Effects of relative position errors of grounding holes on the performances of interdigital bandpass filters

Laser technology becomes the preferred way in the fabrication of grounding holes of interdigital bandpass filter on the Al₂O₃ substrates. The relative position errors of grounding holes are unavoidable because of serial processing of drilling holes. The performances of interdigital bandpass filters with grounding holes of 0.25mm diameter and relative position errors of 0.02mm in the longitudinal or horizontal direction were mainly discussed. The frequency responses were investigated by means of simulation, experiment verification, and theoretical analysis in this paper. The results showed that relative position errors of 0.02mm in different direction had completely different effects on the properties of interdigital bandpass filters. Grounding holes overall shifting 0.02mm in the longitudinal direction leads to the frequency response deterioration about 4dB around 18GHz in the passband of 16-20GHz, because the electrical length of the coupling units is changed. While grounding holes overall shift 0.02mm in the horizontal direction, passband of filter is flat and without obvious frequency response deterioration. Priority should be given to ensure the longitudinal accuracy of grounding holes in the process of manufacture.