Matching Networks on Narrowband Multistage Low Noise Amplifier (LNA)

Question

How does the inter-stage matching network of a narrowband LNA compare to that of a wideband LNA for the same multistage design? I've read somewhere that narrowband LNA does not necessarily require a matching network between the stages and can be ignored when the design consists just of identical single-stage design in cascade.

Shouldn't the matching network be necessary for matching the impedance of the stages? Or, does it serve another purpose?

Here is the link: Design, Analysis and Optimization of Multistage LNA at KU- Band.

Answer 1

Microwave amplifiers are tricky. Fets and transistors have so strong internal leakage from output to input that the result is easily an oscillator. Matching networks are needed for stability. Even a single stage amp can be an oscillator with mismatched signal source or load. Another reason for matching is to avoid wasting all gain to the attenuation caused by reflections. Generally also noise optimization is tried as the term LNA suggests and in wideband applications some gain equalization can be needed. The circuit is a compromise between different requirements.

Wideband amp is surely more complex because everything should work in the whole operating band, calculations at the center frequency alone do not provide useful results.