An Optimised Two Gigabit Dual Gate FET Switch for Satellite Systems using QPSK Modulators

With the present trend for high quality digital modulation systems having fast modulation rates and low bit error rates it is beneficial to combine such features with low power consumption and size reduction. A suitable candidate, particularly for space applications, is the GaAs dual gate FET which has been used to realise hybrid MIC switch modules. These provide extremely fast transition times (low cross talk) and eliminate the need for weighty isolators. The properties of a single device are exploited to achieve low consumption modulation. The approach entails firstly, a detailed device characterisation, secondly its design and realisation based on a careful tradeoff using CAD techniques. Thirdly, recorded results show gains of 10 dB and `on´ to `off´ ratios of 40 dB. Good terminal VSWRs, phase tracking and modulation rates of several hundred MBits are presented.