Vol.0 (200x) No.0, 000–000

11institutetext: Key Laboratory of Solar Activity, National Astronomical
Observatories, Chinese Academy of Sciences; Datun Road 20A, Chaoyang District,
Beijing 100012, China<EMAIL_ADDRESS>
22institutetext: Key Laboratory of Radio Astronomy, Chinese Academy of Science
33institutetext: University of Chinese Academy of Sciences 10049

# Antenna system characteristic and solar radio burst observation

Sha Li 112233 Yi-hua Yan 1122 Zhi-jun Chen 1122 Wei Wang 1122 Dong-hao Liu 11

(Received 2015 month day; accepted 2015 month day)

###### Abstract

Chinese Spectral Radio Heliograph (CSRH) is an advanced aperture synthesis
solar radio heliograph, developed by National Astronomical Observatories,
Chinese Academy of Sciences independently. It consists of 100 reflector
antennas, which are grouped into two antenna arrays (CSRH-I and CSRH-II) for
low and high frequency bands respectively. The frequency band of CSRH-I is
0.4-2GHz and for CSRH-II, the frequency band is 2-15GHz. In the antenna and
feed system, CSRH uses an Eleven feed to receive signals coming from the Sun,
the radiation pattern with lower side lobe and back lobe of the feed is well
radiated. The characteristics of gain $G$ and antenna noise temperature $T$
effect the quality of solar radio imaging. For CSRH, measured $G$ is larger
than 60 dBi and $T$ is less than 120K, after CSRH-I was established, we have
successfully captured a solar radio burst between 1.2-1.6GHz on November 12,
2010 through this instrument and this event was confirmed through the
observation of Solar Broadband Radio Spectrometer (SBRS) at 2.84GHz and
Geostationary Operational Environmental Satellite (GOES). In addition, an
image obtained from CSRH-I clearly reveals the profile of the solar radio
burst. The other observational work is the imaging of Fengyun-2E
geosynchronous satellite which is assumed to be a point source. This data
processing method indicates that, the method of deleting errors about dirty
image could be used for processing other surface sources.

###### keywords:

Reflector antenna :Noise Temperature : Eleven antenna : Low cross polarization
: Aperture synthesis

##  1 Introduction

In solar radio observations, the Sun exhibits a variety of large dynamic
phenomena in different frequencies. At the same time, it transmits constant
energy to the Earth (Takano [1996]). These phenomena reveal the links between
solar astronomy and other branches of physics. For example,
magnetohydrodynamics(MHD)and plasma physics can be well explained through
solar observations. The fundamental concept behind MHD shows that the magnetic
fields can induce currents in a moving conductive fluid, which creates forces
on the fluid and also changes the magnetic field itself. The plasma is
composed of ions and electrons, it is the key to understand the propagation of
radio wave coming from the Sun. CSRH observations with high spatial resolution
could provide important diagnosing tools on the magnetic field, solar radio
density, plasma temperature,etc (Yan [2008]). Imaging spectroscopy over
centimeter and decimeter wavelength range are important for CSRH to explain
fundamental problems such as energy release, particle acceleration and
particle transport.

In view of the available solar radio astronomical instruments all over the
world, two main kinds of instruments are used in solar observations. One is
radio heliograph at single or discrete frequencies, for example, Nancay Radio
Heliograph (NRH) observes the Sun at 150, 164, 237, 327 and 410MHz, Nobeyama
Radio Heliograph (NoRH) (Nakajima [1994]) observes the Sun at 17 and 34GHz and
Siberian Solar Radio Telescope(SSRT)(Uralov [1998]) observes the Sun at 5.7GHz
(Les [2014]). The other instruments are spectrometers at certain frequency
band and frequency points, such as Solar Broadband Radio Spectrometer (SBRS)
at 1-2GHz, 2.6-3.8GHz, 5.2-7.6GHz, 2.84GHz. Although scientists have developed
some good theoretic models from the observations of these instruments, there
were still a lot of phenomena that could not be explained by the current
observations and theories. So a radio heliograph which could give solar images
in ultra wide band width is required. Now, an undergoing CSRH with high
temporal, high spatial and high spectral resolution will create radio images
in ultra wide band width. It could be expected to provide better observations
explaining these phenomena(Chen [2014]).

