A single-structure, two-bit phase shifter useful for steering the beam of an antenna such as an aeronautical antenna. The phase shifter includes an input line, an output line, a plurality of switched lines such as quarter-wavelength microstrip lines connected directly or indirectly between the input line and the output line, and a plurality of switches for selectively and controllably connecting one or more of the switched lines between the input line and the output line. The phase shifter controllably connects one or more of the switched lines in series between the input line and the output line, thus providing phase shifts of an input radio frequency (RF) signal between one of four discrete phase shift amounts. Using up to three quarter-wavelength switched lines, the phase shifter provides phase shifts in increments of ninety degrees, e.g., phase shifts of zero, ninety, one hundred eighty, and two hundred seventy degrees (0.degree., 90.degree., 180.degree., and 270.degree.). The inventive phase shifter is formed as a single two-bit structure, rather than two one-bit structures; thus it has a relatively smaller size than conventional two-bit phase shifters. Also, the inventive two-bit phase shifter may be configured such that the input signal passes through only one closed switch in any phase shift configuration, which reduces the overall insertion loss by reducing the insertion loss caused by passing the input signal through multiple switches.