An Improved Design of A Bias Tee Using A Modified Radial Stub

This paper presents a microstrip line high performance bias tee for microwave active circuits. A conventional radial stub is first modified by connecting two shunt open-stubs to design a bandstop filter (BSF) with wide rejection band. Then, it is used in the DC line for isolation improvement. Two modified bias tees, one with single BSF unit and another with two BSF units are fabricated for X-band applications. Measurement results show that the second unit provides at least 37.4 dB isolation over 7.9-13 GHz. Design guidelines are provided for other frequency range.