Modelling and Test Setup for Sandwich Radomes
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Sandwich radomes are structures providing communication- and radar antennas with protection from the environment. The sandwich materials are designed to affect the electromagnetic radiation as little as possible with respect to transmission- and reflection loss, boresight error, boresight error slope, increased sidelobe levels and depolarization. In order to match the frequency response of the radome material to the specifications, simulation and optimization of the thickness and dielectric properties of the individual sandwich layers is done.To simulate the transmission- and reflection coefficients for sandwich materials a Matlab scripts has been developed. The script calculate the response for up to 10 different layers for incidence angles and frequencies defined by the user. Verification of the results has been done by comparing the simulated data to results in Kozakoff (2010) and show that the script works correctly.Waveguide measurement and calibration components have been designed and manufacturedin order to measure samples of dielectric materials and samples of complete radome sandwich materials. The results have been compared to results from simulations done in CST Microwave Studio and show a good match for complete sandwich materials and thicker dielectrics. However the measurement results for thin material samples show more deviation compared to the simulation results. The deviation seems to be dependent on the thickness of the sample.Two optimization routines have been developed in Matlab. The first compare the measuredresults from measurements to the simulated results from Matlab. Least square optimization is used to adjust the dielectric properties (relative permittivity and dielectric loss tangent) used by the simulation script in order to match the simulation values to the measured values. The results show good match of the optimized relative permittivity for a 22 mm thick sample of Teflon with the optimized value deviating 1.3% from the specified permittivity value. With decreasing thickness of the test samples the deviation increased to approximately 3-12%. The optimized loss tangent values however show very large deviation from the specified values and should be treated as invalid. The main reasons are believed to be the low loss of the materials combined with the thickness relative to the measurement wavelength.The second optimization routine adjust the thickness of the individual layers to achieveminimum loss for one- or more predefined frequency bands. The results show that theoptimization work as intended. To investigate the effect of production errors/productiontolerances the core thickness of an A-sandwich has been adjusted with +/-10% from theoptimized thickness. The result show that the thickness deviation has a bigger impact onhigh frequencies.