Fig. 3: Field-testing of the heterodyne synthesizer in a 95-GHz continuous-wave radar.

a Simplified block diagram of the frequency-modulated continuous-wave (FMCW) radar. A millimeter-wave source at 92 GHz is mixed with a frequency-chirped modulation waveform around an IF of ~3 GHz. A band-pass filter (BPF) rejects un-wanted mixing components, and the signal is amplified through a W-band power amplifier (PA) before being sent to the transmitter optics. Back-reflected signals are demultiplexed through polarization duplexing and passed through a low-noise amplifier (LNA) and BPF, and are mixed with the 92 GHz source down to the IF, prior to de-modulation and digitization in the back-end electronics. b shows a photograph of the radar test-bench with the primary aperture pointed at a distant hill, with the heterodyne synthesizer breadboard mounted on top. c plots measured back-reflection data from a building ~207 m away, when using either the radar’s existing 92 GHz CMOS synthesizer (dark gray) or the microwave-photonic heterodyne synthesizer (red). Phase noise fringes are significantly suppressed when using the low-noise photonics-based source. d plots Doppler data when the radar is pointed at a distant hill as in (b). Weak signals from drizzle are visible as slow-moving signatures at ranges closer than 1 km. When using the relatively noisy CMOS synthesizer (left), bright reflections from stationary hills lead to strong Doppler artifacts that would obscure the observation of co-located moving objects. By contrast, when using the heterodyne synthesizer (right), these artifacts are practically eliminated.