A 360° all-pass tunable phase shifter is proposed in this study. The device consists of three high-pass filters and one 180° phase shifter based on a high-pass/low-pass filter structure. Diode switches are used instead of their FET counterparts. The phase shifter needs only approximately half of the bias power sources to significantly reduce the complexity of the circuit. It adopts five sets of controlling voltages to achieve a four-bit 360° phase-tuning range and lower the variation of insertion losses. The size of the chip, including the pads, is 0.78 mm × 1.69 mm. The insertion loss is 12.5 ± 1.5 dB at 36 GHz, while the return loss is better than 10 dB.