A low pass/Band pass filter transformation using lumped capacitors and DGS configuration for wireless networks

In this work, the design of the LPF/BPF transformation bandpass filter is specifically suitable for wireless communications. The filter utilizes microstrip lines and the defected ground structure (DGS) loaded with lumped capacitors. The overall dimensions of the filter are 20 × 30 mm². The design includes Rogers 4003 substrate with a dielectric constant of 3.55 and 0.813-mm thickness. First, the LPF is designed to have a cutoff frequency and attenuation pole at 3.5 and 5.4 GHz, respectively. The LPF achieved S₂₁ ≤ -0.6 dB in the pass band and band rejection ≤ -10 dB from 4.2 GHz to 8.17 GHz. Moreover, the resulting BPF exhibits a central frequency of 2.45 GHz, with a frequency range extended from 2.1 to 2.8 GHz (0.7 GHz) and the fractional bandwidth (FBW) of 28.57%. The S₁₁ is nearly − 17 dB, while the S₂₁ is about − 0.7 dB, with a transmission zero at 3.1 GHz and a band stop ≤ -10 dB from 3.1 to 8 GHz. The study includes a parametric analysis to achieve the ideal value of S₂₁ and S₁₁. To assess the filter’s behavior, simulations and investigations were implemented using the EM simulator. The achieved outcomes illustrate that the LPF/BPF is appropriate for wireless applications.