Calibration-Based Phase Coherence of Incoherent and Quasi-Coherent 160-GHz MIMO Radars

Abstract

Imaging radars are usually realized fully coherently. However, the distribution of one common radio frequency signal to all transmit and receive paths requires a high degree of hardware complexity. In order to reduce the hardware effort significantly, a novel phase synchronization method for incoherent and quasi-coherent frequency-modulated continuous-wave (FMCW) imaging radars with individual signal synthesis per channel is presented. The quasi-coherent setup uses one common oscillator for all frequency synthesizers. It is shown that in the case of the quasi-coherent system, only a phase difference between the calibration and the measurement has to be corrected to achieve coherence. In comparison, an incoherent system causes additional time, frequency, and FMCW ramp slope errors due to the different behavior of the oscillators. In order to achieve phase coherence and to correct the error sources, a calibration-based method using a defined signal path as part of the radar system is proposed. The imaging radar used for verification of the theory consists of individual single-channel radar monolithic microwave integrated circuits (MMICs) at 160 GHz; each MMIC fed by an individual frequency synthesizer. As shown by measurements, it is possible to achieve phase coherence for both system approaches and to perform angle estimation.

Range-Angle Coupling and Near-Field Effects of Very Large Arrays in mm-Wave Imaging Radars

“…In order to realize a MIMO system with an electrically large aperture, signal coherency must be guaranteed across the whole aperture [20]. This is particularly challenging at higher frequencies and comes with an increased hardware effort.…”

“…However, for large apertures, high losses of the distributed signal aggravate a coherent LO distribution concept. Signal coherency can also be achieved for incoherent signal synthesis by using a parasitic coupling path of the radar system [20]. Alternatively, phase synchronization between incoherent signals can be achieved by a joint processing of all bistatic TRx pairs (i.e., TX i RX j and TX j RX i , i = j ) and the generation of a synthetic beat signal [22].…”

“…8(a) and (b). The radar incorporates single-channel radar MMICs using separate integrated on-chip antennas both for the TX and RX signal path [20], [27]. The aperture is dividable in two identical eight-channel subarrays, which are itself not much affected by the range-angle coupling and the NF influence.…”

Coherent Automotive Radar Networks: The Next Generation of Radar-Based Imaging and Mapping

“…Synthetic coherence of the carrier phase can also be established by correction of the unknown initial phases [29], [30]. This method can be used with reference targets or reflection at a dielectric lens [31], [32].…”

OFDM-Based Radar Network Providing Phase Coherent DOA Estimation

“…In addition, while the impact of phase noise at near ranges in monostatic radar evaluation is suppressed by range correlation [8], this is not the case for incoherent networks [9]. Phase coherency can be achieved by distributing a joint radio frequency (RF) signal to the different radar nodes [10], which results in a costly RF link, or by synchronizing the signal sources of different radar sensors [11]. However, this synchronization approach does not only result in a more complex topology by means of a distribution of the synchronization signal.…”