offset feed dish calculations - k5trak5tra.net/graphics/10 ghz/offset feed dish calculations.pdf ·...
TRANSCRIPT
K5TRA
OFFSET-FEED DISH
CALCULATIONS
1T.Apel
K5TRA
Parabola
T.Apel 2
0.00
0.50
1.00
1.50
2.00
2.50
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
• All parabolas are similar
• Scaling parameter determines:– Relative curvature
– f/D
– How ‘shallow’ or ‘deep’ the dish
x
yP
K5TRA
Paraboloid
3T.Apel
• Plane waves are focused IN-PHASE to the focal point
• A paraboloid surface is a parabola rotated about the focal axis
• Dish reflectors are usually defined by the intersection of a parapolid and a plane
• Axial feed: intersecting plane is perpendicular to focal axis
• Offset feed: intersecting plane cuts through the origin (end of focal axis)
K5TRA
Single Reflector Dish Feeds
AXIAL FEED OFFSET FEED
T.Apel 4
• AXIAL FEED HORN BLOCKS DISH APERTURE
• AXIAL FEED MATCH IS AFFECTED BY DISH REFLECTION
• OFFSET FEED HAS A LARGER EFFECTIVE f/D
K5TRA
Assumptions
• Analysis based on measurements along vertical cross-section of dish
• Bottom of dish is origin of full parabola
• Two measurements determine solution:
– Vertical width of dish
– Depth of dish at center
5T.Apel
K5TRA
Deep-Dish Example
T.Apel 6
0.00
0.50
1.00
1.50
2.00
2.50
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Yp
0.00
0.50
1.00
1.50
2.00
2.50
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
Yp
Yl
K5TRA
Shallow-Dish Example
T.Apel 7
0.000.100.200.300.400.500.600.700.800.901.001.101.201.301.401.50
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
Yp
0.000.100.200.300.400.500.600.700.800.901.001.101.201.301.401.50
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
Yp
Yl
K5TRA
HughesNet Dish
T.Apel 8
0.00
5.00
10.00
15.00
20.00
25.00
-25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0
Yp
0.00
5.00
10.00
15.00
20.00
25.00
0.0 5.0 10.0 15.0 20.0 25.0
Yp
Yl
K5TRA
Offset-Feed Geometry
9T.Apel
FOCUS
F
Fe
hD Ymax
Y(Xe)
q
f
½ f
XeX=0
YL
YP
½ Xe
K5TRA
Analysis
10T.Apel
K5TRA
Analysis
11T.Apel
K5TRA
HughesNet Dish Solution
12T.Apel
MEASUREMENTS
SOLUTION