Six-port Reflectometer Research Articles

A Novel Direct Geometric Algorithm for Worst-Case Error Analysis of Six-Port Reflectometer and Its Guiding Significance in Application

A Novel Direct Geometric Algorithm for Worst-Case Error Analysis of Six-Port Reflectometer and Its Guiding Significance in Application

Design and Implementation of a Microstrip Six-Port Reflectometer (SPR) with Enhanced Bandwidth

A compact microstrip six-port reflectometer (SPR) with extended bandwidth is proposed in this paper. The design is based on using 16-dB multi-section coupled line directional couplers and a multi-section 3-dB Wilkinson power divider operating from 1 to 6 GHz. The proposed SPR employs only two calibration standards: a matched load and an open load. As compared to other dielectric substrates, fabricating the proposed SPR involves using a low-cost (FR4) substrate. A novel algorithm is also proposed to estimate the complex reflection coefficient over the frequency ranges at which the standard performance of the circuit components is not fully satisfied. The new algorithm is based on the circles’ intersection points, which have been derived from basic SPR equations, to estimate the complex reflection coefficient. To validate the SPR performance, a multiband microstrip patch antenna has been measured and the resulted reflection coefficient is compared with those obtained using a vector network analyzer (VNA). Results show that the proposed SPR provides a good estimation of the complex reflection coefficient within the frequency range of 1 GHz to 8 GHz. Owing to its compact size and ease of fabrication, the proposed reflectometer is suitable for various microwave broadband applications.

A 20-GHz On-Chip Six-Port Reflectometer Using Simple Lumped Passive Devices and Bipolar Junction Transistors

This paper proposes an on-chip six-port reflectometer (SPR) fabricated in the 0.13-μm IBM BiCMOS-8HP technology. The SPR enjoys a compact circuit structure, with only four amplitude detectors as active devices, one resistive power divider, and one lumped phase shifter as passive devices. The power divider and phase shifter are responsible for manipulating the radio-frequency (RF) signals appropriately, whereas the detectors are responsible for sensing the processed signals. The chip area, which can be further reduced, is 1.25 mm in width and 1 mm in height. The SPR can perform in-situ measurement of reflection coefficients of devices under test (DUTs) and reduce testing costs of RF chips by using vector network analyzers (VNAs). The SPR demonstrates excellent performance in measuring the reflection coefficients of DUTs at around 20 GHz. The experimental results indicate that the maximum error of the measured reflection coefficients in absolute value is about -26 dB.

Fully Analytical Approach to Calibration of Six-Port Reflectometers Using Matched Load and Unknown Loads for One-Port Measurements

Fully Analytical Approach to Calibration of Six-Port Reflectometers Using Matched Load and Unknown Loads for One-Port Measurements

Prototype of a sensor for measuring moisture of a single rapeseed (Brassica napus L.) using microwave reflectometry

Rapeseed moisture content is one of the key physicochemical parameters of the seeds, because of its importance for ensuring optimal conditions for seed storage, as well as for determining the time of harvesting. There are many devices available on the market for measuring rapeseed moisture content. Measurement techniques usually use a large sample of seeds (in the case of capacitance meters e.g., 100 g). Therefore, the obtained result is an average value representative for the tested sample, but does not give the range of moisture of single seeds in a given batch of material. The paper presents a prototype of a sensor and a method of measuring moisture content of individual rapeseeds. The system utilizes multiple measurements of a complex reflection coefficient that correspond to different positions and orientations of a seed under test along the sensor. As a result, the impact of non-uniform shape and inner heterogeneity of the seeds on the measurement results is limited. A novel robust algorithm for moisture determination is proposed, which does not need any calibration of the microwave measurement circuitry realized as a six-port reflectometer operating at 2.4 GHz.

