Electromagnetic MeasurementsRF, Microwave and Millimeter-Wave MeasurementsThermistor DetectorsTechnical Contacts: Thomas P. Crowley John Lomax Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
2 Measurement Frequencies:
back to top of page | back to index of electromagnetic measurements The Reports of Calibration and Special Test give, with uncertainties, the magnitude and phase of the reflection coefficient, effective efficiency, and calibration factor of the device under test. Definitions: Effective Efficiency η e The effective efficiency η e is the ratio of the bolometrically substituted dc power for a thermistor detector or the power read from the power meter for a thermocouple detector to the net CW rf microwave power delivered to the power detector. Bolometrically Substituted dc Power The bolometrically substituted dc power is the change in dc (or audio frequency) bias power required to maintain the resistance of the thermistor element at a constant value following the application of rf or microwave power. Calibration Factor, K B The calibration factor is the ratio of the bolometrically substituted dc power for a thermistor detector or the power read from the power meter for a thermocouple detector to the CW rf microwave power incident upon the thermistor detector. K B = η e (1- | Γ | 2 ). Reflection Coefficient Magnitude, | Γ | and Arg ( Γ ) The reflection coefficient magnitude and phase (argument of reflection coefficient) is the ratio of the reflected wave voltage amplitude to the incident wave voltage amplitude and phase. back to top of page | back to index of electromagnetic measurements
back to top of page | back to index of electromagnetic measurements NIST Model CN Reference Standard (61137C-61138C)This premium service provides he measurements as a function of frequency for a NIST-designed coaxial reference standard with a Type N connector. The reference standard, designated Model CN (Coaxial with a Type N connector), is a bolometric, dc-substitution power detector that must be used with a NIST Type IV power meter (available from several commercial sources). The detector is designed as an optimum transfer standard which can be measured directly in the NIST coaxial microcalorimeter. To use this service, the customer needs to have a CN detector (contact staff for information).
Measurements are made at frequencies over the range from 50 MHz to 18 GHz (Service ID Number 61137C) or customer specified frequencies (Service ID Number 61138C). Figure 9.1 compares the expanded uncertainty of the premium service with that of the regular service for coaxial thermistor detectors. back to top of page | back to index of electromagnetic measurements References-Thermistor DetectorsDirect Comparison Transfer of Microwave Power Sensor Calibration, M. Weidman, Natl. Inst. Stand. Technol. (U.S.), Tech. Note 1379 (January 1996). A Calibration Service for Reference Standards for Microwave Power, F. Clague, Natl. Inst. Stand. Technol., Tech. Note 1374 (May 1995). Microcalorimeter for GPC-7 Coaxial Transmission Line, F. Clague, Natl. Inst. Stand. Technol., Tech. Note 1358 (August 1993). Coaxial Reference Standard for Microwave Power, F. Clague and P. Voris, Natl. Inst. Stand. Technol., Tech. Note 1357 (April 1993). Measurement Service for High-Power CW Wattmeter at the National Institute of Standards and Technology, J. A. Jargon and G. Rebuldela, Proc. of the Meas. Sci. Conf., Anaheim, CA (Jan. 1993). Basic RF and Microwave Measurements: A Review of Selected Programs, A. J. Estin, J. R. Juroshek, R. B. Marks, F. R. Clague, and J. Wayde Allen, Metrologia 29, 135-151 (1992). High Power CW Wattmeter Calibration at NIST, G. Rebuldela and J. A. Jargon, J. Res. Natl. Inst. Stand. Technol., 97 (6), pp. 673-687 (Nov.