Compact low pass Bessel filter using microstrip DGS structure

We report the design and performance of 5
^th
order DGS based Bessel type LPF with 3 dB cut-off frequency at 2.5 GHz. It significantly improves the cut-off performance of the lumped element based Bessel type LPF. The sharpness of pass cut-off of the DGS based Bessel filter is comparable to that of the sharpness of the Butterworth kind LPF. The frequency range of 10 dB return loss of the DGS based Bessel LPF is 1.91 GHz as against 0.8 GHz for the lumped element based Bessel LPF. The variation in group delay of the DGS based Bessel LPF in pass-band is 42.8 ps; whereas the DGS based Chebyshev and Butterworth LPF have group delays 277 ps and 120 ps respectively.