Design of the Complex Permittivity Measurement System Based on the Waveguide Six-Port Reflectometer

This paper proposes a simple and cheap complex permittivity measurement system at the frequency of 2450 MHz based on a waveguide six-port reflectometer (SPR) and a ridge waveguide. The six-port reflectometer composed of a waveguide-stripline-coaxial directional coupler and three SubMiniature version A (SMA) probes is designed. The general theoretical model, simulation and implementation of the waveguide six-port reflectometer with an optimal accuracy are given. Within the dynamic measurement range of the power meters, the designed six-port reflectometer can accurately measure the reflection coefficient and have high measurement stability at different power levels. The ridge waveguide is used as the carrier of the material to obtain good monotonicity of the complex permittivity, and a back propagation neural network (BPNN) is established for the relationship between the complex permittivity and the reflection coefficient. Compared with the reference values in the literature, it can be found that the error of the whole system in measuring the complex permittivity is also within the acceptable range. The six-port reflectometer based on rectangular waveguide provides a basis for the measurement while heating with high power microwave energy.

Six-Port Reflectometer Insensitive to Power Detectors’ Impedance Mismatch

This paper presents the first six-port reflectometer, which is insensitive to power detectors’ impedance mismatch. It exhibits optimum measurement conditions and provides low measurement error regardless the reflection coefficient of the used power detectors. Simultaneously, the developed six-port is of low complexity, comparable to other solutions. A theoretical analysis reveals that by application of identical power detectors the impact of their impedance mismatch on the six-port’s measurement performance is completely eliminated. To validate this concept experimentally two six-port reflectometers are developed i.e., the proposed one and a reference six-port, which for ideally matched power detectors provides theoretically identical power distribution. Both reflectometers are calibrated and applied to measure reflection coefficients over the frequency range from 5.7 GHz to 5.9 GHz with both well-matched and highly reflective power detectors. The obtained results clearly show that the proposed six-port provides low measurement errors for both types of power detectors, whereas the reference six-port cannot operate properly with highly reflective power detectors.

Balanced Six-Port Reflectometer With Nonmatched Power Detectors

In this article, a six-port reflectometer is proposed, which utilizes nonmatched power detectors. In the presented solution, the signals reflected from power detectors are efficiently used to obtain a signal flow required for correct measurements. As a consequence, impedance matching networks for power detectors are no longer needed. Simultaneously, due to its balanced topology, the developed six-port exhibits advantageous measurement conditions and theoretically ideal matching at both its input and measurement ports. To experimentally validate the proposed concept, a six-port reflectometer operating at 2.4 GHz is designed, manufactured, and utilized in reflection coefficient measurements. The obtained results are consistent with the values measured using a commercial vector network analyzer. For additional verification, the impact of power detectors’ asymmetry is investigated theoretically and experimentally.

A Low-Loss Load Correction Technique for Self-Healing Power Amplifiers Using a Modified Two-Tap Six-Port Network

This article presents a low-loss correction technique for a self-healing load-insensitive power amplifier (PA) using a modified two-tap six-port network, wherein the varying (complex) load is first compensated for its unwanted susceptance part, followed by adjustment of the transistor output stage to the ohmic load variation, by modifying its supply voltage and drive level. This two-step approach avoids the high-Q conditions that occur in tunable matching network solutions, which aims to correct for both the real and imaginary load deviations, such as providing lower insertion loss and voltage stress. Next, to facilitate a fully automated load mismatch correction without the need for calibration, a modified two-tap six-port network for impedance detection and control loop approach is proposed. As proof of principle, a prototype 900-MHz class-AB PA featuring the proposed correction technique, as well as, the six-port reflectometer and the control loop, has been implemented as a PCB demonstrator. Measurement results show that the self-healing load-insensitive PA in the events of load mismatch significantly improves the performance and approaches the 50- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> performance. On a 2:1 VSWR 360° mismatch trajectory and driven by a 64-QAM 3.86-MHz signal, the PA achieves a linear output power of 22 dBm with only ±0.1-dB variation and better than −45-dBc adjacent channel power ratio (ACPR).

New Baseband Radio Channel Impulse Processing Algorithms

In this paper the method for radio channel pulse response processing with baseband conversion by six-port reflectometer technique is described. The received signal is converted by baseband conversion, digitized and the pulse response of radio channel is processing by proposed algorithms. These algorithms are working in real time and are able to estimate the amplitude, phase and delay of the received signal in each of propagation paths. The most promising algorithm (Exponential Power Descend Algorithm) achieved recovery successfulness of all signal paths equal approximately 90 % for SNR = 2.5 dB.

