An Active Bias Network for the Characterization of Low-Frequency Dispersion in High-Power Microwave Electron Devices

In this paper a new active bias network (ABN) for the technology-independent characterization of low-frequency (LF) dispersion in the output impedance and transadmittance of high-power microwave transistors is described. The proposed bias network is capable of synthesizing a high-impedance active DC-feed in the range of 10 Hz-1 MHz, where III-V microwave devices typically exhibit frequency response dispersion due to energy traps and/or self-heating. The input impedance values obtained in such a large bandwidth (five decades) are considerably higher than those that can be achieved with passive resistive and inductive solutions. In fact, these lead to severe limitations in terms of achievable impedance values, calibration accuracy, power handling capabilities, and physical dimensions. The ABN is particularly suitable for the characterization of high-voltage and high-current devices. In particular, here it is used, along with standard laboratory instrumentation, for the characterization of the LF dispersion of an AlGaN/GaN HEMT, suitable for microwave power amplifier applications.