Design of Compact Ultra-Wideband Filter with Low Insertion Loss and Wide Stopband

This paper proposes a compact ultra-wideband filter, which skillfully utilizes the magnetic and capacitive coupling to obtain sharp rejection. And, the filter contains a small number of lossy elements, thus the low insertion loss and compact size will not be compromised. The measured results show that the filter prototype has a measured 3 dB fractional bandwidth of 128% from 2.8 GHz to 11.4 GHz, a minimum insertion loss of 0.3 dB within the passband, a superior 20 dB stopband rejection from 12.4 GHz to 24 GHz, and a very compact circuit size of 0.23 lambda x 0.31 lambda, where lambda is the guided wavelength of the microstrip structure at the center frequency f(0) = 7.1 GHz.