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Digital Frequency Control Loop for Continuous-Wave and Stepped-Frequency Radars

A common technique to control the transmit frequency of modern radar systems are phase-locked loops (PLLs). This paper presents an alternative PLL-free design, where a microcontroller (MCU) is used in a digital control loop to stabilize the output frequency of a voltage-controlled oscillator (VCO). Using a commercial 24 GHz integrated radar transceiver and the MCU, a discrete proportional (P) control algorithm tunes the VCO in real time without requiring a hardware PLL. In continuous-wave (CW) mode, a measurement precision of 7.6 µm is achieved. In a pulsed dual-tone operation mode, the unambiguous range is extended to 1.4 m by still achieving an accuracy of 25 mm.