Institute of Radio Frequency Engineering and Electronics (IHE)


Distributed active transformer based power amplifiers

In millimeter-wave systems the available bandwidth and output power of the circuits are nowadays the main limiting factors. Therefore, starting in 2012 the IHE investigated, in the framework of the MilliDat project which was funded by the Deutsche Forschungsgemeinschaft (DFG), novel coupler designs, so called distributed active transformers. The couplers unify the power splitting and the impedance matching and offer inherently low loss and a very high bandwidth. This is the foundation of high bandwidth and high linearity amplifiers which are intended directly as a power amplifier in front of the transmitting antenna. In 2015 the project was completed yielding, among other things, an broadband amplifier covering the frequency range from 50 to 146 GHz, providing about 100% bandwidth which was realized employing these novel coupler cells.  Such high performance building blocks are key to future generation communication- and radar-systems. For further information the interested reader is referenced to the following articles.

Chip photograph of a distributed transformer test circuit based on the Fraunhofer IAF mHEMT process
Chip photograph and schematic of a LC-network based power amplifier

Selected Publications

Pahl, P.; Wagner, S.; Maßler, H.; Leuther, A.; Kallfass, I.; Zwick, T. (2017). Efficiency Optimized Distributed Transformers for Broadband Monolithic Millimeter-Wave Integrated Power Amplifier Circuits. IEEE transactions on microwave theory and techniques, 65 (12), 4901–4913. doi:10.1109/TMTT.2017.2729514
Pahl, P.; Wagner, S.; Massler, H.; Diebold, S.; Leuther, A.; Kallfass, I.; Zwick, T. (2015). A 50 to 146 GHz power amplifier based on magnetic transformers and distributed gain cells. IEEE microwave and wireless components letters, 25 (9), 615–617. doi:10.1109/LMWC.2015.2456639
Pahl, P.; Diebold, S.; Schwantuschke, D.; Wagner, S.; Lozar, R.; Quay, R.; Kallfass, I.; Zwick, T. (2013). A 65 - 100 GHz impedance transforming hybrid coupler for a V- /W-band AlGaN/GaN MMIC. European Microwave Integrated Circuits Conference (EuMIC’13), Nürnberg, October 6-8, 2013, 412–415, IEEE, Piscataway (NJ).