A Miniaturized High-selectivity Filter by Embedding Nested U-shape Resonators in SIW

A substrate-integrated waveguide (SIW) miniaturization filter is proposed, which features high attenuation characteristics, effectively reduces filter loss and size, and improves frequency selectivity.The filter is miniaturized using the evanescent-mode theory and embeds a nested U-shaped resonator in the upper metal surface of the SIW.The proposed filter's equivalent circuit structure incorporates two LC parallel resonant loops with resistance characteristics that can, in turn, create two transmission zeros in the filter's stopband to enhance its selectivity.The filter has an effective size of only 0.39λg ×0.23λg with a center frequency of 2.5 GHz.The -3 dB bandwidth measures 120 MHz, while the relative bandwidth is 4.8%.The insertion loss is -0.6 dB in the passband, and the return loss is more than 25 dB.Out-of-band rejection exceeds 40 dB in the range of 2.9 ∼ 4.4 GHz.The measured and simulated results agree well.The filter offers benefits in terms of high rejection, miniaturization, and low insertion loss.It can be implemented in 5G (sub-6 GHz) wireless communication systems.