Design of a microwave group delay time adjuster and its application to a feedforward power amplifier

This article presents a design method for a microwave group delay time adjuster (GDTA) and its application to a feedforward (FFW) power amplifier (PA). The GDTA consists of a variable capacitor and a variable equivalent inductor. The variable equivalent inductor is realized using a high impedance transmission line terminated with a variable capacitor. These components are controlled by two separate bias voltages. The group delay time can be adjusted by varying the capacitance and inductance while keeping a fixed resonance frequency. The proposed GDTA is fabricated for the Korean RFID frequency band (908.5 to 914 MHz). A group delay time variation of approximately 3 ns is obtained with satisfying transmission flatness. When the proposed GDTA was applied to the base station FFW PA system, the loop group delay time matching was much easier and required less effort and time, while achieving an excellent linearization result compared to the conventional FFW PA system.