Identification of multiple reflections in high frequency structures
Necessity of identifying reflections is not only an interest for engineers working at high frequencies. Engineers from other societies such as geophysics, mine-field detections and civil engineering are also concerned about the reflections. While in these fields mainly identifying the positions of the reflections is important rather than identifying the complete shape of the echoes.
However identifying the reflections has always been a remarkable concern in high frequency society and many studies in the literature have been devoted to this concern. Methods such as Time Domain Reflectometry (TDR), Frequency Domain Reflectometry (FDR) and time gating have been proposed. But most of the existing methods in the literature need definite assumptions to be able to identify the reflections. Assumptions are mainly on the magnitude of the reflections that should be moderate or low.
In our work not only we can identify reflections without those assumptions but also we can deal with multiple reflections. Multiple reflections occur when the incident wave traveling through the system reflects back and forth. The modeling strategy is based on using a finite sum of delayed damped complex exponentials (Cisoids) to obtain the initial values for the delays in the first step. Then each of the echoes is modeled with a common denominator rational model. This method can be applied to any structure that can be modeled as a mix of transmission lines and lumped elements shown in Figure 1. Where the lumped elements are the cause of the reflections and the transmission lines introduce the delay to the system.
Applying the method on measurement examples show that the order of the model remains reasonably low even for modeling large reflections in the price of devoting more delays to be able to estimate the complex reflections accurately.
In the next stage we will try to expand the model to a more complicated full rational model and hope that we will be able to model the same examples as before but with the less number of estimated delays.
 Identifying multiple reflections in distributed-lumped high frequency structures, Zyari.M & Rolain.Y. April 2016, IEEE Transactions on Microwave Theory and Techniques, Vol. 64,No. 4,pp.1306-1312