Theoretical Based Design of Ultra-Wideband Filter with Dual Band-Notch

In this paper, a compact ultra-wideband microstrip band-pass filter with single/dual-notched bands is proposed. The filter is theoretically designed based on a multiple-mode resonator which consists of a short circuit stub loaded-ring resonator. A multi stepped impedance resonator is also applied to reject unwanted in-band frequencies and extend the upper-stopband. The proposed filter is analyzed by utilizing graphs according to odd- and even-mode method. The resonant modes are allocated between 3.1 GHz to 10.6 GHz and transmission zeros are adjusted at upper stopband to create a sharp roll-off and suppress the spurious harmonics, as well as a compact physical size. Full-wave simulations are performed for three types of filters, with and without notch-bands, to verify theoretical results. The measurement results demonstrate that not only − 3 dB fractional bandwidth is more than 120% and but also at least − 20 dB suppression can be achieved at upper-stopband.