In-line microwave reflection measurement technique for determining moisture content of biomass material

An in-line microwave reflection measurement technique for determining moisture content of biomass material (sawdust) moving past the sensor on a conveyer is presented. The proposed system consists of four open-ended rectangular substrate-integrated waveguide (ORSIW) sensors mounted on the conveyor walls, three RF-switches and a 3.0 GHz six-port reflectometer for the reflection measurement from the sensors. The dielectric permittivity of the biomass as a function of moisture content and bulk density can be extracted by using the six-port measurement technique. The density-independent algorithm for moisture content determination was developed based on the power readings from the six-port circuit at conveyor speeds of 0.15, 0.23 and 0.35 m s−1. Finally, the predicted moisture contents were compared with those determined by the standard oven-drying method with standard errors of calibration (SEC) of 1.75%, 1.70% and 1.28% for conveyor speeds of 0.15, 0.23 and 0.35 m s−1, respectively.

A Calibrating Six-Port Compact Circuit using a New Technique Program

In this paper, a calibration of six-port reflectometer using a new technique program is presented. It has been shown that a calibration procedure is based on explicit method, the method that capturing the output wave forms of six-port junction and determines the complex relationship between the two waves present at the input from the value of four outputs. The number of calibrating standards and the computation effort required are the most important parameters in selecting a calibration technique. Comparison between the results obtained from the new calibration method program with measurement results show the validity of the method proposed. This calibration technique can be used in general six-port direct digital receiver.

A Portable System for Rapid Measurement of Dry Rubber Content With Contaminant Detection Feature

This paper presents a system which is able to determine dry rubber content (DRC) as well as detect contaminants in latex. The system was designed and implemented with a six-port reflectometer. An open-ended coaxial sensor was designed as a measurement probe. The constant amplitude sinusoidal wave at 1 GHz transmits from the probe tip, incidents on the test sample and reflects back to the probe. A standing electromagnetic wave is formed and converted to the electrical signal by the probe. This electric signal is digitized and fed to the algorithms programmed in the microcontroller. These algorithms were developed for classifying the latex sample and determining its DRC. The system accuracy was tested with several pure and contaminated latex samples. The contaminated samples were prepared by mixing pure latex with 10 and 15% (by volume) of cassava flour solution. One hundred and ten samples, 50 pure, 40 contaminated of 10%, and 20 contaminated of 15%, were tested. The overall detection accuracy was 91.8% across the DRC range from 24 to 55%. For DRC determination, the system was tested with 30 latex samples at 27 °C. This was compared with the standard oven method (ISO 126:1972 DRC, BS 1672:part 1:1950 and ASM D 1076–80) where the mean absolute error of DRC achieved was 0.74%.

Broadband and compact complex ratio measuring unit

AbstractThis study designs and analyzes Complex Ratio Measuring Unit (CRMU) and a Six‐port Reflectometer (SPR) at a center frequency of 2.4 GHz. CRMU is designed using a compact size and wideband 3 dB‐branch line coupler (BLC) and 3 dB‐Wilkinson power divider with enhanced series‐diamond stubs. The usage of these compact components leads to a compact size and improves the operating bandwidth. The idea of designing SPR is based on integrating a CRMU with 2 directional couplers along with isolator rather than a single BLC; to get a signal balance that enhances the quality of the reflection coefficient measurement. From the measurement result, it is found that the bandwidth of the CRMU and SPR is 1.7 GHz and the dimension of the CRMU is 60 × 45 mm. The proposed CRMU is fabricated using RT/duroid 5880 substrate with thickness of 0.38 mm. The dimension of the CRMU is 13 × 6.5 mm. The simulation and measurement results for both CRMU and SPR show good agreement.

Design of a wide band six port reflectometer using broadside coupled lines

AbstractThe authors present in this article an overview of the six port reflectometer (SPR). They realized SPR using broadside coupled lines for achieving ultrawide band, which is essential for its working as an alternative network analyzer.

