The Enhancement of Signal-to-Noise Ratio of SAW Tags Using 5-bit Barker Code Sequence

초록

Passive tags suffer from limited interrogation distance due to the absence of signal generation in them. Surface Acoustic Wave (SAW) tags, one of passive type tags, are also required to have a long interrogation distance in many applications. To enhance the read range, a larger Signal-to-Noise Ratio (SNR) is required. In this paper, the correlation method using 5-bit Barker code sequence was proposed to increase SNR for the long interrogation distance. The SAW device was fabricated on 128 degrees Y-X LiNO3 piezoelectric substrate for operation at 100MHz. Each SAW tag had 5-bit Barker code sequence to generate BPSK modulated signal. The BPSK modulated signal from a SAW tag was further processed through a correlator. For the experiment, the correlator identical to the measured SAW tag was employed. Even though the correlator did provide only partial correlation, the code gain through the correlation was achieved. The SNR improvement was 19.3 dB by using Barker code and the correlator, which can be improved further by properly designing the correlator.