Novel performance of QPSK modulator subsystem with matched filters for GSAT-4 satellite

Raised Cosine (RC) type of digital FIR Pulse Shaping Filters (PSF) have been developed & implemented in the QPSK Modulators for GSAT-4 regenerative payload. These filters maintain stable spectrum against wide temperature variation across different panels of the satellite. They also ensure minimum Inter Symbol Interference (IST) and hence, provide excellent eye opening (= 90 %) at the sampling instances. The performance of the modulator is comparable to standard Satellite Modulator. They meet stringent amplitude and group delay requirement suggested by Intelsat Earth Station Services (IESS-309). Matching concept is introduced between onboard modulator and ground demodulator to provide optimal downlink performance in AWGN environment.