A Coaxial Calorimeter for Use as a Microwave Power Standard

A coaxial calorimeter has been built for use in the comparison of power at high frequencies with dc resistance and voltage standards. The temperature rise of the metal jacket of a 50-ohm coaxial termination is measured with a thermopile when a known level of dc power is fed into the calorimeter. The high-frequency sensitivity of the calorimeter is obtained by modifying the dc sensitivity for: 1) Input VSWR of the calorimeter, 2) Attenuation of a 6-inch length of thermally insulating input coaxial line, 3) The effect of current distribution in the load. The accuracy is estimated at better than ±1 per cent below 4 Gc/s with the largest errors due to the input VSWR of the calorimeter.     

Microwave Two-Port Coaxial Power and Voltage Mounts

Two-port coaxial mounts to measure power, voltage, and current from audio to 36 GHz are described. These mounts need no RF calibration (thus eliminating accuracy degradation in the calibration hierarchy) and remove serious difficulties in measurements and equipment evaluation.     

Stirling Cryocooler for High-Temperature Super Conductor RF Filters

The High Temperature Super Conducting (HTSC) radio frequency (RF) filters (as used, for example, in ground base stations for cellular phone systems) are passive devices. To operate properly, they must be cooled well below their transition temperature to super conducting stage (usually to 65–80 K). These HTSC RF filters are connected through a coaxial cable to an array of Low Noise Amplifiers (LNA), which are active devices and, therefore, induce a few hundreds mWatts of heat. On the other hand, the LNA array is connected by coaxial cable to a feedthrough of the vacuum chamber. This coaxial cable also contributes a few hundreds mWatts of heat load. The third source of heat load is the thermal radiation from the vacuum jacket wall to the cryogenically cooled surfaces. This portion of heat load is assessed as hundreds of mWatts as well. The signal-to-noise ratio of LNA devices is improved significantly when they are cooled down to a temperature of 90–110 K and their effectiveness reaches 99% at a temperature of 77 K. Traditionally, cooling of the system is achieved by placing both the HTSC RF filters and the LNA array device on the cold tip of a single-stage cryogenic cooler. Hence, both devices are cooled down to a temperature of 60–80 K, which is required by the manufacturers of HTSC RF filters. Because of the high level of heat loads induced by the LNA array, this method requires an extra cooling capacity from a cryogenic cooler. This increases power consumption, weight, and size and decreases its reliability. This paper describes a method of reducing the overall heat load. This method relies on the idea of maintaining the HTSC RF filters and the LNA arrays in different operational temperatures. The objective of this method is to provide a reduction in thermal losses, input power, weight, and size and to increase the reliability of the entire cryogenic cooler. The method allow for better ruggedising of the mechanical support for cooled electronic package of the LNA array plate.     

Assigning RF/DC Transfer Difference to High Frequency Voltage Primary Standard up to 1 GHz at NPLI

National Physical Laboratory (NPLI) India is the premier research and development center and the National Metrology Institute, which provides traceability in measurements by calibration throughout the country. High frequency (HF) voltage is one of the important parameter in electrical metrology. At NPLI the primary standard of HF voltage at frequencies from 1 to 1,000 MHz is a twin resistance coaxial power mount. The calibration technique and establishing the traceability by assigning the RF/DC transfer difference to HF voltage primary standard are described in this paper. The HF voltage primary standard has been characterized by assigning RF/DC transfer differences to it in terms of effective efficiency, RF impedance and DC resistance. The calibration results of the primary standard have been discussed in this paper. The assigned RF/DC transfer difference (δ) and the expanded uncertainty of HF voltage primary standard at 1.0 GHz is (?5.2 ± 5.4) mV/V.     

Validation of RF power standard in the frequency range of 100 MHz to 18 GHz by an inter laboratory data comparison

Radio frequency (RF) power is one of the most important quantities in RF metrology. An inter laboratory data comparison of RF power for the validation of a coaxial microcalorimeter has been carried out between Physikalisch-Technische Bundesanstalt (PTB-Germany) and National Physical Laboratory India (NPLI). A coaxial thermistor mount equipped with type N connector is used for this intercomparison. The results show good agreement in measuring the effective efficiency of the coaxial thermistor mount between the two laboratories within their claimed expanded uncertainty. It confirms the equivalence of national standards for RF power in the frequency range of 100 MHz to 18 GHz.     

