Optimization of Near-Field Image Capture With Millimeter-Wave Bow-Tie Probes

Near-Field Millimeter Wave Vector Measurements -- Experimental Design & Measurement Interpretation

“…1 with its central element for the vector output: the subharmonic IQ mixer which operates at zero intermediate frequency in the band 55-65 GHz. Compared to our previous intensity reflectometer [24], the whole mmW transmitting/detecting system has changed and now uses an HF synthesizer followed by multiplication chains for the detection and LO signal. In the measuring path, an active ×4 multiplier delivering 10 dBm is used in the front of a 3 dB coupler which returns the reflected signal at the input of the mixer.…”

“…As in [24], probes are homemade bow-ties attached to a WR15 open end. Metal triangles used for the bow-tie were produced using fs-laser cut on a 10 µm thick tungsten sheet.…”

“…Beyond that, the decrease in intensity is huge for sinusoidal modulation, which generates those high harmonics only by the nonlinear probe-to-sample interaction caused by the rapid decrease of intensity in the near-field. This peculiarity of probe-to-sample interaction is often used to improve the spatial resolution [24], [30], [31]. For other modulation waveforms, higher harmonics are less attenuated, especially in the case of square modulation.…”

“…Although most of near-field experiments in the mmW have focused on intensity measurements [6], [17], [21]- [24], local vector characterization is necessary to distinguish material changes from loss changes. Many such experiments have recently been proposed in scattering-type scanning near-field optical microscopy (s-SNOM) applied to the THz domain [25]- [28], but only the latter seems to be easy to translate to mmW.…”

“…Many such experiments have recently been proposed in scattering-type scanning near-field optical microscopy (s-SNOM) applied to the THz domain [25]- [28], but only the latter seems to be easy to translate to mmW. We do the same transformation on our 60 GHz test bench [24] and chose to include a subharmonic IQ mixer to simultaneously detect the two quadratures of the reflected field, but we kept a complete waveguide configuration. This paper details the new experiment and elaborate the required processing of experimental signals in order to determine without systematic error and with reasonable accuracy the vector voltages and reflection coefficients related to the nearfield probe-sample interaction.…”