COMMISSION A : Electromaganetic Metrology (November 2004 - October 2007)
Edited by Mizuhiko Hosokawa
A1. Time and Frequency Standards and Time Transfer Technique
NICT headquarters has been keeping UTC(NICT) and Japan Standard Time (JST). A maximum of eighteen Cs atomic clocks and four hydrogen masers are used for making the timescale. A new JST generation system including various upgrades was completed after four years for development and started operation in February 2006 [Nakagawa et al. 2005, Hanado et al. 2006, 2007]. The timescale algorithm of UTC(NICT) has been investigated by NICT staffs [Hosokawa et al. 2005], and some improvements have been added to suppress the undesirable effects of anomalous clocks.
As for dissemination, two LF radio stations continuously transmit 40kHz and 60kHz respectively of JST time signal and the standard frequency signal. The field strength of LF signals during transmission was theoretically modeled. [Wakai et al. 2005]. To verify this model, two observation cruises on the Southeast Asian line and the North Pacific line using container ships were carried out in 2007. Results of the observation will be submitted to ITU-R WP7A in 2008. Public dial up time service via telephone lines has satisfied a large number of accesses.
NICT has started the accuracy evaluations of TAI unit by the Cs atomic fountain primary frequency standard NICT-CsF1 [Kumagai et al., 2005, 2006a, b, 2007]. Frequency uncertainty of NICT-CsF1 was estimated as 1.9x10-15 [CIRCULAR T 221].
NICT has developed an engineering model of space-borne hydrogen maser atomic clock. The weight of the physical part is reduced from 36.5 kg (breadboard model) to 27 kg. [Ito et al. 2007a].
NICT newly developed a Network Time Protocol (NTP) server with high-performance and started a public time service from 2007. The number of access is about fifteen million per day [Toriyama et al. 2007]. A new protocol for high-speed network time transfer has been investigated by using this server [Iwama et al. 2006, 2007].
On-site calibration system for frequency standards at NICT was equipped with a new system and approved by a peer review in 2006. Accordingly measurement uncertainty was improved from 10-13 to 5x10-14. NICT has also started a remote calibration system since 2005[Saito et al. 2006].
regularly performing Two Way Satellite Time and Frequency Transfer (TWSTFT)
between Germany (PTB) and Asian T&F institutes (KRISS, TL, NTSC, SPRING,
and NMIJ), and calibrated their station delays for TL, KRISS and NMIJ. Obtained
data by TWSTFT and GPS are reported to BIPM. The TWSTFT data for NICT/PTB link has
been adopted for TAI link since April 2007 in place of GPS data [CIRCULAR T
231]. Researches about GPS carrier phase method and TWSTFT for a long baseline
are in progress. NICT is developing
a new TWSTFT method using dual Pseudo Random Noises (PRN). NICT and USNO plan
to install a new TWSTFT relay station in
To distribute precise frequency by optical fiber, basic experiment using delay control has been started in a lab and a field.
NICT achieved pico-second order precision for two-way time and frequency comparison between the ground clock and the on-board atomic clock on ETS-8 satellite, which has been launched on December 2006. Both code phase and carrier phase showed consistent result and capability to monitor on-board atomic clock.
The time transfer subsystem (TTS) of the engineering model (EM) of the Quasi-Zenith Satellite System (QZSS) passed the environmental test, and the development of its proto-flight model (PFM) has been started. Its ground system is also been developing. The first QZS will be launched in 2010.
NICT has developed an engineering model of space-borne hydrogen maser atomic clock. The weight of the physical part is reduced from 36.5 kg (breadboard model) to 27 kg. [Ito et al. 2007a].
In NMIJ, following researches have been conducted.
