Synthesis and Design of Lumped-Element Filters in GaAs Technology Based on Frequency- Dependent Coupling Matrices

A novel synthesis method for lumped-element bandpass filters is proposed on the basis of frequency-dependent coupling matrices, which can preserve the moderate bandwidth response matching with coupling matrix prototype better. The available element values of resonators and inverters with the acceptable quality factor are determined by adjusting normalized slope parameters or reference susceptance parameters. To validate the design approach, two third-order inline filters with the fractional bandwidth of 20% at a center frequency of 3 GHz are designed and fabricated in the GaAs HBT technology. Good agreement is obtained between the simulated and measured results. The measured shape factors K20dB of the two filters with and without external couplings are 1.8 and 1.85, respectively. The filter followed by a one-stage amplifier also demonstrates the high frequency selectivity.