-Dec. 1992). WR-10 Millimeter Wave Microcalorimeter, M. Weidman and P. Hudson, Natl. Bur. Stand. (U.S.), Tech. Note 1044 (June 1981). A Semiautomated Six-Port for Measuring Millimeter-Wave Power and Complex Reflection Coefficient, M. Weidman, IEEE Trans. Micro. Theory Tech. MTT-25, 12 (Dec. 1977). Performance Characteristics of an Automated Broad-Band Bolometer Unit Calibration System, E. Komarek, IEEE Trans. Micro. Theory Tech. MTT-25, 12 (Dec. 1977). Theory of UHF and Microwave Measurements Using the Power Equation Concept, G. F. Engen, Natl. Bur. Stand. (U.S.), Tech. Note 637 (Apr. 1973). Application of an Arbitrary Six-Port Junction to Power Measurement Problems, G. Engen and C. Hoer, IEEE Trans. Instrum. Meas. IM-21, 470 (Nov. 1972). WR-15 Microwave Calorimeter and Bolometer Unit, M. Harvey, Natl. Bur. Stand. (U.S.), Tech. Note 618 (May 1972). Accurate Microwave High-Power Measurements Using a Cascaded Coupler Method, K. E. Bramall, J. Res. Natl. Bur. Stand. (U.S.), 75C (3 and 4), 185 (July-Dec. 1971). back to top of page | back to index of electromagnetic measurements Scattering Parameters of Passive One and Two-Port DevicesTechnical Contacts: John Lomax Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements General InformationMicrowave devices are characterized by their reflection and transmission properties. One-port devices such as matched terminations and offset shorts are characterized by measuring their reflection properties or voltage reflection coefficient. Two-port devices such as attenuators are characterized by measuring both their reflection and transmission properties. Figure 9.2 shows the reflected and transmitted voltage waves for a typical two-port device. The voltage waves incident to the device are defined as a 1 and a 2. The voltage waves reflected from the device are defined as b 1 and b 2.
Figure 9.2 Reflected and Transmitted Voltage Waves for a Typical Two Port Device. The scattering parameters specify the relationship between the incident and reflected waves. In the case of the two-port in Figure 9.2, the scattering matrix is, [b 1] = [S 11 S 12] [a 1] The scattering matrices shown are complex quantities conveying information on both the magnitude and phase of the quantities of interest. The attenuation of a two-port device is defined as S 12 and S 21. Most passive microwave devices are reciprocal where S 12 = S 21. The magnitude of the attenuation for a reciprocal device is commonly expressed in dB as A = -20 log10 ( | S 12 | ), dB = -20 log10 ( | S 21 | ), dB Similar definitions exist for single port devices such as terminations and offset shorts. A one port device can be thought of as the special case of a two port device where S 12 = S 21 = 0. The voltage reflection coefficient for a one port device is commonly given as Γ = b/a, where a is the voltage wave incident on the device, and b is the voltage wave reflected from the device. All scattering parameters are referenced to some idealized transmission line. At NIST, all coaxial measurements are referenced to an idealized, air dielectric, 50 Ω transmission line of specified dimensions. Similarly, all waveguide measurements are referenced to an idealized, air dielectric, precision waveguide section of specified dimensions. Details of the reference standard are available on request. Devices submitted for measurement should be in good repair and require only very minor cleaning of connector surfaces. NIST does not provide repair services. Items received requiring maintenance will be returned to the customer, and a handling fee will be charged. back to top of page | back to index of electromagnetic measurements Fixed and Variable AttenuatorsCoaxial fixed and variable attenuators are measured on either a NIST Dual Six-Port Vector Network Analyzer (VNA) or on a commercial VNA. Coaxial attenuators are measured relative to a reference characteristic impedance of 50 Ω. For fixed attenuators, the complete set of two-port, complex s-parameters are measured. The measurement report gives the magnitude and phase of S 11, S 22 and S 12 = S 21. For variable attenuators, normally only the change in attenuation from the zero setting is of interest. The test report for variable attenuators show the change in the magnitude of S 12 from the zero setting versus frequency for selected attenuator settings. Complete scattering parameter measurements for variable attenuators are