Design Of Quad-Band Bandpass Filter Using Modified Quarter Wavelength Resonator With Multiple Transmission Zeros

This paper proposes a modified quarter-wavelength resonator with transmission zeros for a quad-band bandpass filter. Two short-ended modified quarter-wavelength resonators are part of the filter design. The proposed filter utilizes a dielectric material of Rogers 4003 of height 0.8 mm and a relative permittivity of 3.55. The fabricated design shows strong alignment between the simulated and measured results. Four passbands with fractional bandwidths of 143%, 46%, 28%, and 17% are obtained using the filter. The return losses for these passbands are 25 dB, 14 dB, 25 dB, and 25 dB, respectively. The insertion losses for the four passbands are 0.2 dB, 0.2 dB, 0.5 dB, and 0.7 dB. The proposed filter enhances attenuation near the passbands by achieving seven transmission zeros and displaying a flat group delay of less than 1 ns within the passbands. The suggested filter's overall dimensions are 30 x 20 x 0.8 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>.