A new true-time delay phase shifter concept is proposed exploiting the distributed Miller effect in coupled transmission lines. Simultaneous change in Miller capacitance and inductance controlled by a single analog voltage changes the propagation delay of a transmission line with constant input impedance and insertion loss. The true-time delay line feature of the proposed architecture accommodates a wide bandwidth signal without group delay distortion. A theoretical framework for understanding Miller inductance from voltage and current duality and the distributed Miller effect using coupled wave equations is presented. As a proof of concept, a four-stage tunable delay line with a high-speed phase modulation capability was fabricated in a 45-nm RF SOI CMOS process and occupies an active area of 0.28 mm2. The measured IC demonstrates a broadband tunable true-time delay with a measured group delay tuning range of 18 ± 1 ps from 11 to 24 GHz. The measured phase shift ranges are 173° and 182° with insertion losses of 10.6 ± 0.7 dB and 11.6 ± 1 dB at 28 and 30 GHz, respectively. The measured dc power consumption is 22 mW from a 1.2-V supply.