This paper presents an electronically reconfigurable dual-mode integrated beam-steering array. The core building block to fulfill the design is the reconfigurable synthesized transmission line (RSTL), whose transmission characteristic is controlled by a varactor diode as an on/off RF switch. By integrating the RSTLs to the array feed network, the proposed array is capable of, at a given frequency, switching its functionality as a beam-switching Butler matrix or a retro-directive array combined with data modulation. The switching is only dependent on the bias voltage of the varactor diodes, and the dc power consumption is very low (µW). The circuit response of the feed network and the radiation characteristics of the phased array are verified experimentally.