Abstract
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,0.004λg2, whereλgis the guided wavelength at the cut-off frequency. The filter structure is simple and easy to fabricate as well.
Highlights
High-performance low-pass filters (LPFs) with the compact size are highly desirable to remove the unwanted highfrequency harmonics and intermodulations in various wireless communication systems
In order to excite multiple transmission zeros to broaden the stopband and sharpen the roll-off skirt, multisection structures have been engineered in [7,8,9], for instance, in [7], a cascaded unit composed of two asymmetrical hairpin units as well as a connecting line is employed to obtain a very wide stopband LPF with five proposed transmission zeros; in [8, 9], the cascades of various TFSs and several CPW tapered sections are exploited to obtain an extraordinary sharp-rejection, ultralarge attenuated band LPF with multiple transmission zeros
Based on the above-discussed attractive features, a prototype LPF having fc of 0.63 GHz and a wide 20 Demon. FBW (%) Rej. (dB) stopband extended up to 5fc is implemented on a substrate with thickness of 0.5 mm and relative dielectric constant of 2.65 and loss tangent of 0.02
Summary
A novel structure with sharp roll-off, wide stopband, and very compact size is presented in this paper. By combining a capacitorembedded 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. The filter structure is simple and easy to fabricate as well
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