Design of tri-band bandpass filter based on the interdigital structure and rectangular resonator for LTE and radar applications

This paper presents the design and implementation of a novel tri-band bandpass filter (BPF) using interdigital structures combined with rectangular resonators to achieve compactness and high performance. The proposed BPF effectively addresses challenges such as size reduction, high isolation between passbands, wide stopband and low insertion loss, which are critical for modern telecommunications applications. First, a single-band BPF is designed based on high-impedance coupled lines and selecting the best line values, then by adding resonators, the second and third bands are formed. The proposed filter is analyzed by an LC equivalent circuit. The filter achieves three distinct passbands at central frequencies of 2.12 GHz, 2.79 GHz, and 4.185 GHz. Key design features include the use of interdigital structures, high-impedance coupled lines and the creation of transmission zeros to improve sharpness and isolation between passbands. The proposed filter is fabricated and the good agreement of the measurement results with simulation results, making it suitable for applications in LTE, and radar applications. The compact size and efficient performance of the proposed BPF demonstrate its potential for integration into modern telecommunication devices, enhancing their overall efficiency and functionality.