Six-port Reflectometer Research Articles

Repetitive and single shot pulse microwave six-port reflectometer

The six-port reflectometer technique is extended to make pulsed-RF measurements. It is shown that a time resolution on the order of 1 mu s is possible in both repetitive and single-shot mode of operation of the reflectometer. A proof of the principle of the method is carried out using passive and active loads. A simple method for the linearization of diode-detector response is presented. Because of its good time resolution, this method can be used to study thermal and burn-out effects in high-power solid-state amplifiers, or to characterize, for example, pulse devices used in phased-array radars. Its ability to operate in single-shot mode is in contrast to existing reflectometers. It is easily extendable to the millimeter-wave frequency range and can be used to make multiport measurements. >

A millimeter-wave six-port reflectometer using dielectric waveguide

A six-port reflectometer circuit that is particularly suited to dielectric-type waveguides is described. Its scattering matrix is derived, allowing for flexibility in design. A phase-shifting network is incorporated in the circuit, and it is shown that a quadrature hybrid can be configured for this purpose. The reflectometer was implemented in a dielectric waveguide for W-band (75 GHz-110 GHz) operation, and measurements are presented. >

A six-port network analyzer load-pull system for active load tuning

An experimental six-port network analyzer has been used as a load-pull system in an active load tuning configuration. It is shown that by using a dual six-port reflectometer and an appropriate calibration procedure, it is possible to measure at the same reference plane the ratio between the incident and reflected waves and the power flow at the output of the test transistor. Using these two values the simulated load impedance seen by a transistor and the microwave power delivered to the simulated load are calculated. Experimental results on microwave transistor characterization confirm the validity of this method. This technique uses less hardware than conventional methods, and presents a comparable accuracy to conventional techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A critical study of the open-ended coaxial line sensor technique for RF and microwave complex permittivity measurements

An HP 8510 automatic network analyser and a six-port reflectometer have been used with a purpose-built calculable open-ended coaxial line sensor to measure the reflection coefficients of various materials, including dielectric reference liquids, in the frequency range 50 MHz-2.0 GHz. Factors crucial for calculable measurements have been identified including associated measurement uncertainties. The reference material measurements have been used in critical studies of: a commonly employed lumped equivalent circuit model of the fringing fields of the sensor; and a numerical point-matching theory of the propagating and evanescent modes, at the termination of the sensor. It is concluded that the inverse point-matching theory should enable a more widespread and accurate exploitation of the sensor technique for various applications including those in biomedicine and industrial quality control.

Measurement of microwave permittivity using a six-port reflectometer with an open-ended coaxial line

A nondestructive broadband permittivity-measurement method using an automatic six-port reflectometer is presented. The impedance sensor is an open-ended coaxial line terminated by a semi-infinite medium. The equivalent model of the sensor used is based on an equivalent effective transmission-line length which models the fringing field at the extremity of the probe. The proposed method is useful to measure relatively high-loss dielectric liquids and provides a precision comparable to other methods already in use; however, the equipment costs are considerably reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Using metallic post and inductive diaphragms to match symmetrical five-port waveguide junction

A first-order model of the symmetrical five-port waveguide junction with metallic post and inductive diaphragms is developed. Supplementing the theoretical data thus obtained with empirical adjustments, a suitable prototype is designed for use as the essential component of a six-port reflectometer capable of yielding optimum performance.

A statistical method for calibrating the six-port reflectometer using nonideal standards

An alternative method is presented for calibrating the six-port reflectometer. Through the use of a redundant set of calibration standards, an estimate of the 11 real calibration constants is determined in the minimum-mean-squared-error sense. This technique enables the user to weight the contribution of each standard to the calibration process as a function of confidence in the quality of that standard. The resulting computer algorithm is quite straightforward and provides a direct measure of the tightness of fit between the estimated six-port model and the observed data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Technical memorandum: The sixth port reflectometer and its complete calibration by four standard terminations

An alternative nonlinear method to calibrate the six-port reflectometer is developed. Using this method four standards and iteratrive procedure are needed to calibrate the reflectometer.Experimental results show that this method coverges very rapidly, provides a good accuracy in calibration parameters and at the same time avoids degenerate solutions which produce unwanted singularities in the mesurement.

Alternative approach to the calibration of six-port reflectometers using four standards

Other researchers have proposed sixport reflectometer calibration procedures that require only four standards. The memorandum describes an alternative approach to the implementation of such a calibration routine. The standards required are a matched load, a short circuit and two offset terminations. Laboratory tests indicate that measurement accuracies of within ±0.01 in magnitude and within ±1° in phase can be obtained.

