The test and evaluation of absorbers and the materials we use in designing and constructing them depends on the information needed. To design absorbers, we need to know the intrinsic properties of the materials we hope to use, whether they already exist or we cook up new batches to test. The determination of those parameters generally requires the use of enclosed test systems in the form of transmission lines, cavities or interferometers, or admittance tunnels. We emerge from such tests with characterizations of bulk permeability and permittivity or, in the case of thin sheets, the sheet admittance or impedance. We noted that sheet materials are not easily measured in transmission-line systems, and in the case of bulk materials, we must ensure that the sample is reasonably homogeneous throughout the small sample we insert in our sample holder.

Chapter Contents:

• 9.1 Overview
• 9.2 Transmission Line Theory
• 9.2.1 Basic Relationships
• 9.2.2 TEM Lines and Waveguides
• 9.2.3 Sample Holders
• 9.3 Transmission Line Measurements
• 9.3.1 Open- and Short-Circuit Measurements
• 9.3.2 The Network Analyzer and the Scattering Matrix
• 9.3.3 Time-Domain Reflectometry
• 9.4 Free-Space Methods
• 9.4.1 The NRL Arch
• 9.4.2 The RCS Method
• 9.5 Other Methods
• 9.5.1 Large Waveguides
• 9.5.2 Interferometers
• 9.5.3 The Admittance Tunnel
• 9.6 Summary
• References

Inspec keywords: permeability; permittivity; interferometers; radar absorbing materials; transmission lines

Other keywords: intrinsic properties; admittance tunnels; sheet impedance; transmission-line systems; cavities; thin sheets; bulk permeability; absorber design; radar absorber measurement techniques; sheet admittance; bulk permittivity; bulk materials; interferometers

Subjects: Microwave materials and structures; Radar equipment, systems and applications