Self-Jamming Mitigation via Coding for Millimeter-Wave Imaging With Direct Conversion Receivers

Undesired local oscillator (LO) leakage and dc offset impairments are commonly observed when direct conversion (or homodyne) receivers (RXs) are used for coherent millimeter-wave (mmW) active imaging, and are particularly severe when imaging short-range, slow-moving targets where the target's baseband response is close to dc. This letter proposes a binary phase shift keying (BPSK) coding scheme, which modulates the illumination source to mitigate dc offset and self-jamming in the receiver I/Q demodulator. This modulation permits the separation of the desired point-scatterer returns that form the mmW image from the undesired components. In a proof of principle experiment using a K -band (17.5-26.5-GHz) short-range mmW imaging setup, the suppression of dc offset and LO leakage using a BPSK-modulated source is demonstrated. It is shown that the dc offset has been reduced by over 400× and the receiver sensitivity has improved by over 40 dB. The proposed direct conversion approach with coded illumination holds promise for reducing the cost and complexity of mmW imaging systems versus conventional superheterodyne mmW imaging systems.