A High Bit Rate Miniaturized QPSK Modulator for Satellite Data Transmission

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  • Author: By D.V. Ramana and Jolie R., ISRO Satellite Centre
A high bit rate miniaturized Quadrature Phase Shift Keying (QPSK) modulator was designed at X-band using microstrip line techniques. The modulator was tested for its performance for a data rate of upto 800Mbps. The paper discusses the practical realization of the unit. The existing on-board QPSK modulator at X-band transmits 105Mbps on a single carrier. The modulator is reflection type consisting of a hybrid, two BPSK modulators and a power combiner. Each BPSK modulator consists of a hybrid ring with switching diodes in two arms. The diodes are switched by data to include or exclude /4 lines to get 0º or 180º phase shift at the output of the modulator. The modulator MIC was realized on a 2" x 2" alumina substrate.