Environmental Engineering Reference
In-Depth Information
Chapter 3
Broadband Reflectometry: Theoretical
Background
'A scientist's aim in a discussion with his colleagues is not
to persuade, but to clarify'.
Leo Szilard
Abstract. In this chapter, the basic approaches of broadband microwave reflectome-
try are described in detail. More specifically, time domain reflectometry (TDR) and
frequency domain reflectometry (FDR) are presented and the involved instrumenta-
tion is fully described. Successively, the FDR/TDR combined approach is described
in detail: this approach can help exploit the benefits of both TDR and FDR, without
necessarily employing two different measurement setups. Additionally, since the
sensing element (or probe) plays a major role in all the aforementioned approaches,
a comprehensive description of its design and of the corresponding performance is
given. Finally, the basic principles leading to the possibilities of enhancing accuracy
in BMR measurements are presented.
3.1
Broadband Microwave Reflectometry: Theoretical
Background
Broadband microwave reflectometry (BMR) is a powerful technique that can be ef-
fectively employed for a number of practical applications; in particular, the high ver-
satility, the real-time response and the potential for practical implementation have
contributed to the success of microwave reflectometry for monitoring purposes.
Generally, in BMR, a low-power electromagnetic signal is propagated into the
system under test (SUT): the analysis of the reflected signal along with specific
data-processing are used to retrieve the desired information on the SUT [32].
Two main elements are involved in BMR measurements:
1. the instrument for generating/receiving the electromagnetic (EM) signal, and
2. the measurement cell, which includes the sensing element (or probe) and the
SUT.
Microwave reflectometry-based measurements can be performed either in time do-
main (time domain reflectometry - TDR) or in frequency domain (frequency domain
 
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