ISSN 1882-3432

CONTENTS
Proceedings of the 13th NICT TDC Symposium (Kashima, June 4, 2014)
Flux monitoring observations of Sgr A∗ at S and X bands with the NICT . . . . . . 1
Kashima–Koganei VLBI System II
Shunya Takekawa, Tomoharu Oka, and Mamoru Sekido
A New Veriﬁcation Method of Applied Calibrations onto Visibility Data
Makoto Miyoshi...... 3

Report of VLBI Experiments between Australia and Japan
Yoshiaki Hagiwara, Syunsaku Suzuki, Tomoaki Oyama, and Takashi Nishikawa...... 6

Receiving performance of Ishioka VGOS Antenna
Yoshihiro Fukuzaki, Kojin Wada, Jiro Kuroda, Shinobu Kurihara, Ryoji Kawabata, and Takahiro Wakasugi...... 8

Regular Geodetic VLBI Observation with a Wide-band Recording System
Takahiro Wakasugi and Ryoji Kawabata. . . . . 11

The Tian Ma 65-m radio telescope of Shanghai Observatory
N. Kawaguchi. . . . . 14

Status of Broadband VLBI Observation System (Gala-V) Development
Mamoru Sekido, K. Takefuji, H. Ujihara, M. Tsutsumi, S. Hasegawa,Y. Miyauchi, E. Kawai, R. Ichikawa, Y. Koyama, and T. Kondo. . . . . 17

Development of digital ﬁlters toward GHz-width VLBI
Kazuhiro Takefuji, Mamoru Sekido, Hideki Ujihara, Masanori Tsutsumi, Shingo
Hasegawa, and Tetsuro Kondo. . . . . 20

On a Wide-Band Bandwidth Synthesis
Tetsuro Kondo and Kazuhiro Takefuji. . . . . 23

Development of Wideband Feed
Hideki Ujihara, Kazuhiro Takefuji, and Mamoru Sekido. . . . . 28

- News - News - News - News The 13th IVS NICT- Technolgy Development Center Symposium. . . . 32

October 2014

1

Flux monitoring observations years ago[1]. It is possible that currently inactiveA∗ may be active sometime. Such variationsof Sgr A∗ at S and X bands with Sgrmay be caused by intermittent accretion of interthe NICT Kashima–Koganei stellar gas onto the central SMBH.
Recently, the Max-Plank-Institut für extraterVLBI System II
restrische Physik (MPE) group has reported the
Shunya Takekawa1 (shunya@z2.keio.jp),
Tomoharu Oka1,2 , Mamoru Sekido3
1

School of Fundamental Science and Technology,
Graduate School of Science and Technology, Keio
University
3-14-1 Hiyoshi, Kohoku-ku, Yokohama,
Kanagawa, Japan2
Department of Physics, Faculty of Science andTechnology, Keio University
3-14-1 Hiyoshi, Kohoku-ku, Yokohama,
Kanagawa, Japan
3
Space-Time Standards Laboratory, Kashima
Space Technology Center, National Insitute ofInformation and Communications Technology
893-1 Hirai, Kashima, Ibaraki, Japan
Abstract: A compact radio source Sgr A∗ is the nucleus of our Galaxy and harboring a supermassive
black hole with the mass of 4 × 106 M . While thecurrent activity of the Galactic nucleus is extremely
low, an activation subsequent to the infall of theG2 cloud is expected within several years. In order to search for the ﬂux variation which is causedby the interaction between the G2 cloud and theaccretion disk, we have been conducting ﬂux monitoring observations of Sgr A∗ at S band (2 GHz)and X band (8 GHz) using the NICT KashimaKoganei VLBI system (109 km baseline) since midFeburuary 2013. Until 3 June 2014, we observed
Sgr A* for 42 days. Four quasars (NRAO 530, PKS
1622–253, PKS 1622–297, PKS 1921–293) were also
observed as ﬂux calibrators. No signiﬁcant change
nor variation has been detected in the 8 GHz ﬂux
density of Sgr A∗ so far. The 8 GHz ﬂux density
was 0.81±0.06 Jy, while no signiﬁcant 2 GHz emission was detected by our system.

discovery of a dense gas cloud, G2, which is on
its way toward Sgr A∗[2] . The G2 cloud has themass of ∼ 3M⊕ and is on the elliptical orbit withhigh eccentricity. The G2 cloud has been stretched
and will be disrupted by the strong tidal force fromthe central SMBH. The tidal disruption of the G2
cloud will increase mass accretion rate onto thecentral SMBH, causing a multi-wavelength ﬂare.
The interaction between hot plasma around Sgr
A* and the G2 cloud may cause a bow shock, accelerating electrons, which emit synchrotron radiation in centimeter wavelength[3]. The G2 cloud
had been expected to reach the pericenter, ∼ 2400
Schwarzschild radii from the nucleus, in Spring
2014[4][5]. However, according to the most recent report, the G2 cloud has not yet reached its
pericenter[6] .
2.

Observations

In order to search for the centimeter-wave ﬂux
variations caused by the G2 event, we have conducted ﬂux monitoring observations of Sgr A∗ at 2
GHz and 8 GHz using the NICT Kashima–Koganei
VLBI system since mid-February 2013[7]. ThisVLBI system consists of K5/VSSP32 samplers andtwo 11-m diameter antennas which are located at
Kashima and Koganei in Japan. The baseline
length is 109.1 km. The observing frequencies are
2.21–2.29 GHz and 8.2–8.5 GHz. The spatial resolutions of this VLBI system are  250 mas and 70 mas at 2 GHz and 8 GHz, respectively. Until 3 June 2014, we observed Sgr A∗ for 42 days
in total, about ﬁve hours (EL > 15◦ ) each day.
Since 78th day-of-year (DOY) 2013, four quasars(NRAO 530, PKS 1622−253, PKS 1622−297, PKS
1921−293) are observed as ﬂux calibrators, while
only NRAO 530 had been used before 78th DOY.
The integration times are, 300 s, 30 s, 240 s, 240 s,
and 30 s, for Sgr A∗ , NRAO 530, PKS 1622−253,
1. Introduction
PKS 1622−297 and PKS 1921−293, respectively,
Milky Way has a 4 × 106 M supermassive black in each observing sequence. All the sources werehole (SMBH) at its center, which is recognized as observed by turns in the observing ﬁve hours.
a compact radio source Sgr A∗ . Despite the hugemass, Sgr A∗ is extremely dim and quiet. This ex- 3. Results
treme dimness suggests a very low mass accretion
Figure 1 shows a plot of the 8 GHz ﬂux densirate (< 10−5 M yr−1 ), and/or a low radiation eﬃties of Sgr A∗ and the calibrators. No signiﬁcantciency. On the other hand, the widespread (∼ 200
emission at 2 GHz has been detected so far. Wepc) distribution of Fe 6.4 keV ﬂuorescent line emis∗∗
39 determined Sgr A ﬂux by using the correlation
sion implies that Sgr A was far brighter (∼ 10
amplitudes of calibrators, and the 8 GHz ﬂux of
erg s−1 ) than the present about several hundred
NRO 530 (5.4 Jy[8] ). Note that quasars are variable

IVS NICT-TDC News No.34

2100

Flux density [Jy]1622-253
NRAO 530
Sgr A*
1622-297
1921-293
101

0.1
40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520
Day of year 2013

Figure 1. Flux densities of the observed sources at 8 GHz. These ﬂux densities are values averaged overeach observing day. Error bars show 1σ standard deviation for each day.
objects in every wavelength, thus the ﬂux calibration method employed here is a little controversial.
Nevertheless, the 8 GHz ﬂux of Sgr A∗ is reallystable, exhibiting no signiﬁcant ﬂare or variation.
We obtained the average ﬂux is 0.81±0.06 Jy.
4.

Summary

In order to search for the radio ﬂux variations of
Sgr A∗ associated with the G2 event, we have conducted the ﬂux monitoring observations at 2 GHz
and 8 GHz with the NICT Kashima-Koganei VLBI
system. We obtained the 8 GHz ﬂux densities of
Sgr A∗ from the mid-February 2013 to 3 June 2014
for 42 days, while no signiﬁcant emission from Sgr
A∗ at 2 GHz has been detected by our system. SgrA∗ is very stable at 8 GHz, and the average ﬂux is
0.81±0.06 Jy. These monitoring observations arevery important for studies of SMBHs and active
galactic nuclei. When the ﬂare is detected in ourmonitorings, we will alert it to the world as soon as
possible. We intend to continue these monitorings
as often as possible for the next several years.
References[1] Ryu, S. G., et al. 2013, PASJ, 65, 33[2] Gillessen, S., et al. 2012, Nature, 481, 51[3] Narayan, R. et al. 2012, ApJL, 757, L20[4] Gillessen, S., et al. 2013, ApJ, 774, 44[5] Phifer, K. et al. 2013, ApJ, 773, 13[6] Eckart, A. et al. 2014, ATEL #6285[7] Takekawa, S. et al. 2013, IVS NICT-TDC
News, No.33, 18[8] Healey, S. E. et al., 2007, ApJS, 171, 61

October 2014

3

A New Verification Method of Gaussian probability distributions in the x and ywith an rms deviation σ given by Eq.
Applied Calibrations onto Vis- coordinates(6.43) in Thompson et al. (2001)[2]. Z have aibility Data
probability distribution given by

National Astronomical Observatory Japan,
2-21-1 Osawa, Mitaka Tokyo, Japan 181-8588
Abstract: Visibility calibrations are essentially important for VLBI astronomical imagings. In general, however, the VLBI data calibrations lack their
veriﬁcation methods testifying the validation. For
that reason, too much nervous data ﬂagging often fails to utilize an original spatial resolutionof VLBI. Or adversely, incorrect results from improper calibration and analysis can be reported.
Therefore, it is better to establish an objective index to show the validity of VLBI data calibrations.
We here show our approach to establish such a veriﬁcation method by comparing statistical propertyof calibrated visibility data and theoretical prediction from thermal noise property. We have no wayof knowing about the structure of observed astronomical source in advance, while thermal noises
which will be included in calibrated visibility data
can be estimated from measurements of Tsys andantenna performance during observations. If we
can subtract the components of observed source
structure from calibrated visibility data, the residuals of the calibrated visibility should show a statistical property as of pure thermal noise (if the calibrations are correctly performed). If not, the performed calibrations are not suﬃcient for reducing
systematic errors from visibility data and the resultant synthesis images should be not perfectly correct. Here we show such a trial using calibrated visibility data of Miyoshi et al. (2011)[1] and demonstrate their visibility data calibrations are correctly
performed.

p(Z) =
where Z =
p(φ ) =

Z 2 + |V |2 |
Z|V |
Z
exp(−
)I0 ( 2 )
σ2
2σ 2
σ

(2)


Zx2 + Zy2 .



|V |2
π |V | cos φ1exp(− 2 ) 1 +
2π
2σ
2
σ
2
2 
|V | cos φ)· exp(2σ 2
|V | cos φ
√×[1 + erf (
)]
(3)
2σ

where I0 is the modiﬁed Bessel function of orderzero, and erf is the error function. φ is the phaseangle measured from the direction of V vector.

y (Imaginary)

Makoto Miyoshi (makoto.miyoshi@nao.ac.jp) ,1(Zx − Vx )2 + (Zy − Vy )2
exp(−
)
2πσ 2
2σ 2
(1)
It is often useful to deal with the magnitude andphase of the visibility, denoted by Z and φ. Respective probability distributions are:p(Zx , Zy ) =[Z䠖 correctly calibrated visibility]= [V: signal] + [ε䠖 thermal noise]ε:㻌 thermal noiseφ’φ㻌 x(Real)

1.

