Tunable isolator using variable capacitor for multi-band system

A novel tunable isolator for multi-standard mobile handsets has been successfully developed. A new circuit configuration for tuning operation frequency of the isolation is proposed. It shows that the isolation band is tuned widely by varying the variable capacitor value without increasing the insertion loss. A 1.5 × 0.9 × H0.4mm³ Core-Isolator and a 0.5 × 0.5 × 0.2mm³ (BaSr)TiO₃ (BST) variable capacitor have been fabricated on a PCB. By using this circuit, usable isolation band could be expanded to 698-915MHz, which is 6 times wider than conventional one. The developed isolator keeps other characteristics such as 0.6dB max of insertion loss, 12dB min of isolation and -60dBc level of ACLR (5MHz).