loss tangent of 0.0019. The-measured results agree well with the simulated ones and show that the BPF has an IL of 0.5 dB at 1.2 GHz, 0.4 dB at 3.5 GHz, and 0.5 at 5.6 GHz.