Up: The gain-elevation correction of
Following Ruze's (1966) antenna tolerance theory, the normalized
elevation-dependent on-axis antenna gain of the reflector optimized at
0 is
| ![\begin{displaymath}
{G}({\epsilon},{\epsilon}_0) =
{\rm exp}[-(4{\pi}{R}{\sigma}_{\rm g}({\epsilon})/{\lambda})^{2}]\end{displaymath}](/articles/aas/full/1998/18/ds1530/img12.gif) |
(3) |
where the factor R (
) takes into account the steepness of
the reflector and the illumination taper of the receiver so that
R
is the radio-effective surface deformation
(Greve &
Hooghoudt 1981). The function G(
,
0) depends
exclusively on the construction-specific values 
(
)which do not change with time and surface adjustment. The homology-corrected
telescope-independent flux [S] of a source is obtained from its calibrated
flux [S'(
)] measured at the elevation
by application of
the correction G-1(
,
0) so that
|  |
(4) |
The literature does not provide explicit information how to deal with
extended sources. We will show that for the specific case of the IRAM 30-m
telescope, the on-axis gain-elevation dependence
,
0) holds also for extended sources not exceeding
in diameter approximately two half-power beamwidths
(i.e.
2
); a weaker gain-elevation
dependence applies for more extended sources (i.e. 2
<

). The half-power beamwidth (FWHP) of the 30-m telescope
is 
= 1.16
[rad], with
the wavelength
of observation and D the diameter of the reflector; the relevant beamwidths
are given in Table 1. Note that the diameter of the full beam is
2.4
.
Table 1:
Beamwidth 
of the 30-m telescope for receivers
of
-13 dB edge taper, and the largest source diameter
* [planet] suitable for determination of the gain-elevation
dependence at the specific wavelength
|
Up: The gain-elevation correction of
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