High Data Rate Direct X-Band QPSK Modulator

This paper describes an X-Band QPSK modulator designed for data rates up to 1 Gbps and with flexibility in adaptation to different applications and environments. Trade-offs have been conducted to find the optimum approach for the target application of high data rate X-band transmitters. The results lead to a direct modulation topology where the base band data directly modulate the X-Band carrier. This approach reduces hardware complexity and size. The modulator design covers the whole X-Band transmit frequency range from 7.25 to 8.5 GHz and uses mixed signal base band processing techniques implemented in space grade ASIC technology. The serialized and conditioned I/Q data signals are fed to the high precision broadband I/Q modulator core with typical carrier and side band suppression of better than 30 dBc. In order to control the modulator within the spacecraft a tailored TM/TC FPGA as well as all necessary DC functions are implemented. As an option, a high-power SSPA delivering up to +36 dBm output power can harmonically be integrated into the X-Band transmitter without the need of an additional DC-DC converter.