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This paper explores the use of a microwave-reflectometry- based system for the automatic control and real-time monitoring of the flow and of the liquid level in intravenous (IV) medical infusions. In medical and hospital contexts, other kinds of devices, mainly based on the optical detection and counting of the infusion drops, are used. Nevertheless, the proposed system is aimed at circumventing some typical drawbacks deriving from the adoption of these traditional methods, thus allowing an efficient alternative for automatically monitoring the instantaneous flow of IV medical solutions. To this purpose, the proposed system combines microwave time-domain reflectometry (TDR) measurements with a noninvasive sensing element (i.e., strip electrodes directly attached to the external surface of the infusion bottle). Experimental results confirm that, by using low-cost portable TDR devices, the solution flow process can be controlled with acceptable accuracy. Therefore, the proposed method can be regarded as a promising control tool for in-hospital patient management as well as for telemedicine programs.

Time domain reflectometry (TDR) is commonly used for several monitoring applications, particularly in hydrology and soil science for soil water content evaluation. Furthermore, significant advantages of TDR methodology, such as its relevant performance characteristics in terms of high flexibility and high sensitivity, as well as a non-destructive detection approach, render this technique an appealing candidate for a variety of environmental and industrial applications. In a previous paper [A. Cataldo, L. Tarricone, F. Attivissimo, A. Trotta, Simultaneous measurement of dielectric properties and levels of liquids using a TDR method, Measurement, doi:10.1016/j.measurement.2006.11.006 ] the authors demonstrated that TDR can be successfully used for a simultaneous real-time qualitative and quantitative monitoring of liquids. In this paper, a rigorous metrological characterization of the proposed method is formulated, and the uncertainty contributions are identified. The obtained results, confirm that the system is definitely adequate for simultaneously measuring dielectric constants and levels of liquids, with the associated relative uncertainties of 2% and 3%, respectively, for all the considered liquid samples. This way, challenging perspectives for several monitoring applications are open, especially in the processing of industrial liquids.

Six-port reflectometers have traditionally employed hybrid couplers as their building blocks, but the instruments reported thus far in the literature do not comply with the optimum design specifications. This paper describes a six-port reflectometer based on four-port coplanar-waveguide couplers that have been modified so as to meet such design requirements. Additional design parameters have been incorporated so that adjustments may be made to correct for residual hardware imperfections. Laboratory tests have confirmed an operating bandwidth of 90% (from 1.1 to 2.9 GHz) for the resulting reflectometer.

Time-domain-reflectometry (TDR) measurements, which were originally used to locate and diagnose faults in transmission lines, have been widely applied in geology and soil science for accurate and flexible measurements of soil moisture and water content. Furthermore, the most attractive advantages of TDR rely on the possible determination of the spatial location and nature of various objects, both in real time and with a nondestructive approach. This makes the TDR technique an appealing candidate for a variety of environmental and industrial applications. Although the TDR instruments are commonly used to date, particularly for the aforementioned purposes, the state of the art is rather lacking in liquid-monitoring applications. This paper describes how the suitable combination of TDR detecting functionalities can lead to a simultaneous monitoring of quantitative and qualitative properties of liquid samples. In fact, the proposed TDR method allows, in one shot, the measurement of liquid levels, the determination of multiple interfaces in layered media, and the evaluation of dielectric properties such as dielectric permittivity or electrical conductivity. Some applications to real cases are proposed, which are referred to petrol–chemical mixtures or water-based liquids, thus validating the approach on a wide range of materials.