The aim of CSRH is to provide a new tool observing solar radio emissions,
including radio bursts from primary energy release sites of the solar
energetic events such as flares and coronal mass ejections (CMEs). Solar radio
bursts are rich with different types during solar flares, which are believed
due to the sudden energy release process of the solar magnetic field
topological re-organization or through the magnetic reconnection. CSRH will
make full disk of solar radio images with multiple frequency channels with
25ms cadence in the measurement.

Errors in radio heliograph, such as correlation-based error, antenna pointing
precision error, the receiver output noise error. Because of so many errors,
we have to calibrate the phase and amplitude errors of each output signal. The
amplitude calibration is performed by comparing and equalizing the signal
levels in the element of antenna array. With consideration of the instrument’s
errors, the measurement of phase calibration between different channels is to
make use of celestial radio source from this theory, and the phase corrections
are applied to the actual solar observations. As we know, the sensitivity of a
point source is proportional to the effective collecting area of the
telescope, this area is decided by one antenna multiplied by the number of the
antennas, in fact, the Sun is larger than the beam of the individual antennas
(Liu [2007]), so a number of pointing directions are used.

To evaluate CSRH antenna system, the gain and noise temperature of the
antenna, the sensitivity of the receiver should be measured. This paper
presents a method for computing the characteristics of CSRH, and provides the
results of the antenna gain $G$ and antenna temperature $T$. This paper also
gives two observation work, one is solar radio burst observation and the other
is satellite source imaging. The solar radio burst was observed by CSRH-I
5-element array on December 12, 2010. This instance was also captured by SBRS
at 2.84GHz and GOES in X-ray. Another result came from observing the
Fengyun-2E geosynchronous satellite at the height of nearly 35600km. The
output signal from each antenna was calibrated with reference to the known
standard satellite source. Then, we produced the images by using Common
Astronomy Software Application (CASA) which is an image layout software used
for aperture synthesis telescope.

The content of this paper is arranged as follows. Section II gives the
description of CSRH along with the measured and simulated radiation patterns.
In section III, the antenna noise temperature and gain of the system are
calculated in detail. Section IV gives images of the solar radio burst and
satellite point source, which are drew by using the calibrated data of CSRH.
Finally, the conclusions are given in section V.

##  2 Antenna system

###  2.1 About CSRH

CSRH is a radio interferometer which contains 100 parabolic reflector
antennas. CSRH-I consists of 40 4.5-m-diameter antennas operating between
0.4-2GHz, CSRH-II consists of 60 2-m-diameter antennas from 2 to 15GHz.
(Figure 1) shows the photo of constructed CSRH, which includes 3.87 hectares
and locates in Inner Mongolia, 400km away from Beijing. The exact geographical
coordinates of the central antenna is located at 115 degrees 15 minutes 1.8
seconds east longitude and 42 degrees 12 minutes 42.6 seconds north latitude.
The antenna configuration (Yan [2008]) is a non-redundant array with good
(${u}$,${v}$) coverage. The baseline vector has components
(${u}$,${v}$,${w}$), where ${w}$ points in the direction of interest.
${u}$,${v}$,${w}$ are measured in wavelengths at center frequency of the RF
signal band, and in the directions towards the East, the North, and the phase
tracking center respectively. For (${u}$,${v}$) coverage, if we assume the
spatial frequencies as follows:

$\overrightarrow{\rm{f}}{\rm{=}}{\rm{(u,v)}}$ (1)

which are the conjugated coordinates of the spatial coordinates (x,y) in the
image plane. While (x,y) measure angles, usually expressed in arcseconds,
spatial frequencies measure distance in the incident wavefront measured in
wavelength units, they are usually expressed in $arcsec^{-1}$, shown in
(Equation 2),

$\overrightarrow{\rm{f}}{\rm{=}}{\rm{(u,v)}}{\rm{=}}\frac{1}{\lambda}(\Delta{\rm{X,}}\Delta{\rm{Y}})$
(2)

During the imaging process, the incoming wavefront is spatially sampled by the
radio heliograph, we need to make our measurements in a plane and measured in
terms of the wavelength. When we observe the Sun, the sampling of the incident
wavefront is no longer continuous and depends on the array configuration. The
Fourier components of the object are measured at different spatial
frequencies. (Figure 2) shows the arrangement of CSRH-I. (Figure 3) gives the
(${u}$,${v}$) coverage (Lindsay [2008]) of (Figure 2). All the antennas are
arranged in three spiral arms (named A axis, B axis and C axis) respectively.

