Compact tri-band notched UWB bandpass filter based on interdigital hairpin finger structure

In this paper, a novel compact tri-band notched UWB (Ultra-Wide-Band) bandpass filter is proposed. Based on the interdigital hairpin finger structure, three adjacent folded fingers are added at both sides for tri-band notched control. With this symmetrical structure, each notched band can be controlled by its corresponding pair of folded fingers independently. Without changing other rejected bands, by just changing the parameters of the corresponding pair of fingers, the specified notched band can be adjusted easily. To demonstrate our novel structure, a tri-band notched UWB bandpass filter is designed, fabricated and tested for harmonic control application. At rejected bands 6.42 GHz, 10.7 GHz and 14.98 GHz, the measured insertion loss is 15.7 dB, 31.7 dB and 30.1 dB, respectively. Simulated results are found in good agreement with measured results. The compact size of our proposed filter is 5.8 mm × 19.8 mm.