Radar, like a bat in a cave, sends out a pulse and listens for the echo. But a microscopic imbalance in the receiver is unavoidable: it scrambles frequencies and creates a phantom twin for each target, like a second, slightly distorted echo.

Usually, these phantoms just get in the way and are cleaned up beforehand. In this new work, ghost echoes become an ally. Each real target and its twin are tightly linked, like a figure and its shadow. Scientists built an algorithm that, for any point in space, cycles through all possible 'target-phantom' pairs, comparing them through a special mathematical pattern. This makes it easier to spot faint objects — even when receiver distortions are large.

The method was tested in simulations. Surprisingly, the more noticeable the hardware defect, the more reliably the algorithm works, because the phantoms become brighter. This approach is a step toward systems that simultaneously transmit data and scan the surroundings (ISAC). In spirit, it resembles the search for dark matter by its invisible influence or teasing out gravitational waves from noise. At its core lies signal spectroscopy — breaking down frequencies, without which radar would remain blind.