A compact LTCC ultra-wideband bandpass filter using semi-lumped parallel-resonance circuits for spurious suppression

A very compact ultra-wideband (UWB) bandpass filter with both high selectivity and suppressed spurious passband is implemented in the low-temperature co-fired ceramic (LTCC) substrate. By using the optimum distributed highpass filter structure of 11^th-order, an ultra-wideband filter with the bandwidth from 3.1GHz to 10.6GHz is realized. In this study, the semi-lumped parallel resonance circuits are adopted in conjunction with the optimum distributed highpass filter, so that two finite transmission zeros may be created to suppress the spurious passband. The implemented filter exhibits a good frequency response to meet the Federal Communication Committee’s (FCC’s) limit and has a very compact size of 0.22λg × 0.187λg × 0.0246λg (4.2mm × 3.5mm × 0.46mm), where λg is the guided wavelength of the multilayer structure at 6.85GHz.