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 3 lambda/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 0.25 lambda(g) x 0.14 lambda(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.