MEASURING MICROWAVE FIELDS DIRECTLY WITH AN OPTICALLY MODULATED SCATTERER

The modulated scatterer technique allows one to measure fine structure in electromagnetic fields with the minimum of perturbation. The authors present a general theory for the monostatic use of a modulated scatterer and show that in certain circumstances, for example in the reactive near-field of an antenna, the modulated scatterer may be used monostatically where conventional techniques would fail. They have verified the technique experimentally by constructing a broadbanded homodyne detector, working over the frequency range 2-18 GHz, and using it to measure scattering from an optically modulated electric dipole in the near-field of an open-ended waveguide. The modulating waveform is conveyed to the scatterer via a flexible plastic optical fibre, this provides a constant level of modulation as the scatterer is moved around, without introducing any conducting material into the neighbourhood of the scatterer.