Miniaturized Substrate Integrated Waveguide Filters with Stepped-Impedance Slot Resonators for Millimeter-Wave Application

This paper presents a type of novel miniaturized millimeter-wave band-pass filters based on substrate integrated waveguide (SIW) incorporated with stepped-impedance slot resonators (SI-SR), which are also considered as complementary split ring metamaterial resonators. These proposed filters are operated far below the characteristic cutoff frequency of the waveguide. The center frequency of the filters can be controlled independently by adjusting the SI-SR size. And the coupling coefficients could be adjusted by changing the position and distance between SI-SRs. The size of the SI-SR can be further miniaturized by increasing the internal inductance, resulting in filter total size reduction. One two-pole filter and two three-pole filters are designed and implemented on Rogers-5880 substrate using the standard PCB process. Good agreement has been observed between simulation and measurement. For the three-pole filters, the RF signal are transmitted directly through a microstrip line from the second to the third SI-SR leading to a compact filter size. The proposed filters well cover 27–31 GHz, which could be applied in 5G millimeter-wave communication systems. They offer the advantages of compact size, easy integration, low loss, high stopband rejection and selectivity.