An L-band 4-bit RL/RC-switched active phase shifter using differential switches is developed. It employs RL/RC circuits in the design of series feedback loops of the quadrature differential amplifier and achieves 90°, 45°, and 22.5° of phase shift by switching on and off the RL/RC circuits alternatively. On the other hand, a 180°phase shift is achieved with the use of a phase difference between the differential outputs. By cascading all four bits, an insertion gain of 16 to 23dB, a phase error of less than ±8.5°, and an RMS phase error of 4.6°have been achieved at 1GHz.