K- and W-Band Free-Space Characterizations of Highly Conductive Radar Absorbing Materials

This work presents a characterization technique of highly conductive material in the K- and W-bands. The transmission line theory model is modified to adapt to the phase challenges observed in the measured S-parameters at high frequency. The S-parameters measurements are obtained using the nondestructive focused beam free-space system connected with the network analyzer and the millimeter-wave frequency extenders. The system provides measurements in a frequency range from 5.8 to 110 GHz, and it includes focused beam horn lens antennas to minimize sample edge reflection. The thru-reflect-line (TRL) calibration and the time-gated feature of the network analyzer are used. Good agreement between the measured and calculated S-parameters in the transmission mode is achieved using the extraction algorithm. The measured S-parameters are further used to obtain the electromagnetic shield effectiveness parameters and the percentage of power absorbed in the material. In addition, the return loss of the metal-backed material is calculated using the extracted permittivity to obtain the maximum absorption at the desired frequencies.