Low-loss Miniaturized Tri-band Bandpass Filter with High Selectivity and Good Passband Symmetry
DOI:
https://doi.org/10.13052/2024.ACES.J.400705Keywords:
Bandpass filters, high selectivity, low-loss feature, passband symmetry, TSSIRsAbstract
This paper introduces a low-loss microstrip line tri-band bandpass filter, utilizing quarter-wavelength (λg/4) tri-section stepped impedance resonators (TSSIRs). In this design, the adoption of a non-edge-coupled structure effectively eliminates the presence of coupling gaps. As a result, additional radiation losses are avoided, leading to lower insertion loss. In addition, the operating frequencies of the three passbands can be flexibly adjusted by tuning the impedance ratios in the TSSIR. Moreover, the λg/4 TSSIR exhibits a smaller size compared to existing λg/2 TSSIRs, resulting in a more compact overall design. In order to validate the proposed design methodology, a tri-band bandpass filter with passbands centered at 1.0 GHz, 3.5 GHz, and 6.0 GHz was designed, fabricated, and measured. The minimum insertion losses for each passband were measured to be 0.07 dB, 0.52 dB, and 1.14 dB, respectively. The filter occupies a compact area of 31×21.5 mm2 (0.17λg×0.12λg), demonstrating excellent passband symmetry for each frequency band. The proposed tri-band bandpass filter not only achieves three desirable operating frequencies but also benefits from the inherent characteristics of conventional filters, such as remarkably low insertion loss and good passband symmetry.
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