Abstract
A novel compact wideband bandpass filter with grounded spiral-shaped resonators and quarter-wavelength stepped-impedance resonators is proposed. In this study, the dual-metal-plane structure is adopted to achieve the required strong coupling, so that a wide bandwidth filter may be realized. Then, by designing the spiral-shaped inductor to form a miniaturized resonator, a very compact filter may be implemented, having a size of 0.169 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , times 0.127 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , where lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> is the microstrip guided wavelength on the substrate at center frequency. Specifically, the implemented filter has the merits of wide 3-dB fractional bandwidth of 35%, wide stopband up to 3.5 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , better selectivity, and good insertion/ return losses, where f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the passband center frequency of the filter. Agreement between the measured and simulated results is also observed.
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