The radio frequency interference (RFI) due to the X-band telecommunication with the LiteBIRD spacecraft was computed using a 3D electromagnetic field simulator to evaluate its field strength at the ...instrument detectors. First, the level of RFI with different materials for the spacecraft main body was evaluated. The attenuation effects for aluminum (Al) and carbon-fiber-reinforced plastic (CFRP) in comparison with a perfect electric conductor (PEC) were 1.5 dB and 10.5 dB, respectively. Then, the electric field strength for various shield plate structures on the solar panels was evaluated. In the best case, the RFI level could be attenuated by another 31 dB with an optimum design. Finally, the frequency dependence of the RFI was evaluated across the X-band, giving an attenuation slope of − 10 dB/oct, leading to an electric field intensity of − 116.8 dBV/m at the detector position for a frequency of 8.4 GHz.
We are developing a detector array for astronomical observations in the 100-GHz band using microwave kinetic inductance detectors (MKIDs) and a readout system for the array with frequency sweeping ...scheme, which uses a frequency sweeping probe signal instead of a fixed-frequency probe signal. This scheme enables us to simultaneously obtain the resonance spectra of MKIDs in an array and to derive the resonance frequencies corresponding to the power of incoming radiation. It has the advantage of the dynamic range being higher than the standard scheme and the derived resonance frequencies not being affected by changes of the gain or delay in the transmission line. The resonance profile measured, however, can be distorted by frequency sweeping, and hence, it is necessary to evaluate the effect of frequency sweeping on the resonance spectrum. We made measurements using the scheme with several frequency-sweep velocities and checked its effect on the resonance frequency and the quality factor. A slow frequency sweep causes only small differences in the resonance spectrum compared to an ideal profile, and hence suitable for astronomical applications.
GroundBIRD is a ground-based experiment for a precise observation of the cosmic microwave background (CMB) polarizations. To achieve high sensitivity at large angular scales, we adopt three features ...in this experiment: fast rotation scanning, microwave kinetic inductance detector (MKID), and cold optics. The rotation scanning strategy has the advantage to suppress 1/
f
noise. It also provides a large sky coverage of 40%, which corresponds to the large angular scales of
l
∼
6
. This allows us to constrain the tensor-to-scalar ratio by using low
l
B-mode spectrum. The focal plane consists of 7 MKID arrays for two target frequencies, 145 GHz and 220 GHz band. There are 161 pixels in total, of which 138 are for 145 GHz and 23 are for 220 GHz. This array is currently under development, and the prototype will soon be evaluated in telescope. The GroundBIRD telescope will observe the CMB at the Teide observatory. The telescope was moved from Japan to Tenerife and is now under test. We present the status and plan of the GroundBIRD experiment.
We are developing detector arrays using microwave kinetic inductance detectors (MKIDs) for astronomical observations in the 100-GHz band and a readout system for MKID arrays with frequency sweeping ...scheme. Probe tones in this scheme are generated and acquired by a frequency sweep probe (FSP) which is a digital fast Fourier transform spectrometer (FFTS), while the probe tones are converted and modulated by an intermediate frequency (IF) section. Since the values of the resonance frequencies change under different photon backgrounds, an appropriate method to configure the probe tones is essential to preserve the dynamic of the detected signals. We considered a general IF section which is a cascade of up/down converter pairs and found that its characteristics can be described with the base band, the target band, the sign of probe tone order, and the sign of frequency sweep direction. We implemented an algorithm to make a list of tone frequencies from a list of resonance frequencies given. Using this configuring method, we assembled IF sections for an antenna-coupled MKID array and for a LEKID array and set up a prototype FSP. The resonance frequencies of the antenna-coupled MKIDs and the LEKIDs are at 4.6–5.1 GHz and 0.6–1.0 GHz, respectively, and their spectra were obtained successfully. The method enables us to configure the readout system for both types of arrays.