Statistical Behavior of Visibility

Statistical behavior of visibility including signal
and thermal noise is theoretically well known. Below we show the equations modiﬁed from Thompson et al. (2001)[2] but the deﬁnition is modiﬁed
suitable for the issue. The measured (and correctly calibrated) visibility is represented by avector Z = V +  where V and  represent thetrue visibility (the signal) and noise components,
respectively. Because the observed source has acomplex structure in general the signal V is presented as a vector so that V = (Vx , Vy ). The phaseof the measured visibility is here denoted by φ.
The components of  have independent zero-mean

Figure 1. Deﬁnition of Visibility

2.

Diﬀerence of Visibilities between Channels

Because the source structure is unknown to us
in general, we cannot predict how the signal V behave. If we can subtract the V from the visibility
Z, the residual is a pure noise , whose nature canbe estimated from measured system temperatures

IVS NICT-TDC News No.34

y (Imaginary)4

Z2-Z1 = 䠄V+ε2䠅-䠄V䠇ε1)= ε2-ε1= [difference of thermal noise]ε2ε1

㻌 x (Real)

Figure 2. Cancelation of Signal in Visibility
and antenna performance. A diﬀerence of visibilities between diﬀerent video channels recorded at
the same time with the same baseline corresponds
to such quantities. If the applied calibrations to
the visibilities are precisely appropriate, the diﬀerence should statistically show the noise nature.
As for the distribution function of amplitude diﬀerence of visibilities, we found the following formula.
We denote the amplitude diﬀerence of visibilities
as t which can be negative.
√|t|t2
πt|t|exp(− 4σ2 )erf ( 2σ )p(t) = +
8σ 3
√
|t|
t2
πtexp(− 4σ2 )erf ( 2σ )
−
4σ|t|
√ 2
t2
πt exp(− 4σ
2)
−
8σ 3
√
t2
πexp(− 4σ
2)
+
4σ
t2
texp(− 2σ
2)
(4)
+
2
4σ

plied calibrations are proper or not. If the distributions followed those of diﬀerence between thermal noises, the calibrations are proper and the resultant synthesis images are free from systematic
errors. In Figure 3, we show examples of real distributions of visibility diﬀerence both in amplitude
and phase from calibrated visibility data in Miyoshi
et al. (2011)[1]. The data were calibrated in eachchannel individually using tasks likes FRING andCALIB in AIPS, the obtained solutions for delay,
rate, phase and amplitude are totally independent
for each channel. Both of distributions are ﬁtted
the theoretical thermal noise curves quite well sothat the applied calibration solutions to the visibility data reduced systematic errors properly. We
checked not only these but all of diﬀerences between all channels in all base lines except MKbaselines and found that 92.56% of amplitude differences and 87.20% of phase diﬀerences are within
95% conﬁdence level of Chi-square test. Whichmeans almost of data set were well calibrated bytheir manner. We further made synthesis images
using visibility data set within 3 − σ distributions
and the resultant images are almost the same asones reported in Miyoshi et al. (2011) [1]. These results demonstrated that their report of QPO detections in SgrA∗ from VLBA images were not caused
from systematic errors by improper calibrations.
4.

Summary

By checking distributions of diﬀerences of visibility (both in amplitude and in phase) between
recording channels obtained from the same baseline at the same time, we can testify the validationof the applied calibrations to the data. Using thismethod we proved that the image-QPO detectionin Miyoshi et al. (2011) [1] are not from improper
calibrations of VLBA data. About the details wewill report in our preparing paper.
5.

Acknowledgments

We thank Nitta S. for his kind analytical calculations for the distributions of diﬀerence of visibilAs for the distribution function of phase diﬀerence
ities.
of visibilities, we found that the function has no
analysis solution, however, we can make a concrete References
table from numerical solution. 1 Here we assumed[1] Miyoshi, M., Shen, Z-Q., Oyama, T., Takathe same noise level in respective channel.
hashi, R., Kato Y., Publ. Astron. Soc. Japan,
63, p1093-1116 (2011).
3. Real Distribution of Visibility Diﬀer[2] Thompson, A. R., Moran, J. M., Swenson, G.
enceW., (2001), Interferometry and synthesis in raBy checking the distributions of diﬀerence of visdio astronomy, 2nd ed., John Wiley & Sons,
ibilities of recording channels, we can verify the apInc.

1 The equation shown in Miyoshi et al. (2011)[1] is incorrect.

October 2014

Figure 3. Distributions of Visibility Diﬀerence. Those of Phase (left) and Amplitude (right)

5

IVS NICT-TDC News No.34

6

Report of VLBI Experiments
between Australia and Japan

2.

Experiment Conditions

The experiments were conducted on February
23 in 2014 by employing four 20m telescopes of
VERA and the Tidbinbilla 70m telescope (DSSYoshiaki Hagiwara43) located in the Canberra Deep Space Commu(yoshiaki.hagiwara@nao.ac.jp), Syunsaku
nication Complex (CDSCC). The experiments were
Suzuki, Tomoaki Oyama, Takashi
conducted at 22 GHz for sources of Orion-KL and
Nishikawa , National Astronomical Observatory
0420-014 and total time of the experiments wasof Japan 2-21-1 Osawa, Mitaka, Tokyo 181-8588,
about 1 hour. The parameters of the experimentsJapan
are summarized in Table 1.
VLBI Data were recorded with 1024 Mbps (16Shinji Horiuchi(shoriuchi@cdscc.nasa.gov)
channels x 16 MHz x 2 bits/sample) recording rate
CSIRO Astronomy and Space Science, Canberra
at each site using the Mark 5C terminal of the
Deep Space Communications Complex, PO Box
Tidbinbilla 70m and the OCTADISK for VERA.
1035, Tuggeranong, ACT 2901, Australia
The data obtained at each site were converted to
Abstract: We report on recent VLBI experiments ﬁles following the VLBI Data Interchange Format
linking the DSN-Tidbinbilla 70m telescope in Aus- (VDIF) [2]. The data were then transmitted to thetralia with the four 20m telescopes of VERA in correlator center at the National Astronomical ObJapan in early 2014. The data recorded at each servatory of Japan (NAOJ) in Tokyo via network
telescope were shipped to to Mitaka in Japan and processed on the NAOJ soft correlator systemand processed using the NAOJ software correlator (Softcos) after the experiments. A schematic dia(Softcos), resulting to successful fringe detection. gram describing the experiments is shown in Fig.1.
The maximum telescope separation in this experiment was over 8,300 km, and an resultant angular
Table 1. VLBI experiments
resolution is 0.38 arcsecond at 22 GHz. The amTelescopes
DSN-Tidbinbilla, VERA
bitious plan for this experiment is to connect theObservation date 2014 February 24
Tidbinbilla 70m to the East Asia VLBI Network
Duration
1 hour(EAVN) across the Paciﬁc Ocean.
Frequency
22.235 GHz
Rec terminals
Mark5C(Tid), OCTADISK(VERA)
1. Introduction
Sources
Orion-KL, 0420-014
Data
processor
NAOJ Software Correlator
VLBI experiments have been conducted by
the radio telescopes in East Asia VLBI Network(EAVN) in which 14 telescopes in China, Japan,
and Korea participated. Many attempts to organize the East Asia VLBI Network (EAVN) havebeen made for radio astronomy observations. The
EAVN will combine more than 10 radio telescopes
distributed over the countries of China, Japan, andKorea. One of the aims of the EAVN is to obtain abetter angular resolution that is provided telescope
separation between China and Japan and improved
imaging sensitivity by adding large telescopes suchas the new 65m telescope in Shanghai. It should
be noted that scientiﬁc results of astronomy using
the EAVN have been reported [1].
The EAVN has a more ambitious plan to extend
its maximum telescope separation that is currently
limited to at most 5,500 km. In order to extend
telescope separation for obtaining a better angularresolution, we organized VLBI experiments by linking the Tidbinbilla 70m telescope in Australia with
the VERA (VLBI Exploration of Radio Astrometry) in Japan. This might extend outside Asia andAustralia.

3.

Results

Fringes between the 70m and VERA using 8 seconds of data were detected in the both spectralline (Orion-KL) and continuum (0420-014) sources(Fig.2). For example, the peak of the fringe amplitude of Orion-KL from the Mizusawa-Iriki baseline (∼1,200 km) was obtained in signal-to-noise
ratio (SNR) of 620, while the fringe from the IrikiTidbinbilla baseline (∼8,100 km) was detected in
SNR of 430. This demonstrates that the source
structure of the maser in Orion-KL is more resolved by the longer Australian baseline. The same
trend can be seen for the fringe of the continuum
source (0420-014): The fringe peak amplitude of
the Mizusawa-Iriki baseline was obtained in SNRof 15, while that of the Mizusawa-Tidbinbilla baseline was 10, which shows that the source structureof the quasar, 0420-014 was certainly more resolvedby the longer baseline.

October 2014

Figure 1. Schematic diagram of the VLBI experiment: The data in VDIF format were recorded with
1 Gbps recording rate at Tidbinbilla and VERA
each. After the experiments, data ﬁles of the Tidbinbilla were transmitted to the correlator center at
NAOJ via network and fringe-search was made by
the software correlator (Softcos).
4.

Summary

7

Figure 2. The fringe plot of the TidbinbillaMizusawa (VERA) baseline for the source of 0420014: Fringe was detected in SNR of 10 using 8
seconds data. The data were processed using theSoftcos at NAOJ.
binbilla 70m telescope in the Canberra Deep Space
Communication Complex.

We succeeded in the fringe detection in the VLBI References
experiments connecting the 70m telescope at Tid[1] Fujisawa, K., Sugiyama, K., Motogi, K.,
binbilla in Australia with 20m VERA telescopes
Hachisuka, K., Yonekura, Y., et al., Observadistributed over Japan. The maximum telescopetions of 6.7 GHz methanol masers with Eastseparation in this experiment was over 8,000 km,
Asian VLBI Network. I. VLBI images of theresulting in a resolution of 0.38 arc seconds, ∼1.5
ﬁrst epoch of observations, Publications of thetimes better than that of the EAVN or ∼4 times
Astronomical Society of Japan, Vol. 66, Issue
better than the VERA (Table 2). The ambitious
2, 31 (1-29), 2014
plan for this experiment is to connect telescopes inAustralia to the EAVN. In future, those telescopes [2] Sekido, M., Takefuji, K., Kimura, M., Hoare expected to be connected via the ﬁber network
biger, T., Kokado, K., Nozawa, K.,Kurihara,
across the Ocean to transmit data for nearly realS., Shinno, T., Takahashi, F., Development
time correlation. This idea might extend to outsideof an e-VLBI Data Transport Software Suite
Australia and east Asia.
with VDIF, in Proceedings from the 2010 General Meeting, ”VLBI2010: From Vision to Re5. Acknowledgments
ality”, February, 2010 in Hobart, Tasmania,
Australia. (eds) D. Behrend and K.D. Baver.
We are grateful to Dr. Shinji Horiuchi and otherNASA/CP 2010-215864., p.410-414, 2010
staﬀ for support for this experiment at the TidTable 2. Array performance
Diameter Tsys SEFD
Ba
[m]
[K]
[Jy]
[km]
DSN-Tidbinbilla
70
40
48
0
VERA
20
150
2400 8336(Kashimad
34
140
304
7990
Telescopeθb[arcsec]
0
0.38
0.41

σc
[mJy]
2.2
0.78 )a) Baseline lengthb) Angular resolutionc) One sigma baseline sensitivities, assuming 256 MHz bandwidth and 60 seconds integration timed) Estimation by assuming that the NICT Kashima 34m telescope participated to this experiment

IVS NICT-TDC News No.34

8

Receiving performance of Ish- 2. Observing Facilities
ioka VGOS Antenna
In the new project, observing facilities are now
Yoshihiro Fukuzaki (fukuzaki@gsi.go.jp),
Kojin Wada, Jiro Kuroda, Shinobu
Kurihara, Ryoji Kawabata, Takahiro
Wakasugi

being constructed. The conceptual design consisting of the six components is depicted in Figure
1. The temporary operations rooms are installed
instead of the Operations Building, which will becomplete by the end of 2015.

