UWB bandpass filter with compact size and wide upper stopband

Abstract

AbstractA novel ultra‐wideband (UWB) bandpass filter (BPF) with a very compact size and improved out‐of‐band performance is proposed in this letter. The main circuit structure is a composite right‐/left‐handed transmission line unit cell, which has UWB bandpass characteristic as well as compact size. Moreover, two anticoupled line structures added at both ends of the unit cell can produce a new resonant mode and three transmission zeros, so the passband response and upper stopband performance can be improved. The proposed filter is implemented and measured, which shows its 3 dB passband ranges from 3.3 to 10.9 GHz with a fractional bandwidth of 110.9%. Its insertion loss is about 0.6 dB at the centre frequency, while the return loss is better than 13 dB. In addition, the measured results also show the proposed filter has a wide stopband from 11.4 to 30 GHz, whose rejection level is greater than 18 dB. The size of the filter is only 7.4 × 6.4 mm, equal to 0.22 × 0.20 λg. Both the simulated and measured results are in good agreement.