GHz SAW delay line for direct sequence spread spectrum, CDMA in-door communication system

Abstract

This paper presents the design technique for the 1.9 GHz SAW delay line and its application to the diversity scheme to provide a spectrally efficient and robust in-building communication system. In-building communications presents a harsh environment and generally requires additional diversity. A simple and economical way of providing this diversity in a spread-spectrum system is to add time delay between diversity antennas using the SAW delay lines. The SAW delay lines provide the essential flat amplitude and time offset for the different antenna elements. Conventional SAW design is generally limited to less than 1 GHz because of line size resolution problems. However, by using asynchronous sampling and spatially modulated transducers, with line sizes greater than 0.6 micron, a flat amplitude response across the 140 MHz frequency band, can be achieved for a 1.9 GHz delay line. The device has an insertion loss of about 32 dB, a time delay greater than 2.0 microseconds, and the amplitude variation over any two MHz across the passband is less than 0.2 dB