Antennas 101

1
ABA 2009 Annual Convention Ennes Workshop
Antennas 101
Bob Surette
Director of Sales Engineering
Friday May 15th, 2009
2
What is the definition of
?
dBm
0 dBm 1 milliwatt
dull
Boring
monotonous
So pay attention
Shively Labs
3
Some basic equations on how to calculate
wavelength (lambda), Far Field, Power Density
and Field Strength (dBu)
Elevation patterns of Isotropic point sources
which define Array Factors
Prove that ½ wave spacing is the optimum spacing
for reducing downward radiation
Show how bay to bay spacing effect downward
radiation
How to calculate Beam Tilt and Null Fill of an
antenna
The use of Pascals Triangle to predict a
Binomial feed system that Allows us to shape an
elevation pattern
4
?
Speed of light / Frequency
Speed of Light 3 x 108 m/sec
Speed of light 299,792,458 m/sec
39.371 inches 1 Meter
299,792,458 X 39.371 11803 X 106 inches/sec
11803 X 106 inches/sec / 1 X 106 Hz 11803 inches
? 11803 / 98.1 120.3 inches
5
Far Field
r 2D2 / ?
Far Field
5 Bay _at_ 98.1 MHz
? 11803 / 98.1 120.3 inches 10 Feet
D Length of Antenna 40 Feet
r Distance to Far Field
r 2 D2 / ?
320 Feet
6
Surface Area 4 p R²
Power Density S
P / 4 p R² Watts / Metter ²
7
Calculating Field Strength
100 kW at a distance of 30 Kilometers ( 20
Miles)
Power Density S P / 4 p R²
S 100,000 Watts / 4 p (30,000 Meters)²
S 0.0000088 Watts / Meter ²
S 8.8 X 10 -6 Watts / Meter ²
Calculate Electric Field from Power Density
E in dBu 20 log E/ 1x 10-6 20 log 58 x 10-3
/ 1 x 10-6
E 95 dBu
8
Questions
9
Array Factor
10
Array Factor
2 bay Full
11
Array Factor
12
Array Factor
2 Bay 1/2
13
Array Factor
2 bay Full
14
Array Factor
2 Bay 1/2
15
Array Factor
16
Array Factor
3 Bay 1/2
17
Array Factor
3 Bay Full
18
Array Factor
3 Bay 1/2
19
Unit Pattern
20
2 bay Full
Array Factor
21
2 bay Full
Array Factor x Unit Pattern Elevation Pattern
22
2 Bay 1/2
23
3 Bay 1/2
24
Questions
25
?
d
26
c
-1
1
-2
-3
2
3
Phase Shifters




Combiner / Power Divider
27
(No Transcript)
28
Questions
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Questions
37
(No Transcript)
38
Distance from the tower where RF hits the ground
1st Null 60 / No. of Bays
1st Null 60 / 6 10 Degrees
Center of Radiation/Tangent of the Angle
1000 feet / tan 10 degrees 5,671 feet
1000 feet / tan 70 degrees 364 feet
39
Null Fill
40
(No Transcript)
41
Beam Tilt
42
1
43
Beam Tilt Null Fill
44
1
45
Questions
46
6 Bay ½ Wave Spacing
47
(No Transcript)
48
(No Transcript)
49
0.03
6 Bay ½ Wave Spacing with Binomial Feed
50
(No Transcript)
51
0.03
6 Bay 0.78 Wave Spacing with Modified Binomial
Feed
52
(No Transcript)
53
250 Watt Translator with Center of Radiation
above 250 Feet
6 Bay 0.78 Wave Spacing with Modified Binomial
Feed
54
Final
Questions
Visit us at www.shively.com Call toll free
888-744-8359 Email us at sales_at_shively.com