A W-Band Heterodyne FMCW Radar Based on TX IQ-Modulation

Abstract

In this paper a method to realize a heterodyne frequency-modulated continuous-wave (FMCW) radar is presented. The proposed principle relies on the use of an inphase/quadrature (IQ)-modulator as single-sideband-mixer to shift the frequency of the FMCW-output away from dc. Since in any IQ-modulator phase and amplitude imbalances occur, the effect of these imbalances will be investigated by deriving the corresponding signal model. Based on this analysis, a method to compensate the imbalances by a predistortion of the modulation signal will be derived. The presented method does not require special test signals or additional hardware, but relies on a standard FMCW measurement onto a calibration target. A prototype radar system was built and used in test measurements to verify the proposed principle. The measurement results show that a suppression of unwanted signal components caused by IQimbalances better than 45 dB is achievable.

A Delta–Sigma modulator-based heterodyne FMCW radar for short-range applications

“…Secondly, the frequencies are digitally down-converted to zero. Thus, the same peak search as in the homodyne mode can be directly applied to (11) to find the beat frequency related to the target parameters. In Fig.…”

“…Alternatively also frequency multipliers with differing multiplication factors can be used to implement a frequency shift of the radar's IF signal [8], but these solutions often operate at relatively high offset frequencies to avoid large multiplication factors. Examples for digitally generated frequency shifts are the systems based on switched on–off modulation [9] or in-phase/quadrature (I/Q) modulator-based single sideband (SSB) modulation [10, 11]. These systems offer the possibility of coherently operating radio frequency (RF) signal generation, modulation and analog-to-digital conversion.…”

“…Compared to [9] the proposed approach reduces switching harmonics by ΔΣ noise-shaping. Furthermore, the hardware setup is simplified compared to [10, 11] since no digital-to-analog converter (DAC) or I/Q modulator is required. Due to the latter, there is no need for calibrating possible I/Q imbalances.…”