Michael Jakob

A SAW duplexer with superior temperature characteristics for US-PCS

The system requirements for US-PCS are very hard to fulfill with conventional SAW filters, since the duplex gap between Tx and Rx bands is only about 1% wide. Furthermore, current PCS CDMA systems impose strong demands on isolation and rejection levels. Typical SAW devices on rotated Y-X LiTaO/sub 3/ cannot meet these requirements over the whole operating temperature range, because of the large temperature coefficient of frequency (TC/sub f/) of the substrate. SiO/sub 2/ films can be applied to lower the effective TC/sub f/. However, since the necessary film thickness is rather high, this causes fundamental changes in the electro-acoustic properties of this new material system. Using one-port resonators and ladder-type base sections as test structures, we have conducted a series of experiments to identify interrelations between parameters defining the layer system and its electro-acoustic properties like TC/sub f/, piezoelectric coupling factor, reflectivity, and propagation loss. We have determined requirements for realisation of a SAW duplexer in the US-PCS hand and have designed a suitable layer system. We also demonstrate that the effects of a SiO/sub 2/ layer can be simulated accurately by a standard P-matrix model with suitably adjusted parameters. Finally, we present a complete SAW duplexer device for the PCS band featuring a TC/sub f/ of -17 ppm/K.

Design study on a compact, high performance SAW duplexer

In this paper various design aspects concern- ing SAW duplexers are presented. Special focus is placed on an integrated lumped matching network, which allows to save space within the LTCC package. This corresponds with the trend of miniaturization of RF front-end components for cellular phones. To show the feasibility of this approach a SAW duplexer has been designed accordingly. In the design process two different modelling techniques for the electromagnetic computation of the package are compared in terms of their accuracies. Simulation and measurement of the device agree very well.