Miniaturized Microstrip Dual-Mode Filter with Three Transmission Zeros

A novel miniaturized microstrip dual-mode filter using a half wavelength resonator with centrally loaded open stub and quasi-L shaped feed-lines is proposed. The advantage of using such a resonator is inherently generating a transmission zero by itself. To further improve the selectivity, quasi-L shaped feed-lines are introduced to create additional transmission zeros. Theoretical and simulated analyses of this filter are performed. A demonstration filter centered at 2.33 GHz with a fractional bandwidth of 4.7% is designed, fabricated and measured to validate the design methodology.