A compact branch-line coupler using π-equivalent shunt-stub-based artificial transmission lines

In this paper, a compact branch-line coupler is developed using π-equivalent shunt-stub-based artificial transmission lines (SSB ATLs). A conventional quarter-wavelength microstrip can be equivalent to a SSB ATL realized by a series high-impendance microstrip with two sets of branch-type shunt stubs. The circuit configuration of the SSB ATL is beneficial to miniaturize the circuit size using the folding technique. At the design frequency 0.9 GHz, the developed branch-line coupler occupies about 8 % of the conventional design.

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