Balance characteristics studies using Wigner distribution analysis for SAW devices

The Common-mode rejection (CMR) parameter and the direct amplitude / phase unbalance value are used for evaluation of balance type SAW devices in order to compare the balance port impedance dependence. Time-domain analysis based on unbalanced scattering matrix elements and Wigner distribution based on CMR characteristics arc also proposed to apply to balance type SAW filters. Unbalanced responses of imbalanced filter (A) are observed at concentrated area for delay and frequency domain. It can be found that the unbalance origin of filter (A) is acoustical mode. A good agreement with time-domain response of each balanced port and a low Wigner CMR distribution are obtained for balanced filter (B). Unbalanced response of filter (B) with circuit asymmetry are observed at whole area corresponding to main signal. Consequently it is verified that these time-domain and Wigner distribution methods are effective for analyzing the origin of imbalance.