Build-up of surface contamination on high voltage insulators can lead to an increase in leakage current and partial discharge, which may eventually develop into flashover. Conventional contamination level monitoring systems based on leakage current, partial discharge, infrared and ultraviolet camera are only effective when the contamination layer has been wetted by rain, fog or condensation; under these conditions flashover might occur before there is time to implement remedial measures such as cleaning. This paper describes studies exploring the feasibility of applying microwave reflectometry techniques to monitor insulator contamination levels. This novel method measures the power generated by a 10.45 GHz source and reflected at the insulator contamination layer. A theoretical model establishes the relationship between equivalent salt deposit density (ESDD) levels, dielectric properties and geometry of contamination layers. Experimental results demonstrate that the output from the reflectometer is able to clearly distinguish between samples with different contamination levels under dry conditions. This contamination monitoring method could potentially provide advance warning of the future failure of wet insulators in climates where insulators can experience dry conditions for extended periods.

The optimum-performance criteria originally developed for use with six-port reflectometers may, under certain circumstances, be extended to the design of the multistate reflectometer (which utilizes two power detectors to measure the reflection coefficients of microwave components). Test results-from simulations as well as experiments-have confirmed that the novel WR90 multistate instrument proposed in the present paper is able to yield near-optimum performance over the entire waveguide bandwidth.

In this paper, a time domain reflectometry (TOR)based system for the non-invasive localization of leaks in underground pipes is described and experimentally validated. The proposed system simply relies on TOR measurements performed on a two-wire cable (biwire) that is rolled out on the underground pipe at the time of installation of the pipe (but made accessible from the road surface through an inspection well); the biwire on the pipe acts as a permanent, distributed sensing element and can be connected to the TOR instrument whenever it is necessary to perform a check. Two of the major advantages of the proposed system are that it can be employed with pipes made of any material and that it strongly reduces the inspection time typically required by traditional leak detection methods. To validate the system and to assess its performance, a new pipe was installed and a leak condition was intentionally provoked at a reference position. The TOR system was then used to evaluate the position of the leak as if had been unknown. The results of this experimental test are reported and thoroughly discussed.

An automatic method for self-calibrating six-port reflectometers is reported in this paper. It is based on the use of an active impedance synthesis system. This self-calibration method allows a completely autonomous operation, reduces measurement errors caused by the frequent connecting and disconnecting of calibration standards, and is suitable for low and high frequencies, where sliding shorts are difficult to manufacture. In addition, it simplifies operation of six-port reflectometers to nonspecialized users. The experimented impedance synthesis presented relies on an in-phase and quadrature vector modulator, and the entire system is computer controlled.

This article explores the use of a microwave reflectometry-based system for the automatic control and real-time monitoring of the flow and of the liquid level in intravenous medical infusions. In medical and hospital contexts other kind of devices, mainly based on the optical detection and counting of the infusion drops, are used. Nevertheless, the proposed system is aimed at circumventing some typical drawbacks deriving from the optical sensing, thus allowing an efficient alternative solution for automatically monitoring the instantaneous flow of intravenous medical solutions. To this purpose, the proposed system combines microwave time domain reflectometry (TDR) measurements with a non-invasive sensing element (i.e.: strip electrodes directly attached to the external surface of the infusion bottle). Experimental results confirm that, by using low-cost portable TDR devices, the solution flow process can be accurately controlled. Therefore the proposed method can be successfully adopted as a promising control tool for in-hospital patient management as well as for telemedicine programs.

In this chapter, the basic concepts behind broadband microwave reflectometry (BMR) are recalled. First, a brief overview of the transmission line theory is provided, and the most common electromagnetic structures are introduced. Secondly, the major parameters that are used to characterize electrical networks are introduced, and the related theoretical background is briefly discussed. Finally, a short overview on dielectric spectroscopy is provided, thus anticipating its connection with reflectometric measurements. © 2011 Springer-Verlag Berlin Heidelberg.

Reflectometry is a powerful technique that can be effectively employed for a number of practical applications; in particular, the high versatility, the real-time response, and the potential for practical implementation have contributed to the success of microwave reflectometry for monitoring purposes. In this regard, this paper provides a survey of the current state of the art of reflectometry-based methods for diagnostics and monitoring applications. After a brief overview of the theoretical principles at the base of this technique, the different approaches of microwave reflectometry (time domain, frequency domain, and combined approaches) are fully discussed; particular attention is given to the strategies for enhancing measurement accuracy. Finally, the major practical applications of reflectometry and related results are discussed, thus evidencing current achievements, limitations, and potential. © 2010 IEEE.