Geospatial Information Authority of Japan,
Kitasato-1, Tsukuba, Ibaraki, Japan
Abstract: The Geospatial Information Authority ofJapan (GSI) has started a new project for constructing a VGOS station in Japan. The construction of the antenna (radio telescope) has been
complete and the necessary equipments (Front-end,
Back-end, H-maser, and so on) have also been delivered. The name of the new site is Ishioka, which
is located 17 km away from Tsukuba 32-m antenna.
We brieﬂy report the current status of the construction of the new antenna, and the initial receiving performance of the antenna and front-end
system.
1.

Introduction

The Geospatial Information Authority of Japan(GSI) has carried out VLBI observations since1981. In the ﬁrst period from 1981 to 1994, wedeveloped transportable VLBI systems with a 5m antenna and a 2.4-m antenna, and carried out
domestic observations by using them. As a result,
8 sites in Japan were observed and precise positions determined. In addition, Japan-Korea VLBI
observations were carried out by using a transportable 3.8-m antenna in 1995. In these observations, the Kashima 26-m antenna, which was removed in 2002, was used as a main station. Next,
in the second period from 1994 to 1998, GSI established four permanent stations: Tsukuba 32m, Sintotsukawa 3.8-m, Chichijima 10-m and Aira
10-m antennas. Up to the present, regular VLBI
observations by using the four stations have been
carried out. Especially, Tsukuba 32-m antenna isa main station for not only domestic but also international VLBI observations now.
In 2011, GSI started a project for constructing
a new antenna following the VLBI2010 concept,
which is recommended by the International VLBI
Service for Geodesy and Astrometry (IVS) as thenext-generation VLBI system.
This paper gives the outline of the project, thecurrent status of the construction of the new antenna, and the receiving performance of the antenna and front-end system as the initial result of
the performance measurement.

Figure 1. Conceptual design of the new observing
facilities
3.

Receiving Performance

3.1

Antenna

The antenna (radio telescope) is the main partof the observing system (Figure 2). Since a single
antenna is employed, very high slew rates are speciﬁed in order to be compliant with the VLBI2010
concept. In addition, Ring Focus optics is applied
for the antenna design in order to match the beam
pattern of the broadband feed. The receiving performance of the antenna with tri-band feed system was measured by receiving some strong radio stars (Cas-A, Taurus-A, Virgo-A). As a result,
the SEFDs for S and X band are approximately
1,700Jy and 1,300Jy, respectively. This means thatthe aperture eﬃciencies for S and X band are 59%
and 77%, respectively, if the system noise temperature is assumed as 50K. High receiving performancefor X band is conﬁrmed as the feature of the Ring
Focus optics.
On the other hand, RFI is more serious than expected because of the feature of Ring Focus optics.
In the case of Ring Focus optics, the aperture efﬁciency is better but the artiﬁcial radio signal canbe reach the feed more easily than the usually-used
optics like Cassegrain. In the new station, the radio signal for cellular phone is so strong in the frequency range less than 2.1GHz that the saturationof the ampliﬁer for S band may occur. Installation

October 2014

9of the High Pass Filter to cut the frequency lessthan 2.2GHz is necessary to avoid the saturationof the S band ampliﬁers. The speciﬁcations andthe performance of the antenna are listed in Table
1.

Figure 2. Photo of the new antenna.

Table 1. Speciﬁcations and performance of the newantenna.

of Technology in Sweden, and Quadruple-Ridged
Flared Horn (QRFH), which is developed at California Institute of Technology (Caltech), are thepractical as a broadband feed, so both feed systems are purchased. The employment of the feed
will be determined after the evaluation of the antenna performance with these two feeds. For thedesign of the antenna optics, employing the Elevenfeed was assumed.
In the both cases, the feeds and Low Noise Ampliﬁers (LNAs) are integrated into the each cryogenic system, whose physical temperature is lessthan 20K. The measured receiver noise temperatures for QRFH system are less than approximately
30K for the both polarizations (see Figure 3.). In
addition, in order to achieve the compatibility withthe legacy S/X band observation, tri-band feed system is also purchased, and used for the measurement of the initial receiving performance. (See theabove section)
The phase and cable calibration system are also
installed. A new type of P-cal unit is developedand employed. In addition, instead of the present
D-cal a new cable calibration system developed by
NICT is also employed. The speciﬁcations of thefront-end are shown in Table 2.
Table 2. Speciﬁcations of the front-end.

Parameter
Diameter
RF frequency range
Optics
Surface accuracy
Measured SEFD
Measured Aperture efﬁciency
AZ maximum slew rate
EL maximum slew rate
AZ maximum acceleration rate
EL maximum acceleration rate
Special feature

3.2

Value
13.2 m
2–14 GHz
Ring Focus≤ 0.1 mm (rms)
1,700Jy (S band)
1,300Jy (X band)
59% (S band)
77% (X band)
12◦/sec
6◦/sec3◦/sec2
3◦/sec2
Reference point canbe measured directlyfrom the ground for colocation.

Front-end

According to the VLBI2010 concept, a broadband feed is necessary to achieve high aperture efﬁciency over 2–14 GHz. At present the Eleven feed,
which has been developed at Chalmers University

Parameter
RF frequency range
Polarization
Feed
Dewar

Physical temperature
Receiver noise temperature
Total gain
Outputfrequency
range
Number of output
Phase and delay calibration

Injectionofcal/noise-source

P-

Value
2–14 GHz
Dual linear polarization
Eleven feed or QRFH
Feed, LNAs, and otherdevices should be included and cooled bycryogenic system.
≤ 20K
≤ 30K
≥ 45 dB
2–14 GHz
2 (for dual linear polarization)
New-type P-cal unit
New cable calibration
system developed by
NICTIn the front of the feed
(Eleven feed) or thefront of LNA (QRFH)IVS NICT-TDC News No.34

10

Figure 3. Receiver noise temperature for QRFH system (Upper: Horizontal polarization, Lower: Verticalpolarization.)
4.

Site Information

The site name is Ishioka, which is near Tsukuba(about 17km-NE from GSI). The location is shownin Figure 4. According to the results of a soil investigation of the site, the bedrock is located nearto the surface at less than 3 meter depth, which
could avoid the groundwater eﬀects in contrast to
Tsukuba 32-m station.
5.

Summary

A new project for constructing a new antenna inJapan has started. The new station will be fullycompliant with the VLBI2010 concept. The construction of the antenna was complete by the endof March 2014. The measurement of the receiving
performance of the antenna was done, and highaperture eﬃciency for X band is conﬁrmed. Implementation of the station will be done continuously
to start regular VLBI observation from April, 2015,
and this station will play an important role as amain station in the Asian region in the future.

Figure 4. Location of the site of the new observing
facilities.

October 201411

Regular Geodetic VLBI Ob- one channel, but it was necessary to select 8MHz
order to participate in IVS-R1 sessions. In adservation with a Wide-band indition, we also modiﬁed down converter a little to
Recording Systembe adaptable for IVS-R1 frequency sequences.
Takahiro Wakasugi (t-wakasugi@gsi.go.jp),
Ryoji Kawabata
Geospatial Information Authority of Japan,
Kitasato-1, Tsukuba, Ibaraki, Japan
Abstract: Aira VLBI Station, which is one of the
VLBI stations operated by the Geospatial Information Authority of Japan (GSI), had taken part in
IVS-R1 sessions while Tsukuba VLBI Station could
not participate in all IVS sessions due to damage tothe substructure of the antenna during 2013. For
this purpose, we installed a wide-band recording
system. After the improvement of the initial instability of the system, we succeeded in obtaining
good data and showed the usefulness of the system
for regular VLBI experiments.
1.

Introduction

The Geospatioal Information Authority of Japan(GSI) has participated in a lot of international
VLBI sessions under the framework of International VLBI Service for Geodesy & Astrometry(IVS) in order to maintain the International Terrestrial Reference Frame and to observe the Earth
Orientation Parameters. GSI has also carried out
domestic (JADE) sessions to determine the position of Japanese land on ITRF and to monitor platemotions around Japan by using four domestic radio telescopes (Figure 1).
Tsukuba VLBI Station is not only main facility of
GSI but also one of the central stations in eastern Asia. It has regularly taken part in IVS-R1,
IVS-INT2, IVS-INT3, IVS-T2 and JADE sessions.
However, Tsukuba had suspended all the sessions
from early May to the end of November 2013 dueto damage to the substructure of the antenna[1].
Instead of Tsukuba, we decided to take part in
IVS-R1 sessions with Aira VLBI Station (Figure2), which had mainly participated in IVS-T2 andJADE so far. The speciﬁcations of the Aira VLBI
Station are summarized in Table 1.
2.

In order to record the frequency sequence of IVSR1 sessions, we employed high speed A/D sampler
ADS3000+ and the versatile data recording system
K5/VSI (Figure 3) instead of K5/VSSP recording system with the video converter. ADS3000+
is a high speed A/D sampler, which is developed by NICT, JAXA/ISAS and COSMO RESEARCH Corp[2]. ADS3000+ can sample analog data 1Gsps*4ch and output digitized signal
64Msps*16ch for maximum by Digital Base-Band
Converter (DBBC) with VLBI Data Interchange
Format (VDIF). K5/VSI is a data recording andtransferring system, which is also developed by
NICT[3]. K5/VSI system is conﬁgured by a commercial Linux PC with PC-VSI board and RAID
controller board that are both inserted into the expansion bus slot. It can record data with up to
2Gbps at the maximum recording speed. The data
sampling and recording process with a set of digitalback-ends are adaptable for the coming new VGOS
observations.
The sampled data by ADS3000+ were recoded into
the RAID 0 system that was conﬁgured by some of
hard disks with K5/VSSP format by VDIF/SUDP
recording control software. The recorded data wasconverted to mark5b format and simultaneouslytransfered to the hard disks attached by USB. The
hard disks were shipped to Tsukuba soon after ﬁnishing sessions. Finally, the data were e-transferedto the correlator from Tsukuba via Internet.

Recording System

Before participating IVS-R1 sessions, we had tomodify the recording system of Aira because the ordinary recording system, which is usually used for
JADE, could not record the frequency sequencesof IVS-R1 sessions. Especially, the video converter
had a selection of 2MHz or 4MHz bandwidth for

Figure 1. Geodetic VLBI network of GSI.