available by special request. Fixed and Variable One-port DevicesWaveguide one-port devices must be fitted with standard waveguide flange connectors. The faces of these flanges should be machined flat and smooth and should not contain protrusions or indentations. Considerable care must be exercised in keeping the mating connector flange surfaces smooth and clean. Accurate alignment of the waveguide joint and flanges is also very important. The back of the flange which makes contact with the connecting bolts should be nominally flat and free of soft materials, including paint. The connecting holes of the flange should be symmetrically and accurately aligned to the rectangular waveguide opening. back to top of page | back to index of electromagnetic measurements References-CS-Parameters of Passive 1-Port and 2-Port DevicesMeasurements of the Characteristic Impedance of Coaxial Air Line Standards, J. R. Juroshek and G. M. Free, IEEE Trans. on MTT, 42 (2), 186-191 (Feb. 1994). Basic RF and Microwave Measurements: A Review of Selected Programs, A. J. Estin, J. R. Juroshek, R. B. Marks, F.R. Clague, and J. Wayde Allen, Metrologia 29, 135-151 (1992). "Thru-Reflect-Line": An Improved Technique for Calibrating the dual Six-Port Automatic Network Analyzer, G. F. Engen and C. A. Hoer, IEEE Trans. Micr. Theory Tech. MTT-27, 987 (Dec. 1979). A Network Analyzer Incorporating Two Six-Port Reflectometer, C. A. Hoer, IEEE Trans. Micr. Tech. MTT-25, 1070 (Dec. 1977). The Six-Port Reflectometer: An Alternative Network Analyzer, G. F. Engen, IEEE Trans. Micr. Theory Tech. MTT-25, 1075 (Dec. 1977). Application of Waveguide and Circuit Theory to the Development of Accurate Microwave Measurement Methods and Standards, R. W. Beatty, Natl. Bur. Stand. (U.S.), Monogr. 137 (Aug. 1973). Specifications and Test Methods for Fixed and Variable Attenuators, dc to 40 GHz, IEEE Standard 474 (1973). Basic Theory of Waveguide Junctions and Introductory Microwave network Analysis, D. M. Kearns and R. W. Beatty, Intl. Ser. of Monogr. in Electromag. Waves 13, 59, Pergammon Press, New York, NY (1967). Electrical Parameters of Precision, Coaxial, Air Dielectric Transmission Lines, R. E. Nelson and M. R. Coryell, Natl. Bur. Stand. (U.S.), Monogr. 96 (June 1966). back to top of page | back to index of electromagnetic measurements Thermal Noise MeasurementsTechnical Contacts: James P. Randa John Lomax Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements Noise Temperature Measurements (61410S-61465S)Noise temperature measurements are available on single-port, coaxial and rectangular-waveguide noise sources under conditions of continuous, unmodulated operation. Precision coaxial connectors or clean, smooth, and flat standard EIA waveguide flanges are required. Measurement results on devices submitted with adapters attached may apply only to the source/ adapter combination. Complete operating instructions and special electronic connectors should be supplied, and pertinent operating conditions (voltages, circuits, etc.) should be specified for the noise source to be measured. Devices submitted that are not of sufficient quality or not mechanically compatible with the measuring system will be rejected, and an appropriate fee will be charged. Availability of measurements at specific frequencies and for various connector types is specified above. The measurement uncertainty varies with noise temperature, reflection coefficient, connector type, and source stability. The relative expanded uncertainty typically lies between 0.9 % and 1.5 % of the noise temperature. The noise temperature measured and reported is the available noise temperature, defined to be the available noise power per unit bandwidth divided by Boltzmann's constant. For noise temperatures above T 0= 290K, we also report the excess noise ratio delivered into a reflectionless load (ENR0). It is defined by