Primary Frequency Standards; NMIJ has made the calibration of the International Atomic Time (TAI) with the Cs atomic fountain frequency standard, NMIJ-F1, a few times per year with a combined uncertainty of 3.9x10-15 since September 2005. This uncertainty is larger than that in the preliminary evaluations [Kurosu et al. 2004, Yanagimachi et al. 2005] and is limited by the evaluation uncertainty of a collision shift. We have changed the trapping scheme of atoms from MOT to optical molasses, in order to improve the long term stability. Laser systems, optics, and microwave systems have been upgraded for a better operationality [Yanagimachi et al. 2006]. NMIJ-F1 will be used as a reference oscillator for the evaluation of the optical lattice clocks in NMIJ, the development of our second fountain (NMIJ-F2), as well as used for the TAI contribution. Recently, we have started the construction of NMIJ-F2 to reduce the uncertainty.
Ultra-stable microwave oscillator; NMIJ has developed two cryogenic sapphire oscillators (CSOs) for local oscillator of a Cs atomic fountain and reference signal of a femtosecond mode-locked laser. The CSOs employ a loop oscillator configuration, which is servo controlled by a Pound-type frequency stabilization scheme and a power control servo. These oscillators exhibited a fractional frequency stability of 1.1 ~ 10-15 at an averaging time of 1 s [Watabe et al. 2006]. For averaging times between 2 s and 640 s the measured oscillator fractional frequency instability was below 10-15 with a minimum of 5.5 ~ 10-16 at an averaging time of 20 s. Also, we have implemented optical frequency synthesis from a CSO using a fiber-based frequency comb. The synthesized optical frequency exhibited an Allan deviation of ~6 ~ 10-14Ń-1/2 for averaging times between 1 s and 100 s and a minimum frequency instability of 3.0 ~ 10-15 at averaging times of 1280 s by comparing a rubidium two-photon stabilized laser. The short-term frequency stability was limited by the rubidium two-photon stabilized laser [Watabe et al. 2007].
Time Keeping; Four cesium atomic clocks with high-performance beam tubes (Agilent 5071A) and three active hydrogen maser frequency standards are operated for time keeping in NMIJ. One of the hydrogen maser frequency standards has been used for the generation of UTC(NMIJ) since March 2006 to improve the short term stability of UTC(NMIJ).
Time and Frequency Transfer; In NMIJ, dual frequency GPS receiver is one of the main international
time and frequency transfer tools. In addition, the Two Way Satellite Time and
Frequency Transfer (TWSTFT) have been conducted between NICT and several
analysis software named GCAST for short base line, such as 50 km, was developed
at NMIJ. Its main purpose is the data analysis for the time and frequency
transfer between NMIJ in Tsukuba and the
An optical fiber bidirectional frequency transfer system using Wavelength Division Multiplexing technology is also studied in NMIJ as future precise time and frequency comparison technique [Amemiya et al. 2006b].
Frequency Calibration Service; NMIJ and related organizations have been conducting to construct remote calibration systems for several metrology areas since 2001. Time and frequency division of NMIJ has been developing a frequency calibration system using GPS common-view method and Internet. NMIJ's remote frequency calibration service has been started since 2006 to the calibration laboratories. NMIJ has also started to develop the user equipment for the end users of the remote frequency calibration service [Imae et al. 2006]. A simple and cost effective frequency dissemination method also has been developed in NMIJ. In this method, optical fiber network service (INS-1500) is used for generating 10 MHz reference signal. Stability test results showed a good performance with an uncertainty of less than 1~10-12 at an averaging time of one day [Amemiya et al. 2006a].
Other activities related to Time and Frequency standards; One of other groups in AIST has been focusing its efforts on the development of a remote synchronization system for an onboard crystal oscillator (RESSOX) of the Japanese Quasi-Zenith Satellite System (QZSS). This system can synchronize ground time standard and the onboard crystal oscillator within 10 ns using signal delay models and pseudo-ranges of QZSS positioning signals [Tappero et al., 2006]. Through hardware simulation, AIST has demonstrated that synchronization within a few nanoseconds can be realized [Iwata et al., 2006, 2007].