IVS NICT-TDC News No.34

12

Table 1. Aira VLBI antenna speciﬁcations.
Owner and operating agency Geospatial Information Authority of Japan
Approximate position
130◦ 35’ 59.51” E, 31◦ 49’ 25.66” NYear of construction
1997
Radio telescope mount type
Az-El
Antenna optics
Cassegrain
Diameter of main reﬂector
10 m
Azimuth range
20 – 700◦
Elevation range
5 – 88◦Az/El drive velocity
3◦ /sec
Tsys at zenith (X/S)
120 K / 150 K
SEFD (X/S)
10300 Jy / 7400 Jy
RF range (X1)8180 – 8680 MHz
RF range (X2)8580 – 8980 MHz
RF range (S)2120 – 2520 MHz
Recording terminal
K5/VSSP, ADS3000+ with K5/VSI

Figure 2. Aira VLBI Station.
3.

Figure 3. ADS3000+ and K5/VSI recording system in Aira.

ResultAira participated in IVS-R1 sessions 20 times
from R1604 (Sep 2013) to R1613 (Nov 2013) andfrom R1621 (Jan 2014) to R1630 (Mar 2014). However, we missed large number of scans at the initial sessions because of the insuﬃcient memory capacity of the PC that composed K5/VSI recording
system. Moreover, the RAID controller board that
was also installed in the PC was unstable. We operated multiple K5/VSI system as recording servers
and replaced the RAID controller boards with new

ones. Finally, we were able to record most of observations successfully.
The number of the missed scans is shown in Figure
4. The missed scans were drastically decreased by
the addition of recording servers and the improvement of the RAID controller board.
Furthermore, the help of NICT with new, morestable recording control software enabled us toperform later sessions certainly. As a result, themissed scans became almost zero from the latter
half sessions. The percentage of the correlated

October 201413

baseline to the scheduled are also shown in Figure References
4. The percentage has certainly increased in ac[1] Wakasugi, T., Status report of the Tsukuba
cordant with the improvement and been kept withVLBI Station - damage of the antenna basehigh level after that.
ment due to over loading -, TDC News, IVS
NICT-TDC News, No.33, pp.8-10, 2013.
4. Summary
We carried out some VLBI experiments of IVSR1 sessions by using Aira VLBI Station instead of
Tsukuba, which faced to serious trouble of the substructure. We recorded the observation data withhigh-speed A/D sampler ADS3000+ with DBBC
and K5/VSI data recording system. The improvement of the performance of the PC that composed
recording system allowed us to obtain good datastability. We showed that the system was usefulfor regular VLBI experiments.
Finally, we sincerely thank for the NICT VLBI
members who gave us very kindly help.

[2] Takefuji, K., M. Tsutsumi, H. Takeuchi, Y.
Koyama, Current Status of Next Generation
A/D Sampler ADS3000+, TDC News, IVS
NICT-TDC News, No.31, pp.6-9, 2010.
[3] Koyama, Y., T. Kondo, M. Sekido, M.
Kimura, Developments of the K5/VSI System
for Geodetic VLBI Observations, TDC News,IVS NICT-TDC News, No.29, pp.15-18, 2008.

Figure 4. The session status of the Aira VLBI Station. The bar graph shows the number of themissed scan. The percentage of the correlated observations to the scheduled is also discribedin this plot. The solid line is percentage of Aira, the broken line is that of the average of all
stations.

IVS NICT-TDC News No.34

14

The Tian Ma 65-m radio telescope of Shanghai Observatory

N. Kawaguchi (kawagu.nori@nao.ac.jp)
Shanghai Astronomical Observatory
1.

Introduction

The Tian Ma 65-m radio telescope (Fig. 1) wasconstructed in 2012 and was started in the operation in 2013. Now it was primary used in thespace project (Chinese moon exploration project,
ChangE) in frequency bands of 2- and 8-GHz.
It was operated for radio astronomy observations,Pulsars, Hydrogen and Carbon recombination lines
in 1.6-, 2.3- and 5-GHz. The telescope is the largest
and the most sensitive radio telescope in the east
Asian region, and is expected as a major telescopein the EAVN, East Asian VLBI Network.
In this paper I present the recent activities ondeveloping new facilities to be installed into the
65m telescope. New frequency bands of Ka, K and
Q-band are going to be added to the 65-m. In
order to keep aperture eﬃciency in such high frequency bands, it is inevitavble to keep the best
optimized shape at low and high elevation angles
by compensating the unexpected gravitational deformation caused on a large main reﬂector. In thispaper an active surface control system is also presented.
The sheshan campus of the shanghai observatory
was established very recentry scince 2013. So also
the breif introduction of the new campus is presented here.

Figure 1. The Tian Ma 65m telescope

Figure 2. The Tian Ma 65m telescope

1.1

Location

The geometry around the Sheshan is shown inﬁg.2. The 65-m telescope is located at 3-km west
to the Sheshan Campus, opposite side of the 25-m
telescope. The 25-m telescope was founded almost
25 years ago but still has been working for the international VLBI observation. The 65-m telescopeis connected to the 25-m with an optical ﬁber cable and near-real-time fringe detection is possibleon the baseline between the 65-m and the 25-m
telescopes. The DiFX correlator is working at theSheshan Campus.
1.2

Sheshan Campus

The sheshan campus was opened in 2013, where
research staﬀs and students have just started working. In this campus we have a main hall (Fig.3) andresearch oﬃces (Fig.4). In the main hall computer
fasilities for VLBI correlation and space data analysis are installed. A big conference room with alarge display attached on the all span of the wide
wall. In the reserch building oﬃces of the research
staﬀs and students are prepared.

Figure 3. The main hall of the Sheshan Campus

October 201415

Figure 5. The Tian Ma 65m telescope

Figure 4. The research building of the Sheshan
Campus2.

Toward High Frequency Observation

The 65-m telescope is now working in frequency bands lower than 9GHz, i.e. L-band (1.251.75GHz), S-band (2.2-2.4GHz), C-band (4-8GHz)
and X-band (8.2-9GHz). New frequency bands,
i.e. Ku-band (12-18GHz), K-band (18-26.5GHz),
Ka-band (30-34GHz) and Q-band (35-50GHz) aregoing to be added. In such high frequency bands,
however, the gravitational deformation of the main
reﬂector is a serious problem to keep the high eﬃciency. On the 65-m telescope many actuators are
set behind the pannels to compensate the gravitational deformation. Before starting the active
surface control, the measurements of the surface
accuracy were started.
2.1

Holographic Surface Measurement by
a Satellite Signal

To see the potential accracy of the main reﬂector, the holograhic surface measurements were conducted to receive a signal from a geosynchronous
satellite orbiting just above the Shanghai city,which locates at azimuth angle 180degree and theelevation 52degree. The result is shown in Fig. 5
and at this ﬁxed elevation angle we can see thatthe 65-m telescope has good surface accuracy of
0.32mm-rms. The surface accuracy is good enoughin the highest observing frequency of 50GHz, one
twentyth of the wavelength (λ=6mm).
2.2

surface measurements by using a celestial strong
masers as a reference signal are planned. The
strongest water maser source, W49N, will be observed with two radio telescopes of 25-m and 65-m
and the interferometer fringes will be analyzed tomeausre the surface accuracy of the 65-m telescope,
which is scanned around the W49N while the 25-m
telescope keeps tracking on the W49n at the center
beam. For the W49N holography, a test 22-GHz
receiver is prepared as shown in Fig.6. It is used
under a room temperature environment but hasenough performance to detect W49N with enoughsignal-to-noise ratio.

A test 22-GHz receiver

The main reﬂector of the 65-m telescope has thepotential surface accuracy of 0.32mm, which is conﬁrmed by holographical surface measurement described in the previous section. It is necessary,
however, to know the gravitational deformation at
the diﬀerent elevation angles. The holographicalFigure 6. A conﬁguration of a 22-GHz test receiver
The perfomance was tested and shown in Fig. 7
and Fig. 8.
2.3

Holographic Surface Measurement by
a strong maser

The ﬂux density of the W49N is conﬁrmed witha VERA telescope and found to be 40KJy. The
baseline sensitivity between 25-m and 65-m telescopes at Sheshan has well been estimated to be
2200Jy. The SNR of 8000 is expected with integration time of one second. The hollography test withthe dynamic range of more than 30dB is possible
to do. The test result will be reported later.

IVS NICT-TDC News No.34

16

Figure 7. The system gain of an LNA anda mixer

Acknowledgement
The LNA and the mixer was loaned by
Japan Communication Equipment Co. Ltd.(NihonTsusinki). Also I got many supports from the staﬀsin Shanghai Observatory.I would like to express
my great thanks to the company and colleaguesin Shanghai Observatory. The data of the satellite holography was provided by Dr. Wang Jinqing.
Great thanks to him.

Figure 8. Noise performance at a room
temperature environmentOctober 201417

Status of Broadband VLBI Observation System (Gala-V) Development
Mamoru Sekido(sekido@nict.go.jp),
K. Takefuji, H. Ujihara, M. Tsutsumi,
S. Hasegawa, Y. Miyauchi, E. Kawai,
R. Ichikawa, Y. Koyama, and T. Kondo
NICT Space-Time Standards Laboratory,
Kashima Space Technology Center,893-1 Hirai, Kashima Ibaraki, Japan
Abstract: The Gala-V is a broadband VLBI system composed of two small diameter antennas andlarge diameter one for precise time and frequency
transfer over intercontinental distances. The prototype of the broadband feed for the Gala-V has been
newly designed for the 34m radio telescope. First
light observation has been successfully made as simultaneous observation of 6.7GHz and 12.2GHz
Methanol maser line spectrum from W3OH in January 2014. Pair of small diameter antenna MARBLE1 (1.6m diameter) and MARBLE2 (1.5m diameter) are ready for broadband observation withsingle linear polarization. The MARBLE1 antenna
has been moved to National Metrology Institute ofJapan (NMIJ) at Tsukuba in March 2014. Sinceboth the NMIJ and NICT are time keeping laboratory of UTC(k), thus time comparison between
NICT and NMIJ is good test bed for evaluationof the time comparison techniques. Three sessionsof 24 hours geodetic VLBI experiments were conducted in April - May 2014, and their station coordinates are determined within 5 mm horizontal
and within 5cm in vertical repeatability.
1.

Introduction

Counting microwave frequency emitted from Cs
atoms is used for standard unit of length of timeat present. More accurate clock based on counting optical emission from particular atoms are investigated and will become atomic time standard
in the next generation(e.g.[1]). For establishingre-deﬁnition of second, precise frequency comparison between laboratories over intercontinental distances is required. For the purpose of distantfrequency comparison, we are developing transportable broadband VLBI system (Gala-V). The
data acquisition of the system is made by acquiring signal of 4 bands of 1 GHz width each in thefrequency range of 3.2–14 GHz. Fixed frequency
array is designed in the Gala-V at present, and thefrequency array is selected based on (1) RFI surveyand (2) minimum redundancy array for high delay
resolution [2]. Although the frequency array is tentatively ﬁxed in our project whereas ﬂexible choiceof the band is speciﬁcation of VGOS[3], compatibility with the VGOS observing system is always in

Figure 1. Prototype of Iguana Feed install at
Kashima 34m antenna. SEFD is 1000 – 1500 Jy
in 6.5–14 GHz frequency range.