NIST noise-temperature measurements are performed on total-power radiometers, using two primary thermal noise standards, one of which is at ambient temperature and one of which is at cryogenic (liquid nitrogen) temperature. For measurements at 30 and 60 MHz, tunable coaxial standards [1] are used. From 1 to 12.4 GHz, coaxial standards [2] are used, and for 12.4 GHz and above, waveguide/horn standards [3,4] are used. The radiometers themselves are described in references [1,5-7]. The NIST radiometers are double-sideband, total-power radiometers. The IF frequency is 0 (i.e., the LO frequency is set to the measurement frequency), and the IF bandwidth BIF ranges from 5 MHz to 20 MHz, depending on the particular radiometer. Thus the reported noise temperature represents an average over a frequency range of 2BIF centered at the measurement frequency. At least three independent measurements (including separate system calibrations, where applicable) of the noise temperature are made at each frequency. The noise source is allowed to warm up before any measurements are made. For many connector types and frequencies, the measurements are made through adapters. The procedure for characterizing the adapter and removing its effect is described in references [8,9]. The combined standard uncertainty is composed of type-A and type-B uncertainties [10,11]. Type-A uncertainties (u A) are those that are measured and determined by statistical methods, such as the standard deviation of the means of several independent measurements of the quantity of interest. Type-B uncertainties (u B) are those determined by other means, such as estimates of systematic uncertainties. The uncertainty reported is the expanded uncertainty, given by
back to top of page | back to index of electromagnetic measurements Special Noise Temperature Measurements (61495S)Measurements of electromagnetic thermal noise other than those listed above can sometimes be arranged on a case-by-case basis. These may include measurements through adapters, measurements out of the parameter ranges specified above, and measurements on systems currently under development. Such measurements should be discussed with one of the technical contacts before submitting a device for calibration. back to top of page | back to index of electromagnetic measurements References-Noise Temperature Measurements[1] NBS 30/60 Megahertz Noise Measurement System Operation and Service Manual, G. J. Counas and T. H. Bremer, NBSIR 81-1656 (Dec. 1981). [2] A Coaxial Noise Standard for the 1 GHz to 12.4 GHz Frequency Range, W. C. Daywitt, NBS Tech. Note 1074 (Mar. 1984). [3] Design and Error Analysis for the WR10 Thermal Noise Standard, W. C. Daywitt, NBS Tech. Note 1071 (Dec. 1993). [4] The noise temperature of an arbitrarily shaped microwave cavity with application to a set of millimetre wave primary standards, Metrologia, 30 (5) 471-478 (Oct./Nov. 1993). [5] The 30/60 MHz Tuned Radiometer-The NIST System for Noise Temperature Measurements, C. A. Grosvenor and R. L. Billinger, NIST Tech. Note 1525 (Mar. 2002). [6] Design and Testing of NFRad-A New Noise Measurement System, C. A. Grosvenor, J. Randa, and R. L. Billinger, NIST Tech. Note 1518 (Mar. 2000). [7] Noise-Temperature Measurement System for the WR-28 Band, J. Randa and L. A. Terrell, NIST Tech. Note 1395 (Aug. 1997). [8] Determining adapter efficiency by envelope averaging swept frequency reflection data, W. C. Daywitt, IEEE Trans. on Microwave Theory and Techniques, MTT-38 (11) 1748-1752 (Nov. 1990). [9] Single-port technique for adaptor efficiency evaluation, S. P. Pucic and W. C. Daywitt, 45th ARFTG Conference Digest, 113-118, Orlando, FL (May 1995). [10] Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results , B. N. Taylor and C. E. Kuyatt, NIST Tech. Note 1297 (Sept. 1994). [11] ISO Guide to the Expression of Uncertainty in Measurement, Intl. Org. for Standardization; Geneva, Switzerland (1993). [12] Uncertainties in NIST Noise-Temperature Measurements, J. Randa, NIST Tech. Note 1502 (Mar. 1998). back to top of page | back to index of electromagnetic measurements Program questions: Calibrations Phone: (301) 975-2200, Fax: (301) 975-2950 NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363 |
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