Compact low-loss 2.4GHz ISM-band SAW bandpass filter on the LTCC substrate

This paper describes a design of a surface acoustic wave (SAW) ladder-type bandpass filter (BPF) for 2.4-2.5 GHz ISM-band, based on the low temperature co-fired ceramic (LTCC) substrate, which can be used in 802.11b/g wireless LAN and Bluetooth applications. It obtains an excellent state-of-the-art performance in the ultra small package. The proposed architecture is based on a combination of SAW and low temperature co-fired ceramic (LTCC) technologies, where the multilayer LTCC substrate is used for integration of matching and passband-driving elements and for obtaining additional transmission zeros. It is comprised of three series and two parallel SAW resonators, realized on the LiTaO₃ piezoelectric substrate and connected accordingly to a ladder-type T-topology circuit design, and an additional resonator to obtain an attenuation at 2.57-2.62 GHz IMT-E (TDD) band. Two input/output matching inductors and three additional inductors, permitting to obtain a sufficient suppression level at 2.11-2.17 GHz UMTS (DL) band and harmonics, are completely integrated within ceramic. The described bandpass filter has ultra small dimensions of 1.1 × 1.4 × 0.9 mm, very low insertion losses of -1.5 dB max in the passband. This fully matched SAW bandpass filter has achieved excellent selectivity performance with the up-to-date smallest package size.