A Novel Bandpass Filter Design Using E-shaped Resonator and Dual Square-loop Defected Ground Structure

This paper presents a bandpass filter (BPF) using two E-shaped microstrip resonators and a dual open square-loop defected ground structure (DGS). The proposed novel DGS structure is realized by implementing two opened square loop topologies on the ground plane. The etched DGS structure interferes with the shield current distribution in the ground plane which affects the characteristics of the two E-shaped resonators laid above it. This disturbance creates beneficial capacitance and inductance effect on the filter design, which results in the desired filter response. Two E-shaped resonators are laid on the top conductor layer. The behavior of the E-shaped resonators can be represented using even and odd mode analysis. For odd mode analysis, an electric wall is inserted between the two E-shaped resonators to enable a quasi quarter wavelength to be extracted. In the case of even mode analysis, a magnetic wall is added in between the two E-shaped resonators. Thus the resonators can be associated with a folded quasi half-wave resonator. By manipulating the E-shaped resonator and dual open square-loop DGS design, the desired BPF response can be achieved. The proposed BPF is fabricated on FR4 substrate with a relative permittivity of 4.7 and thickness of 0.8 mm. The center frequency is 2.4 GHz and the dimensions of the prototyped BPF are 12.41 mm by 13.70 mm. The best matching return loss S-11 response is obtained at 2.2 GHz with a value less than -10 dB. The corresponding insertion loss S-21 is -2.2 dB. The lower and upper stopband attenuation is 10 dB/GHz and 15 dB/GHz respectively. Both simulation and measurement results are presented and discussed for the proposed BPF.