Compact microstrip elliptic function lowpass filter with sharp roll-off and wide stopband by cascading multiple patch resonators

A new compact microstrip elliptic function lowpass filter with very good roll-off and wide stopband by cascading multiple patch resonators is presented. The sharp skirt near the cutoff frequency is due to the presence of series resonators formed by the connecting stub and patches which are in parallel with the 106 Ω central microstrip line. The 3 dB cutoff frequency of the filter is at 2.4 GHz and a compact size of 0.2444λ_g×0.1694λ_g where λ_g is the guided wavelength at cutoff frequency. The experimental results illustrates that, the filter achieves a very good roll-off of 90 dB/GHz and a wide stopband from 2.55 GHz to 7.03 GHz with a suppression level of 16 dB.