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A method is presented for measuring the AM noise of signal sources as a function of frequency offset from the carrier. This method is particularly helpful for local oscillator sources for sub-millimeter wave single-ended mixers with wide IF bandwidths. Measurements on ALMA LO sources are presented using the described tests. The measurements are com...
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... results at a frequency corresponding to a LO frequency of 678 GHz are shown in Fig. 8. A narrower bandpass filter was then installed in the warm LO and the LO source was remeasured, showing less noise. The modified warm LO was sent back to SRON where it was reconnected to the band 9 SIS receiver and remeasured. The new measurements are shown in Fig. 9 and show that the excess LO noise has been significantly reduced, as predicted by the warm AM noise measurements. CONCLUSIONS AM noise measurements using the method described in this paper were presented for ALMA band 8 and 9 local oscillators. Comparisons with receiver noise measurements using the sources under test as local ...
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Citations
... It consists of cryogenic multiplier (x 6) operated at 100 K and warm cartridge assembly (eg. [22]). The output of the multiplier is transmitted with an oversize waveguide (WR6.3) to the OMT/2SB assembly. ...
We have developed a cartridge-type receiver covering from 385 to 500 GHz for pre-production of ALMA Band 8. It receives two orthogonal polarizations and down-converts the sideband-separated signals to intermediate frequencies (IF) between 4 and 8 GHz. The cartridge-type receiver consists of a cold optics, a feed horn, an OMT, two sideband-separating SIS mixers, cryogenic multipliers of local oscillator (LO). These components were individually tested and then the cartridge was integrated and tested as a complete assembly. We have also developed equipment to test both components and the integrated receiver. The single sideband (SSB) noise temperature of this receiver is 130 K at the band center and 180 K at the band edges. The beam pattern and cross-polarization pattern are consistent with physical optical calculation. These results are promising for receiver production to the Atacama Large Millimeter/submillimeter Array (ALMA).
We have successfully demonstrated low-noise and wideband SIS mixers for the 275-500 GHz radio frequency (RF) band, aiming to cover ALMA band 7 (275-373 GHz) and band 8 (385-500 GHz) simultaneously. The waveguide SIS mixers integrate a multi-section impedance transformer and an Nb/AlN/Nb parallel-connected-twin-junction or single-junction circuits with a critical current density greater than 25 kA/cm2. In order to achieve the targeted broadband performance, we designed an asymmetric one-side waveguide probe design placed across a reduced height waveguide with dimensions 100 μm x 580 μm. The shape of the waveguide probe was optimized to have nearly constant impedance at around 35
$\Omega$
in the desired RF range. For evaluation of the receiver performance, we have established a dual band noise temperature measurement system. The system implements a broadband corrugated horn antenna, and a 15-dB RF/local oscillator(LO) waveguide coupler based on WR2.3 (290 μm x 580 μm) waveguide size. The target bandwidth is too wide for typical LO sources at these high frequencies, and therefore, we applied a dual band LO injection system utilizing two different LO sources and an LO diplexer. The IF chain uses a cryogenic isolator and a low-noise amplifier with a typical noise temperature of 2.1 K over the 4-8 GHz range. The measured double sideband receiver noise temperature is about 2 to 3 times the quantum noise at all LO frequencies for both the twin-junction and the single-junction circuits.
This paper reports the simulation, performance, and detailed characterization of a low-noise heterodyne module with very wide intermediate frequency (IF) bandwidth in the 385–500-GHz radio frequency (RF) range. The module integrates a superconductor–insulator–superconductor (SIS) mixer with a 3–21-GHz cryogenic low-noise preamplifier (CLNA). The utilization of high current density SIS junctions offers wide RF bandwidth and facilitates better matching between SIS junctions and the CLNA. Based on an equivalent circuit of the SIS mixer chip, we calculate the IF output impedance and simulate how different matching conditions affect the performance of the CLNA. Simulations predict that low-noise module performance can be obtained over a 3–18-GHz IF range, limited mainly by parasitic elements in the SIS mixer chip. The measurement results of the heterodyne module demonstrate flat gain and a typical noise temperature of 70–80 K over the 3–18-GHz IF range, at local oscillator frequencies of 400–480 GHz. Mixer chip output impedance and CLNA input impedance have been directly measured by recording S-parameters at cryogenic temperatures. The results enabled us to quantify the contribution of various parasitic elements in the mixer IF circuitry. Calculations based on our model are in good agreement with measurements.
We have developed a low-noise balanced superconductor-insulator-superconductor (SIS) mixer using a waveguide 3-dB 90-degree hybrid coupler over the radio frequency (RF) range of 790-950 GHz and intermediate frequency range of 4-12 GHz at an operating temperature of 4 K. The RF coupler was carefully designed in regards to machining errors so that the entire amplitude imbalance including the mixer gain became smaller. The fabricated coupler was characterized at both room and cryogenic temperature. The receiver noise temperature of the balanced SIS mixer was below 350 K over the entire frequency band and the local oscillator (LO) noise rejection ratio was estimated to be more than 15 dB. This result is equivalent to state-ofthe-art mixer performance at this frequency range.
High signal-to-noise ratio sub-millimeter wave local oscillators (LOs) were developed and produced for the Atacama Large Millimeter Array (ALMA). They cover fractional bandwidths of 15–25% from 92 to 942 GHz. The LOs were designed and tested for high signal-to-noise ratio since they are used to drive single-ended mixers. Integrated millimeter-wave multi-chip MMIC modules, employing custom and commercial MMICs, were designed to yield the required power and SNR performance. 73 modules of the LO have been produced for each of the six bands to date, with two more bands currently under construction.
This article presents a heterodyne experiment which uses a 380-520 GHz planar
circuit balanced Nb-$\mathrm{Al_2O_3}$-Nb
superconductor-insulator-superconductor (SIS) quasiparticle mixer with 4-8 GHz
instantaneous intermediate frequency (IF) bandwidth to quantitatively determine
local oscillator (LO) noise. A balanced mixer is a unique tool to separate
noise at the mixer's LO port from other noise sources. This is not possible in
single-ended mixers. The antisymmetric IV characteristic of a SIS mixer further
helps to simplify the measurements. The double-sideband receiver sensitivity of
the balanced mixer is 2-4 times the quantum noise limit $h\nu/k_B$ over the
measured frequencies with a maximum LO noise rejection of 15 dB. This work
presents independent measurements with three different LO sources that produce
the reference frequency but also an amount of near-carrier noise power which is
quantified in the experiment as a function of the LO and IF frequency in terms
of an equivalent noise temperature $T_{LO}$. In a second experiment we use only
one of two SIS mixers of the balanced mixer chip, in order to verify the
influence of near-carrier LO noise power on a single-ended heterodyne mixer
measurement. We find an IF frequency dependence of near-carrier LO noise power.
The frequency-resolved IF noise temperature slope is flat or slightly negative
for the single-ended mixer. This is in contrast to the IF slope of the balanced
mixer itself which is positive due to the expected IF roll-off of the mixer.
This indicates a higher noise level closer to the LO's carrier frequency. Our
findings imply that near-carrier LO noise has the largest impact on the
sensitivity of a receiver system which uses mixers with a low IF band, for
example superconducting hot-electron bolometer (HEB) mixers.