In this chapter, the basic approaches of broadband microwave reflectometry are described in detail. More specifically, time domain reflectometry (TDR) and frequency domain reflectometry (FDR) are presented and the involved instrumentation 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. © 2011 Springer-Verlag Berlin Heidelberg.

This paper derives the TRL and LRM calibration algorithms using S-parameters instead of the traditional T-parameters. The advantage of this approach is that they do not need separate solutions. Instead LRM becomes an integral part of the TRL algorithm. The expression for the transmission coefficient of the line standard has the surprising property that in many cases the transmission coefficient is obtained directly without a need for a root choice.

Antenna-characterization measurements are traditionally performed in the frequency domain (FD) through a vector network analyzer (VNA) in an anechoic chamber. Nevertheless, the high cost of the required setup strongly limits the possibility of using this approach. Starting from these considerations, a time-domain (TD)-based approach for characterizing antennas without using an anechoic chamber is assessed. As a matter of fact, instruments operating in TD are usually less expensive than VNAs; nevertheless, with appropriate data processing, they provide as much information. Particularly, it is demonstrated that the selection of an optimal time windowing is the main factor that guarantees a high accuracy level in the corresponding FD. The proposed approach leads to the accurate evaluation of the reflection scattering parameter S 11 (f) from time-domain reflectometry (TDR) data. The experimental validation is tested on a commercial radio-frequency identification (RFID) reader antenna, and the results are compared with reference VNA measurements performed in an anechoic chamber. The ultimate goal of this paper is to demonstrate that, through calibrated TDR measurements, along with an optimal time windowing, an accurate antenna characterization can be achieved. © 2008 IEEE.

Several techniques for measuring the moisture levels of materials, particularly in the soil science area, are available. Nevertheless, the state of the art is rather lacking in moisture-sensing methods that are both inexpensive and noninvasive. The time-domain reflectometry (TDR)-based method, despite being a well-established low-cost technique for sensing moisture content, is intrinsically invasive due to the configuration of the probes that are commonly used. These considerations motivated the authors to investigate the adoption of simple inexpensive microstrip antennas as sensing elements for TDR-based moisture content measurements. For this purpose, the water content of the monitored material is sensed through the changes in the reflection scattering parameter S 11 (f) of the antenna. In particular, the change in the resonant frequency of the antenna, which is evaluated through an appropriate processing of the TDR waveforms, is correlated with the water content of the material under investigation. The ultimate goal is to assess a sensing method that can be implemented for inexpensive real-time noninvasive monitoring applications. © 2009 IEEE.

Measurement and control of the dielectric parameters of liquids play a major role in industrial quality-control applications. Although several techniques are currently available to this aim, none of them is simultaneously accurate, cost-effective, and reasonably quick. On the other hand, reflectometry has become a very attractive method for monitoring applications, mostly thanks to its accuracy and flexibility. In this paper, a combined method based on time-domain reflectometry (TDR) and frequency-domain (FD) analysis is presented: the aim is to substantially improve the measurement accuracy of the dielectric parameters of liquids. Starting with typical TDR measurements, the associated FD evaluation of the dielectric parameters is considerably enhanced through the combined effect of the following: 1) specific data-processing techniques; 2) the implementation of a calibration procedure; and 3) the final modeling and minimization routine. Furthermore, to definitively assess the proposed combined procedure, results are compared with measurements directly performed in the FD through a vector network analyzer (VNA). The ultimate goal of the work is to pave the way for the adoption of inexpensive and portable TDR devices in practical industrial monitoring applications.

