Design of an ultra wideband bandpass filter by using microstrip spur-line and ring shaped DGS with improved out of band response

Abstract

This paper presents an Ultra Wideband (UWB) microstrip Bandpass Filter (BPF) using spur-line and ring shaped Defected Ground Structure (DGS) with improved out of band rejection. This microstip UWB provides a 3 dB bandwidth from 3.1 GHz to 10.6 GHz, with centre frequency of 6.85 GHz. The attenuation band has been improved using cascaded step-impedance ladder type L-C Low pass filter (LPF) in addition to main ultra wideband filter structure. The final response provides an UWB with a negligible passband insertion loss around the midband. This structure also provides good sharpness factor in the rising edge and falling edge of 10.33 dB/GHz and 18.34 dB/GHz respectively, and attenuation greater than 20 dB up to 32.5 GHz outside the passband.