Narrow band compact non-degenerate dual-mode microstrip filter

A compact narrowband non-degenerate dual-mode microstrip filter is presented. The structure is developed by loading the conventional non-degenerate dual-mode resonator by open circuit stubs at two opposite corners. The filter bandwidth is controlled by only decreasing the higher cutoff frequency of the conventional type. Fractional bandwidth from less than 1% to about 7% can be achieved with a simple direct procedure. A 6% fractional bandwidth filter is designed and implemented on FR4 material with 4.3 dielectric constant and 0.78 mm thickness at about 2 GHz. Analysis has been achieved using the IE3D simulator. Experimental results do agree with simulations.