Portable Six-Port Reflectometer for Determining Moisture Content of Biomass Material

A portable six-port reflectometer for determining moisture content of biomass material is proposed for the first time in this paper. The proposed system consists of a 5.13-GHz reflectometer used with an open-ended half-mode substrate-integrated waveguide sensor. The complex permittivity of biomass (sawdust) was measured, and a dielectric-properties-based algorithm for moisture determination was developed. The reflectometer performance was verified by comparing the measured complex permittivity to results obtained with a commercial automatic network analyzer. Finally, the predicted moisture content was compared with the standard oven drying method.

Advanced Terahertz Sensing and Imaging Systems Based on Integrated III-V Interband Tunneling Devices

Owing to the unprecedented development in terahertz (THz) sources and detectors in the last decade, technologists and researchers have intensified their efforts to develop advanced THz sensing and imaging systems with superior performance and unique functionalities. One of the key elements to realize such systems is the ability to monolithically integrate high-performance semiconductor devices with THz antennas and other passive structures. In recent years, devices based on interband tunneling in III-V heterostructures have emerged as promising candidates for THz detection that offer extremely high nonlinearity, high sensitivity, low noise, fast response, and room temperature operation. In this paper, we first review the development of heterostructure backward tunnel diodes (HBDs) in the InAs/AlSb/AlGaSb material system that have been demonstrated with detection sensitivity that outperforms the current state of the art (e.g., the fundamental limit of Schottky diodes) and with noise-equivalent power (NEP) below 0.2 pW/Hz½. We then present the monolithic integration of HBDs with planar folded dipole antennas (FDAs) using submicrometer-scale airbridges to achieve optimized impedance matching for high-performance and compact THz detectors and focal-plane array (FPA) imaging systems. In addition, the potential of using HBDs for realizing THz systems with advanced functionalities such as spectroscopic FPAs (using frequency-tunable THz antennas) and polariametric detection/imaging systems will be discussed. Finally, the integration of HBDs into waveguides for more advanced THz sensing and imaging (e.g., a six-port reflectometer for near-field imaging) will be discussed.

Six-Port Reflectometer Using Edge-Coupled Microstrip Couplers

This letter presents the design of a six-port reflectometer (SPR), which makes use of edge-coupled, coupled-line microstrip couplers. By designing the couplers to have coupling slightly larger than the isolation, good Q-point placement on the complex Γ-plane is obtained. The SPR Q-points are obtained by a proposed two-step process using two standard terminations-a matched load and an open circuit load. The designed SPR has been tested using various loads and the computed load reflection coefficients have been compared against those of a standard commercial Vector Network Analyzer. The raw dynamic range is 21-39 dB in the frequency range from 1.6 to 2.2 GHz and the uncalibrated load reflection coefficients follow the expected values closely, with average phase error spread of only about 2.7%-7.7%. The designed SPR is fabricated on FR4 substrate. It achieves a reduction in size due to lesser number of components and is ideal for narrowband and low cost use.

Six-port microwave system for volatile organic compounds detection

An interdigital capacitor with resonant frequency fres ≈ 8.6GHz coated by comb polymer Pc-based thin film as a sensitive layer was investigated under exposure to different concentrations of various VOCs, such as: acetone, ethanol, methanol, isopropanol, butanol and ethylbenzene in a 0–25ppm concentration range. The measurement system has been significantly simplified due to measurement of the reflection coefficient at a single frequency f0=8GHz, at which the sensor exhibits the largest change in reflection coefficient's magnitude. For the reflection coefficient's measurement a new six-port reflectometer has been developed, which provides an enhanced measurement accuracy for the measurements of reflection coefficients having small magnitudes. The developed detector based on microwave measurements can be utilized in a portable exhaled breath analyzers.

Using Monte Carlo simulations as design aid for six-port reflectometer configurations based on symmetrical six-port waveguide junction

Abstract Monte Carlo simulations have been employed in the present paper to study the symmetrical six-port waveguide junction for use as the key component of a six-port reflectometer. Experimental results have additionally confirmed that the resulting reflectometer (in three possible configurations) can achieve accuracies of ±0.015 and ±2° for magnitude and phase, respectively, when measuring the reflection coefficient of a device under test between 9.7 GHz and 11.8 GHz.