Figure 1: A view of CSRH

For multiple-element antenna arrays, it is convenient to specify the antenna
positions relative to the reference point measured in a Cartesian coordinate
system, a system with axes pointing towards hour-angle h and declination
$\delta$ equal to (h=0, $\delta=0$) for X, (h=-${6^{h}}$, $\delta=0$) for Y,
and ($\delta=90\deg$) for Z. If we assume $\L_{X}$, $\L_{Y}$ and $\L_{Z}$ are
the corresponding coordinate differences for two antennas, the baseline
components (${u}$,${v}$,${w}$) are given by (Equation 3):

$\left(\begin{array}[]{l}u\\\ v\\\
w\end{array}\right)=\frac{1}{\lambda}\left(\begin{array}[]{l}\begin{array}[]{*{20}{c}}{}\hfil&{\sin{H_{0}}}&{\begin{array}[]{*{20}{c}}{}\hfil&{}\hfil\end{array}\begin{array}[]{*{20}{c}}{}\hfil&{\sin{H_{0}}}&{\begin{array}[]{*{20}{c}}{}\hfil&{}\hfil\end{array}\begin{array}[]{*{20}{c}}{}\hfil&{}\hfil\end{array}}&0\end{array}}\end{array}\\\
-\sin{\delta_{0}}\cos{H_{0}}\begin{array}[]{*{20}{c}}{}\hfil&{\sin{\delta_{0}}\sin{H_{0}}\begin{array}[]{*{20}{c}}{}\hfil&{\cos{\delta_{0}}}\end{array}}\end{array}\\\
\cos{\delta_{0}}\cos{H_{0}}\begin{array}[]{*{20}{c}}{}\hfil&{-\cos{\delta_{0}}\sin{H_{0}}\begin{array}[]{*{20}{c}}{}\hfil&{\sin{\delta_{0}}}\end{array}}\end{array}\end{array}\right)\left(\begin{array}[]{l}{L_{X}}\\\
{L_{Y}}\\\ {L_{Z}}\end{array}\right)$ (3)

where ${H_{0}}$ and $\delta_{0}$ are the hour-angle and declination of the
phase reference position, and $\lambda$ is the wavelength corresponding to the
center frequency of the receiving system. The elements in the transformation
matrix in (Equation 3) are the direction cosines of the (${u}$,${v}$,${w}$)
axis relative to (X,Y,Z) axes. Thus as the interferometer observes a point
source on the celestial sphere, the rotation of the Earth causes the ${u}$ and
${v}$ components of the baseline to trace out an elliptical locus. This
ellipse is simply the projection onto the (${u}$,${v}$) plane of the circular
locus traced out by the tip of the baseline vector, and at any instant the
correlator output provides a measure of the visibility at two points in the
(${u}$,${v}$) plane. For an East-West baseline Lz=0, and a single ellipse is
centered on the (${u}$,${v}$) origin.

The characteristics and specifications of CSRH-I are shown in Table.1. This
array has 64 frequency channels and 16 channels per sub-band. The detailed
specifications of CSRH-II will be introduced in further paper.

Figure 2: The 2D configuration of CSRH-I, the antennas are arranged in three spiral arms (named A axis, B axis and C axis respectively), every axis has 13 antennas, IA0 is in the center of the antenna array, its correspondent coordinate is (0,0)m, the locations of other antennas are reference to IA0 antenna, the black circle shown in this figure is the location of each antenna Figure 3: (${u}$,${v}$) coverage of CSRH-I. The blue points correspond to the locations of each (${u}$,${v}$) coverage of the source image. The number of the baselines is 780 for this radio heliograph. A stellar interferometer measures only one visibility per baseline. Table 1: CSRH-I characteristics and specifications Observing band | 0.4-2GHz
---|---
Spatial Resolution | 51.6”-10.3”
Temporal Resolution | 100 ms
Dynamic range of images | $\geq(25dB)$
Polarization | left and right circular polarization
frequency channel | 64
Observing period | 0UT to 8UT in winter, -1UT to 9UT in summer
antenna efficiency | $\geq(0.4)$
antenna noise temperature | $\leq(120K)$

To cover a wide frequency range with high sensitivity, the bandwidth of CSRH-I
is divided into four sub bands: 0.4-0.8GHz, 0.8-1.2GHz, 1.2-1.6GHz and
1.6-2.0GHz. When the radio frequency (RF) signal of the Sun arrives at the
analogue receiver of CSRH, it is mixed with two local oscillators. The first
oscillator mixes the four sub bands at 3.6GHz, 4.0GHz, 4.4GHz and 4.8GHz
respectively. So all the four sub bands become 2.8-3.2GHz after the operator
of the first oscillator. Then, the output of the first oscillator is further
mixed with the second oscillator at the frequency of 3.25GHz. Thus, the output
frequencies of all the four sub bands range from 50MHz to 450MHz.