We have developed a broadband corrugated horn in the 120-270 GHz and a horn array in the 80-180 GHz bands. The geometry of corrugations is so simple that the horn array can be directly machined from ...a bulk of aluminum with an end mill. The cross polarization and near sidelobe levels are less than -20 and -30 dB, respectively. The return loss is less than -15 dB in most design frequency bands, and the beam pattern is symmetric. The beam pattern and the return loss are measured in the 120-170 GHz range at room temperature. They are in good agreement with the simulation. It is possible to reduce reflection at the aperture surface and to reduce the weight by carving the unnecessary part. This design provides an octave bandwidth of the corrugated horn array at reasonable machining time.
The surface impedance of a superconductor has been calculated using the extended Mattis-Bardeen theory, in which the complex gap energy are taken into account. It is found that the surface resistance ...of the superconductor increases with increasing magnitude of the imaginary part of the gap energy. It is also found that the surface resistance of an NbN film calculated by the extended Mattis-Bardeen equation quantitatively agrees well with the measured one. It is shown that temperature dependence of not only values but also residual numbers of quasiparticles of superconducting resonators agree well with those calculated by the extended Mattis-Bardeen equation. It is also shown that phonon-assisted gradual relaxation of excess quasiparticles passing through the intragap states is dominant rather than the direct recombination into Cooper pairs.
Pyramid-type antireflective subwavelength structures for large-diameter (
>
30
cm
) silicon lenses are promising for broadband astronomical observations. The refractive index and dielectric loss ...tangent of the lens material, columnar crystal silicon which is manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd., were measured at around 30 K using a Martin–Puplett-type Fourier transform spectrometer. The measured refractive index and dielectric loss tangent between 200 GHz and 1.6 THz were
∼
3.42 and 1–
5
×
10
-
4
, respectively. Three different pyramid-type structures with a period of
265
μ
m
and depth of
600
μ
m
were simulated to obtain their reflectance using an electromagnetic field simulator, HFSS. The structures were fabricated on both sides of a 100-mm-diameter plane-convex lens made of columnar crystal silicon with a 150-mm radius of curvature using a metal-bonded V-shaped blade and a dedicated three-axis machine. The fabrication errors in the period and depth were less than
10
μ
m
. The reflectance of the lens flat surface was measured using a vector network analyzer to be between
-
8
and
-
17
dB in the range of 110–170 GHz, which was consistent with the result from the simulation.
Cosmic microwave background (CMB) radiation is an afterglow from the Big Bang. CMB contains rich information about the early stage of the universe. In particular, odd-parity patterns (
B
-mode) in ...the CMB polarization on a large angular scale would provide an evidence of the cosmic inflation. The aim of the GroundBIRD experiment is to observe the
B
-mode on large angular scales from the ground. One of the most novel characteristics of the telescope used for this experiment is its rapid rotational scanning technique. In addition, the telescope uses cold optics and microwave kinetic inductance detectors. We have developed a telescope mount with a three-axis rotation mechanism (azimuth, elevation, and boresight) and measured the vibration at the focal plane stage at 20 RPM scan rotation rate. We also performed focal plane detector tests on this mount. The tests confirmed the expected response from the geomagnetism associated with the mount rotation. We have also developed a design for the magnetic shields and a detector array on a 3-in wafer. The preparations to begin the observations at the Teide Observatory in the Canary Islands in 2018 are proceeding smoothly.
We are developing a superconducting camera based on microwave kinetic inductance detectors (MKIDs) to observe 100-GHz continuum with the Nobeyama 45-m telescope. A data acquisition (DAQ) system for ...the camera has been designed to operate the MKIDs with the telescope. This system is required to connect the telescope control system (COSMOS) to the readout system of the MKIDs (MKID DAQ) which employs the frequency-sweeping probe scheme. The DAQ system is also required to record the reference signal of the beam switching for the demodulation by the analysis pipeline in order to suppress the sky fluctuation. The system has to be able to merge and save all data acquired both by the camera and by the telescope, including the cryostat temperature and pressure and the telescope pointing. A collection of software which implements these functions and works as a TCP/IP server on a workstation was developed. The server accepts commands and observation scripts from COSMOS and then issues commands to MKID DAQ to configure and start data acquisition. We made a commissioning of the MKID camera on the Nobeyama 45-m telescope and obtained successful scan signals of the atmosphere and of the Moon.
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