Reflectometer

A reflectometer is an instrument that measures the amount and characteristics of a signal that is reflected from a device, material, or interface. By comparing the reflected signal with the incident signal, it provides information about impedance discontinuities, refractive index contrasts, or surface properties. Reflectometry is used across radio frequency, microwave, optical, and fiber environments.

The basic principle involves sending a probe signal into a test port and detecting how much of it is reflected back. In time-domain reflectometry, a pulsed or short-duration source launches a signal and the detector records reflected echoes as a function of time, allowing the location and magnitude of discontinuities to be mapped along a transmission line. In frequency-domain reflectometry, a continuous or swept signal is used and the return loss or reflection coefficient is measured as a function of frequency to characterize impedance across a range of wavelengths.

Common types include time-domain reflectometers for cables and connectors, optical time-domain reflectometers for fiber optic cables, and frequency-domain or swept-reflectometry instruments for electrical networks. Optical reflectometers may also be used for thin-film and surface metrology, measuring film thickness, refractive index, and layer structure by analyzing reflected light spectra.

Applications range from quality control and fault finding in cables and networks to fiber-optic network commissioning, non-destructive testing, and material characterization. Key performance metrics include reflectance or reflection coefficient, return loss, dynamic range, resolution, and, in time-domain systems, spatial or distance resolution.