Characterization of Microwave Absorber and Frequency Selective Surface (FSS) in Time Domain: A new Approach

The characterization of RF/Microwave absorbers or Frequency Selective Surface i.e. FSS over a wide band always a challenging task for their course of development. Electrical circuit equivalent of RF absorber is an attenuator, where the input reflection coefficient and insertion loss are the main parameters of interest. Whereas for FSS of electromagnetic domain the electrical equivalent is band pass filter, and the parameters of interest are same reflection coefficient and insertion loss but, both in pass, and stop bands. Thus, for both whether microwave absorber or FSS the reflection (Γ, Greek capital Gama) and transmission coefficient (T, Greek capital Tau) are the primary parameter for their electrical characterization. The measurement setup in frequency domain with precisely positioned antennas is widely used for these kinds of measurements. The advantages of time domain method over the frequency domain are many and it is very fast. A detail theoretical development and its engineering implementations are described in this paper. Measurement setup and the results are also presented in detail.