A Single Bead Broadband Coaxial Thermistor Mount

A new broadband coaxial thermistor mount is described which has as its major feature the virtual elimination of a dc to RF substitution error commonly encountered in the measurement of the RF power. Secondary features include the simplicity of the design and the potential ease of matching thermistors for temperature-compensated power measurements. The termistor mount utilizes a single center tapped thermistor in place of the two thermistor beads normally used in coaxial mounts. The data taken on the thermistor mount indicate the elimination of an error described in detail in a paper by Glenn Engen, "A dc-RF Substitution Error in Dual Element Bolometer Mounts." Typically, this error is in the order of 1 percent at 10 mW and 2 percent at 15 mW of applied RF power for conventional dual bead thermistor mounts, and is due to the two beads having different dissipation constants and a shift in resistance when RF power is applied. Measurement of resistance shifts and the dissipation constants of the respective sections of the thermistor for a number of tapped thermistor beads and mounts have been made. The results indicate that this substitution error is typically reduced to below 0.1 percent up to 15mW of applied RF power. The error calculation is based upon a derived expression for the substitution error. A coaxial thermistor mount is described which is usable at RF frequencies up to 12.4 Gc/s.     

Measurement techniques and results of an intercomparison for RFpower in a 3.5 mm coaxial line up to 26 GHz

The methods and results of an international comparison are presented for measurements of RF power in a 3.5 mm coaxial line at seven frequencies up to 26 GHz. Three national laboratories of metrology having different measurement techniques participated in the comparison. The agreement between the mean values of the calibration factor of the traveling standard reported by the participants is well within their reported uncertainties (k=2), which are between 0.5% and 3.1%     

Calibration of gradient calorimeters

We describe a pulsed energy method for calibration of a gradient calorimeter (in which the temperature gradient in the load is measured) and an automated apparatus for realization of the method. We determine the sensitivity of the calorimeter to cw power and pulsed energy.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 58–59, November, 1995.     

Automatic Calibration System for a Laser Power Meter

A microprocessor-based calibration system for a CW laser power meter has been developed. The system consists of an isothermal calorimeter with a thermopile unit, an electrical, and an optical subsystem. Temperature control of the thermopile unit is achieved through a digital technique. The calibration of a power meter is performed using the effective efficiency of the unit as measured by a calorimeter. From error analyses, an overall accuracy has been obtained as ±1 percent in root mean square for a power level of 1 ~ 200 mW.     

Development of an RF Conditioning System for Charged-Particle Accelerators

Charged-particle accelerators use various vacuum windows on their accelerating radio-frequency (RF) cavities to throughput very high RF power. Before being placed on the cavities, the windows should be cleaned, baked, and fully RF conditioned to prevent a poor vacuum from outgassing, as well as other forms of contamination. An example is the coaxial fundamental power coupler (FPC) with an annular alumina ceramic window for each of the 81 superconducting RF cavities in the Spallation Neutron Source (SNS) linear accelerator. The FPCs needed to be tested up to 650-kW peak in a traveling wave and 2.6 MW with standing wave peaks in 1.3 and 60 pulses/s at 805 MHz. In this paper, an Experimental-Physics-and-Industrial-Control-System-based RF conditioning system for the SNS RF test facility is presented. This paper summarizes the hardware and software design strategies, provides the results obtained, and describes the future research scope.     

Development of a High-Precision Calorimeter for Measuring Power Loss in Electrical Machines

This paper is concerned with the development of a high-precision 30-kW (40-hp) calorimeter and is specifically focused on how experimental errors resulting from calorimeter design and operating procedures are eliminated or mitigated. A complete calibration for the calorimetric system using a dc heater is conducted, and two induction motors rated at 5.5 and 30 kW (7 and 40 hp, respectively) are carefully tested both within and outside of the calorimeter. Loss segregation is in accordance with the IEEE 112 method B. Experimental results for the comparison of calorimetric and input–output methods clearly confirm the effectiveness of the calorimeter in terms of accurate power loss measurement. The accuracy of the calorimeter is approximately 5.6 W in the measurement of power loss of up to 4.5 kW with a resolution of 0.1 W.      

Finite-difference time-domain model for the feeding gap of coaxial probe driven antennas

In the finite-difference time-domain (FDTD) method, a simple and realistic feed model for coaxial probe driven antennas is proposed here. The feed zone of the antenna may be considered as an equivalent source in view of the antenna theory and a load port in view of the transmission line theory. The proposed feed model is constructed by combining the infinitesimal-gap source condition of the antenna and the equivalent load condition of the feed line. It leads to perform no additional FDTD cell modelling of the line. The transient reflected voltage and the input impedance of cylindrical monopole antennas fed by coaxial lines are calculated numerically and then compared with the accurate measurement and a full fine-grid. The FDTD results of the proposed model have a good agreement with the measured data and the fine-grid results.     

