24GHz SIW band rejection filter for 5G millimeter wave base station using dual-hole coupling

A band rejection filter for millimeter wave band 5G base stations was studied to eliminate interference with earth observation satellites operating in the 23.6~24 GHz band. Because it is difficult to steeply attenuate adjacent bands in a BPF covering a 5G system, a BRF structure was used to attenuate only specific frequencies. Furthermore, low-loss passband characteristics were achieved by using a SIW structure resonator with an alumina substrate, which exhibits low-loss characteristics in the millimeter-wave band. To solve the problem of large asymmetry in the conventional coupling method, a metallic post was loaded in the center of the coupling hole to realize a BRF with good symmetry by using a configuration with two coupling holes. The prototype 4-stage BRF achieved high attenuation of more than 37.8 dB in the rejection region, with a loss including connector loss of about 1.1 to 1.9 dB.