Figure 2. Frequency Spectra 6.7GHz and 12.2 GHz
of Methanol maser source W3OH observed with
Iguana prototype Feed of Kashima 34m antenna.
mind. Following section describes the progress ofbroadband system development and time and frequency transfer project since the last issue of TDC
News[2].
2.

Broadband system Development

Known broadband feeds such as eleven feed[4]and QRFH[5] have wide beam size, thus we had
to develop new broadband feed for our Cassegrain
type 34 m antenna, whose viewing angle fromthe focal point to the sub reﬂector is 34 degrees
wide. The ﬁrst prototype of the broadband feed
(Named ’Iguana Feed’) developed by NICT, whose
frequency range is 6.5–14GHz, was installed in Dec.
2013(Fig.1). The ﬁrst light observation was successfully made in January 2014, where two emission lines of methanol maser at 6.7 GHz and 12.2
GHz were simultaneously observed from the radiosource W3OH(Fig.2). Current system equivalent
ﬂux density of the broadband system of Kashima
34m antenna is 1000–1500 Jy in 6.5–14GHz range.
Though this feed will be used by the end of 2014 forIVS NICT-TDC News No.34

18

Table 1. Station coordinates determined by ﬁve
VLBI experiments (22-13 April 14-15 May, 30-31
May, 26-27 Jun., and 1-3 Aug.). Station Coordinates are estimated with Kashima 34m station
coordinates ﬁxed. Its epoch is MJD=56808.0.
Station
MARBLE1(Tsukuba)
MARBLE2(Koganei)(Fixed)KASHIM34

X
Y
Z
X
Y
Z
X
Y
Z

XYZ [mm]-3962276706.9
3308884000.7
3733538093.0-3942062034.9
3368277053.9
3702003875.0-3997650058.0
3276690071.0
3724278461.0

σerr [mm]
8
10
6
6
7
8

Table 1 shows the station coordinates determinedby 34m antenna station coordinates ﬁxed.
4.

Figure 3. MARBLE1 station installed at the top of
3-7 building of NMIJ at Tsukuba.
evaluation, upgrade of the feed design is under theplan to enable 3.2–14 GHz observation with bettereﬃciency.
3.

Moving MARBLE1 to Tsukuba (NMIJ)The Gala-V system is composed of pair of small
antennas and Kashima 34m telescope. Two small
antennas (MARBLE1 and MARBLE2) have prime
focus parabolic antenna with 1.6 m and 1.5 m diameter dishes, respectively. Quad Ridge Horn Antenna (QRHA)[6] is used for the feed, and has been
ready for broadband single linear polarization observation. The MARBLE2 antenna has been installed at the top of the second building of NICT
headquarters at Koganei. The MARBLE1 antenna
was moved from Kashima Space Technology Center(KSTC) to National Metrology Institute of Japan(NMIJ) at Tsukuba in the end of March 2014
(Fig.3). Both NICT and NMIJ have been keeping
their own time scale by atomic time standards, andtheir UTC(k) are regularly compared with UTC
determined by the BIPM (Bureau International desPoids et Measure). Therefore time comparison between NICT (Koganei) and NMIJ (Tsukuba) is agood test-bed for development of frequency comparison technique. After installation of MARBLE1
to NMIJ(Tsukuba), 24 hours geodetic VLBI experiments were conducted three times with X-band.

Three station experiments and frequency Comparison

Since baseline of small diameter antenna pairdoes not have enough sensitivity, VLBI data of AB
baseline was formed by linear combination of observable of OA,OB baseline, where A:MARBLE1,
B:MARBLE2, O:KASHIM34.
The convertingfrom two baseline data of OA,OB to single baseline AB data is given by following equation:
τAB (tprt )= τOB (tprt − τOA (tprt )) − τOA (tprt − τOA (tprt ))∼˙ (tprt )τOA (tprt )= τOB (tprt ) − τOA (tprt ) − τAB
where tprt is Epoch of data to be analyzed. Latter
equation is expression of the ﬁrst order approximating with respect to τOA with observed values
τOA , τOB and computed values of τAB
˙ . This equation has precision better than 1 pico second on any
ground based VLBI observation.
By using the geodetic VLBI data in April andMay, clock diﬀerence between NICT and NMIJ
was examined. Clock diﬀerence estimated by using
VLBI, GPS, and diﬀerence of UTC(k) publishedfrom BIMP1 are displayed in Fig. 4. Vertical position of the GPS and VLBI data in the plot are
indicated with oﬀsets to be in the same range with
UTC rapid and ﬁnal data of the BPIM. These plots
demonstrating that VLBI and GPS have similar
performance on clock rate comparison and bothdata shows good agreement with the diﬀerence ofUTC(k) rate reported from BIPM. Although thisequation is neglecting the source structure eﬀects,
there are no signiﬁcant problem at present becauseof relatively short baseline.
1 http://www.bipm.org/jsp/en/TimeFtp.jsp?TypePub=
publication

October 2014

19
-13

-4

GPS-AVVLBI
NMIJ-NICT(Final)
NMIJ-NICT(Rapid)
Final

VLBI

-6

UTC(NMIJ)-UTC(NICT) [nsec]

UTC(NMIJ)-UTC(NICT) [nsec]

-5

GPS

-7

GPS-AVVLBI
NMIJ-NICT(Final)
NMIJ-NICT(Rapid)

VLBI

-8
UTCr

-13.5

GPS

Final

-14

-14.5

UTCr

-9

-10
56768.5

56769

56769.5

56770

56770.5

56771

56771.5

-15
56805

56806

56807

56808

56809

56810

56811

56812

MJD

MJD

Figure 4. Clock comparison between UTC(NMIJ)- UTC(NICT) via VLBI(’+’) and GPS(’×’). Rapid
UTC comparison UTCr and ﬁnal UTC(k) comparison data published from BIPM are over plotted withsolid and dashed lines, respectively. Left panel is data during 22-24 Apr. and right panel is from 29th
May to 2nd Jun.

UTC(NMIJ)-UTC(NICT) [nsec]

0

References-0.5

GPS(ppp)[1] Gill P., “When should we change the deﬁnitionof the second?”,Phil. Trans. R. Soc. A, 369,
doi: 10.1098/rsta.2011.0237,2011.

-1
-1.5

UTCr

-2

[2] Sekido, M., et al., Development of Wide-band
VLBI system (Gala-V), IVS NICT-TDC NewsNo. 33, 11-14, 2013.

-2.5

VLBI

-3
-3.5

NMIJ-NICT(GPS)NMIJ-NICT(VLBI)NMIJ-NICT(UTCr:BIPM)

-4
-4.5
56870

56871

56872

56873

56874

56875

MJD

Figure 5. Clock comparison via VLBI(’+’) andGPS(’×’) performed during 1 – 3rd Aug. Vertical
position of the GPS and VLBI plots are adjusted
by arbitrary oﬀset.
Continuous VLBI experiment for frequency comparison was conducted during 1st - 3rd of August.
The clock data estimated by VLBI observation,
GPS, and UTCr data provided from BIPM weredisplayed in Fig.5. As the same with the results ofApr. - May, it is conﬁrming that the VLBI analysis
gives the consistent results with others. The scattering of the VLBI data is slightly larger than GPS
in this experiment. Since the VLBI data is not always obtained in uniform interval, then statistics
such as Allan variance is not applicable. Other
statistical evaluation such as sigma-z[7] have to beconsidered.
Acknowledgments
We thanks to Dr. K. Watabe, Dr. T. Suzuyama,
and Dr. M. Amemiya of NMIJ for supporting the
VLBI experiment and the collaboration. We acknowledge Prof. K. Fujisawa of Yamaguchi University, Dr. M. Honma, and Dr. N. Matsumoto of
National Astronomical Observatory for supporting
broadband feed development.

[3] Bill Petrachenko, VLBI2010: Progress andChallenges, IVS 2012 General Meeting Proceedings, 42-46 2012.
[4] Yang J., et al., “Cryogenic 2-13 GHz Eleven
Feed for Reﬂector Antennas in Future Wideband Radio Telescopes” IEEE Trans. Ant. &Prop., Vol. 59, NO. 6, pp.1918-1934, 2011.
[5] Akgiray A., et al., “Circular QuadrupleRidged Flared Horn Achieving Near-Constant
Beamwidth Over Multioctave Bandwidth:
Design and Measurements” IEEE Trans. Ant.
& Prop., Vol. 61, NO. 3, pp.1099-1108, 2013[6] V. Rodriguez, “A multi-octave open-boundary
quadridge horn antenna for use in the S to Kubands,Microwave Journal, March, pp. 84-92,
2006.
[7] Matsakis D., and Josties F. J., “PulsarAppropriate Clock Statistics”, ADA419480.
28th Annual Precise Time and Time Interval(PTTI) Applications and Planning Meeting,
Reston, VA, 3-5 Dec 1996.

20

IVS NICT-TDC News No.34

Development of digital filters meet the VGOS requirements, have been constructed for example GGAO 12 m antenna andtoward GHz-width VLBI
18 m Westford in the United States, TWIN Radio Telescope Wettezell (TTW) in Germany,the
RAEGE telescope at Yebes in Spain and Ishioka
telescope in Japan.
We, NICT/Kashima, has been also developing a broad-band system from 3 GHz to 15
GHz to our Kashima 34 meter antenna and two
small/transportability antennas. The broad-band
Kashima Space Technology Center,
project is named “Gala-V”. The most diﬀerent
National Institute of Information
things from other VGOS antenna, ﬁrst we use
and Communications Technology,893-1 Hirai, Kashima, Ibaraki 314-8501, Japan a 30 m class antenna, a feed horn (proto-typeNo.2) was installed on December 2013, has a sharp
Abstract: We have been studying a frequency com- beam pattern of 12 degree to illuminate the subparison technique with VLBI between 34 m in reﬂector. Moreover, We decided that no-redundant
Kashima, Ibaraki and two 1.5 m compact anten- frequency array of 3.2 GHz, 4.8 GHz, 9.6 GHz, 12.8
nas located in Koganei, Tokyo and in Tsukuba, GHz is ﬁxed. This array has ﬁne delay resolution
Ibaraki, respectively. Therefore, it is necessary to with minimum side-lobes and the array is got int
have a broad-band system to get better signal to line straightly in case of sampling speed at 16 GHz
noise ratio because of the compact antenna small- without DBBC. [1].
ness. To improve the performance of VLBI between
Out two compact antennas have 1.5 and 1.6 m
the compact antennas and Kashima 34 m, we have diameter, thus it is not easy to obtain fringes.
developed digital ﬁlters using a signal processor of
ADS3000+. Here we describe the techniques of 2. Digital signal processing for the broadband receiver
digital equalizer to compensate a steep band-pass
proﬁle and digital band-pass ﬁlter for a VLBI obFigure 1 shows an internal signal ﬂow ofservation of a maser.
ADS3000+[3]. Two Intermediated frequency (IF)signals are sampled simultaneously at speed of
1. Introduction
2048MHz and 8-bits quantization. Then, Finite
National Institute of Information and Commu- Impulse Responce ﬁlter (FIR), whose coeﬃcientnications Technology (NICT) has been not only are manually loaded through LAN-based telnet, aredeveloping VLBI observation system as the IVS- applied to sampled stream in real-time. If the coTDC, but also maintenance and keep the Japanese eﬃcient of the FIR is made within 65 taps, any
time standard. Recently NICT, AIST and Tokyo designs of the ﬁlter such as low-pass, high-pass,university have been developing an optical-lattice band-pass, band-rejection and equalizer are possiclock for the next generation time standards and ble to realize. ADS3000+ has other FPGA core
for the redeﬁnition of ”the Second”. Thus, it is nec- of the digital base-band conversion, a comaprison
essary to compare the distant clocks somehow with test between other Digital-Backend (DBE) was reseveral techniques. If two stations are close in a few ported by Whitney [5].
hundreds kilometer, optical-ﬁber transmission [4]is the best technique for the comparison. However
distant stations comparison over thousand kilometer and inter-continent is needed some techniquethrough space for example GPS, Two-Way Satellite Time and Frequency Transfer (TWSTFT) andVLBI.
As for the Time and Frequency transfer (T&F)
by VLBI, the order of 10−16 in a few days is targeted. Since our two compact 1.5 m antennas arequite small for VLBI, it is necessary to have abroad-band system such as a VLBI2010 Global Ob- Figure 1. Signal ﬂow of ADS3000+, FPGAs reserving System (VGOS).
alize any FIR ﬁlters.
For the next generation of the geodetic VLBI,VGOS has been speciﬁed a fast moving antenna
and broad-band receivers. Some antennas, which
Kazuhiro Takefuji (takefuji@nict.go.jp),
Mamoru Sekido, Hideki Ujihara,
Masanori Tsutsumi, Shingo Hasegawa,and Tetsuro Kondo

