A Design of 3-pole Coupled Line Bandpass Filter Using Group Delay Analysis Approach

In this paper, we present a design of 3-pole coupled line bandpass filter using group delay (GD) analysis approach. The proposed 3-pole BPF consists of two-coupled line with short-circuited stub instead of four coupled lines conventional BPF. The design equations are derived by equating GD of the proposed and conventional 3-pole BPF. The GD value of the proposed BPF is controlled by adjusting fractional bandwidth of filter. For proof of concept, the proposed BPF was designed and fabricated at center frequency of 3.50 GHz. The measured results are well agreed with simulations and theoretically predicted results. The measurement results revealed that the proposed BPF achieved the insertion loss of 0.8 dB with fractional bandwidth of 21.71% (760 MHz) and GD of 0.92 ns.