Errors associated with reflections can be suppressed.

The two-transmission method is an improved method of determining, from microwave measurements, the complex permeability and complex permittivity of a sample of a material typified by a lossy dielectric or a magnetic radar absorbing material. The two-transmission method is so named because it involves two microwave transmission- measurement runs: one on the sample alone and one on a two-layer stack comprising the sample plus a layer of an acrylic material that has known permittivity and permeability. The name of the two-transmission method also serves to distinguish it from a prior method that involves microwave-reflection measurements with which errors have been associated.

A Focus Arch can be used in the frequency domain in a prior method or in either the frequency or time domain in the present improved method.

In the frequency-domain variants in the waveguide laboratory setup, it is necessary to perform a through-reflect-line calibration of the waveguide apparatus that includes a holder in which the sample or the sample/acrylic stack is to be placed. The sample or the sample/ acrylic stack must be accurately machined to fill the holder to ensure that only the dominant waveguide mode is present. The S-parameters of the sample or the sample/acrylic stack are obtained from the network-analyzer measurements. Then the complex permittivity and permeability are extracted from the S-parameters by means of a suitable algorithm, which is typically based on equations known as the NRW formulas [wherein “NRW” signifies the surnames (Nicolson, Ross, and Weir) of the originators of the equations] that are well known to specialists in this art. The NRW formulas require transmission and reflection measurements. If, as in the two-transmission method, the NRW formulas cannot be used, then an iterative method such as a Newton two-dimensional root search is used.