Designing a symmetrical five-port waveguide junction

Studies have shown that for a symmetrical five-port junction to be used in a six-port reflectometer set-up, it should ideally be matched over the operating bandwidth. Using the results obtained from an electromagnetic model, a suitable symmetrical five-port E-plane waveguide junction (with five attached H-plane tapers) was designed. The junction-with-tapers prototype when tested yielded a residual mismatch of less than 0.18 over the entire waveguide bandwidth.

A comparative worst-case error analysis of some proposed six-port designs

A detailed analysis of the accuracy in complex-reflection coefficient measurement by the six-port technique is discussed. The expression of the relative error in amplitude measurement of the complex reflection due to power-reading errors are derived in worst-case situation using both the basic six-port and sensitivity analysis theories. The precision of measurement of any point in the Smith chart is obtained by reference to lines of constant errors (amplitude and phase) drawn on the Smith chart for various proposed six-port correlators (junctions). A comparison of three proposed six-port designs shows that the Engens six-port design presents the best performance for a given power measurement accuracy. A maximum dynamic range of 60 dB seems to be a limit for six-port reflectometers using a good-quality power detector ( alpha =0.1%). >

A Comparative Statistical Study of Some Proposed Six-Port Junction Designs

Reflection coefficient measurements obtained from six-port reflectometers are analyzed from a statistical and geometrical point of view. The analysis concentrates on the effect of using noisy power meters, and a simply computed, geometrically interpretable estimator of the reflection coefficient possessing certain optimality properties is derived. A suitable performance measure for this estimator is calculated for a number of different six-port designs as the true reflection coefficient ranges over the area of the Smith chart. For each design, a contour map of the measure allows for easy comparison of the designs in different regions of the Smith chart.

Using six-port reflectometer measurement of complex dielectric constant

This paper presented the measuring principle of complex dielectric constant using six-port reflectometer and the mathematical model of computer software to perform this measurement. The experiment results of measuring Teflon material using six-port reflectometer at X-band are given. The complex dielectric constant of the same material is measured using the resonant cavity technique. The agreement of two results provides evidence of the validity of this theory.

Six-port reflectometer

A six-port reflectometer consisting of a symmetrical five-port waveguide junction and a directional coupler was analysed, constructed and tested. Theoretical and experimental results showed that the circuit yielded optimum q-point distributions over the waveguide bandwidth. Actual measurements taken using the prototype reflectometer indicated that accuracies of ±005 in magnitude and ±0.5° in phase were obtainable.

The impact of automation on NBS noise temperature measurements

The accuracy of calibrating a thermal noise source using the National Bureau of Standards' automated radiometer and cryogenic primary noise standards is typically ±2 percent, compared with ±3 percent for corresponding services that used manual radiometers and hot primary standards. Using the automated radiometer, a noise source can typically be calibrated at three frequencies in the time a manual radiometer requires to calibrate one. The automated radiometer contains a six-port reflectometer, and noise sources with reflection coefficients as great as 0.3 can be tolerated without significantly affecting the calibration accuracy. This makes it practical to use a single broad-band, coaxial noise standard from 0.03 to 14 GHz. The six-port reflectometer also makes it possible to calibrate sources with connectors different from those of the primary standard's with almost no additional accuracy degradation.

Six-port reflectometer theory for symmetrical five-port junction with directional coupler

In the ideal case, a symmetrical five-port junction, together with a directional coupler, forms one of those few six-port networks that satisfy the criteria for optimum six-port reflectometer performance. Imperfections however exist in the actual hardware, and they degrade the performance of this otherwise ideal circuit. Although the six-port technique accounts for these imperfections globally in the calibration procedure, it is nevertheless important that a proper analysis of how the system degradations arise be made. The paper provides such a theoretical study. In the course of the investigations, it was found that improvements in the performance of the hardware circuit may be obtained simply by re-arranging the inter-connections among the constituent components.

An Improved Method for Six-Port Reflectometer Calibration

An improved method for six-port reflectometer calibration is presented using a matched load and three offset short circuits as calibration standards. An iterative method is used to solve a system of nonlinear simultaneous equations. The information from four standards has been fully utilized. There is no limitation that one of the ports must indicate incident power only, and no need to make additional measurements to determine the sign ambiguity. The redundancy could be used to estimate errors caused by measurement system and calibration inaccuracies.

Automatic stepped-frequency six-port reflectometer for WG22

Automatic stepped-frequency six-port reflectometer for WG22

Simple derivation of six-port reflectometer equations

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.

An Explicit Six-Port Calibration Method Using Five Standards (Short Papers)

A six-port reflectometer calibration method using five standards is developed, and gives explicit unambiguous expressions for the calibration constants. The standards are restricted only in that their impedances may neither all have the same magnitude nor all have the same argument. The method permits exact (nonidealized) descriptions of the standards to be used, and the redundancy inherent in the analysis is utilized to reduce the problems associated with measurement noise.