October 2014
2.1

21

Digital equalizer

2.2

Since our vlbi experiment are carried out over 1
GHz bandwidth, a band-proﬁle has a diﬃculty tokeep ﬂat. For the purpose of the band-proﬁle to
be ﬂat, We made a digital equalizer to compensate
a bad band-proﬁle. Actually the digital equalizer
is made by a “bad-proﬁle” itself. Firstly we takethat spectrum as a template. Secondly we make amatched ﬁlter by inversing the template. Thirdly acoeﬃcient of FIR completes after the matched ﬁlter converts into 8-bits length. A wider bit length
has wider dynamic range. Equation 5 shows therelation-ship between dynamic range (here it issame as SNR) and bit length [6],SN R = 6.02N + 1.76[dB],

Digital band-pass ﬁlter

In case of observing a maser source with wideband VLBI, RFI signals become major issues.
To suppress the RFI, we realize a digital bandpass ﬁlter with ADS3000+. We make the digital
BPF, which focused on a spectral line 6.7GHz of
methanol maser emission.

(5)

where N is bit length. Since ADS3000+ has a dynamic range of 50 dB ( 6.02*8+1.76 ), the realized
digital ﬁlter becomes also high dynamic range even
1 or 2-bits re-quantization. Figure 2 shows before
and after the applied digital equalizer. A 10 dB
diﬀerence on the X-band of the 34 m could be reduced to a few dB. There are still some ripples
on the band-proﬁle. However, the ripple must be
much ﬂat when the number of the coeﬃcient tap
can increase.

Figure 5. The digital band-pass ﬁlter is demonstrated the spectral line of methanol maser. Dynamic range was slighly improved when digital BPF
was applied.

Figure 5 shows the on-oﬀ operation of the digital BPF. Most RFI could be removed. Moreover,dynamic range of the maser line (ground level-topeak) increased 1.65 dB to 2.23 dB. Since the time
diﬀerence of the on-oﬀ operation was only 2 min,we considerd that the improvement was caused
by eﬀective sampling. We carried out the maser
source observation between the compact antenna
and Kashima 34 m
3.

Summery

We have been developed the digital equalizer anddigital band-pass ﬁlter to improve a performanceof VLBI and to suppress RFIs. Since the digiFigure 2. The digital equalizer is demonstrated to tal equalizer compensates the band-proﬁle to be
X-band of the Kashima 34 m.
ﬂat, we could obtain better fringes. The digital
BPF suppressed the RFI and we could focus on the
spectral line of the maser emission which becomes
Then we carried out VLBI observation for the slighly wide dynamic range. The other digital ﬁlter
digital equalizer between the compact antenna and can be created to satisfy other requirements.
Kashima 34 m. Figure 3 and 4 show the results.
A eﬀect of the digital equalizer can be seen on the References
cross-spectrum even the VLBI. The cross-spectrumof the ﬁgure 4 became much ﬂat comparing with [1] Mamoru Sekido, Kazuhiro Takefuji, Hideki
Ujihara, Thomas Hobiger, Masanori Tsutﬁgure 3. The SNR of the fringes also increased thesumi, Shingo Hasegawa, Yuka Miyauchi,
strength of 20 % with three times on-oﬀ operations.
Ryuichi Ichikawa, Yasuhiro Koyama, and TetTherefore, We could use the sampling bits with ﬂatsuro Kondo, Development of Wide-band VLBI
spectrum much eﬀectively.

IVS NICT-TDC News No.34

22

Figure 3. Result of a VLBI experiment without the digital equalizer

Figure 4. Result of a VLBI experiment with the digital equalizer. The SNR was improved about 20 %.

Figure 6.
BPF.

Result of VLBI with digital BPF. RFIs could be suppressed outside the bandwidth of thesystem (Gala-V), IVS NICT-TDC News No.
33, 2013.
[2] Mamoru Sekido, K. Takefuji, H. Ujihara,
M. Tsutsumi, S. Hasegawa, Y. Miyauchi, E.
Kawai, R. Ichikawa, Y. Koyama, and T.
Kondo, Status of Broadband VLBI Observation System (Gala-V) Development, IVS
NICT-TDC News No. 34, 2014.
[3] Kazuhiro Takefuji, Masanori Tsutsumi, Hiroshi Takeuchi, Yasuhiro Koyama, Current
Status of Next Generation A/D Sampler
ADS3000+, IVS NICT-TDC News No.31,
2010.

[4] M.Fujieda, M.Kumagai, S.Nagano, Coherent
microwave transfer over a 204-km telecom
ﬁber link by a cascaded system, IEEETUFFC,
vol.57, no.1, pp.168-174, 2010.
[5] Alan Whitney, Chris Beaudoin, Roge r
Cappallo, Arthur Niell, Bill Petrachenko,
Chester A. Ruszczyk, and Mike Titus, VLBI
Digital-Backend Intercomparison Test Report,”http://www.haystack.mit.edu/workshop/ivtw/2012.12.17 DBE testing memo ﬁnal.pdf”[6] Walt Kester, ”Understand SINAD, ENOB,
SNR, THD, THD + N, and SFDR so
You Don’t Get Lost in the Noise Floor”,
http://www.analog.com/static/imported-ﬁles/tutorials/MT-003.pdf

October 201423

On a Wide-Band
Bandwidth Synthesiseq.(6) can be written as
 t1  f0 +fB

S(f, t)
t0f0
· exp{−i2πf (Δτ + Δτ̇ t)}df dt.

F (Δτ, Δτ̇ ) =Testuro Kondo (kondo@nict.go.jp)
and Kazuhiro Takefuji
Kashima Space Technology Center,
National Institute of Information
and Communications Technology,893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

Introduction

The bandwidth synthesizing software named“KOMB” is a software package to obtain delay residual and delay rate residual from crosscorrelation data [Kondo and Kunimori, 1984;
Kondo et al., 1999]. KOMB was initially developed for treating the correlated data consisting of
a number of channels (14 or 16) where each channel has a narrow frequency bandwidth of 2 – 32
MHz and is distributed in dual RF bands (S-band(2 GHz) and X-band (8 GHz)).
Recently it becomes possible to sample signals
with a sampling frequency of 1024 MHz (corresponding to 512MHz bandwidth) and higher because of a remarkable progress in the performanceof a sampling device. Now a wide band observation
system exceeding a band width of 10 GHz is under
the development. The current version of KOMB
cannot process such wide-band observation data.
We are, therefore, investigating a realistic method
to obtain delay residual and delay rate residualfrom wide-band data to revise the software KOMB.
2.

Changing an integration range for frequency fromf0 ∼ f0 +fB to 0 ∼ fB , i.e., introducing fv = f −f0 ,eq.(8) can be re-written as
F (Δτ, Δτ̇ ) = exp(−i2πf0 Δτ )·

 t1  fB
t0

0

S(fv , t) exp(−i2πfv Δτ )
· exp(−i2πf0 Δτ̇ t) exp(−i2πfv Δτ̇ t)dfv dt (9)Here, | exp(−i2πf0 Δτ )| ≡ 1 and the last termexp(−i2πfv Δτ̇ t) is considered as 0 under the condition of conventional VLBI observation, i.e., fB ∼10 MHz and t1 ∼ 100 sec. Finally, we get
F (Δτ, Δτ̇ ) = t1  fBS(fv , t) · exp(−i2πfv Δτ )dfv

t0
0


(10)
· exp(−i2πf0 Δτ̇ t)dt.
Eq.(10) is a two-dimensional (2-D) Fourier transform with respect to Δτ and f0 Δτ̇ , so we can use a
2-D fast Fourier transform (FFT) to calculate thesearch function.
2.2

Search function(8)

Fine search function

A bandwidth synthesis combines a number ofA “coarse search” and a “ﬁne search” were inichannels. A search function of a bandwidth syntially developed by Whitney [1974] and have been
thesis is deﬁned as
used for long time to obtain delay and delay rate
 t1  fB
residuals from correlated data.
 N
F (Δτ, Δτ̇ ) = Sn (fv , t)
0
2.1 Coarse search function
n=1 t0· exp[−i{2π(fn + fv )Δτ + φn }]Eq.(6) shows the integration of a cross-spectrum
S(f, t) over time t and frequency f with correcting· exp{−i2π(fn + fv )Δτ̇ t}dfv dta trial phase θ for a cross-spectrum. This equation
is called a search function, and a θ which maximizes N≈ 
exp(−i2πfn Δτ )F (θ) is a solution, i.e., a search result.
n=1
 

 t1  fB
F (θ) = S(f, t) exp{−iθ}df dt(6)·
S (f , t) exp{−i(2πf Δτ + φ )}t0

When θ is expressed by using a residual delay (Δτ )and a residual delay rate (Δτ̇ ) as follows,θ = 2πf (Δτ + Δτ̇ t),

(7)

0

n

v

v



· exp(−i2πfn Δτ̇ t)dfv dt

n

(11)

where a frequency range for channel n is fn ∼fn + fB and φn is an additional instrumental phase

IVS NICT-TDC News No.34

24

at each channel, and exp(−i2πfv Δτ̇ t) ≈ 0 is as- If 2π(fn −f1 )Δτ̇ Δtk
1, eq.(16) can be expressed
sumed again. Let Δτ = Δτm + Δτs and Δτ̇ = asΔτm
˙ + Δτ˙s where Δτs and Δτ˙s corresponds to the
K
N
 
residual obtained by the coarse search and assumF (Δτ, Δτ̇ ) = Ds (n, k)1, eq.(11) can be re-written as
ing |2πfv Δτm |k=1 n=1
 N
F (Δτ, Δτ̇ ) = exp(−i2πfn Δτ )·

 t1  fB
t00· exp(−i2πfn Δτ )
· exp(−i2πf1 Δτ̇ Δtk).

n=1

Sn (fv , t)Eq.(17) is a two-dimensional (2-D) Fourier transform with respect to Δτ and f1 Δτ̇ , so we can use
a 2-D FFT again to calculate this function.

