Novel approach for loss reduction in LPF for satellite communication system

This paper gives an approach for loss reduction in the design of maximally flat low pass filter (LPF) using two different methods. First using defected ground structure (DGS) and second by using series of grounded patches (SGP) for surface wave compensation. The fourth order maximally flat low pass filter is designed at cut-off frequency of 3 GHz. To achieve arbitrary cut-off frequency and impedance level specification, it is converted to low pass filter using frequency scaling and impedance transform. Loss reduction is investigated first by defected ground structure and then for series of grounded patches structure (SGP) of small square patches of 2 mm by 2mm on microstripline. The simulation is performed using PUFF and IE3D software and simulation results are reported. Simulation result shows improvement in reflection co-efficient for 3 GHz cut-off frequency by -7.18 dB for filter with DGS and -2.56 dB for filter with SGP, in comparison with simple LPF. However, for 2.68 GHz frequency, LPF with SGP shows -20.18 dB improvements. All the three filters are fabricated i.e. without defected ground, with defected ground and with series of grounded patches. Measured results of all three fabricated low pass filters, using vector network analyser are presented. Insertion loss, radiation loss, transmission loss and return loss are calculated on the basis of the measured and simulated parameters and group delays of each filter are reported. Comparative insight with different losses, group delay and theoretical and practical values for three filters are presented and shows good agreement.