Design of a bandpass hairpin filter with DGS for 5G FR1 applications

In this thesis, a band-pass hairpin filter is designed for wide-band applications required by 5G communication systems. In the design, a dumbbell defected ground structure (DGS) is added to the ground plane to improve the performance of the hairpin filter design. The wide-band design covers the frequency bands n48 (3550 MHz - 3700 MHz), n77 (3300 MHz - 4200 MHz), n78 (3300 MHz - 3800 MHz), and n79 (4400 MHz - 5000 MHz) in the FR1 frequency range. The filter design is made on Rogers RO4003C material with dimensions of 15x25 mm, a dielectric constant of 3.55, and a thickness of 1.524 mm. The filter consists of three U-shaped resonators, and unlike traditional designs, each resonator arm is made different in length and is optimized to be symmetrical with respect to the origin. By applying this method, passbands with similar but different frequencies can be combined into a single wide band. Thus, a wider passband is achieved. During the design process, microstrip line widths, resonator lengths, resonance conditions, and the DGS geometry were analyzed, and the passband width and performance were optimized. Simulation results indicate that the proposed filter provides broadband transmission over a bandwidth of approximately 3.3 GHz and a frequency range of 2.61–5.91 GHz. Furthermore, a dumbbell-shaped DGS added to the ground significantly reduces reflection loss to below -40 dB near the center frequency of approximately 4.25 GHz. With these features, the proposed filter structure is important both for demonstrating the potential of metamaterial structures in microwave filter structures and for providing a high-performance solution.