A novel miniaturized multilayer substrate integrated waveguide (SIW) filter is designed. The filter is constructed with four compact SIW resonator cavities, and each cavity supports TE101 mode, which can be controlled by the slot located between layers. The area of the compact SIW resonator is just 1/16 of that of original substrate integrate waveguide (SIW) resonator. Meanwhile, the area of the four-order filter is 13.2 mm×26.4 mm. The insertion loss and return loss of the fabricated filter are -1.8 dB and -14.6 dB, respectively. Meanwhile, the tunable filter realizes center frequency linearity, which works at 1.6 GHz with an adjustable range of 51.8%. The insertion loss is -1.2 dB, and the return loss is less than -15 dB. The coplanar cavity coupling structure achieves a switchable bandwidth.
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