· exp{−i(2πfv Δτs + φn )}dfv· exp(−i2πfn Δτ̇s t)· exp(−i2πfn Δτ̇m t)dt.

(12)

 fB
0

Sn (fv , t)

· exp(−i2πfv Δτs )dfv
· exp(−i2πfn Δτ̇s t),then we have
 N
exp(−i2πfn Δτ )F (Δτ, Δτ̇ ) = 
n=1

 t1

·
Ds (n, t) exp(−i2πfn Δτm˙ t)dt.

2.3

Condition for 2-D FFT

A 2-D FFT cannot be used for calculating a ﬁne1 issearch function when |2π(fn − f1 )Δτ̇ Δtk|
not satisﬁed. Let’s investigate a condition allowed
to use a 2-D FFT. Assuming an X-band, let a bandwidth be 1 GHz (i.e., fn − f1 = 1 GHz), and integration time Δtk(= T ) be 100 sec, then solving
the conditionWe, now, deﬁne Ds (n, t) as
Ds (n, t) = exp(−iφn )(17)|2π(fn − f1 )Δτ̇ T |

(13)

1

(18)

regarding Δτ̇ , we get the condition as follows.
|Δτ̇ |

1≈ 1.6×10−12 (s/s) (19)2π(fn − f1 )Δτ̇ T

Namely, residual delay rate must be suﬃciently less(14) than 1.6×10−12(s/s) to use an FFT. If in the case oft0
a residual delay rate of about 1.6 × 10−12(s/s), thisis often occurred in an actual observation, a bandEq.(14) can be re-written as
width should be suﬃciently smaller than 1 GHz.
N
Actual processing in KOMB is performed as folK 
Ds (n, k)
F (Δτ, Δτ̇ ) = lows. At ﬁrst, a coarse-search is carried out. Folk=1 n=1
lowed by coarse search results are reﬂected to crossspectra through eq.(13), and then a ﬁne-search, i.e.,· exp(−i2πfn Δτ )a bandwidth synthesis is carried out. Hence rate
residual at the bandwidth synthesis is thought to· exp(−i2πfn Δτ̇ Δtk)
(15) be close to zero. Thus we can use an FFT for calculating a ﬁne-search function in the time domain.
where k(= 1, 2, · · · , K) is an index number in the Although if there exists a large rate residual, an ertime domain, Δt is its interval period, and Δτ̇ is ror due to this rate residual can be avoided, because
now used instead of Δτm
˙ . Eq.(15) is called a ﬁne a ﬁnal calculation to ﬁnd out a peak is carried out
search function. By using the lowest RF frequency by calculating a search function directly (without
f1 , eq.(15) can be further re-written as
use of an FFT).
When rate residual is suﬃciently small to sat
N
K 
isfy
the condition discussed above, considering fB
F (Δτ, Δτ̇ ) = Ds (n, k)in eq.(10) as a total bandwidth of an X-band and
k=1 n=1
using the suﬃcient number of FFT points in a frequency domain, it is possible to carry out a band· exp(−i2πfn Δτ )width synthesis by a 2-D FFT without a coarse· exp(−i2πf1 Δτ̇ Δtk)
search process. When KOMB was developed, thenumber of FFT points suitable for ptactical use was· exp{−i2π(fn − f1 )Δτ̇ Δtk}.
(16) limited to at most 8192 or so. It was, therefore,

October 201425

unable to execute a bandwidth synthesis withouta coarse-search process eﬃciently at that time. So
that, a search process was divided into two steps,
such as a coarse-search and a ﬁne-search. However, it was a quite reasonable processing method
considering from the case that large rate residual
remained.
The discussion so far is the case considering a
bandwidth of at most 1 GHz. If we consider thecase of a bandwidth of up to several GHz with anionospheric delay, how a search function can be expressed?
3.

Wide band search function

In order to discuss a search function in the case ofwide band under the existence of ionospheric delay,
eq.(7) is modiﬁed as
θ = 2πf {Δτ + Δτ̇ t + Δτion (f )}(20)

where Δτion (f ) denotes an ionospheric delay and
it is expressed asΔτion (f ) = αf −2 ΔD(21)(8GHz) is about 3 nsec for the diﬀerence of TECs
of 1017 /m2 (this TEC diﬀerence can occur sometimes). Using eq.(20), we can write a search function as t1  f1

F (Δτ, Δτ̇ ) = S(f, t)t0

f0· exp{−i2πf (Δτ + αf −2 ΔD)}
· exp(−i2πf Δτ̇t)df dt.
(22)
Now we assume a wide band such as from 2 GHz(f0 ) to 14 GHz (f1 ). In this case eﬀect of ionosphere can no longer be neglected. Therefore weshould use eq.(22) as a search function. In otherwords, it has the possibility of estimating TEC as
well as a residual delay. However the frequency dependency of the term exp(−i2πf Δτ̇ t) in the time
direction becomes large, and it is diﬃcult to adopt
an FFT for calculating the integration in the time
domain.
In the mean time, the term of frequency integral
in eq.(22) is called a delay resolution function, i.e.,
 f1
S(f )
D(Δτ ) =for a frequency range suﬃciently higher than theplasma frequency of ionosphere (≈ 10 MHz) [see,e.g., Ratcliﬀe, 1959], where ΔD is the diﬀerence off0
total electron content (TEC) in ray pathes to two·
exp{−i2πf(Δτ+ αf −2 ΔD)}df.
(23)
stations (unit is electron/m2 ), and α = ±1.34 ×
10−7 where a positive sign is for a group delay and Let’s investigate an ionospheric eﬀect on a widenegative for a phase delay.
band observation by using the delay resolutionfunction.
3.1

Examples of delay resolution function

Fig.2 shows an example of frequency allocation
at a wide-band observation.
Fig.3 shows the

1 2
0

1.6

3.2

4.8

3
6.4

8.0

4

9.6 11.2 12.8 14.4 GHz

4 3 1 20

Figure 1. Relation between total electron content (TEC) and frequency for various ionospheric(group) delays.

1.6

3.2

4.8

6.4 GHz

Figure 2. An example of frequency allocation ata wide-band observation (upper panel). The lower
panel shows a frequency allocation after sampledwith a sampling frequency of 12.8 GHz. As shown
Fig.1 shows a relation between total electron in the ﬁgure, the frequency allocation is a nocontent (TEC) and frequency for various iono- redundant allocation.
spheric (group) delays. For an example we canread from the ﬁgure that the diﬀerence of iono- delay resolution function (eq.(23)) without ionospheric delays between S-band (2GHz) and X-band sphere (i.e., ΔD = 0) for the case of the frequency

IVS NICT-TDC News No.34

26

Figure 3. A delay resolution function without ionosphere (i.e., ΔD = 0) for the frequency allocation
given by Fig.2 for a bandwidth of 1.6 GHz (upper)and for 0.5 GHz (lower). In case of 0.5 GHz bandwidth, an ambiguity of 0.625 nsec appears causedby the least common multiple of frequency spacing(1.6 GHz) of each band.
allocation given by Fig.2 and for bandwidths of
1.6 GHz and 0.5 GHz for each frequency channel(band). In case of 0.5 GHz bandwidth, an ambiguity of 0.625 nsec appears caused by the least
common multiple of frequency spacing (1.6 GHz).
Fig.4 shows the case of a TEC of 4.0×1016 el/m2 .
The shift of the main peak occurs. Moreover, symmetry of the function is lost and a larger peak appears at a position diﬀerent from the original delay position. Fig.5 shows the case for larger TEC(10.0 × 1016 el/m2 : this situation can occur commonly). Peak amplitude is weakened by half forthe case of a 1.6 GHz band width.
As shown in these examples, it is diﬃcult to determine residual delay by calculating a delay resolution function. Furthermore, the frequency dependency of the term exp(−i2πf Δτ̇t) cannot be
neglected for a large delay rate residual, then wecannot calculate a wide-band search function eﬃciently by using a 2-D FFT. In this case, what kindof a search method is realistic?

Figure 4. Same as Fig.3 for a TEC of 4.0 ×
1016 el/m2 .
4.

Realistic approach

4.1

Integration period available to use 2-D
FFTAs have mentioned, we cannot use a 2-D FFT
for calculating a search function in the case of abandwidth of exceeding several GHz. However, anintegration period of 100 sec has been assumed in
the discussion. Thus, let’s investigate the maximum integration period that 2-D FFT can be used
for the calculation of a search function. A condition equation eq.(18) is shown below, but fn − f1
is replaced by fB .
|2πfB Δτ̇ T |

1

(24)

Fig.6 shows a relation between delay rate residual (Δτ̇ ) and frequency range (bandwidth) (fB )for various integration periods (T ). Their relation
satiﬁes the condition of |2πfB Δτ̇ T | = 1. For an
example, we can read from the ﬁgure that in caseof a bandwidth of 1.6 GHz an integration period
is about 100 sec for Δτ̇ of 1 ps/s. This is derived
from the condition of |2πfB Δτ̇ T | = 1, so that aband width should be small enough than 1.6 GHz
1 for theto satisfy the condition of |2πfB Δτ̇ T |same integration period and rate residual. We canalso read from the ﬁgure that Δτ̇ should be smallenough than 1.6ps/s for the case of a bandwidth of

October 2014

27

Figure 6. Relation between delay rate residual (Δτ̇ )and frequency range (bandwidth) (fB ) for various
integration periods (T ) where their relation satiﬁes|2πfB Δτ̇ T | = 1.

Figure 5. Same as Fig.3 for a TEC of 10.0 ×
1016 el/m2 .

can avoid this situation by scheduling an observation span length properly, so that we will develop
a software program under the assumption that an
SNR is assured for each band data.
5.

10 GHz and an integration time of 10 sec. If thecondition is not satisﬁed, we cannot use a 2-D FFT
for the calculation of a search function.
4.2

Realistic search method

Here we consider a realistic search method. The
most realistic method is a two-step search that isconventionally carried out in the current version of
KOMB, i.e., at ﬁrst a coarse search, then followed
by a ﬁne search. Delay rate residual is determinedby a coarse search under the condition of a bandwidth of at most 1 GHz (ionospheric eﬀect is not
so large unless Δτ̇ is not so large), and then a result is fed back to the correction of cross-spectra
to calculate a wide-band search function by a 2-D
FFT. If Δτ̇ is determined accurately enough at acoarse search process, rate search at a wide-bandsearch can be omitted.
As for a ﬁne delay search, two methods are considered as follows.
1. at ﬁrst estimate TEC from each band results,then combine each band data with correcting
ionospheric delays to obtain a ﬁne delay.
2. calculate a delay resolution function directlyfor various combinations of TEC and delay,
then ﬁnd a peak to obtain a ﬁne delay.
Method 1 will not work properly when a signal
to noise ratio (SNR) of each band data is low. We

Conclusion

Eﬀects of delay rate residual and ionosphere ona wide-band bandwidth synthesis of which bandwidth reaches upto 10 GHz have been investigated.
We have concluded that a two-step search consisting of a coarse search and a ﬁne search is a realistic
method so far, which is adopted in the current version of band width synthesizing software KOMB.
However suﬃcient SNR at each band should beguaranteed to perform the search successfully. As
for the case of insuﬃcient SNR, we will continue toinvestigate a possible method.
References
Kondo, T. and H. Kunimori, III-5 bandwidth synthesizing software (KOMB), Rev. Radio Res. Lab.,
Vol.30, No.1, pp.199–216, 1984 (in Japanese).
Kondo, T., M. Sekido, and H. Kiuchi, 3.2.3 KSP bandwidth synthesizing software, J. Commun. Res. Lab.,
Vol.46, No.1, pp.67–76, 1999.
Ratcliﬀe, J.A., The magneto-ionic theory and its applications to the ionosphere, Cambridge University
Press, 1959.
Whitney, A.R., Precision geodesy and astrometry
via very-long-baseline interferometry, Ph.D. Thesis,
M.I.T., 1974.

