Multiple Reflection Reduction in mm-Wave Antenna Characterization Using Scattering Caps

Multiple reflections, particularly between the probe and the antenna under test, degrade measurement accuracy. Conventional absorber-based mitigation techniques lose effectiveness above 100 GHz, and their large size cause them to extend undesirably close to the antenna aperture. Perturbing impedance and radiation pattern measurements. In this study, we analyze the contributions of these multiple reflections and reintroduce a metal flange cover, e.g., ‘scattering cap,’ to mitigate the errors introduced by such reflections and with it, improve the measurement system. The design methodology is presented and validated across three frequency bands within 26–330 GHz using simulations, for probe geometries including open-ended waveguides and horn antennas. Its effectiveness is experimentally evaluated for near- and far-field measurements with an open-ended waveguide probe antenna alongside various types of electromagnetic absorbing materials in the 90–140 GHz frequency band. However, whereas carbon based absorbers typically degrade and inconsistently affect the probe antenna behavior, the scattering cap does not. The scattering cap reduces standing-wave ripples in near-field measurements from 1.3 dB to 0.5 dB peak-to-peak, representing a reduction of more than 60%. The proposed scattering cap provides an effective, cheap and easy-to-manufacture solution with wideband applicability to reduce multiple reflections, making it highly suitable for accurate and consistent antenna measurements.