[mmaimcal] Re: [Almasci] Two antennas

[Mark Holdaway]

Bryan Butler wrote:

>
> if it really *is* only 0.3%, then the nearly obvious conclusion would 
> be that the antenna-to-antenna variation will be almost that large 
> anyway, so nothing need be done.  i don't think we can even measure 
> the beam (polarized or not) to 0.3% in any case.
>
> i'd be surprised if it really *were* only 0.3%, though, theoretically 
> or in practice.  how much do we trust the beam simulation?  has 
> anybody put it through GRASP yet?  if it's only 0.3% difference 
> between the two designs, then this means that the entire effect of the 
> feed legs on the polarization beam is only 0.3% (peak), and that the 
> differences between the two designs have little to no area where they 
> give opposite effects.  seems a bit small to me - if you simulate the 
> polarization beam with and without the feed legs, you only get 0.3% 
> difference?  and is that absolute or relative difference?
>
That 0.3% is an RMS difference for some PB level (ie, all pixels with PB 
value ranging from 0.05 to 0.10). 
The peak difference (given the geometrical shadowing profiles I was given)
will be.....   huh?   3.3%    OK, I was expecting a bigger number too.

Keep in mind that there will likely be other beam effects which are 
different between the two
antennas -- for example, the dishes will deform differently from 
gravity, so at high freqs, the
beams will behave differently with elevation.   While things look good 
at the moment for
two different ant designs, there is a whole mountain of work we will 
need to do, and at each
step we will need to determine if we can treat the antennas as the same 
or as different.

    -Mark

>     -bryan
>
>
> On 11/7/05 11:35, Richard Hills wrote:
>
>> Dear All,
>>
>> It would certainly be good to get a definite statement from the 
>> software IPT as to what is presently planned and budgeted in this 
>> area.  Meanwhile, could we go back to the original issue please, 
>> which was whether anyone thinks that the 0.3% (peak) difference 
>> between the patterns caused by the different blockage patterns 
>> requires that we implement special data processing and/or makes a 
>> case for having the legs rotated.
>>
>> Best Richard
>
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