Different approaches and techniques are commonly available for the continuous monitoring of moisture levels and dielectric properties of materials; typically, related applications, are largely used in soil science area. Nevertheless, the state of the art is actually rather lacking in specific sensing methods that combine the low cost and the non-invasive approach of the involved instrumentation. To fill this gap, in this paper the authors study the feasibility of the adoption of the time-domain reflectometry analysis for such purposes, using a patch antenna as sensing element. This way, the extrapolation of the scattering parameters is suitably correlated to the water content levels of the materials under test. Furthermore, the adopted methodology is assessed through full-wave simulations, thus corroborating the experimental measurements. ©2008 IEEE.

Traditionally, antenna characterization measurements are performed in the frequency-domain through a Vector Network Analyzer (VNA) in anechoic chamber. Nevertheless, the expensiveness of this set-up prevents itfrom becoming widespread in laboratories. On such bases, in this paper a time-domain-based approach is comparatively investigated; such a method virtually makes the anechoic chamber unnecessary, thus dramatically reducing the related costs. The proposed approach, based on the evaluation of the scattering parameter (S 11) from Time Domain Reflectometry (TDR) data, has been tested for the characterization of a commercial Radio Frequency Identification (RFID) reader antenna. Data acquired in the time-domain are processed in the frequency-domain through a dedicated algorithm, thus allowing the S11 extrapolation. Furthermore, results are compared to VNA measurements performed in an anechoic chamber. In order to assess the investigated method, from a metrological point of view, the root mean square error between the results is reported as a figure of merit. This way, it is demonstrated that calibrated time-domain measurements represent an alternative, inexpensive and accurate method for characterizing antennas. © 2008 IEEE.

This paper presents two new structures for four-port-based systems with ultrawide operating bandwidth, using a combination of power dividers and delay lines. The prototype circuits, initially conceived to operate in the frequency band from 1 to 4 GHz, are fabricated to validate these new architectures by means of a hybrid integrated-circuit technology. Associated with these systems, a new explicit calibration solution is developed to extend the frequency band of use up to 10 GHz. Comparison between the results obtained from the new structures with those given by a conventional network analyzer show the validity of the systems proposed.

This paper describes the use of the microwave techniques of time domain reflectometry (TDR) and de-embedding in an acoustical application. Two methods of calibrating the reflectometer are presented to evaluate the consistency of the method. Measured and modeled S-parameters of woodwind instruments are presented. The raw measured data is de-embedded to obtain an accurate measurement. The acoustic TDR setup is described.

The LRR method (Line, Reflect) and the extended LNN method (Line, Network) for the calibration of 4-channel-network analyzers are presented. These self-calibration procedures have the advantage that the calibration circuits are all of equal mechanical length in contrast to the well-known TRL method (Through, Reflect, Line). The TRL method needs a line-standard with a different length than the other calibration standards. For the LNN and LRR method it is thus not necessary to displace the connectors of the vector network analyzer during calibration in order to contact the calibration structures. The LNN and LRR calibration standards consist of objects which have to be placed at three consecutive positions. While the LNN obstacles have a transmission, the LRR obstacles are realized as reflective networks. In addition to the known LNN procedure all extended theory is presented here which accounts for different distances between the obstacles. The circuits are thus easy to realize. Measurement results are presented in order to verify the robust functionality of the methods.

A Time-Domain-Reflectometry (TDR) characterization technique has been investigated to enhance the detection of discontinuities in packaging and PCB structures. Three groups of test vehicles have been fabricated, on which special features were purposely introduced. From the locations of these special test features, the detection of discontinuities was improved significantly.

Combined differential-mode and common-mode (mixed-mode) scattering parameters (S-parameters) are well adapted to accurate measurements of linear networks at RF and microwave frequencies. The relationships between standard S-parameters with two-port vector network analyzer (VNA) and mixed-mode S-parameters with four-port VNA are derived in this paper. An example differential structure was measured with standard two-port VNA and mixed-mode four-port VNA. The correlation of standard s-parameters and mixed-mode S-parameters is presented as well.