In CSRH-I, to ensure all RF signals arriving simultaneously, the optic fibers
transmitted the received RF signals of all channels with the same length. Each
pair of two antennas is correlated to output a Fourier component of a solar
radio image. Then we can reconstruct the brightness image through gathering
all possible Fourier components from this interferometry.

###  2.2 Simulation of the radiation pattern for the feed and reflector
antenna system

CSRH is an ultra wide band radio heliograph, in reference to choosing feed
used in CSRH, there are many kinds of ultra wide band feeds (Taylor [1999]) in
antenna system but with some shortcomings. For example, ridged horn is too
heavy and expensive; log-periodic antenna has variable phase center location
and it spills over the edge of the dish to reduce the gain of the antenna
system. In addition, the 3dB beamwidth of the radiation patterns of these two
feeds are not wide enough, so the reflector surface cannot be fully
illuminated by the feed, which will result in the low usage of the reflector
antenna. For CSRH, we use Eleven feed to receive radio signals. Because it has
many advantages, such as a fixed phase center location, well-shaped radiation
patterns and low return loss. This feed is comprised of 13 folded dipoles. The
bandwidth is decided by the ratio of the length of the ”next-to-shortest”
dipole to the length of the ”next-to-longest” dipole. ”next-to-shortest” means
the shorter dipole of the two adjacent dipoles and ”next-to-longest” means the
longer dipole of the two adjacent dipoles. The length of the longest dipole is
given by the wavelength of the lowest frequency. (Figure 4) gives the photo of
CSRH-I feed.

Figure 4: The photo of CSRH-I feed

In the simulating stage, we use High Frequency Structure Simulator (HFSS)
software to simulate the radiation pattern of the feed and reflector antenna
system of CSRH. In order to get good radiation pattern, dipoles in different
heights vary one by one (Qing [1999]) according to the optimized scaling
ratio. Then, the derived radiation pattern of the feed is substituted to the
feed and reflector antenna model, we can obtain the radiation pattern of the
whole system. (Figure 5), (Figure 6) and (Figure 7) show the simulated 3D
radiation patterns of the feed and reflector antenna system at 0.4GHz, 1.2GHz
and 2GHz respectively. The feed is located in the focus of the parabolic
reflector antenna, the pattern is symmetric about the z-axis. We can see that
the radiation patterns behave a good symmetrical property on boresight.

Figure 5: Simulated 3D radiation pattern of feed and reflector antenna in
0.4GHz, the right scale shows different colors corresponding to different
values of Gain total in dB Figure 6: Simulated 3D radiation pattern of feed
and reflector antenna in 1.2GHz, the right scale shows different colors
corresponding to different values of directivity total in dB Figure 7:
Simulated 3D radiation pattern of feed and reflector antenna in 2GHz, the left
scale shows different colors corresponding to different values of Gain total
in dB

To check the consistence between the simulated and measured radiation
patterns, we observed Fengyun-2E satellite at 1.7GHz. This satellite bacon
signal is received by IA0 antenna. The antenna moves in up and down directions
and in left and right directions, so the measured radiation patterns in
elevation and azimuth directions are obtained by receiving signals coming from
the maximum satellite downlink signal independently. The simulated and
measured radiation patterns are illustrated at 1.7GHz in (Figure 8).

In antenna system, the parameter $G$ is measured using two antennas(IB11 and
IA0). IB11 was connected to a signal source, and it radiated signal to IA0,
IA0 received signal from the source and the spectrum analyzer was connected
with IA0. The ratio of the powers from the signal source and from the spectrum
analyzer could be obtained, we could get the measured antenna gain $G$ from
(Equation 4).

Figure 8: Simulated and measured 2D radiation pattern in 1.7GHz, the black
line with square and red line with circle represent radiation pattern in
elevation and azimuth directions; the blue line with up triangle and the dark
cyan line with down triangle represent radiation pattern in elevation
direction and azimuth directions

$G=\frac{{(27000\sim 31000)}}{{\theta_{azimuth}\theta_{elevation}}}$ (4)

where $\theta_{azimuth}$ and $\theta_{elevation}$ are 3dB beamwidths in
azimuth and elevation directions (Kildal1 [2009]). The directivity coefficient
$D$ is calculated by (Equation 5).

