A simple transformation of improved WLAN band pass to low pass filter using defected ground structure (DGS), defected microstrip structure (DMS) and multilayer-technique

A novel transformation of band pass- to low pass filter is introduced in this paper. First a compact microstrip band pass filter designed, optimized and realized by combining a simple multilayer method with magnetically coupled microstrip U-shaped DGS resonators is proposed. The DGS- and DMS-techniques demonstrated the ability to suppress the undesired harmonic response. The proposed band pass filter is transformed to a new structure with low pass characteristics using a simple strip connection between the neighboring microstrip resonators. The designed compact filters have low insertion loss, sharp transition regions due to the presence of two-transmission zeros at both edges of the pass bands. The measured resonance frequency, bandwidth and insertion loss are 3.4 GHz, 40%, and 0.5 dB respectively. The compact transformed low pass filter offers a wide stop band with a rejection higher than 20 dB up to more than 10 GHz. The undesired harmonic has been successfully suppressed. The simulated and measured results show good agreement and validate the proposed approach.