A miniaturized wideband bandpass filter based on 3λ/4 resonator loaded with stepped impedance

This article presents the design of a highly miniaturized wideband bandpass filter. The proposed filter unit consists of 3λ/4 resonator loaded with stepped impedance section of short-ended stub. The required scattering parameters are derived using even-odd mode analysis. For validation, a prototype of the proposed filter is fabricated and tested. The overall area of the prototype is 0.25λ
_g
× 0.14λ
_g
, equivalently 1.95 cm
²
. The bandpass filter exhibits a 3 dB fractional bandwidth of 121.6% for 1 dB insertion loss. Stopband response of better than 15 dB is achieved up to 2.8f
₀
by placing two transmission zeros. The measured results indicate good agreement with the simulated results.