<p>An article in Astronomy &amp; Astrophysics <a href="https://www.aanda.org/articles/aa/full_html/2015/05/aa25529-14/aa25529-14.html" rel="nofollow noreferrer">1</a> (A. M. Baryshev et al., A&amp;A 577, A129 (2015)) titled “The ALMA Band 9 receiver
Design, construction, characterization, first light” covers this.</p>
<p>The relevant quote from the Methods section is:</p>
<blockquote>
<p>The ALMA Band 9 receiver units (so-called “cartridges”), which are installed in the telescope’s front end, have been designed to detect and down-convert two orthogonal linear polarization components of the light collected by the ALMA antennas. The light entering the front end is refocused with a compact arrangement of mirrors, which is fully contained within the cartridge. The arrangement contains a grid to separate the polarizations and two beam splitters to combine each resulting beam with a local oscillator signal. The combined beams are fed into independent double-sideband mixers, each with a corrugated feedhorn coupling the radiation by way of a waveguide with backshort cavity into an impedance-tuned superconductor-insulator-superconductor (SIS) junction that performs the heterodyne down-conversion. Finally, the generated intermediate frequency (IF) signals are amplified by cryogenic and room-temperature HEMT amplifiers and exported to the telescope’s IF back end for further processing and, finally, correlation.</p>
</blockquote>
<p>So, that covers band 9, not quite 10.</p>
<p>A recent article <a href="https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11453/114533Q/Upgrade-of-an-ALMA-Band-10-prototype-receiver-for-ASTE/10.1117/12.2561076.short" rel="nofollow noreferrer">Poster/paper</a> from SPIE. I don’t currently have access to the full paper, but the abstract includes</p>
<blockquote>
<p>A new 790 – 940 GHz heterodyne receiver, ASTE Band 10, was installed in October 2019 on ASTE (Atacama Submillimeter Telescope Experiment), a 10 m submillimeter telescope near of the ALMA site in Chile. An ALMA Band 10 prototype receiver was upgraded with SIS mixers employing high-Jc junctions.</p>
</blockquote>
<p>which to me implies a very similar architecture. Note that this particular receiver is actually installed on a telescope near ALMA, intended to be focused as a test bed for Band 10 experiments (most ALMA time is spent on other bands).</p>
<p>As for what has (likely) been installed on ALMA, an article in <a href="https://ieeexplore.ieee.org/document/5676213" rel="nofollow noreferrer">IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011</a>, p606-611 by Yasunori Fujii et al. discusses the prototype they developed. It also used a superconductor-insulator-superconductor (SIS) mixer on the front end to directly downconvert to a 4-12GHz intermediate frequency.</p>

