High-performance low-pass filter using complementary square split ring resonators defected ground structure

In this study, a complementary square split ring resonator (CSSRR) using defected ground structure in microstrip line form is introduced. The CSSRR unit has interesting filtering characteristics, such as a very high attenuation rate, couple of the dimension-dependent finite attenuation poles and a very low-passband ripple level. Cascading CSSRR units with different dimensions has been used to design a high-performance low-pass filter (LPF) with a cutoff frequency (f_c) of 1.80 GHz through a simple, straightforward design procedure. The designed LPF exhibits an attenuation rate of 300 dB/GHz and passband ripples of less than 0.30 dB. Moreover, it has a wide 20-dB stopband at up to 4.5 times f_c with an attenuation of more than 30 dB in most of the stopband. To the authors knowledge, the overall performance of the LPF, particularly the attenuation rate, is the best among published reports to date. The designed filter has been fabricated and validated by measurements.