IVS NICT-TDC News No.34

28

Developmentof Wideband Feed

Hideki Ujihara (ujihara@nict.go.jp),
Kazuhiro Takefuji and Mamoru Sekido
Kashima Space Technology Center,
National Institute of Information
and Communications Technology,893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

Status of development

No other wideband feed ﬁts for our antennas inbeam size. Thus, two diﬀerent types of wideband
feeds were developed and now in production for
Kashima 34m and MARBLE.
One was named IGUANA feed after our GalaV(Galapagos VLBI) project in Kashima and aimed
for cassegrain focus of conventional radio telescopewith bandwidth of 2.2-18GHz(or 22GHz in plan).
This feed is consisted with a smaller Daughter
feed for higher frequency(above 6.5GHz) and bigger Mother feed for lower frequency(Fig.1).

Figure 2. IGUANA daughter feed

Figure 3. Testing IGUANA daughter feed at METLAB in Kyoto UNIV. Physical dimensions are
φ133mm(N o.1), φ120mm(N o.2) × L300mm

Prototype feed No.1 were set on the place ofprevious C-Band horn(5GHz) of Kashima 34m inthe end of 2013, then replaced by No.2, and they
are tested and compared. Fringes of methanol
masers(6.7/12.2GHz) were successfully obtainedwith MARBLE, which is small VLBI antenna with
Figure 1. Simulation model of IGUANA feed 1.5m or 1.6m diameter dish and its feed is placed
in COMSOL Physical dimensions : φ400mm × at focus of parabola. IGUANA cannot stay on foL800mm, more or less.
cus of MARBLE due to its size, thus another feedis needed. The other wideband feed has sill noname, temporary here, it may be called as the new
The daughter feed is a multimode horn(Fig.2), feed(Fig.4). The small one is for MARBLE andwhich realizes nearly same beam patterns in both the other fat one is for 34m. They are designed
E/H planes with low cross polar, without thick and for using at the center focus of parabola antenna,
complex wall structure in corrugated horn. Be- such as MARBLE or small antennas. However its
cause it is placed in the mother feed, its wall should beam size can be easily arranged for another optics.
be thin, thus no choice for me. The two daughters Gala-V uses 4 channels of 1.6GHz in 3.2-14.4GHz.
were made as prototypes in early 2013 and tested They are 3.2-4.8GHz, 4.8-6.4GHz 9.6-10.4GHz andin METLAB (Fig.3) and 34m antenna before the 12.8-14.4GHz. This new feed can receive over 3.2third and her Mom were designed. The second is 14.4GHz and its ﬂat-head beam in higher channels
resemble the ﬁrst, but slim and its beam pattern is will improve aperture eﬃciency of MARBLE withslightly fat.
out ring focus optics.

October 2014

29

3.

Measurements

3.1

Feeds

Far ﬁeld beam patterns of the feeds were measured with near ﬁeld scanner in METLAB of Kyoto Univ. IGUANA daughter feeds have circular
waveguide output with nearly 6.4GHz cutoﬀ frequency. We can use it with higher cutoﬀ waveguide
adaptor following SMA converter for single linear
polarization output.
3.2
Figure 4.
New feed with WRD350D24-SMA output.
Physical dimensions : φ240mm × L300mm

2.

Numerical Simulation

Today, we can use 3D simulations for antenna
design, but the simulator and computers do notgive us the solution. The solution means a designof the antenna, which is deﬁned as a problem of ﬁxing each dimensions of every part of antenna structure to meet its speciﬁcation, such as beam width,shape, return loss in every operational frequency.
Conventional feed, which is conical horn with orwithout corrugation, have very few design parameters, such as axial length, aperture diameter andinput waveguide diameter...that’s all, countable ina hand. However multimode horn or wideband feed
has complex structure so it has much more physicalparameters, thus the combination of the parameters will soon be greater than the numbers we canhandle in our life. So heuristic choice of various
ideas may be helpful. Before you dive into simulation, remember Chinese Postman Problem.
Also the choice of the numerical scheme aﬀects incomputational time. Iteration scheme take longer
time for higher frequency because scales of themesh against the wavelength become larger, thus
declination rate of errors in each iteration steps
become smaller. Fig.5 shows an example. Computational time for 12GHz is tenth longer than for
8GHz. However, this is eﬃcient in memory size.
On the other hand, direct scheme oﬀers nearly
constant calculation time, however this is memory
eater and its solution may have errors in higher
frequency which may not be negligible. These aretrade-oﬀ which you can choice. Highest frequencyof the antenna deﬁnes resolution of the mesh andlowest deﬁnes antenna aperture size, thus simulations of whidband feed needs huge memories. In
my case, typical simulation time for one model isa day, using 256GB physical memory...Let it Go!
The heat of CPUs never bothered me anymore.

34m antenna

Measured Tsys and SEFD of 34m with No.2
prototype daughter feed are shown in Fig.6 andFig.7 Aperture eﬃciency in Fig.8 was calculated
from Tsys and SEFD. However it should be notedthat is a preliminary result, Tsys is low at both of
methanol frequencies, that is good for astronomers.
The aperture eﬃciency is around 40% due tooﬀset of the feed position and alignment error.
These feeds were expected nearly 50% eﬃciency for
Gala-V high band(9.6-10.2GHz and 12.8-14.4GHz).
Lower frequency is deﬁned by cut-oﬀ of the waveguide, it is clearly shown in ﬁgures. The eﬃciency
gradually downs to higher frequency and cross 30%
at 15GHz, so 15GHz is concluded as practical upper limit. This degradation is not so severe problem, thus may be ﬁxed in next replacement ormaintenance time.
4.

Plans

Complete IGUANA feed is delayed due to production schedule of its complexed waveguides.
However, we can use 6.5-15GHz with the prototype
daughter feed in 34m antenna.
The new feed will replace previous wideband feedof MARBLE and bring better eﬃciency. Anothernew feed will be used in 34m for Gala-V before theproduction of IGUANA completes.
All of our wideband feeds now are used in single linear polarization with commercial waveguideSMA converter. Dual polarization output will be
designed in 2014 for replacement of single-pol output.
Acknowledgement:
Extension of receiver band for methanol masersof this work was achieved with the grant of Joint
Development Research supported by the Research
Coordination Committee, National Astronomical
Observatory of Japan (NAOJ).
The new feed was developed with the incentive
fund in NICT in FY2013.
Also, all of our wideband feeds were made in theWorkshop of NICT.

IVS NICT-TDC News No.34

30

Figure 5. An example of convergence time in COMSOL.
the solution time for 12GHz is 10th longer than 8GHz.

Figure 6. Tsys of 34m with No.2 test feed

October 2014

Figure 7. SEFD of 34m with No.2 prototype feed.Solid line shows moving average of 10 points

Figure 8.
Aperture eﬃciency of 34m with No.2 prototype feed.
Solid line shows moving average of 10 points

31

32

IVS NICT-TDC News No.34∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼ News ∼The 13th IVS NICT- Technolgy Development Center Symposium
The 13th VLBI Technology Development Center Symposium was held on June 4th in 2014 at the
Kashima Space Technology Center. This symposium has been held annually since 2001. At the endof this March 2014, three big leaders of Japanese VLBI community have formally retired. They are
Prof. Fujinobu Takahashi of Yokohama National University, Prof. Noriyuki Kawaguchi of National
Astronomical Observatory of Japan(NAOJ), and Dr. Tetsuro Kondo of NICT. They started VLBI
carrier from Radio Research Laboratory (current NICT) and played great leadership in especially technology development in VLBI community. This symposium was held with meaning of memorizing theirachievements,too.
Seventeen talks were presented in the symposium, which include variety of VLBI research subjects
from technology developments to scientiﬁc observations. Although proceeding papers of following presentations are not included in this issue, they suggest fruitful aspects of further VLBI technology developments: “Improvements of Delta-DOR measurements for Spacecraft Navigation” by Dr. Takeuchi
of JAXA/ISAS, two talks on “Development of balloon VLBI observation system for higher frequency
VLBI” by Dr. Okada of Osaka Prefecture Univ. and by Dr. Kono of NAOJ., “Big data of space geodesy
achieved by the database system and log records managemeent” by Prof. Takahashi of Yokohama National Univ., “Study on synchrotron emission mechanism from Jupiter” by Dr. Kita of Tohoku Univ.,“VLBI observation with Internet and Opt-link” by Prof. Takaba of Gifu Univ., and “Current status ofIbaraki VLBI station (Hitachi and Takahagi)” by Dr. Yonekura of Ibaraki Univ.
We thank all the contributions to this symposium and to proceeding papers of this issue.
On behalf of VLBI group of NICT.
Space and Time Standards Laboratory
Mamoru Sekido

Figure 1. Group Photo of the participants of the 13th IVS NICT-TDC Symposium on 4th June 2014.

“IVS NICT Technology Development Center News” (IVS NICT-TDC News) published by the
National Institute of Information and Communications Technology (NICT) (former the Communications Research Laboratory (CRL)) is the continuation of “IVS CRL Technology Development
Center News” (IVS CRL-TDC News). (On April 1, 2004, Communications Research Laboratory(CRL) and Telecommunications Advancement Organization of JAPAN (TAO) were reorganized
as “National Institute of Information and Communications Technology (NICT)”.)
VLBI Technology Development Center (TDC) at NICT is supposed
1) to develop new observation techniques and new systems for advanced Earth’s rotation observations by VLBI and other space techniques,2) to promote research in Earth rotation using VLBI,
3) to distribute new VLBI technology,4) to contribute the standardization of VLBI interface, and5) to deploy the real-time VLBI technique.
The NICT TDC newsletter (IVS NICT-TDC News) is published biannually by NICT.

This news was edited by Mamoru SEKIDO, Kashima Space Technology Center. Inquires on thisissue should be addressed to Mamoru SEKIDO, Kashima Space Technology Center, National
Institute of Information and Communications Technology, 893-1 Hirai, Kashima, Ibaraki 3148501, Japan, e-mail : sekido@nict.go.jp.
Summaries of VLBI and related activities at the National Institute of Information and Communications Technology are on the Web. The URL to view the home page of the Radio Astronomy
Applications Section of the Space-Time Measurement Group of Space-Time Standards Laboratory is : “http://www2.nict.go.jp/aeri/sts/stmg/index e.html”.

IVS NICT TECHNOLOGY DEVELOPMENT CENTER NEWS No.34, October 2014
International VLBI Service for Geodesy and Astrometry
NICT Technology Development Center News
published by
National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Koganei,
Tokyo 184-8795, Japan