Design and Realization of a 6 GHz Doherty Power Amplifier from Load-pull Measurement Data
Examensarbete för masterexamen
Wireless, photonics and space engineering (MPWPS), MSc
In this report, a Doherty power amplifier (DPA) design method is developed based on load-pull measurement data. The developed approach is particularly suitable for realization of high frequency hybrid DPAs. This is enabled by including the bias and stability networks in the characterization test board as well in addition to the transistor. Thereby, the design method avoids having to rely on discrete component models being highly accurate. The described design method was used to fully realize a hybrid DPA. For characterization a passive load- and source-pull setup was built around two tuners and two power meters. After finding the optimal impedances for the transistor and surrounding circuitry, the results are de-embedded to a reference plane which includes said circuit elements, thereby automatically including their effects into the design. The components of the DPA are then designed based on the measurement results. An analytical approach was used for the combiner synthesis. The resulting amplifier exceeds 45% power-added efficiency (PAE) for 38dBm of output power at 6 GHz, with 42 %, 32% and 23% PAE at 3, 6 and 9 dB of output back-off respectively. The small-signal gain exceeds 14 dB. This high gain is attributed to careful source-pull measurements enabling a very good input match. The gain is well-centered around 6 GHz. We conclude from the good performance of the demonstrator unit that the design method is a viable approach for DPA design even at such high frequencies, which is of interest when a MMIC design would be impractical such as in the case of low-volume production.
Informations- och kommunikationsteknik , Elektroteknik och elektronik , Telekommunikation , Information & Communication Technology , Electrical Engineering, Electronic Engineering, Information Engineering , Telecommunications