A compact dual‐band bandpass filter based on the substrate integrates suspended line platform is proposed in this letter. The design is implemented using low‐cost FR‐4 material, while the loss can be reduced by 3D metal connections with substrate cutout. 0.97 dB/1.6 dB improvement of insertion loss is achieved and verified at 3.45 GHz/4.9 GHz. By paralleling quarter wavelength step impedance resonators with different operating frequencies, two paths formed between source and load. Both bandwidth and location of transmission zeros can be adjusted independently. Two stubs are added working not only as feed structure but also as a stop band resonator, which can provide 20 dB out‐of‐band suppression up to 4.4f0. The obtained performances are good enough to compare with the state of art, though very low‐cost FR‐4 materials are used.
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