Miniaturized IF CDMA SAW filters based on three-channel structures

The size reduction is a permanent tendency in the development of IF SAW filters for CDMA mobile phones. The implementation of three-channel structures is known as a method, which provides reducing IF-filter size. In three-channel SAW filters, the triple transit signal serves as useful one. The direct acoustic signal is compensated due to the 120/spl deg/ phase shifts between the channels. However, a strong transverse acoustic coupling occurs between the adjacent channels. It results in a strong distortion of the frequency response of such filters, degradation of selectivity and increased phase ripples in the pass-band. In this paper, a modified structure of the three-channel filter, which is free of the above shortcoming, is described. The modified structure has been used in filters for CDMA system: 210.38 MHz, 220.38 MHz and 85.38 MHz in packages SMD 5.0/spl times/5.0 mm/sup 2/, 5.0/spl times/7.0 mm/sup 2/ and 9.0/spl times/5.0 mm/sup 2/, respectively.