A super compact high-selectivity bandpass filter based on a metamaterial and silicon substrate for emerging RF and communication systems

Abstract This paper presents a super-compact and highly selective bandpass filter (BPF), designed using a metamaterial (MTM) characterized by epsilon-near-zero (ENZ) and near-zero-index (NZI) properties, combined with coupled lines and a high-permittivity silicon substrate. This design achieves a bandwidth of 2800 MHz, ranging from 2.95 GHz to 5.75 GHz, with a 3-dB fractional bandwidth of 61.17% and three transmission poles. The shape factor is 1.146, with roll-off rates of 168.75 dB GHz −1 and 108 dB/GHz for the lower and upper bands, respectively, along with two transmission zeros, demonstrating the high selectivity of the proposed filter. The insertion loss remains remarkably low, below 0.87 dB across the entire passband, while the group delay is quasi-flat, not exceeding 0.72 ns. The voltage standing wave ratios (VSWRs) are maintained below 1.102 within the passband, indicating excellent input and output impedance matching. The filter size is extremely compact, measuring 16.53 mm × 17 mm ( 0.66 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> </mml:msub> </mml:math> × 0.68 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>λ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>g</mml:mi> </mml:mrow> </mml:msub> </mml:math> ). The filter was modeled using an equivalent RLC circuit and experimentally validated, with measured results showing good agreement with simulations. This BPF exhibits significant potential for advanced applications in RF technologies.