A bulk suppressed low loss TDNM-IF filter using LBO substrate

This paper describes for bulk suppression of SPUDT filter on LBO substrate. To suppress the bulk response, new advanced dual track filter is developed. The main track and sub track are identical structure, but phase-inversion each other. To prevent canceling the SAW responses of main track and sub track, all over of the sub track are covered with the absorber that avoid excite the SAW. However, sub track generates bulk acoustic wave (BAW) that are phase inversion against main track. Consequently, the BAW responses are canceled out for dual track without degrading SAW response. The developed 157MHz TDMA-IF filter is installed 5×7mm sized ceramic package, and achieves low loss of 4.5dB. Regarding to the bulk spurious, it is improved about 10dB comparing with conventional one track type SPUDT using LBO substrate, and its out of band rejection level is better than 50dB in 185-500MHz frequency range.