I noticed that in most of designs there are extra microstrip stubs along transmission line or at input and output of RF power amplifier. Is it for matching purpose? But these amplifiers are already 50 ohm internally matched then why we need those extra stubs at input and output of the amplifier? How to design those stubs and shape?
Is there any particular technique for designing it? In these two picture they have different type of matching network at input and output of power amplifier.
Are asking about radial stubs? If so then those are used to form RF chokes in bias tees.
The transistors are narrow band and the stubs create a short circuit at the operating frequency on the bias line; this is transformed by the quarter wave transmission line to present an open circuit on the main output line. By using two at slightly different lengths & offsets you can broaden the bandwidth to be close to the operating band.
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