Design of a novel wideband quasi-elliptic filter based on SIR and asymmetric coupled lines

Abstract

Stepped impedance resonator (SIR) and asymmetric coupled-line sections are used to design a novel fifth-order wideband bandpass filter in this paper. Even- and odd-mode technique is introduced to design and analyze the filter. The proposed filter possesses the characteristics of spurious-free response up to the third harmonic frequency with two transmission zeros on each side of the passband, thus resulting in the improved selectivity. One prototype with 3-dB fractional bandwidth of 53% (2.2–3.79 GHz) is fabricated for demonstration, and good agreement can be observed between simulated and measured results.

Keywords:

• wideband filter
• transmission zero
• transmission pole
• even and odd technique

Funding

This work was supported by the National Natural Science Foundation of China [No. 61201020].