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I have seen somewhere that there were DDSs with sampling frequency more than 1GHz which designed using GaAs.
Unfortunately i can not remeber where. Also remember that the drawback of that products was high price and low resolution of their DACs(e.g. 8-bit) which yields to worse SFDR than others.
If your application is high frequency but fmax - fmin is less than 200MHz, you can simply use an Analog Devices DDS and mix its output with a fixed oscilator. but if in your application fmax - fmin is so high you can use mixed techniques such as hyprid PLL - DDS synthesizer. In this configuration output of an DDS is multiplyed with a PLL.
I think if you specify your design requirements we can help you more.