A Compact Ultra-Wideband Filter Based on Left Handed Transmission Line by Using Complementary Split Ring Resonators and Series Capacitor

A compact and sharp rejection UWB microstrip bandpass filter is developed using left handed metamaterials. For realizing a backward-wave propagation medium, two split ring resonator (CSRR) in the back substrate side and also one series capacitor etched in the host line, are used to produce a negative effective ε and μ, simultaneously. Moreover, in the proposed structure, two doublets parallel coupling gaps is placed at each side of the series capacitor. In comparison with the other similar filters, this structure shows a significantly wider passband due to the introduction of a cross-coupling between the feed lines (input and output) which generate four pairs of attenuation poles in the passband.  On top of that, using two CSRRs and series capacitor leads to the addition of two extra transmission poles at the lower and upper edges of the filter. Consequently, a compact six-pole ultra-wide bandpass filter is designed and fabricated which exhibits extremely sharp rejection skirts around the target passband. The passband covers 3.67 to 10.42 GHz and its measured 3 dB fractional bandwidth is about 95.8%. To the best of our knowledge, the size of proposed ultra-wideband filter is more compact in comparison with known similar filters.