A2. Laser Stabilization and Frequency Measurement
and developments in
NICT is developing a single Ca+ ion trap optical frequency standard. Matsubara et al. have measured the absolute frequency of the 4s2S1/2 - 3d2D5/2 forbidden transition with the measurement error of +-1.4kHz [Matsubara et al., 2007b]. To observe the a narrow linewidth laser is being developed. Its linewidth is 66 Hz and the floor of the Allan variance is 8.3x10-14 at an averaging time of 32 s. The long term frequency drift was 0.5 Hz / s [Li et al., 2007b].
To measure the laser frequency, NICT is developing two optical frequency comb based on commercially available Ti:sapphire laser [Ito et al., 2006, Nagano et al., 2006]. They measure the relative frequency stability between two combs and estimate the stability as 2x10-14 and 1x10-15 at averaging time of 1 s and 100 s respectively [Ito et al., 2007].
Various time and frequency standards related researches have been conducted in NICT and some Unversities, such as on atomic and molecular physics [Fukuda et al. 2005a, b, 2006, 2004 a, b, Kajita 2005a, b, c, d, 2006a, b, c, d, e, f, Matsubara et al. 2005c, 2006a, b, 2007a, b] and laser frequency stabilization [Li et al. 2005a, b, 2006a, b, 2007a, Matsubara et al. 2005a, b]. Dr. Kajita has proposed an infrared frequency standard based on trapped NH molecule. He estimate the uncertainty of the clock transition can potentially be reduced to lower than 1E-17 [Kajita, 2006].
Katori Group in
Activities in optical frequency region; In the optical lattice clock scheme, a collision-shift-free atomic clock was proposed and realized by using a one-dimensional lattice clock with a spin-polarized fermionic isotope [Takamoto et al., 2006]. Katori group and NMIJ have measured the transition frequency for the Sr lattice clock with an uncertainty of 9.8~10-15 using an optical frequency comb referenced to the SI second [Takamoto et al., 2006]. In October 2006, the International Committee of Weights and Measures (CIPM) decided to adopt the Sr lattice clock as one of gthe secondary representations of the secondh.
NMIJ has conducted the following researches on the optical measurements and standards; One is the development of an Yb optical lattice clock [Yasuda et al., 2007]. Vacuum system and laser systems have been prepared. Magneto-optical trapping of cold Yb atoms was realized using an intercombination transition (1S0 - 3P1; 556 nm). The experiment is under way toward trapping ultracold atoms in the optical lattice. A probe laser to drive the 1S0 - 3P0 transition in Yb atoms, which is stabilized to a high finesse Fabry-Perot etalon, is also being developed. A long-term measurement of optical frequencies has been demonstrated by using a fiber-based frequency comb [Inaba et al., 2006a]. Doppler-free spectroscopy using optical frequency synthesizer has been demonstrated by using a mode-locked Ti:sapphire laser and a continuous-wave optical parametric oscillator [Inaba et al., 2006b].
Takahashi et al. (
Suzuki et al.(
A3. Realization of Electrical Units (DC & LF)
Research works and developments on dc and low frequency electrical standards, that is, standards for dc voltage, dc resistance, ac resistance, capacitance, inductance, ac/dc transfer and so on, are implemented in Electricity and Magnetism division of National Metrology Institute of Japan (NMIJ) and Nanoelectronics Research Institute of Advanced Industrial Science and Technology (AIST). Most of these standards are realized based on Josephson arrays, or Quantum Hall Effect (QHE).
Concerning the research on Josephson arrays, fabrication of 5 V programmable Josephson arrays operated at 10 K has been finished. By connecting two 5 V samples in series, 10 V programmable Josephson voltage standard has been completed. [Shoji, A. et al., 2006-2007].
In order to realize just 10 kohm resistance standard based on the QHE, Quantum Hall Resistance (QHR) arrays are being developed. Using the series and parallel combination of QHE bars, various values of resistance are expected to be realized. Fabrication of single QHE bars used for QHR arrays has been finished. [Kaneko, N. et al., 2006-2007].
In the development of new device for ac/dc transfer staandard, planner multi-junction thermal converters (PMJTC) are being developed for the use of calibration of ac/dc current differences up to 1 A. A prototype of the PMJTC has been developed. [Fujiki, H., 2006-2007].