On-wafer calibration of a double six-port reflectometer includingconstants for absolute power measurements

The complete calibration of a double six-port network analyzer includes constants for the measurement of wave ratios (S-parameters) as well as constants for absolute power level measurements for nonlinear device characterization. This paper describes how a complete set of constants can be obtained for on-wafer measurements from a complete calibration in a coaxial measurement plane and a subsequent on-wafer calibration with the minimum number of elements     

A new microcalorimeter for measurements in 3.5-mm coaxial line

A new microcalorimeter has been realized for implementing the national power standard up to 26.5 GHz in a 3.5-mm coaxial line at the Istituto Elettrotecnico Nazionale (IEN) Galileo Ferraris, Turin, Italy. The system is based on a dry thermostatic cell controlled by Peltier elements. The thermal load consists of a twin sensor system that is alternately supplied with high frequency test power and low frequency or direct current (DC) reference power through adiabatic coaxial lines. This microcalorimeter was originally designed for calibrating bolometric mounts. Recently, it has been modified for thermocouple power sensors, which can operate from DC to 26.5 GHz in a 3.5-mm coaxial line.     

A method for precise RF admittance measurement

An improvement in the theory of the dual admittance bridge with self-calibration ability for precise RF measurement is described. The approach to the bridge function analysis extends utilization of its high resolution and accuracy in immittance standardization into the UHF range. No detailed information about the bridge's internal structure is needed for the theory, which describes it as a multiport device. Thus, the theory has not only contributed to bridge arrangement, but also enables simple and efficient calibration of measurement equipment based on the classical twin-T admittance bridge. Improvement in the accuracy and frequency range of the calibrated equipment should be expected. The theory has been verified on a special coaxial bridge circuit at 100 and 1000 MHz     

3D-modelling of temperature gradients induced by electrical power dissipation in a 3-body Domen-type calorimeter for absorbed dose measurements

The effect of thermal gradients that appear in the core of a Domen-type absorbed-dose calorimeter during an electrical calibration run is revised using a finite element 3D-numerical analysis. The local thermal modelling, that is the method allowing for spatio-temporal distribution of temperature within the three bodies of the graphite calorimeter, combined with both a careful analysis on what really happens when a certain amount of electrical power is dissipated in a NTC heating thermistor and the consideration of heat loss through radiation from the surface of the calorimeter bodies, has led to results which are in agreement with those obtained from experimental measurements and reported in the literature.     

ANA Calibration Method for Measurements of Dielectric Properties

Routine network analyzer calibration procedures in measurements of the dielectric properties of materials using an open-ended coaxial line probe are frequently inadequate and limit the accuracy of measurements. A calibration method, which makes use of liquids whose properties are well known, is proposed to alleviate this limitation. It is shown that even one liquid used as a standard in place of a matched load greatly improves the accuracy of measurements. Theoretical relationships and experimental results as well as some practical suggestions related to the application of this method are given.     

Precision Coaxial VSWR Measurements by Coupled Sliding-Load Technique

The method described employs a slotted line for VSWR measurement and a precision coaxial line as an impedance standard. A sliding load terminates the standard line during the process of transforming the impedance of the slotted line to that of the standard line. This load is coupled mechanically to the slotted-line probe so that the two move together. The VSWR seen by the probe is then, to first approximation, only that due to the reflection from the junction of the two lines. It is simple, therefore, to tune out the residual reflection without requiring a perfect load. The slotted line is then effectively transformed to the impedance of the standard line, and subsequent measurements made with it at the same frequency indicate VSWR with respect to the standard line. In order to minimize the effect of amplitude fluctuations of the RF source and to expand the scale, the detected probe output is compared with the detected output of a directional coupler monitoring the incident power. The difference is recorded with a strip recorder; the paper transport of the recorder is synchronized with the probe travel. In describing the method, considerable background material is presented on other precision impedance-measuring methods and techniques and on the general state-of-the-art. Theory, accuracy, system details, and results are given. The system appears capable of making absolute impedance measurements on a low VSWR termination to a maximum possible error in reflection coefficient of 0.0012.     

雷达射频测试系统现场整体计量校准技术研究

传统的集成系统校准是采用单台仪器计量和系统功能检查来完成,原有的系统性能和技术指标是无法保证的,雷达射频测试系统的整体校准是目前急需解决的问题。本文通过设计组配标准化、通用化的现场传递标准件,即通过组配单件传递标准件、组合传递标准件,建立了与雷达射频测试系统相对应的功率、幅度、相位、噪声和反射系数等电参数的工作标准,通过对以上各参数的不确定度分析评定和重复性、稳定性的考核,解决了雷达射频测试系统的量值传递问题,实现了雷达射频测试系统的现场整体校准。