Compact cascaded directional couplers with continuously tuneable coupling ratios

This paper presents the analysis and development of compact cascaded directional couplers with continuously tuneable coupling ratios. The general approach of cascading two quadrature directional couplers and discontinuities in the connecting branches is analyzed. Two suggested compact individual couplers are analyzed using even-odd-analysis. Two proposed cascaded networks are composed of only 50Ω transmission lines, two variable capacitance diodes and either four capacitors or one capacitor and one inductor. DC supply and decoupling is needed additionally. Prototypes of the two-fold and the one-fold symmetrical network were fabricated and the measurement results are shown.