A Very Compact and Sharp Roll-Off Low-Pass Filter with Four Transmission Zeros

Abstract EN

A novel structure with sharp roll-off, wide stopband, and very compact size is presented in this paper.

By combining a capacitor-embedded transmission line ring and two shunt open stubs, this structure exhibits a high-performance three-pole low-pass filter (LPF) response with four generated transmission zeros.

With the help of these four transmission zeros, the proposed LPF achieves improved roll-off rate, extended stopband, and significantly very compact size.

To verify the feasibility of the proposed structure, a prototype LPF having the cut-off frequency at 0.63 GHz is designed, fabricated, and measured as an illustrative example.

Final result shows that a roll-off rate of 109.3 dB/GHz along with a relative stopband bandwidth of 114.6% can be obtained.

Moreover, the filter dimensions are as small as 15.7 mm × 26.9 mm, that is, 0.004 λ g 2 , where λ g is the guided wavelength at the cut-off frequency.

The filter structure is simple and easy to fabricate as well.