Microwave near-field imaging of conducting objects of a simple geometric shape

We study imaging properties of a 90 GHz microwave scanning probe consisting of a thin slit aperture (width of 10-100 mu m) in the waveguide endwall. W e perform vector measurements of the near-field reflectivity of test sample s (conducting dot, strip, half plane, plane) at various probe-sample separa tions and orientations. Experimental results for small objects agree fairly well with analytical calculations and computer simulations and can be desc ribed by a quasistatic model. Experimental results for extended conducting objects show pronounced deviations from the quasistatic model due to excita tion of the surface waves. Our experimental results demonstrate several pec uliar features which have not been properly addressed in the context of nea r-field imaging, namely: (i) strong collimation of the fields away from the probe up to a distance equal to the probe width, (ii) very weak phase depe ndence on distance in the extreme near field, and (iii) excitation of surfa ce waves above conducting surfaces. (C) 2000 American Institute of Physics. [S0034-6748(00)01810-4].