CC BY-SA 4.0
2022-03-17T22:34:37.293Z
Very nice, *\thanks!* Just fyi [this answer](https://astronomy.stackexchange.com/a/40653/7982) includes arguments that there are limits of "quantum noise in coherent amplifiers" that make it challenging to build electronic amplifiers at a THz; the phase noise would degrade interferometry.
uhoh
CC BY-SA 4.0
2022-03-19T03:57:38.130Z
Just fyi after further searching with "quantum noise amplifiers radio telescope" I found that slides 29 and 30 of [Engineering Aspects for
Radio Astronomy](https://events.asiaa.sinica.edu.tw/ssp/viewFile.php?i=e0ac09c7b674289316abbcb7ed062f65&t=L) by Yuh-Jing Hwang of ASIAA puts the crossover point for downconversion-first around 100 GHz, and the following slides outline various schemes including SIS. (there's also some background [here](https://slideplayer.com/slide/8133352/))
uhoh
CC BY-SA 4.0
2022-03-19T05:44:53.900Z
and now I've just asked in Signal Processing SE [Why can't quantum phase noise in radio astronomy amplifiers just be filtered out after down conversion, instead of down-converting first?](https://dsp.stackexchange.com/q/82041/25659)
uhoh
CC BY-SA 4.0
2022-03-17T19:17:01.970Z
2022-03-21T16:01:08.457Z
2022-03-21T16:01:08.457Z
Jon Custer
<p>A discussion of how astronomers view where &quot;radio&quot; ends and &quot;infrared&quot; begins under <a href="https://astronomy.stackexchange.com/q/48393/7982">What does the celestial sphere look like in thermal IR?</a> led me to wonder just how high of a frequency is currently electronically amplified in radio telescopes before it is instead down-converted via some local oscillator and mixer.</p>
<p><strong>Just for example</strong> <a href="https://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array" rel="nofollow noreferrer">ALMA</a> has ten different frequency bands listed at ESO's <a href="https://www.eso.org/public/teles-instr/alma/receiver-bands/" rel="nofollow noreferrer">ALMA Receiver Bands</a>.</p>
<p>The table says that the lowest two bands (35–50 and 65–90 GHz) use <a href="https://en.wikipedia.org/wiki/High-electron-mobility_transistor" rel="nofollow noreferrer">High-electron-mobility transistor</a> receiver technology, while the top eight use &quot;SIS&quot;.</p>
<p>The top band (Band 10) is listed as 0.3–0.4 mm or 787–950 GHz with a Noise Temperature Specification of 344 Kelvin.</p>
<p>But I don't know how to find out for each of these bands how the front ends work; whether they amplify or mix and down-convert first. So I'd like to ask:</p>
<p><strong>Question:</strong> Do circa 1 THz radio telescope front end amplifiers actually down convert before amplifying? At what frequency does amplification become untenable <em>for radio astronomy applications</em>?</p>
<p>Related and possibly helpful:</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/35975/7982">Highest frequency that&#39;s been imaged by a radio telescope?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/36633/7982">Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?</a> (yes!)</li>
<li><a href="https://astronomy.stackexchange.com/q/28666/7982">How does ALMA produce stable, mutually coherent ~THz local oscillators for all of their dishes?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/35757/7982">Is there any work underway to push the long baseline capabilities of the Event Horizon Telescope to sub-millimeter wavelengths?</a></li>
</ul>

<radio-astronomy><radio-telescope><instruments>
Do circa 1 THz radio telescope front end amplifiers actually down convert before amplifying? At what frequency does amplification become untenable?
uhoh
# Do circa 1 THz radio telescope front end amplifiers actually down convert before amplifying? At what frequency does amplification become untenable?

(Asked by: username_0 on 2022-03-17)

A discussion of how astronomers view where "radio" ends and "infrared" begins under [What does the celestial sphere look like in thermal IR?](https://astronomy.stackexchange.com/q/48393/7982) led me to wonder just how high of a frequency is currently electronically amplified in radio telescopes before it is instead down-converted via some local oscillator and mixer.

**Just for example** [ALMA](https://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array) has ten different frequency bands listed at ESO's [ALMA Receiver Bands](https://www.eso.org/public/teles-instr/alma/receiver-bands/).

The table says that the lowest two bands (35–50 and 65–90 GHz) use [High-electron-mobility transistor](https://en.wikipedia.org/wiki/High-electron-mobility_transistor) receiver technology, while the top eight use "SIS".

The top band (Band 10) is listed as 0.3–0.4 mm or 787–950 GHz with a Noise Temperature Specification of 344 Kelvin.

But I don't know how to find out for each of these bands how the front ends work; whether they amplify or mix and down-convert first. So I'd like to ask:

**Question:** Do circa 1 THz radio telescope front end amplifiers actually down convert before amplifying? At what frequency does amplification become untenable *for radio astronomy applications*?

