COMMISSION A : Electromaganetic Metrology
(November 2004 - October 2007)
Edited by
Mizuhiko Hosokawa
A1. Time and Frequency
Standards and Time Transfer Technique
In
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].
NICT is
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
GPS data
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
The researches
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].
NMIJ and
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].
Prof.
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[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 three coordinate measuring
machine (CMM) was additionally installed and evaluated for the accurate
measurement of the air linefs length as the phase standards [Horibe et al., 2006a,
2007b].
These activities made enhancing the NMIJfs evaluation capability of the air
line with various connector types, i.e. 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].
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