A Wideband Bandpass Filter with Broad Stopband and Ultra-Wide Reflectionless Range for 5G Applications

In this paper, a wideband bandpass filter with the broad stopband and ultra-wide reflectionless range is proposed. Such filter consists of two parallel connected channels. The good in-band performance and broad stopband of the filter are achieved using the dumbbell-shaped defected ground structure (DGS) in the main channel. Meanwhile, the auxiliary channel with a bandstop filter (BSF) and a loaded resistor is introduced to obtain the ultra-wide reflectionless range. Besides, to further enhance the stopband performance of the filter, spur-lines are embedded in the I/O port of main channel. To verify the mechanisms mentioned above, a reflectionless filter operating at 3.1-5.3 GHz is proposed. The measured stopband is expanded to 27.4 GHz with an attenuation level higher than 30 dB. Moreover, the reflectionless range is from 10 MHz to 26 GHz, which is the state-of-the-art performance. With such good performance, the proposed filter shows strong merits for the 5G applications.