Fig. 5

25 GHz 45 nm SOI CMOS circulator S-parameter measurements. a Microphotograph of the fabricated circulator. The total size of the 25 GHz circulator is 1.2 mm × 1.8 mm. Measured S-parameters for 8.33 GHz spatiotemporal conductivity modulation between b ports 1 and 2, c ports 1 and 3, and d ports 2 and 3. Low-loss transmission in the clockwise direction (S ₂₁, S ₃₂, and S ₁₃ are −3.3 dB, −3.2 dB, and −8.7 dB, respectively) and large isolation in the reverse direction (S ₁₂, S ₂₃ and S ₃₁ are −10.3 dB, −9 dB, and −18.9 dB, respectively) are measured at the operation frequency of 25 GHz. A broadband isolation of −18.3 to −20.2 dB (limited by the measurement setup) in S ₃₁ is demonstrated over 4.6 GHz bandwidth (the 1 dB insertion loss bandwidth in S ₂₁ and S ₃₂) without any port impedance tuning