Complex-Valued Signal Recovery in Interferometric Electron Paramagnetic Resonance Spectroscopy

Magnetic resonance spectroscopy is widely used in biomedical research, and electron paramagnetic resonance (EPR) is part of this toolbox as a microwave technique that probes unpaired electrons in an external magnetic field. Broadband EPR spectrometers are particularly valuable for studying frequency-dependent effects. Interferometric detection offers a high usable dynamic range for broadband EPR spectroscopy but can distort the absorptive and dispersive line shapes through residual amplitude and phase imbalances. We show that this behavior can be understood in the complex plane and corrected by a post-processing rotation. The resulting method restores the physical EPR signals without additional hardware or measurement time, enabling robust broadband EPR measurements.