1. A TECHNICAL BRIEFING FOR AMATEUR RADIO OPERATORS
“ANTENNA GAIN: TRUTHS AND MYTHS”
PRESENTED TO:
ARASWF
NAPLES, FL 34119
JANUARY 2016
PRESENTED BY:
DR. AL TORRES
KP4AQI

2. January 2016: “Antenna Gain: Truths and Myths”
For Year 2016
January 2016: “Antenna Gain: Truths and Myths”
February 2016: “Slot Antennas: Wire Reciprocity”
March 2016: “Fractal Antennas and Metamaterial Antennas”

3. PRESENTATION OUTLINE WHAT IS ANTENNA GAIN ANTENNA GAIN EXAMPLES
TYPICAL EFFECIENCY VALUES FOR ANTENNAS
ANTENNA GAIN MEASUREMENTS
STANDARD GAIN HORNS (SGH)
COMMERCIAL ANTENNAS AND THEIR STATED GAINS
SUMMARY

4. G= D  = (Rr + Ro) D= 4 (Ae/ 2)
WHAT IS ANTENNA GAIN
ANTENNA GAIN IS THE PRODUCT OF ANTENNA EFFICIENCY TIMES ANTENNA DIRECTIVITY
G= D
 IS ANTENNA EFFICIENCY WHICH IS MADE FROM THE SUM OF RADIATION RESISTANCE AND OHMIC RESISTANCE
 = (Rr + Ro)
D IS ANTENNA DIRECTIVITY AND IT IS A FUNCTION OF THE TYPE OF ANTENNA
DIRECTIVITY FOR AN ANTENNA IS DEFINED AS:
D= 4 (Ae/ 2)
 is wavelength and Ae is Antenna Effective aperture (size)

5. ANTENNA GAIN EXAMPLES
RADIATION RESISTANCE SHOULD BE AS HIGH AS POSSIBLE
OHMIC RESISTANCE SHOULD BE AS LOW AS POSSIBLE
TYPICAL RADIATION RESISTANCE FOR A DIPOLE IS 73 OHMS
TYPICAL OHMIC RESISTANCE FOR A COPPER DIPOLE IS 6 OHMS
EFFICIENCY IS ~ 92%
THEORETICAL GAIN FOR A DIPOLE IS 2.14 dBi (100% EFFICIENT)
PRACTICAL GAIN FOR A COPPER DIPOLE IS 1.98 dBi

6. CONDUCTIVITY OF METALS
Conductor
Conductivity (m)
Carbon (Graphene)
1.0 x 10-8
Silver
1.59 x %
Copper
1.68 x %
Gold
2.44 x
Aluminum
2.82 x
Zinc
5.90 x
Nickel
6.99 x
Iron
1.00 x
Stainless Steel
6.90 x
Nichrome
1.10 x

7. TYPICAL EFFICIENCY VALUES FOR ANTENNAS
SILVER MONOPOLE: 95%
SILVER DIPOLE: 94%
COPPER MONOPOLE: 93%
COPPER DIPOLE: 92%
ALUMINUM ANTENNAS: %
WITHOUT TRAPS: 55%
WITH TRAPS: 40%
RUBBER DUCK ANTENNAS: 20%
DUMMY LOAD: 1%

8. ANTENNA GAIN MEASUREMENTS
THERE ARE TWO BASIC METHODS THAT CAN BE USED TO MEASURE ANTENNA GAIN: ABSOLUTE-GAIN AND GAIN-TRANSFER (GAIN COMPARISON) MEASUREMENTS
ABSOLUTE-GAIN: THIS METHOD IS USED TO CALIBRATE ANTENNAS THAT CAN THEN BE USED AS STANDARDS FOR GAIN MEASUREMENTS, AND IT REQUIRES NO A PRIORI KNOWLEDGE OF THE GAINS OF THE ANTENNAS
GAIN-TRANSFER: THIS METHOD MUST BE USED IN CONJUNCTION WITH STANDARD GAIN ANTENNAS TO DETERMINE THE ABSOLUTE GAIN OF THE ANTENNA UNDER TEST

