[asac]Band 4 frequency extension

[Tetsuo Hasegawa]

Dear ASAC members,

At the ASAC meeting in Grenoble, I was asked to consult with the 
Japanese frontend development team about the possibility of extension 
of the Band 4 frequency coverage up to 185 GHz to cover the water 
line.  Below is a quick reply from Yutaro Sekimoto, leader of the 
Japanese frontend group.


Answer:
Although it is an interesting development target, it would be very 
difficult to extend the RF frequency range of Band 4 that much, given 
the time schedule for fixing the design.  It is even more true 
because we are aiming at using 2SB mixers that relies on the 
waveguide technology.  Even if it becomes possible, significant 
degradation of the receiver noise temperature and image rejection 
ratio would be unavoidable.  Frequency coverage of the multiplier for 
LO would be another serious problem.

For your reference, below is a list of fractional frequency coverage 
specified for the ALMA receiver bands.

Band f(center)  f(low) - f(high) coverage

  1    35 GHz    30 GHz -  40 GHz  29%
  2    79 GHz    67 GHz -  90 GHz  29%
  3   100 GHz    84 GHz - 116 GHz  32%
  4   144 GHz   125 GHz - 163 GHz  26%  <<< current spec.
  4*  155 GHz   125 GHz - 185 GHz  39%  <<< if extended
  5   187 GHz   163 GHz - 211 GHz  26%
  6   243 GHz   211 GHz - 275 GHz  26%
  7   323 GHz   275 GHz - 370 GHz  29%
  8   443 GHz   385 GHz - 500 GHz  26%
  9   661 GHz   602 GHz - 720 GHz  18%
10   869 GHz   787 GHz - 950 GHz  19%


With best,

Tetsuo
-- 
_______________________________________________________________
Tetsuo HASEGAWA, D. Sc.   <tetsuo.hasegawa at nao.ac.jp>
ALMA-J Project Scientist
Professor, National Astronomical Observatory of Japan
2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
Phone +81-422-34-3780 / FAX +81-422-34-3764
_______________________________________________________________