Spatial mapping of the near-field radiation pattern of a 7-GHz planar resonator

Planar-radiating resonators have gained increasing interest for applications in the mm-wave region. The design of such resonators must avoid excitation of parasitic surface waves or undesired patch or microstrip modes. For the characterization of the mm-wave oscillators, this paper uses external substrate-independent electro-optic (EO) detection. for a spatial mapping of the near-field radiation pattern directly above the device under test (DUT) with a high spatial resolution of 10 μm and a high bandwidth up to 150 GHz. Measurements and calculations for various frequencies and heights will be discussed. Both changes in the spatial distribution and the amplitude are observed during tuning through the fundamental resonance at 6.7 GHz. The evolution of the radiation pattern from the near-field to the far-field mode is traced.