Performance Enhancement of Microstrip Bandpass Filter Using CSSRR

Split ring resonator (SRR) and complementary split ring resonator (CSRR) have been widely used in size miniaturization and performance enhancement of various microwave devices. In this paper, a complementary single split ring resonator (CSSRR) is used to design a wide bandstop filter. Bandstop filter is constructed using two open stubs of length ¿_g/4 and the CSSRR. The designed bandstop filter has a wide rejection bandwidth compared to the conventional open stub filter. By cascading this bandstop filter (BSF) with the conventional parallel-coupled line filter, the spurious pass band at the second harmonic frequency is removed. To evaluate the validity of this method, a first order Chebyshev bandpass filter centered at 0.9 GHz with 10% fractional bandwidth (FBW) is combined with the designed BSF. Simulation result shows a harmonic rejection of 40 dB to the spurious pass band at 2f₀, well validated by the experimental results.