Calibration range for both ac resistance standards and inductive voltage dividers has been expanded from 10 ohm to 100 kohm at 1 kHz and 10 kHz [Domae, A. et al., 2005-2007], and the ratios of 0.01 to 1.0 at 200 Hz, 400 Hz, 1 kHz and 10 kHz [Sakamoto, N. et al., 2005-2007], respectively. Standards for loss angle of capacitors have been developed for 10 pF to 10 microF. [Nakamura, Y. et al., 2005-2006].
NMIJ has designated Japan Electric Meters Inspection Corporation (JEMIC) as an institute to be responsible for national standards of power and energy at 45 - 65 Hz. [Nakamura, Y. et al., 2007].
A4. EM field, Power density and antenna Measurement
In the field
of precision measurements for EM field, a dipole antenna is a simple linear
antenna and it is often used as a reference antenna. Since most of the
electromagnetic compatibility/electromagnetic interference (EMC/EMI)
measurements are carried out on an open-area test site, the antennas used in
the measurement should be calibrated above the ground plane. Several
calibration methods for the antenna factor (AF) have been proposed and widely
applied by the metrology institutes. However, although a critical quantity
sated in their certificate to trace the calibration chain is uncertainty,
detailed uncertainty analysis associated their calibration has not been
published. Uncertainty analysis strictly following the GUM for the three-antenna method and the reference antenna method
was published [
A continuous antenna factor in a wide frequency range is convenient to be used and such a broad-band antenna as a log-periodic antenna was evaluated for a metrology standard. A new method was proposed for evaluating a free-space antenna factor continuously through a wide frequency band. The method is based on a technique of a time-domain analysis and a pulse-compression technology for reducing the influence by the reflected waves from surrounding obstacles. The method was examined for calculating the free-space antenna factor of a log-periodic antenna widely used for EMI measurement [Kurokawa et al. 2005, 2006].
The developments of calibration techniques for loop antennas were carrying out by AIST and NICT. AIST started to develop the calibration method since 2002. Basically they calibrate the standard loop antenna by the g3-Antenna Method [Ishii et al. 2005]h and the customerfs loop antennas by the gReference Antenna Method [Ishii et al. 2007a]h. In order to simply calibrate the standard loop antenna, they also studied another new calibration method gMeasuring Impedance Method [Ishii et al. 2007b]h. AIST also started a calibration service for small loop antennas whose diameters are about 10 cm and 60 cm in the frequency range from 9 kHz to 30 MHz.
On the other
hand, NICT and
A novel optical system was proposed to measure S-parameters in one-path 2-port calibration [Hirose et al 2007a]. This system can completely replace coaxial cables by optical fibers in RF measurements using a vector network analyzer that require many kinds of calibration techniques for the accurate measurements. Using this system, antenna measurements were done blow 2 GHz and proved that the system realizes the dynamic range of 45 dB and the difference within 0.03 at a reflection coefficient compared to the coaxial cable system. This system is especially promising in antenna measurements because it realizes measurements without metallic cables.
A novel method was proposed in antenna measurements [Hirose et al. 2007b]. The method realizes antenna measurements in full 2-port calibration that requires only open-short-load calibration at each port without through calibration because of using the unknown thru algorithm. The residual systematic errors are completely equivalent to the conventional unknown thru method. No need to do through calibration is especially important in antenna measurements because we are released from the hard labor to mate cable connectors directly or to other cable connectors.
