Correspondence - Design of ladder-type SAW/BAW

This paper describes the design of RF SAW/ BAW filters with constant group delay. The band-pass LC filter is designed based on the traditional Bessel filter design. Then, LC resonators in the filter are replaced by SAW/BAW resonators with finite capacitance ratio γ. Finite γ generates passband ripples in the group delay. However, it is shown the ripples can be suppressed by optimal design of the SAW/BAW resonators. Norton's first transform is also applied to the designed filter to reduce variation of resonator shunt capacitances. Finally, extremely flat group delay with deviation of 4 ns over the frequency range of ±20 MHz at the center frequency of 1 GHz is theoretically demonstrated.