Design of Broadband Microstrip Interdigital Bandpass Filter Using Coupling Matrix

This paper proposes a structure for a 15<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order interdigital bandpass filter in the S-band range, designed by extracting the group delay and coupling coefficients through EM simulation using a coupling matrix. The proposed filter is designed as a broadband filter with a center frequency of 3.75 GHz and a bandwidth of 2 GHz. The designed filter has an insertion loss of 3.78 dB and a return loss of 12.17 dB in the specified frequency band. Additionally, to achieve miniaturization, a substrate with a dielectric constant of 10.2 was used, and the substrate's dimensions are 28.5 × 9.5 × 4.4 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>.