The five-port reflectometer has been recently applied to demodulators and radars, offering an alternative to classic In-Phase/In-Quadrature (I/Q) discriminators. In these applications, calibration of the reflectometer is an important task. Most of the methods developed are suitable for the instrumentation and measurement field and present a high degree of complexity. We propose in this paper a new method for calibrating six or five-port reflectometers. This procedure is advantageous for its simplicity and is particularly useful for calibration in manufacturing processes.

The conditions of bad conditionality of system of the measuring equations of the 12-polar microwave converter are found. Requirements to the measuring microwave converter which observance guarantees reception of correct results are formulated.

A newly developed method allows dual 6-port ANAs to be calibrated with a single, known one-port termination instead of air line standards. This technique is especially useful for low frequency calibrations below 30 MHz where air lines cannot be adequately characterized.

This paper presents a new structure for a six-port reflectometer which due to its simplicity can be integrated very easily in MMIC technology. It uses non-matched diode detectors with a high input impedance that are placed around a phase shifter. The circuit has been fabricated by the foundry GEC-Marconi and operates between 1.4 and 2.5 GHz.

Testing active antennas or polarimetric radar calibrators in the far-field (plane wave excitation) is complicated by imperfect isolation between transmitting and receiving channels. We describe a far-field reflectometry setup which overcomes this problem. A large dynamic range is achieved by modulating the active element bias and using a quadrature receiver and lock-in detection scheme. Measured results compare favorably with other existing techniques. >

Although the automated vector network analyzer (ANA) was introduced to the microwave community more than two decades ago, the accuracy assessment of these devices has been a continuing challenge to the national metrology laboratories. The application of a multi-state two-port to this problem has generated a large amount of interest. This paper reviews this development and outlines additional applications for this technology. >

A more efficient implementation of an earlier four-standard calibration procedure for six-port reflectometers (utilizing simple iteration computations instead of other more cumbersome optimization techniques) is presented. Test results show that the calibration software that has been developed is capable of yielding reasonably good accuracies even in the presence of measurement noise. >

Dual six-ports, and other network analyzers that can be treated as mathematically equivalent to dual vector four-ports, are commonly calibrated by the TRL (through-reflect-line) method or one of its variants. The use of unknown one-ports for calibration with this method, and also for super-through-short-delay, an extension of the TRL method. is discussed. >

This paper describes a calibration technique for sixports which incorporates diode non-linearity as part of the calibration procedure of the sixport itself. The calibration is based on five unit reflection standards and relaxes the constraint that all the denominator constants of the bi-linear transform have to be the same. This is to first order, a consequence of the nonlinearity of the diodes.

This paper describes a calibration technique for the dual six-port automatic network analyzer which has different sexed connectors on the test ports. It is based on the thru-reflect-line (TRL) technique, and can give some redundancies in calibration procedure and calibration constants for any combination of the test ports.

The thru-attenuator-x (TAx) family of calibration techniques has been implemented for a two-port optical test set. A wide variety of results demonstrating the good performance of these techniques applied to optical components are presented.

A new design approach for low-cost multiprobe reflectometers is presented. While traditional circuits adopt equally-spaced probes, the presented solution provide a method to greatly enhance the bandwidth of the measuring system by a proper choice of each probe position. As example, a five-probe 0.6-16 GHz system has been designed.

A complete six-port network analyser is proposed that makes use of a single reflectometer. The proposed configuration employes a precision attenuator which dispenses with connections and disconnections with calibration standards, needs no inversion of the two-port device under test for measuring the transmission parameters and as its main feature, avoids the use of switches which are always present in the traditional configurations described in the literature. Its calibration and measurement procedures are also described.

