Stub is a piece of short circuited transmission line which is used to tune out the reactance of the load when connected across the transmission line as close as possible.
Single Stub Matching :
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Single Stub Matching – Stub matches are widely used to match any complex load to a transmission line. They consist of shorted or opened segments of the line, connected in parallel or in series with the line at a appropriate distances from the load. In coaxial cable or two-wire line applications, the stubs are obtained by cutting appropriate lengths of the main line. Shorted stubs are usually preferred because opened stubs may radiate from their opened ends. The single stub match is perhaps the most widely used matching circuit and can match any load.