Re: RF layout in ADS
At high frequency, you had better put a reference plate (ground) beneath the trace (the so call "microstrip"). The width of the trace (transmission line) should be calculated carefully for matching (typically 50 ohm).
The grounding is very important at RF bands, bad grounding may cause severe parasitic effect, and even make the amplifier unstable. The grounding pin of the amplifier (usually is the source or emitter) should be grounding very well.
Sometimes, the both sides of the transmission line are also grounded by many vias. These vias are for EMI/EMC purpose. The typical rule is the interval of the vias should be less than 1/20 wave length.