Fourier phase gratings play a vital role in the multi-beam heterodyne receiver in sub-millimeter astronomical instruments. In this study, a 1×4 beam grating at 660 GHz is developed, by which the surface structure is generated with an iterative algorithm. Far-field beam pattern is simulated with FEKO, where a relative high efficiency of 91% as well as a uniformity of power distribution among 4 beams of less than 1% are obtained. The grating was manufactured in aluminum material by a micro-milling machine. A PC-controlled scanning stage is employed for the beam pattern measurement. Despite the discrepancy from the manufacture of less than 6 μm, measurement results exhibit a good agreement with simulation in both power efficiency and far-field spatial distribution.
Superconductor-insulator-superconductor (SIS) mixers, with nearly quantum-limited sensitivity, have been playing an important role in Terahertz astronomy. For practical THz SIS receivers, however, the measured noise temperatures are sometimes higher than the expected value. The extra noise is mainly due to considerable RF noise contribution from the receiver components such as beam splitter, Dewar window, and infrared filter. In this paper, we mainly present the simulation and measurement results of the three components with different materials and thicknesses. Their noise contributions are also analyzed.
Besides the sensitivity nearly approaching the quantum limit, the intermediate-frequency (IF) bandwidth is of particular interesting for Superconductor-insulator-superconductor (SIS) mixers for radio astronomy research. In this paper, we are going to present the characteristic of IF bandwidth of two type of NbN SIS mixers, Long distributed junctions and Parallel-connected twin junctions. Firstly, the relative mixer gain are measured with different IF load impedance (25Ω, 50Ω, 75Ω) for both two SIS mixers. And also the mixers gain with different IF load impedance is simulated to get the optimum IF load impedance over a relative large IF bandwidth (2-15GHz). Finally, an IF matching circuit is designed and measured associating with SIS mixers, the measurement results show that the mixers gain are flatter over a large IF bandwidth than with 50Ω IF load impedance.
In this paper, we will introduce a dual-THz-band SIS (Superconductor-Insulator-Superconductor) heterodyne radiometer system developed for the atmospheric profiling synthetic observation system project (APSOS). This THz system is intended to have a durable and compact design to meet the challenging requirements of remote operation. The system as well as its major components such as antenna tipping, quasi-optics, cryogenics, SIS mixers and FFTS backend will be discussed thoroughly. Some scientific simulation focusing on the atmospheric profiling components at THz bands will also be investigated.
We report on a twin-slot antenna coupled superconducting NbN hot electron bolometer (HEB) mixer designed for 1.6
THz. Terahertz (THz) radiation is quasi-optically coupled to the HEB with an uncoated elliptical Si lens. Measured DSB
receiver noise temperatures are 1500 K at 0.85 THz, 1200 K at 1.27 THz, 1100 K at 1.31 THz, 1100 K at 1.4 THz, and
1000 K at 1.63 THz. This value at 1.63 THz is reduced to 750 K when the hot/cold loads in vacuum are used. The
frequency dependence of the noise temperature is consistent with the measured FTS spectral response. The measured farfield
beam patterns of the lens/antenna combination show nearly collimated beams with the side lobes below -16dB by
adding a 40 μm extension to a standard Si elliptical lens design, which is understood by considering a slightly lower
dielectric constant of Si (εSi) of 11.4 instead of 11.7. The good performance of such NbN HEB mixers makes it suitable
for future high-resolution spectroscopic astronomical applications.
The submillimeter (submm) regime, ranging from 100 to 1000um, is an important frequency band for radio astronomy.
A large number of astronomical spectral lines are located in this frequency region. Compared with ground-based observation,
which is limited by the atmospheric absorption of signal, space borne platform provides perfect condition for
submm observation. Here we introduce some preliminary results for a compact 500GHz SIS (Superconductor-
Insulator-Superconductor) heterodyne receiver system developed for future space borne observation. Considering
low power consumption requirement for space applications, we adopt a high critical temperature (Tc) NbN/AlN/NbN
SIS tunnel junction for the mixer, a key component of the receiver system, which may work at relatively high temperature
around 10 K. All the components, including the SIS mixer, HEMT low noise amplifier and optical lens, are assembled
into a compact system. The whole system is cooled by a close-cycled 4K cryo-cooler in laboratory and test result
shows a good noise performance, less than 250K at the 500GHz band. Detailed simulation and experimental results will
be presented in this paper.
In this paper, we present the calculation of the impedance and beam pattern of a 6×6 twin-slot antenna array combined
with an extended hemispherical silicon lens. The self and mutual impedance of the twin-slot antenna array are simulated
by High Frequency Structure Simulator (HFSS), while its radiation pattern is computed by using ray-tracing inside the
lens and electric and magnetic field integration on its surface. The distance between two neighboring antennas is set as
282μm (0.61λ0 at 650GHz) to avoid the overlap between the main-lobe beams of the antenna elements. With good
imaging quality (i.e., with a Strehl ratio no less than 0.8), the minimum diameter of the lens is found equal to 23mm
(~50λ0 at 650GHz).