This technology utilizes CRLH zeroth-order resonators instead of half-wavelength resonators to create 3rd, 5th, and 9th-order miniature bandpass filters operating in the 900MHz UHF band. It creates transmission zeros using a cascade triplet cross-coupling configuration, where interdigital lines connected to the input and output ports are linked by T-junction inductor lines, grouping three adjacent resonators together.
Low-frequency communication bands such as UHF, T-DMB, and LTE have long wavelengths, making equipment miniaturization difficult. Conventional metamaterial CRLH bandpass filters relied on periodic unit cell structures, resulting in large sizes and limited design flexibility, which made it difficult to control isolation and rejection characteristics.
This technology connects resonators sequentially using inductive coupling—a mix of series inductors and parallel capacitors—and utilizes cross-coupling between non-adjacent resonators as a branch path to cancel signals. By dividing resonators into triplet groups and aligning the transmission zeros of each group, the number of tuning steps is reduced. Furthermore, the zeros are positioned near the passband edges, resulting in a steeper skirt slope for the same filter order. Applicable to UHF front-ends in mobile base stations and RFID readers, this technology reduces both the volume and the tuning effort required for low-frequency band filters.
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