Design of a miniaturized tri-band bandstop filter using spur microstrip lines and via-hole grounding

The purpose of this paper is to propose a miniaturized tri-band bandstop filter that finds application in a modern dense communication system where size and multi-band plays a vital role.

In this paper, the authors propose a miniaturized tri-band microstrip bandstop filter which combines the conventional bandstop filter and spur microstrip line structures such that this design achieves tri-band operation at 1.8 GHz and 3 GHz. The overall length of the microstrip filter is found to reduce from 126 to 45 mm because of introduction of spur lines and via-hole grounding. The addition of spur lines replaces two resonators, introduces two additional resonant frequencies and enhances the −6 dB bandwidth of the center frequency by 14 %.The addition of via-holes in each resonator reduces its length into half of its original length, thereby reducing filter size.

Resonance occurs at three different frequencies 1.8, 2.4 and 3 GHz. The filter size reduces from 126 to 45 mm, and the −6 dB rejection bandwidth of center frequency improves by 14 %.

The overall filter size is reduced by 65% and it resonates at three different frequencies 1.8, 2.4 and 3 GHz with an improved bandwidth of 10 % around the center frequency.