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Abstract
A novel dual-mode dual-band bandpass filter (BPF), which is fabricated with a 0.5-μm pHEMT MMIC technology is presented. A design method that can precisely determine optimal elements' values of a wide-band dual-mode filter based on desired passband specifications is developed. This filter is constructed using two stacked ring resonators with individual perturbations and feeding capacitors, so both fractional bandwidths and center frequencies of the dual-band filter can be flexibly controlled. Benefiting from the multilayer capability of the advanced process, the feeding structure connecting the two stacked ring resonators can be easily implemented using a compact metal-insulator-metal (MIM) structure rather than a large-sized coupling scheme. The size of the filter is only 0.47×0.8 mm2, and the measured insertion losses in lower and upper pasbands are less than 2.4 dB and 3.0 dB, respectively. The associated return losses in the passbands are all greater than 15 dB.