Dual-Mode Dual-Band Filter Using Steppedimpedance Resonator with Outer Tuning Plus-Sign

This article introduces a dual-band filter employing a folding structure of stepped-impedance resonator with an outer tuning plus-sign. The design integrates a meandered square loop resonator (SIR), with patches positioned at each corner of the square loop to induce a dual-mode response. Furthermore, the second frequency can be fine-tuned by adjusting the outer tuning plus-sign located outside the meandered loop. A dual-mode dual-band filter is designed with the first frequency at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.4GHz</tex> , featuring a loss of insertion of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.58\ dB</tex> . The first frequency exhibits transmission zeroes beside the upper and lower frequencies of the middle frequency, resulting in a sharp skirt. The second frequency, designed at 5.2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GHz</tex> , has a loss of insertion of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.59\ dB</tex> and a return loss better than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 15\ dB</tex> . The design and analysis are validated using the IE3D simulator.