A method and a simple equation for determining the magnetic complex antenna factor (M-CAF) of a shielded loop antenna are presented. The investigated shielded loop antenna has two output ports of which outputs are differentially combined in time domain. The low-directivity of this loop antenna is useful for mapping magnetic fields. The proposed method is based on an equivalent circuit of the antenna system. The derived equation makes it possible to determine the M-CAF from the calculated effective length of the loop element and the measured reflection coefficient at an output port. The proposed method is confirmed by comparison between the waveform reconstruction using the M-CAF and the theoretical calculation for an electromagnetic pulse radiated from a monopole antenna on a ground plane. [Kohmura, 2006]
A method and configuration for generating a calculable electromagnetic pulse is proposed in which the electromagnetic pulse is radiated from a small monopole antenna placed near the edge of a semi-infinite ground plane. The monopole antenna is excited by an impulse train. The radiated electric field at a distance from the edge is calculated by the waveform of the excited impulse with the assistance of the Uniform Theory of Diffraction (UTD) to include the effect of diffraction from the edge of the ground plane. The electric field is also reconstructed by signal processing using the complex antenna factor (CAF) of a receiving wide-band antenna. The estimated systematic effects and the agreement of the calculated and reconstructed waveforms show that the generated electromagnetic pulse has a possibility to be used as a reference wave for electromagnetic pulse measurements. [Iwasaki, 2006]
A5. Power, Attenuation and Impedance Measurement
A direct comparison calibration system for WR-15 waveguide RF power sensors (60 GHz) was developed in NMIJ in 2004 to carry out the calibration system of millimeter wave power in addition to a calorie meter system for microwave power. After that, an international peer review and an ISO/IEC 17025 assessment of the quality management system for 2.9 mm coaxial RF power meter calibration in NMIJ were performed, and the quality management system was accredited by an accreditation body(National Institute of Technology and Evaluation) in February 2005. The report of CCEM.RF-S1.CL international comparison of RF power measurement with 2.4 mm connectors, in which NMIJ had participated in, in April 2004, was approved by BIPM in October 2005. Further, a direct comparison calibration system for 2.4 mm coaxial waveguide RF power sensors (full band) was developed in NMIJ in 2005 in addition to a caloriemeter system to extend the frequency range of calibration service. Besides, the frequency range of the NMIJ WR-15 waveguide calibration system was extended from only a point frequency of 60GHz to full band (from 50 GHz to 75 GHz) in 2006. In addition, a direct comparison calibration system for WR-10 waveguide RF power sensors (W band) was developed in NMIJ in 2006.
A measuring system of the reflection coefficient of reference power source of RF power meters was developed, and the technology was presented in CPEM 2006 in Turin, Italy [Shimaoka et al. 2006a].The result of CCEM.RF-S1.CL international comparison of RF power measurement with 2.4 mm connectors was presented in CPEM 2006 in Turin, Italy [Crowley et al. 2006b]. A new study of an atomic RF power standard started in 2007. This new technology is based on the observation of the Rabi oscillation of the double resonance spectrum of Cs vapor. The absolute RF power in WR-90 waveguide in a frequency of 9.2 GHz is determined by converting the frequency of the Rabi oscillation to the field strength in the waveguide. As a result of a basic experiment, a linear response of the Rabi oscillation frequency to input RF power was observed in 2007. Now, NMIJ is a pilot laboratory of APMP.RF-K8.CL RMO key comparison of RF power measurement with Type N connector. This RMO key comparison is now in preparation.
As for the noise standard, National Meteorology Institute of Japan (NMIJ) has extended a microwave radiometer system for the measurement of noise sources with WR42 waveguide output flanges in the frequency range from 18 GHz to 26.5 GHz. An uncertainty analysis for the thermal noise measurement is applied to the total power radiometer system which is represented by a radiometer equation [Shimada 2006]. NMIJ has been also developing the original cryogenic standard noise source with WR90 waveguide flange by using the sliding short method which is cooled by liquid nitrogen. The estimated value of the noise temperature of the original noise source is good agreement with the noise temperature which is measured by the calibrated radiometer. Uncertainties of the original noise source are being evaluated in detail now.
