Microwave group delay time adjuster using parallel resonator

This letter describes the design of a group delay time adjuster (GDTA) using a parallel resonator. The GDTA consists of a variable capacitor and a variable equivalent inductor. These components are controlled by two bias voltages separately. The variable equivalent inductor is realized using a high impedance transmission line terminated with the variable capacitor. Group delay time can be adjusted by varying the capacitance and the inductance while keeping the fixed resonance frequency. When the proposed GDTA is fabricated on the Korean RFID frequency band (908.5-914 MHz), we could obtain about 3 ns group delay time variation with excellent flatness.