Design of a MMIC tri-band filter for 60-/77-/100-GHz applications

A tri-band dual-mode chip filter, which is fabricated in a commercial pHEMT GaAs technology and suitable for millimeter-wave applications, is presented in this paper. This filter is constructed by using stacked ring resonators with individual perturbations and feeding capacitors; thus, fractional bandwidths and center frequencies of three pass bands can be flexibly controlled. A model of the tri-band filter that considers coupling effects between stacked ring resonators is first proposed, and then a synthesis method that can determine values of all elements of a typical dual-mode ring filter based on specifications of required characteristics is also described. According to the proposed design method, filter designers can quickly determine the layout pattern of the tri-band dual-mode filter which employs proper metal-insulator-metal (MIM) capacitors to obtain the desired filter performance. To verify the proposed design concept, an experimental prototype, locating three pass bands at 60 GHz, 77 GHz and 100 GHz, respectively, was fabricated on GaAs substrate. The size of the filter is about 0.46×0.91 mm² and the measured insertion losses in the three passbands are less than 2.4 dB, 2.7 dB and 3.5 dB. The associated return losses are greater 18 dB, 17 dB and 8 dB over the frequency bands of interest.