The development of a new broadband RF attenuation measurement system was begun in 2000 at the NMIJ, to meet the increasingly growing demands for accurate, traceable, and broad-band standards which have a high attenuation range. The system was planned to cover the frequency range of 10 MHz to110 GHz and the attenuation range of greater than 60 dB. The intermediate frequency (IF) substitution method using the inductive voltage divider (IVD) operated at several kHz as a reference standard was selected for the advantageous broadband characteristics. The IVD was adopted for the high accuracy and direct traceability to the national standard for a low-frequency voltage ratio. An attenuation system using the dual channel type of the IF substitution method with the IVD operated at 1 kHz was successfully produced for the frequency range of 10 MHz to 18 GHz. The system is used as a national standard and provides the attenuation calibration to several service systems including Japan Calibration Service System (JCSS). Improvement to the system was carried out to cover the frequency range of 18 GHz to 40 GHz. Higher accuracy as well as the system at the low frequency range was obtained by raising the IF to 10 kHz and employing two seven-decade IVDs in cascade arrangement [Widarta et al, 2007a]. A 10-kHz voltage-ratio standard was also constructed for uncertainty evaluation of the 10-kHz IF section/receiver of the system [Kawakami et al, 2006]. In order to increase the degree of automation in the measurement process, an automated receiver was constructed using a commercial programmable IVD and an originally designed attenuation constant IF phase shifter [Widarta et al, 2007b]. Comparison results on attenuation measurements between the automated and the manual receivers show good agreements. A study on simplifying structure of the system, particularly on the RF circuit which might be built in hollow waveguides, was carried out for implementation to the frequency range of higher than 40 GHz. A single channel type IF substitution method with the IF phase-locked loop was experimentally constructed and examined at 10 GHz [Iida et al, 2006a]. Satisfied enough IF signals for operating the IVD reference standard were obtained, even applying RF signals under the severe conditions. Good performances of the system in the V-band (50 GHz to 75 GHz) were also ensured [Iida et al, 2006b]. Some improvements and uncertainties evaluations to this system are being proceeded now.
In recent years, the development and dissemination of the microwave impedance standards, that are indispensable for the uncertainty evaluations of the power and attenuation standards in the microwave frequency region, is strongly required because of a traceability demand of the vector network analyzer and the input impedance of various test instruments, i.e. EMI receiver, on the basis of various regulations.
In the year 2004, NMIJ has started to develop the evaluation infrastructure for the microwave impedance standards on the basis of air dielectric coaxial standard lines, so-call eair linef [Horibe, 2005a]. For next two years, the evaluation systems of the air lines have been established for the various types of connectors [Horibe et al., 2004, 2005b]. The calibration services of the complex voltage reflection coefficients, in the frequency range of 30 kHz to 18 GHz, have been started for PC7 connector in 2005, and for Type-N50 connector in 2006 [Horibe et al., 2006c, d, 2007a]. These calibration cervices are based on use of the air line as the original impedance standards in the range of 0.5 GHz to 18 GHz, however, the impedance standards are traced to foreign NMI in other frequency regions. Uncertainty less than 0.0059 for PC7 connector and 0.0069 for Type-N50 connectors were achieved by using the air lines. Furthermore, the calibration services of the characteristic impedance derived from the dimensional measurements were started for the air line with PC7 connector in order to meet the industryfs needs in the traceability issue on the vector network analyzer and impedance analyzers [Horibe et al., 2005c]. In the year 2006, the [Horibe et al., 2006a, 2007b]PC14, PC7, Type-N50, Type-N75, PC3.5, PC2.92, PC2.4, PC1.85 and PC1.0 (up to 110 GHz). In 2006, the calibration services of the complex voltage reflection coefficients for PC3.5 connector, in the frequency range of 30 kHz to 33 GHz, have been started in 2006. Subsequently, in 2007, the scattering parameter (S-parameter) standards have been established for PC3.5 connectors in the frequency range of 0.1 GHz to 33 GHz [Horibe et al., 2007a].
CIRCULAR T 207 ISSN 1143-1393 2005
CIRCULAR T 208 ISSN 1143-1393 2005
CIRCULAR T 218 ISSN 1143-1393 2006
CIRCULAR T 221 ISSN 1143-1393 2006
CIRCULAR T 236 ISSN 1143-1393 2007
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