Following the great availability on the market of the ultra-fast direct digital synthesizer (DDS) and the logarithmic amplifiers, the production of the vector analyzers (VNA) has gained considerable momentum, to the point that they even became accessible to the radio-amateurs for no more than some tens of euro (see the NanoVNA or the vector antenna analyzers).
Original article issued on Radio Rivista 7/8, 9, 10, 11-2020. Translation by my daughter Gaia
Key: Vector Network Analyzer, VNA.