$D=\left({\frac{{\pi d}}{\lambda}}\right)^{2}$ (5)

where $d$ and $\lambda$ represent the diameter of the reflector antenna and
the wavelength of the working frequency. From (Equations 4) and (Equations 5),
the measured $G$ and calculated $D$ are 34.61dB, 38.08dB respectively. Thus,
the relationship between $G$, $D$ and antenna efficiency $\eta$ is expressed
in Equation 6):

$G=D*\eta$ (6)

then, we calculated $\eta$ is 0.45, which is satisfied with the specification
of the antenna design.

###  2.3 The equatorial mount and pointing error of the reflector antenna of
CSRH

To facilitate the observation of the Sun, the reflector antenna of CSRH is
designed with equatorial mount(also called polar mount) and use the quadrupod
structure to support the feed, the foot points of this quadrupod are located
at the edge of reflector antenna to reduce the influence of the plane wave
incoming. The equatorial mount is a mount for instrument that follows the
rotation of the sky (celestial sphere) by having one rotational axis parallel
to the Earth’s axis of rotation. In addition, it makes all the antennas
operating consistently. The monitoring subsystem sends control signal to the
operating unit of an antenna, and the antenna reacts the signal to adjust its
posture working in the best condition.

The pointing error of each antenna is very important to an extended source
such as the quiet Sun. If the pointing error of the antenna is not accurate,
it would influence the phase correlation, which can not be deleted by the
post-processing. The measured pointing error of each antenna of CSRH is less
than 9’. When all the antennas point to the Sun after calibration, the
response of the receivers must be uniform over the whole angular range of the
observation.

##  3 Antenna noise temperature

###  3.1 Theoretical analysis of antenna noise temperature

In CSRH program, it is necessary to choose better amplifier (Kildal [2009])
matching the antenna system. The antenna and receiver system noise temperature
must be lower than the specification of the whole system.

The classical method of measuring antenna noise temperature is based on
detection of astronomical source and sky background. These measurements could
be extended for judging the system independent of the telescope antenna.
Signals coming from the sky background noise and astronomical source need to
be measured at frequencies supported by the antenna-feed. With the requirement
of solar radio observation, the antenna noise temperature(Kildal [1995]) is
measured in the whole system. It relies on the reflector configuration and the
feed radiation pattern, which means that if the feed has low sidelobe and
cross polarization (Olsson [2006]), the reflection from the ground plane will
be reduced. At the same time, it could minimize the spillover from the
sidelobes and the selection of feed is vital to the whole antenna system.

When observing solar radio signals, the circular polarization (Uralov [1998])
is demonstrated from studies of large numbers of storms. The characteristic of
the wave is effected by the terms of antenna gain, effective aperture, antenna
noise temperature and so on. The reduction of the system noise temperature
could improve the sensitivity of a radio telescope(Li [2015]). Minimizing
radio noise temperature usually involves cooling the amplifier from the front
end of the system. It is convenient to use cosmic sources with small angular
as a calibrated source, because the flux density of these sources is already
known. Regarding the Sun, it is impossible to use a cosmic source because the
Sun is stronger than any other sources. Thus, a noise source as a standard
source is equipped in the input port of the analogue system. The input port is
connected to the load, the antenna observation of sky background and the
standard noise generator sequentially, the output data is gathered to compute
antenna noise temperature. The thermal noise sources used in this measurement
is resistor which is connected to receiver by coaxial lines. The noise
temperature of the receiver and antenna system is measured by Y factor method.
The factor Y is represented by:

${\rm{Y=}}10^{{\rm{(P1-P2)/10}}}$ (7)

where $P1$ and $P2$ correspond to the powers of different loads added in the
end of the system. After obtaining Y, the antenna noise temperature $T_{A}$ is
computed by

${\rm{T_{A}=(T_{0}+Tr-Y\times Tr)/Y}},$ (8)

where $T_{0}$ represents the ambient temperature, $T_{0}=290K$, $T_{r}$ means
the temperature of the analogue receiver.