This paper presents two antenna polarimetric calibration methods. One is to use a multi-mode TRL calibration method. This method is generalized from the conventional TRL method, hence its operation bandwidth is limited. The other one is the "TRR (thru-rotation-reflector)" calibration method. This method uses one antenna to rotate along the propagation axis with an unknown angle. It has no limitation on the operation bandwidth.

The complex reflection coefficient measurement by a multiport network analyzer with high precision and calibration precision control is presented. The authors consider a measurement method which permits one, under certain conditions, to make a calibration on one input as well as measurement on other input thus enabling the measurement in a compatible frequency band of the parameters of devices with different types of connectors.

Vector network analyzers represent an indispensable instrument for the design and fabrication of microwave circuits. Classic cumbersome analyzers comprising heterodyne receivers can be replaced by simpler instruments called reflectometers. The paper deals with calibration of a multistate reflectometer. It reviews the current state of the art and presents a new method that requires only three fully known standards.

A novel method for calibrating six-port based wave-correlators is reported in this paper. The calibration procedure uses only one phase shifter and offers simple formulas for determining the calibration parameters. Some experiments using a new six-port junction for the wave-correlator at X-band frequency was carried out and the results confirmed the validity and accuracy of the proposed method.

We have improved our existing Source-Pull/Load-Pull setup to allow independent active tuning, both at fundamental and second harmonic frequency, of the load and source impedance of the device-under-test (DUT). We will present experimental results to validate the calibration procedure and to show the accuracy of the measurements.

In this paper, a new theoretical analysis of the four-standards line-reflect-reflect-match (LRRM) vector network-analyzer (VNA) calibration technique is presented. As a result, it is shown that the reference-impedance (to which the LRRM calibration is referred) cannot generally be defined whenever nonideal standards are used. Based on this consideration, a new algorithm to determine the on-wafer match standard is proposed that improves the LRRM calibration accuracy. Experimental verification of the new theory and algorithm using on-wafer calibrations up to 40 GHz is given.

A new design approach for low-cost multiprobe reflectometers is presented. While traditional circuits adopt equally spaced probes, the solution presented here provides a method to greatly enhance the bandwidth of the measuring system by a proper choice of each probe position. As an example, a five-probe (1-16) GHz reflectometer was designed and the measurement results compared to those obtained with commercial vector network analyzers.

A newly developed method allows dual six-port automatic network analyzers (ANA's) to be calibrated with a single, known one-port termination instead of air line standards. This technique is especially useful for calibrations below 30 MHz, where air lines cannot be adequately characterized. The choice of the value of the standard is also discussed.

A simple technique for measuring the efficiency of adapters with losses less than 2 dB is described. The technique is useful in microwave applications where a moderate error in the measured loss is acceptable. This error is less than 10% of the loss for losses between 0.5 and 2 dB and is less than 0.05 dB below 0.5 dB. An expression for the error is given. >

Although the six-port measurement technique is rapidly gaining the attention of the microwave community, the theoretical development, to date, yields but limited practical insight into its operation. Following a brief review of the prior art, such that the six-port techniques may be placed in proper perspective, this paper presents an alternative introduction leading to much better insight, and to design criteria for a six-port circuit which optimally exploits the concept.

In the absence of phase response the major, if not the primary, sources of error in the scalar network analyzer are the imperfect directivity, etc., associated with its internal and frequently inaccessible test set or measurement network. An explicit expression is obtained for this error in terms of the observed response to a sliding termination and sliding short. This has made possible a more complete error expression than would have otherwise been obtained. >

An explicit six-port calibration method using five standards based on matrix formalism is developed. The method has a number of advantages. There is no limitation on the measurements and in the six-port design to include a specific reference port for setting the power level during calibration and testing. The computation method is an explicit one and there is no need to use iterative procedures. >

It is shown that the fundamental six-port equations can be obtained, almost by inspection, from a suitably normalised flow graph. The form of the six-port equations suited to most practical reflectometers is deduced.