A novel low-cost microstrip bandpass filter for ultra-wideband RF applications

A novel wideband bandpass filter (WBPF) using planar technology with compact size and sharp cutoff frequency is proposed. The presented microstrip filter consists of a three parallel coupled lines (TPCL) with a radial open stub. To validate the designed filter in term of compactness, insertion loss, return loss, and transmission zeros, a high meshing density is applied in two electromagnetic solvers Advanced Design System (ADS) and CST-Microwave Studio. The proposed filter is fabricated on an FR4 substrate with a relative dielectric constant of 4.4 and 1.58mm of substrate thickness and fed by a two 50Ω microstrip lines. Further, the filter is measured which exhibits a return and insertion losses of 20dB and 0.49dB, respectively, with a center frequency around 3.5 GHz and an operating bandwidth (2.1 GHz to 5.22 GHz) of about 85 %. Good agreement between the simulated and measured results demonstrates the proposed filter design. The overall circuit size of the filter was taken to be 23.24 X 40 mm2