The noise temperature of the whole system is the antenna system noise
temperature and receiver noise temperature. (Equation 9),(Equation 10) and
(Equation 11) show different received powers with different loads. In these
equations, $k=1.3806505\times 10^{(-23)}$ J/K, B represents the bandwidth,
$G_{r}$ is the gain of the system coming from the noise source of the
receiving system. the noise temperature $T_{NS}$ means terminal connecting
with the noise source, $T_{50}=290K$, the noise temperature $T_{50}$ means
terminal connecting with standard impedance 50$\Omega$,.

$\left[{\left({{\rm{T}}_{{\rm{50}}}+{\rm{T}}_{\rm{r}}}\right){\rm{kB}}}\right]+\left[{{\rm{G}}_{\rm{r}}}\right]=\left[{{\rm{P}}_{{\rm{50}}}}\right]$
(9)
$\left[{\left({{\rm{T}}_{{\rm{NS}}}+{\rm{T}}_{\rm{r}}}\right){\rm{kB}}}\right]+\left[{{\rm{G}}_{\rm{r}}}\right]=\left[{{\rm{P}}_{{\rm{NS}}}}\right]$
(10)
$\left[{\left({{\rm{T}}_{\rm{A}}+T_{r}}\right){\rm{kB}}}\right]+\left[{{\rm{G}}_{\rm{r}}}\right]=\left[{{\rm{P}}_{{\rm{SKY}}}}\right]$
(11)

The square brackets in (Equation 9), (Equation 10), (Equation 11) mean that
the unit of each value is dB. From (Equation 12), (Equation 13), (Equation
14), we could get the representations of $T_{r}$, $G_{r}$ and $T_{A}$
respectively.

$T_{r}=\frac{{T_{NS}-T_{50}\left({\frac{{P_{NS}}}{{P_{50}}}}\right)}}{{\frac{{P_{NS}}}{{P_{50}}}-1}}$
(12)
$G_{r}=\frac{{P_{50}\left({\frac{{P_{NS}}}{{P_{50}}}-1}\right)}}{{kB\left({T_{NS}-T_{50}}\right)}}$
(13) $T_{A}=\frac{{P_{sky}}}{{P_{50}}}(T_{50}+T_{r})-T_{r}$ (14)

###  3.2 The measured results of CSRH

For CSRH radio heliograph, we test the gain by using Y factor method (Penzias
[1965]) in the whole system. (Table LABEL:tab:noise_source) gives the measured
noise temperatures of the noise source at different frequencies. The
relationship between Excess Noise Ratio(ENR) and the noise source temperature
is:

${\rm{ENR=}}\frac{{{T_{NS}}-{T_{0}}}}{{{T_{0}}}}$ (15)

Where, ${T_{0}}$ is the ambient temperature, ${{T_{0}}=290K}$. From (Table
LABEL:tab:noise_source), it can be observed that the noise temperature
decreases as the frequency increases. (Table 3) lists the noise powers of
different terminals: noise source, 50$\Omega$ impedance, sky background and
the Sun. Based on the measured results of (Table 3), we can calculate system
noise ($Tr$), system Gain ($Gr$) and antenna noise temperature ($T_{A}$) by
using (Equation 12), (Equation 13), and (Equation 14) respectively. The
calculated results are shown in (Table LABEL:tab:Noise). The fourth column of
this table gives the measured antenna noise temperature, they all less than
the specification 120K in different frequencies.

Table 2: The noise temperatures ($T_{NS}$) of the noise source at different frequencies, ENR means the multiple number of the noise source above the ambient temperature, this value could be tested according to an instrument. Radio frequency(GHz) | ENR(dB) | Noise temperature(K)
---|---|---
0.75 | 21.28 | 392230.18
0.8 | 21.03 | 37051.90
1.025 | 20.57 | 33357.24
1.2 | 20.18 | 30517.21
1.45 | 19.82 | 28112.62
1.95 | 18.71 | 21837.56
Table 3: The noise powers of the different terminals including noise generator, 50$\Omega$ impedance, sky background and the Sun at different frequencies ($P_{NS}$, $P_{50}$, $Psky$, and $Psun$ represents the measured powers of the terminals.) Radio frequency(GHz) |  $P_{NS}$(dBm) |  $P_{50}$(dBm) |  $Psky$ (dBm) |  $Psun$ (dBm)
---|---|---|---|---
0.75 | -26.19 | -44.93 | -46.58 | -39.25
0.8 | -24.98 | -42.81 | -44.42 | -37.83
1.025 | -22.21 | -40.52 | -42.78 | -35.65
1.2 | -28.31 | -44.6 | -46.36 | -41.5
1.45 | -29.81 | -46.80 | -48.57 | -42.13
1.95 | -28.86 | -43.61 | -45.2 | -41.5
Table 4: The measured system noise ($Tr$), system Gain ($Gr$) and antenna noise temperature ($T_{A}$) at different frequencies Radio frequency(GHz) | $T_{r}(K)$ | $G_{r}(dB)$ | $T_{A}(K)$
---|---|---|---
0.75 | 268.3 | 61.7 | 92.9
0.8 | 326.05 | 63.12 | 99
1.025 | 235.7 | 66.4 | 58.9
1.2 | 437.3 | 60.61 | 48
1.45 | 308.3 | 59.9 | 69.8
1.95 | 456.42 | 61.49 | 61.17

