Measurement of the fabricated filter is performed using Agilent E8363B network analyzer. Fig. 6 shows the simulated and measured S-parameters of the sext-band BPF, and the photograph of the fabricated BPF is also demonstrated in the inset of Fig. 5. The measured six passbands are centered at 1.88/2.59/3.48/5.26/5.82/6.75 GHz with 3 dB fractional bandwidth of 4.26%/11.97%/6.32%/5.19%/5.17%/2.96%. The minimum insertion losses of each band are 0.85/1.36/0.74/0.98/

1.14/0.82 dB. The band-to-band isolations are above 23.34, 16.59, 28.43, 15.31, 41.93 dB, which generate sharp and deep rejections between the adjacent passbands.

The mismatch between the measured and simulated results may be leaded by the nonuniformity of the relative permittivity of the substrate, the fabrication tolerance and SMA connectors.

In order to evaluate the achieved performance, Table I presents a performance comparison of the proposed sext-band BPF with some previously reported works. The proposed sext -band BPF in this letter exhibits compact size, low insertion and switchable bands.

Conclusion: This letter has presented a miniaturised sext-band BPF by using two split-type multiple-mode resonators. The proposed sext-band BPF features very high design freedom of every single band. The simulated and measured results have a good agreement, which shows that the proposed filter features compact size, low insertion loss, sharp skirt. Owing to these merits, the proposed structure is a good candidate for sext-band BPF design.