Compact ultra-wideband bandpass filter based on novel defected ground structure and folded coupled lines

A compact ultra-wideband bandpass filter is presented. The proposed UWB filter consists of a couple of folded parallel lines and a low-pass filter based on defected ground structure. Good bandpass performance and wide rejection characteristics can be achieved by this new structure. One prototype is fabricated to demonstrate the validity of the proposed strategies. The simulated and measured results indicated that the insertion loss is less than 1.5 dB between the 3.1 and 10.5 GHz with a sharp falling edge of 35 dB/GHz and its group delay is less than 0.5 ns in the pass band. The rejection is better than 20 dB from 12.5 to 25 GHz. The total size of the UWB BPF is 0.78 λ_g × 0.23 λ_g where λ_g is the guided wavelength at the center frequency of 7.4 GHz.