Millimeter apparatus for transmission line and dielectric material measurements by multifrequency methods

It is important to measure not only total reflection coefficient (RC) but the distribution of discontinuities in transmission lines. Frequency dispersion makes it difficult to apply direct time-reflectometry in millimeter waveband waveguides. That is why it is more preferable to measure RC at a set of frequencies and transform experimental data from frequency to time domain using one of the spectral numerical algorithms. Equidistant wave-number sampling allows one to overcome frequency dispersion. Simplicity of a scalar reflectometer (SR) application is very attractive. Such modification of SR as comparison reflectometer measuring the sum of reference reflection and reflection of the device under test (DUT) can be used to obtain the distribution of discontinuities as a result of the transformation into time domain. The sum of exponentials is the general model for not only the distribution of discontinuities in waveguides but also the distribution of interfaces of layers in dielectric materials. Peculiarity of the latter task is positioning materials not in a waveguide but in free space. The authors describe the principles of an original six-port method and the scalar reflectometry, and present some experimental results.