Optimum Distributed Highpass Filter Design Using Spur-line Pairs

This study presents a modified design of the optimum distributed highpass filter (HPF). First, a novel equivalent circuit of the π-network is proposed. The equivalent circuit is composed of two spur lines connected back-to-back, and the impedances of the spur lines are half of those of the line elements in the π-network. The proposed equivalent circuit is then applied to replace the high impedance stubs in the conventional optimum distributed HPF design. An improved design of line elements with reasonable impedances can thus be developed for the practical implementation of optimum distributed highpass filters. A test example with the pole of 11 and the primary passband being 1 to 5 GHz is designed and implemented. Comparisons between the measured and theoretical simulated results are performed to verify the proposed design.