1. CRES Amateur Radio Association
Antenna Fundamentals
Presented by:
Bob Kenyon - K8LJ
CRES Amateur Radio Association
December 6, 2012

2. Agenda Introduction and background Basic antenna theory
Transmission line impacts
Antenna modeling
Members’ antenna questions discussion
Conclusion and next steps discussion

3. Basic Communications System
Antenna
Transceiver
Transmission Line
Electromagnetic Wave
Radiated
Electrical Wave
Propagated
Electrical Signal
Generated
(Voltage)
(Voltage & Current)
(Voltage, Current & Magnetic Field)

4. Antenna Equivalent Circuit
(Feedline Not Included)
Radiation
Resistance
Antenna
Resistive Loss
Ground Losses RG RR RL
Usually not a problem for non-shortened horizontal antennas, such as a full size dipole
This is where we want the power to go
Often a big problem, especially for vertically polarized antennas RR
Ant. Efficiency =
X 100%
RR +
RL + RG

5. Basic Antenna Concepts•
Antenna gain is achieved by pattern alteration (
directivity ) •
All antennas are directive (except an isotropic source) •
Antenna gain = antenna
directivity
- antenna losses •
Gain is affected by antenna design, physical realization, & environment •
For antennas near earth, the pattern (
directivity
, gain) is greatly affected by
reflections from the earth’s surface (ground conductivity impact) •
Reflection of horizontally polarized signals is usually quite efficient •
Reflection of vertically polarized signals is often inefficient •
Theory of Reciprocity: Antennas behave the same transmitting & receiving

6. Zin is High - can range from
Current Feed vs. Voltage Feed
(for a λ /2 dipole, not all antennas) I
Zin is Low ~ 7 3 ohms
in Free Space V
Zin ~ RR
Center Feed (Current Max.) = Current Feed I
Zin is High - can range from
100s to 1000s of ohms V
End Feed (Voltage Max.) = Voltage Feed
Zin >> RR

7. Cable Attenuation - dB Per 100 Feet
Frequency (MHz)

8. Transmission Line Modeling
TLDetails free program
Go to AC6LA.com

9. Practical Example - RG-8A Coax vs. 450  Line
Assume a 100 ft long, 50 ft high, center-fed dipole
Average ground conductivity (5mS/m), & permittivity of 13
Antenna impedance computed using EZNEC (NEC-2 engine)
Frequency
(MHz)
1.8
3.8
7.1
10.1
14.1
18.1
21.4
24.9
28.4
Ant Impedance
(Ohms)
4.5 - j1673
j362
481 + j964
j3292
j123.3
j1552
345 - j1073
202 + j367
j1375
SWR
RG-8A Coax
>1000:1
63:1
49:1
134:1
5.6:1
65:1
73:1
18:1
Loss 100 ft
RG-8A Coax
26.2 dB
5.7 dB
10.2 dB
1.8 dB
8.7 dB
9.5 dB
4.9 dB
9.7 dB
SWR
450  Line
>1000:1
19:1
6.2:1
15.2:1
5.7:1
7.3:1
9.4:1
3.9:1
Loss 100 ft
450  Line
9.2 dB
0.5 dB
0.2 dB
0.6 dB
0.3 dB
0.4 dB

10. Zin is High - can range from
Current Feed vs. Voltage Feed
(for a λ /2 dipole, not all antennas) I
Zin is Low ~ 7 3 ohms
in Free Space V
Zin ~ RR
Center Feed (Current Max.) = Current Feed I
Zin is High - can range from
100s to 1000s of ohms V
End Feed (Voltage Max.) = Voltage Feed
Zin >> RR

11. · · Horizontal Antenna Above Earth Direct Wave Horizontal Antenna
(End View)
To Distant Point α
Reflected Wave +h
Earth’s Surface α -h
180º Phase Reversal
If d = n •180º (n odd)
Wave Reinforcement
Image
Antenna
(- 180º phase)
If d = n •180º (n even)
Wave Cancellation d
n = 0,1,2,3,4 ...
(180º = λ/2)

