dipole  linefeed  
Tsys(za=15)  167  100 
gain(za=15)  .6 K/Jy  10.5 K/Jy 
sefd(za=15) 3C48  270 Jy  9 Jy 
beam width  18 Amin  9.5 Amin 
az pnt err (avg)
zapnt err (avg) 
1.0 amin
.7 amin 
.25 Amin
.1 Amin 
az pnt offset used:
ch pnt offset used 
0.4833 deg
1.5483 

az pnt offset measured
za pnt offset measured 
0.467 deg
1.540 
The path difference for rays from the opposite edges of the dish to a point P is non zero in the near field and tends to zero (rays parallel) in the far field. The picture below shows this difference:
Using the hpbw to define the illuminated area (d=k*lambda/hpbw) and solving for H gives:
lineFd  Yagi  
HPBW (far field)  9.5 amin  18 amin 
Illuminated Diam=1.2*.7/(hpbw)  304 meters  160 meter 
Near/farField Transition: D^2/lambda  132 km  37 km 
Meteors occur around 100km. At this height, the linefeed
is still in the near field while the yagi is in the far field. The
angles and distances of the two beams at 100 km are shown below (assuming
the far field..).



pnt Offset relative to Lf
(farfield) 
0  1.622 deg 
Offset len @100km  0  2.83 km 
angle , distance  angle,distance  
1st sdLb: angle,dist@100km  14.25', .41 km  27', .78 km 
2nd sdLb:angle,dist@100km  23.75', .69 km  45', 1.3 km 
3rd sdlb: angle,dist@100km  33.25', .97 km  63', 1.83 km 
4th sdlb: angle,dist@100km  42.75', 1.25 km  81',2.36 km. 
5th sdlb: angle,dist@100km  52.25', 1.52 km  99',2.88 km. 
The yagi sidelobes move by about .53 km per sidelobe at 100 km. The lf sidelobes move by .28 km/sdlb at 100 km (if they were in the far field). The offset direction of the yagi relative to the linefeed is determined by the az,za pointing offsets.
lf sidelb/dist  yagi sidelb,dist  total
distance 
strength
rel to lf mainbm 
strength
rel to max 
0,0  5,1.52  2.88  3.36e3  1 
1,.41  4,1.25  2.77  2.37e3  .071 
3,.97  3,.97  2.8  6.95e5  .021 
5,1.52  2,.69  2.82  5.5e5  .016 
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