Bandpass Filter based on Square Shaped Double Split Ring Resonator for 5G Millimeter Wave Communication

The need for high-performance RF circuits for mm-wave is increasing due to the impending implementation of the RF wireless system at mm-wave frequency range. Compact, inexpensive, high-performing, and easily integrable bandpass filters, critical front-end components for signal selection, play an important role in mm-wave communication. This work presents a new and novel planar bandpass filter based on a square shaped double split ring resonator for three distinct substrates: FR-4, Rogers TMM4, and Rogers 5880 with a center frequency of 28GHz for n257 mm-frequency band. The project's first stage involves validating the metamaterial unit cell using the Nicholson Ross Weir technique. This technique serves to confirm the presence of negative permittivity in the split ring resonator. The bandpass filter with three distinct substrates is designed in the second section using ANSYS HFSS software. Parametric analysis is performed to optimize the size of the split ring resonator and the bandpass filter. The bandpass filter, utilizing FR-4, Rogers TMM4, and Rogers 5880 substrates, demonstrates a commendable return loss of 32dB. Nevertheless, the FR-4 and Rogers TMM4 substrates exhibit an insertion loss of 1.89dB and 1.18dB, respectively, significantly higher than the 0.49dB seen for Rogers 5880. Due to its importance in the RF transceiver, a higher insertion loss in the bandpass filter can greatly affect system performance. Therefore, filters based on thick substrates are not suited for mm-wave communication. The total bandwidth of the filter in the mm-wave frequency range is 3 GHz, while the fractional bandwidth (FBW) is 15%. The filters have dimensions of 2.5x4.6mm2 for FR-4 and Rogers TMM4 substrate and 2.2x4.0mm2 for Rogers 5880 substrate.