##  4 Data processing for CSRH-I

###  4.1 Solar radio burst observation

A solar radio burst instance is provided to validate the effectiveness of
CSRH, this event occurred on November 12, 2010\. By using a 5-element system
of CSRH-I, we successfully observed a solar radio burst with an associated
X-ray flare C1.5 class. In Huairou observatory station, SBRS also observed
this instance at the same time. Another instrument called GOES also observed
this event in X-ray at that time, (Figure 9) (a) gives the observed fringe
with IB7-IC1 baseline, IB7 and IC1 are two antennas of CSRH-I, the black curve
shows the amplitude of the fourier component, the red and blue curves show
cosine and sin components; (Figure 9) (b) gives the flux density of GOES at
wavelength of 1-8 Angstrom showing in black line and 0.5-4 Angstrom drawing in
red line; (Figure 9) (c) shows the total flux density of Huairou instrument
observation and IC1 observed result.

(a) Observed fringe included the sin and cosine components (b) The flux
density observed by GOES

(c) The measured result obtained by IC1

Figure 9: The comparison between different instruments observations

###  4.2 Satellite image using Aperture synthesis method

In reference to CSRH-I image calibration, the diameter of the antenna is too
small to use non-solar compact sources as calibrating sources. Therefore, we
use Fengyun-2E satellite source as a point source in the beginning stage of
CSRH establishment at 1.7GHz. The observed result of Fengyun-2E is drawn in
(Figure 10), there are totally 930 fourier components using 31 antennas, each
pair of these antennas is interfered to provide a fourier component of the
observed source. The brightness image of the observed source can be obtained
(Wang [2013]) through applying inverse fourier transform to the gathered
fourier components.

Figure 10: Stokes parameter I: the cleaned observed image of Fengyun-2E
satellite at 1.7GHz on June 4th, 2013, the ellipse in the lower left corner is
the synthesized beam, the vertical scale bar represents the relative level of
the background

For detecting satellite source, observation is obtained during the pass of the
source through a stationary beam. (Figure 10) shows the Stokes parameter I,
which represents the total intensity of the satellite source. The phase error
of spherical waves coming from satellite source would be more than
${360^{\circ}}$ for the long baseline, and varies with the motion of the
satellite. However, such error could be removed successfully using two
observations. (Figure 10) is obtained from CASA, the integration time is 30ms
and the beam size of this image corresponding to the antenna beam is
1.25’*2.489’. This observation shows the good performance of the imaging
capability of CSRH-I.

##  5 Conclusion

The characteristics of CSRH are presented in this paper. From these data, we
could know that the system gain $Gr$ is larger than 60dBi and antenna noise
temperature $T_{A}$ is less than $120K$ respectively, which are satisfied with
the specifications of our science requirement. After some of the antennas
installed in Mingantu Observatory, a solar radio burst at 1.302GHz was
successfully captured by CSRH 5-element on 2010, November 12, at the same
time, SBRS and GOES also observed this event. Another result is about the
point source of satellite image at 1.7GHz ,which shows the imaging ability of
this system. CSRH will establish solar radio images in decimeter and
centimeter wavelength more accurately.

###### Acknowledgements.

We acknowledge the anonymous referee for his/her valuable suggestions and
comments of this paper. The author also wish to thank Long Xu, Chong Huang,
Cheng Ming Tan, Jing Huang, for their lots of advice on this paper. This work
is supported by NSFC grants (Nos.: MOST2011CB811401 11221063, 10778605,
11003028, 11203042, U1231205), National Major Scientific Equipment Research
and Design project (ZDYZ2009-3).

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