12. Antenna Modeling

13. Why Model Antennas? Easily perform “what if” analyses
Computer horse-power now available, even on PCs
Significant resource ($) & time savings
Improve accuracy & repeatability
Easily perform “what if” analyses
Learn a lot about antennas quickly
It’s fun! … (warning - can become additive)

14. What Can a Model Tell Us? Antenna physical depiction (view)
Far Field Pattern
- 2D plots (azimuth or elevation)
- 3D plots (both together)
Antenna gain at any angle
Front-to-back, front-to-side ratios, 1/2 power beamwidth etc.
SWR vs. frequency
Impedance (real & imaginary) vs. frequency
Wire currents - magnitude and phase for each segment
Other stuff

15. Antenna Modeling Terms
Wire - Basic antenna model building entity (linear, no bends)
Segment - Sub-division of a wire
Source - Feed point electrical specifics (Volts/Amps & Phase)
Load - R, L, and C values alone or in any combination
Ground Type - Free space, perfect and types of “real” ground

16. Wires and Segments • • Dipole 1 Wire 11 Segments 1 3 = Wire Junction
5 Segments Each
Quad Loop
= Source 4 2 N
= Wire Number 1 2
3 Wires
2 With 2 Segments
1 With 7 Segments
Bent Element 1 3

17. Antenna Modeling Guidelines
A wire should have at least 9 segments per half-wavelength
(times for impedance and SWR plots)
Segment length should be > than 4 times wire diameter
To extent possible, keep segment lengths equal

18. Antenna Modeling Products
(Sample)
Public Domain (Free)
4nec2 - Modeling and optimization program (Dutch)
MMANA - By JE3HHT, Makoto (Mako) Mori (MININEC)
EZNEC Demo By W7EL (
Commercial
Nec-Win Plus (similar to EZNEC)
K6STI - Various modeling & optimization programs (MININEC)
EZENEC 5.0, EZNEC + 5.0, EZNEC Pro (NEC-4)

19. Demo of EZNEC 5.0 DEMO
Available at

20. 1/2 Wave Dipole Elevation Plots vs. Antenna Height
14 Mhz. - Perfect Ground
1/4 Wavelength
(17.5 ft.)
1 Wavelength
(70 ft.)
5/4 Wavelengths
(87.5 ft.)
1/2 Wavelength
(35 ft.)
1 & 1/2 Wave-lengths
(105 ft.)
3/4 Wavelength
52.5 ft.

21. Estimated Ground Conductivity in the U.S.
= 30 mS/meter
= 0.5 mS/meter
mS = .001 siemens = .001 mho
Salt water = 5000 mS/meter

22. (Applies to λ /2 Dipole Also)
Vertical Antenna Patterns
In Free Space
(Applies to λ /2 Dipole Also)
Above a Perfectly Conducting Surface

23. Baluns
Love them
Hate them

27. Long Wires
V Beams
Rhombics

29. Creating a V Beam

30. A Rhombic – Two V Beams Back-to-Back

31. Voice of America Antennas Near Cincinnati
5,370 ft.

32. K8LJ 160 – 6 Meter Antenna Cost Insulator - $ 0 Wire - $ 0.53
PL259 - $ 0.50
Coax - $ 4.00
Total - $ 5.03

33. Bucky

34. References M
- Maxwell, M W. , Reflections: Transmission Lines and Antennas,
Newington, CT: ARRL,1990.
T- The ARRL Antenna Book, Newington, CT: ARRL, 2005.
- Jeffrey S. Beasley & Gary M. Miller, Modern Electronic Communication,
9th Edition, Columbus, OH: Prentice Hall, 2008.
- Kraus, John D. Ph.D., Antennas, New York, NY: McGraw-Hill, 1950.
- The ARRL Handbook, Newington, CT: ARRL, 2002
W- Ward Silver, QST, Smith Chart Fun 1, 2 & 3, Dec. 2007, Jan. 2008, Feb.
2008