Measuring the refractive index of materials with very low reflection coefficients at millimeter wavelengths

The dataset consists of one-port S-parameter measurements collected with the Keysight Technologies E8364C Programmable Network Analyzer (PNA) with an OML, Inc., V12VNA2-T/R millimeter wave Vector Network Analyzer (VNA) extender to operate in E band (60 - 90 GHz). A CustomMicrowave, Inc., Model RCH012R conical horn atnetnna is connected by waveguide to the VNA extender. An aperture in a layer of radar absorbing material (RAM) is used to reduce the radiated beam width; the absorbing material is RAM IS-005A manufactured by TDK RF Solutions, Inc. The materials are measured in free space placed atop a 30.5 x 30.5 cm aluminum plate. The assembly was set atop a breadboard attached to a Thorlabs Model MLJ 050 motorized vertical translation stage with 0.1 micrometer resolution. The S-parameter data is calibrated. The calibration used the aluminum plate for the short and offset short calibration standards, and a similarly-sized piece of RAM for the load. Calibration was done for two reference planes at the front and back of the samples. The one port S11 reflection coefficient frequency spectrum is transformed into the time domain locally in the VNA using Keysight's time domain option. Measurements were performed on cross-linked polyethylene (EPE 3 lb) of density 48 kg/m^3, and closed cell polystyrene (EPS 3 lb and EOS 1 lb) of density 48 kg/m^3 and 16 kg/m^3. The materials were manufactured with the nominal thickness of 7.5 cm, and cut to the dimensions of the metal plate. The derivation of the refractive index of the foams is described in Smith, P. R., J. C. Weatherall, and Barber, J., Measuring the refractive index of foam materials with very low reflection coefficients at milimeter wavelengths, in SPIE Proceedings 13028, pp. 235-241 (June 2024). Application is to the N42.59 standard for evaluating imaging performance of active millimeter wave Advanced Imaging Technology systems for security screening. s1p data file naming conventions: t2 Material time data in vicinity of reference plane: Time & Real & Imagt3 Material time data vicinity of reflection peak: Time & Real & Imagwo Time data without (wo) material Ancillary data:Lx = 7.573 +/- 0.026 (* ave EPS 1b thickness cm *)Lx = 7.593 +/- 0.040 (* ave EPS 3 lb thickness *)