Frequency synthesis for high precision wideband millimeter wave radar systems using a SiGe bipolar chip

The performance of frequency synthesizers with respect to bandwidth and phase noise limits the overall performance of high precision FMCW radar systems. An essential challenge of fractional-N ramp synthesizers is to combine high reference frequency and low division ratio in the loop to minimize phase noise. For an 80GHz radar system with ultra high bandwidth of 24.5 GHz we meet this challenge with a programmable frequency divider with unrivaled high input frequency. These building blocks have been implemented on a single SiGe integrated circuit. The developed phase-locked loop (PLL) includes a reverse phase downconversion mixer driven by a fixed frequency PLL to attain constant loop gain. The phase noise of the fixed frequency PLL has been measured to be -104 dBc/Hz at 20kHz offset from the center frequency of 48 GHz, which enables a phase noise of the 80GHz radar output of -93 dBc/Hz at 20 kHz offset frequency.