A High Efficiency 4W X-Band pHEMT Power Hybrid for Space Application
Moreno, C.; Saura, M.; Gómez, D.; Vilaseca, R.
Mier Comunicaciones, S.A.

This paper presents the development of a spaceborne high power and high efficiency hybrid amplifier dedicated for application in X-Band (8.5GHz) in the frame of ESA Gaia Mission. This amplifier will be integrated in a module which is thermally isolated from the spacecraft, so efficiency becomes a critical issue.

To achieve required output power and efficiency, pHEMT die transistors TGF2021-02 (driver stage) and TGF2021-08 (power stage) from Triquint have been used. These devices are housed in a ceramic hermetically sealed CuMo package, together with matching and biasing networks on Alumina substrate. Special consideration in the substrate height and gold thickness was given in order to minimize output losses and therefore improve overall efficiency. The result is a single 50Ohm/50Ohm power hybrid.

A hybrid prototype has been designed, mounted and tested. With a lineal gain of 21.5dB, the overall power-sweep results of this amplifier reveal a peak PAE at hybrid level of 54% and an output power of 4W, when biased at 6V (driver stage) and 8.5V (power stage) in harmonically loaded class AB. Measured drain efficiency at power stage is higher than 64%. With these results, no alternative with better PAE figure at these conditions has been found up to the date.

The number of active devices in parallel has been selected in order to fulfil the channel temperature standards required in space applications, with transistor junction temperature limited to a maximum value of 110°C. Parts stress constraints have been also considered.