UWB bandpass filter with sharp rejection and narrow notched band

A novel ultra-wideband (UWB) bandpass filter with sharp rejection and a narrow notched band is presented. This filter is designed using a multiple-mode resonator (MMR) which consists of a ring resonator and a stepped-impedance stub. The MMR has six resonance frequencies and three transmission zeros (TZs). All three TZs are close to the resonance frequencies, thus creating sharp roll-off and narrow notched bands. Different passband bandwidths and notched bands can be obtained by tuning the stepped-impedance admittance ratios. The simulated and measured results demonstrate that this simple bandpass filter has 97.3 and 30.6 dB/GHz attenuation slope at the lower and upper transition bands, respectively. The 3 dB notched band is from 5.6 to 5.8 GHz with 10.3 dB insertion loss at 5.7 GHz.