Tunable Directional Coupler With Very Wide Tuning Range of Power Division Ratio

A new tunable directional coupler with a very wide tuning range of power division ratio (PDR) is proposed and demonstrated. The key uniqueness is the introduction of phase reconfigurable synthesized transmission lines (PRSTLs) as the tuning elements whose electrical length and input matching can be controlled simultaneously. By inserting PRSTLs in between two branch-line couplers (BLCs), the PDR at the two outputs of the tunable coupler can be theoretically tuned from 0 to ∞ (or equivalently from -∞ to ∞ dB) with low reflection coefficient and good port isolation. As an exemplum, the proposed tunable directional coupler was fabricated and tested using microstrip technology at 2.4 GHz. The experimental demonstration features the widest PDR tuning range (-39 ~ 29 dB) among the literature, with a power loss of 1.2 dB and good port isolation higher than 22 dB.