Compact Quadband Bandstop Filter Based on Concentric Split Ring Resonators with Perturbation for Multifunctional Wireless Systems

Bandstop filters play an essential role in many radio frequency (RF) and microwave communication systems to block undesired signals or reject spurious harmonics. This paper presents the design and experiment of a compact quadband bandstop filter centered at 1.2/1.97/2.96/4.78 GHz with a passband insertion loss ranging from 1.07 to 2.9 dB. The overall volumetric size of the proposed filter is 0.197 λ g  × 0.197 λ g  × 0.01 λ g , where λ g is the guided wavelength at 1.2 GHz. The desired performance is achieved by introducing two diamond-shaped concentric split ring resonators (DSCSRRs) intercoupled and defected ground structure. The metamaterial properties of the DSCSRR have been verified by extracting and analyzing its effective permittivity and permeability. This research shows that DSCSRRs can generate multiband characteristics and yield high selectivity with good band-to-band isolation by generating transmission zeros between passbands. The filter is designed, optimized, and analyzed using High-Frequency Structural Simulator (HFSS). A good agreement is observed between simulated and experimental results. The measured results demonstrate that the proposed quadband banstop filter exhibits a minimum stopband rejection of 11.22 dB and fractional bandwidth greater than 4.51%, which makes it suitable for front-end transceiver components or multifunctional wireless systems to suppress unwanted signals at four separate frequency bands.