Infrared near-field microscopy can be used to analyze the local field of photonic structures. Near-field images of a resonant (verified by far-field spectroscopy) infrared antenna exhibit the clear signature of a dipolar oscillation mode on the Au rod. Note that the probing tip preferentially selects the z-component (normal to the sample surface) of the optical field. The amplitude image exhibits a high signal at the rod ends which are 180° out of phase. If the antenna structure is modified by e.g. a cut at the centre of the Au rod (fabricated by FIB), the near-field images reveal two dipolar oscillation modes on the segments. Systematic studies allow to analyze the coupling between the segments and to characterize the optical properties of the antenna structures. Polarized measurements allow to filter out specific components of the optical field associated to photonic structures or devices and to investigate the field e.g. in the antenna gap.