Complex dielectric permittivity measurements of materials in millimeter waves

Complex dielectric permittivity data of common materials at Q-, V-, and W-band frequency ranges have been presented. The measurements have been performed using a free-space quasi-optical millimeter wave spectrometer equipped with a backward-wave oscillator as a tunable source of coherent radiation. Frequency dependences of real and imaginary parts of the dielectric permittivity have been calculated from the transmittance spectra. We discuss the prospective application of millimeter wave and terahertz imaging and spectroscopy for homeland security needs.