Related and possibly helpful:

* [Highest frequency that's been imaged by a radio telescope?](https://astronomy.stackexchange.com/q/35975/7982)
* [Has optical interferometry been done at radio frequency using heterodyning with a laser in a nonlinear material?](https://astronomy.stackexchange.com/q/36633/7982) (yes!)
* [How does ALMA produce stable, mutually coherent ~THz local oscillators for all of their dishes?](https://astronomy.stackexchange.com/q/28666/7982)
* [Is there any work underway to push the long baseline capabilities of the Event Horizon Telescope to sub-millimeter wavelengths?](https://astronomy.stackexchange.com/q/35757/7982)

**Tags:** radio-astronomy, radio-telescope, instruments


---

## 1 answers

### Answer by username_1 on 2022-03-17. Score: 4 | Accepted answer

An article in Astronomy & Astrophysics [1](https://www.aanda.org/articles/aa/full_html/2015/05/aa25529-14/aa25529-14.html) (A. M. Baryshev et al., A&A 577, A129 (2015)) titled “The ALMA Band 9 receiver
Design, construction, characterization, first light” covers this.

The relevant quote from the Methods section is:

> The ALMA Band 9 receiver units (so-called “cartridges”), which are installed in the telescope’s front end, have been designed to detect and down-convert two orthogonal linear polarization components of the light collected by the ALMA antennas. The light entering the front end is refocused with a compact arrangement of mirrors, which is fully contained within the cartridge. The arrangement contains a grid to separate the polarizations and two beam splitters to combine each resulting beam with a local oscillator signal. The combined beams are fed into independent double-sideband mixers, each with a corrugated feedhorn coupling the radiation by way of a waveguide with backshort cavity into an impedance-tuned superconductor-insulator-superconductor (SIS) junction that performs the heterodyne down-conversion. Finally, the generated intermediate frequency (IF) signals are amplified by cryogenic and room-temperature HEMT amplifiers and exported to the telescope’s IF back end for further processing and, finally, correlation.

So, that covers band 9, not quite 10.

A recent article [Poster/paper](https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11453/114533Q/Upgrade-of-an-ALMA-Band-10-prototype-receiver-for-ASTE/10.1117/12.2561076.short) from SPIE. I don’t currently have access to the full paper, but the abstract includes

> A new 790 – 940 GHz heterodyne receiver, ASTE Band 10, was installed in October 2019 on ASTE (Atacama Submillimeter Telescope Experiment), a 10 m submillimeter telescope near of the ALMA site in Chile. An ALMA Band 10 prototype receiver was upgraded with SIS mixers employing high-Jc junctions.

which to me implies a very similar architecture. Note that this particular receiver is actually installed on a telescope near ALMA, intended to be focused as a test bed for Band 10 experiments (most ALMA time is spent on other bands).

As for what has (likely) been installed on ALMA, an article in [IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 21, NO. 3, JUNE 2011](https://ieeexplore.ieee.org/document/5676213), p606-611 by Yasunori Fujii et al. discusses the prototype they developed. It also used a superconductor-insulator-superconductor (SIS) mixer on the front end to directly downconvert to a 4-12GHz intermediate frequency.

> **Comments:**
> **username_0**: Very nice, *\thanks!* Just fyi [this answer](https://astronomy.stackexchange.com/a/40653/7982) includes arguments that there are limits of "quantum noise in coherent amplifiers" that make it challenging to build electronic amplifiers at a THz; the phase noise would degrade interferometry.  
> **username_0**: Just fyi after further searching with "quantum noise amplifiers radio telescope" I found that slides 29 and 30 of [Engineering Aspects for Radio Astronomy](https://events.asiaa.sinica.edu.tw/ssp/viewFile.php?i=e0ac09c7b674289316abbcb7ed062f65&t=L) by Yuh-Jing Hwang of ASIAA puts the crossover point for downconversion-first around 100 GHz, and the following slides outline various schemes including SIS. (there's also some background [here](https://slideplayer.com/slide/8133352/))  
> **username_0**: and now I've just asked in Signal Processing SE [Why can't quantum phase noise in radio astronomy amplifiers just be filtered out after down conversion, instead of down-converting first?](https://dsp.stackexchange.com/q/82041/25659)  

---

