A Compact Ultrawide Bandpass Filter on Thin-Film Substrate

This paper presents the ultrawideband filters for UWB fullband (range of 3.1–10.6 GHz) applications. This filter consists of ring filter for wide-bandwidth and coupled line structure for suppressing unwanted passband in upper and lower stopbands. Especially, the filter structure was realized on silicon substrate using thin film technology, adequate for wafer level packaging, which can be integrated with CMOS UWB chipset that is currently on development. To minimize the dimension of the filter, the Hilbert structure was applied in ring filter and the meander shaped broadside coupled structure was also adopted in the coupled line structure. The size of the fully realized filter structure is 4.4 × 3.6 mm2. The insertion loss in passband is 1.5 dB and the return loss is larger than 15 dB, respectively. The group delay in center frequency is 0.2 ns and the group delay variation is less than 0.15 ns. key words: wideband filter, thin film, ring, coupled line