VLBI 3-band Receiver
A novel design for a three-band VLBI receiver with unmatched sensitivity.
VLBI and EHT have started to use simultaneous multi-frequency observations to perform phase transfer from lower to higher frequencies. This can decrease the overall phase noise and, in doing so, improve sensitivity of the array. Nevertheless, multi-frequency receivers come with complex optical systems that introduce additional losses in front of the LNA.
The MPIfR 3-band approach for simultaneous observations in K-, Q-, and W-band reduces the complexity by combining K- and Q-band to one ultra-wide KQ-receiver. The now much more compact optical system is small enough to be cryogenically cooled, which mostly removes its unavoidable noise contributions. The Three-band receivers make use of our highly optimized horn, OMT, and noise coupler designs. They additionally feature optimized first stage cryogenic LNAs from MPIfR / IAF, which are a cornerstone of projects such as ALMA band 2. All these steps allow us to boost the overall sensitivity of the receiver by roughly a factor of two compared to more conventional designs found at other telescopes.
The Effelsberg 3-band receiver features two pixel, each with two polarizations and all three bands. This allows it to stay on source and, in parallel, observe the atmospheric conditions on blank sky with the other horn. The fully reflective optics is cooled to cryogenic temperatures to reduce its overall noise contribution. To avoid spill over on the Effelsberg main dish, the first mirrors of each band are undersized and therefore are acting as a cold-stop.