9. STANDARD GAIN HORNS (SGH)
Model
Frequency
E-Plane
H-Plane
Maximum Continuous Power
Antenna Factor
Gain
Typical Field Strength
GHz
26°
27°
550 W
15.4 dB (1/m)
16.5 dBi
700 V/m
GHz
16.9 dB (1/m)
16.3 dBi
GHz
20.6 dB (1/m)
650 V/m
GHz
250 W
23.7 dB (1/m)
16.7 dBi
500 V/m
GHz
27.3 dB (1/m)
GHz
24°
25°
29.9 dB (1/m)
17.1 dBi
GHz
33.5 dB (1/m)
16.9 dBi
GHz
200 W
37.1 dB (1/m)
435 V/m
GHz
50 W
40.3 dB (1/m)
16.8 dBi
220 V/m
GHz
10 W
43.5 dB (1/m)
17.0 dBi
100 V/m

10. GAIN MEASUREMENTS
THE LOWEST FREQUENCY FOR SGH IS 300 MHZ; THERE ARE NO STANDARDS BELOW THIS FREQUENCY
ENGINEERS HAVE TRIED TO USE 1/2 DIPOLES AS STANDARDS DOWN TO 100 MHZ. MEASUREMENTS HAVE TOO MUCH VARIABILITY FOR MAKING GAIN-TRANSFER MEASUREMENTS
THE TYPICAL RESONANT 1/2 DIPOLE (WITH A GAIN OF 2.14 dBi), IN FREE SPACE, EXHIBITS A HIGH DEGREE OF POLARIZATION PURITY. HOWEVER BECAUSE OF ITS BROAD PATTERN, ITS POLARIZATION MAY BE SUSPECT IN OTHER THAN REFLECTION-FREE ENVIRONMENTS

11. GAIN MEASUREMENTS TYPICAL ANECHOIC CHAMBERS GO DOWN TO ~ 200 MHZ
ACCURATE GAIN MEASUREMENTS BELOW 300 MHZ ARE NOT POSSIBLE

12. HF YAGI ANTENNAS AND GAINS

13. THREE ELEMENT YAGI FOR 2 METERS CUSHCRAFT
A13B2 3 Element Wideband Boomer The A13B2 is as versatile as the A17B2 is specialized. A13B2 will be your choice for high performance across the entire 2 meter band. New and experienced hams will enjoy 15.8 dBi gain on FM, packet, CW, or sideband across the 4 MHz operating range. The A13B2 is easily mounted vertically or horizontally for maximum performance on your favorite mode. Its optimum boom length makes it a popular antenna that fits just about anywhere. The new UltraMatch balanced feed on the A13B2 provides a 50 Ohm match via a standard SO-239 UHF female connector.

14. CUSHCRAFT YAGI ANTENNAS GAIN VALUES
HOW WERE THESE MEASUREMENTS DONE?
LIERS!

15. MFJ-18522-METER YAGI, 6 EL., 144-148MHZ, WIDE BAND
Our versatile new six-element MFJ Meter Band Spanner Yagi delivers 10-dBi gain, 20-dB front-to-back ratio, and covers 144 to 148 MHz plus WEFAX and MARS with rock bottom SWR.
HOW WAS THIS MEASUREMENT DONE? WHAT STANDARDS? MUST BE PFM
LIER, LIER!

16. SUMMARY WE HAVE DEFINED WHAT ANTENNA GAIN IS
ANTENNA GAIN IS MOSTLY DETERMINED BY THE ANTENNA DIRECTIVITY AND ITS EFFICIENCY (MOSTLY OHMIC LOSSES)
WE HAVE ALSO DEFINED DIRECTIVITY WHICH IS PROPORTIONAL TO ANTENNA SIZE AND WAVELENGTH
MEASUREMENTS OF GAIN ON ANTENNAS IS PRESENTLY LIMITED TO 300 MHZ AND ABOVE BECAUSE WE DO NOT HAVE RELIABLE GAIN STANDARDS BELOW 300 MHZ

17. SUMMARY (CONT.)
ANTENNA PRODUCTS WHICH PROVIDE GAIN BELOW THIS FREQUENCY ARE NOT RELIABLE; THEY MAYBE PROVIDING DIRECTIVITY VALUES (THEORETICAL) AND NOT TRUE GAIN VALUE
AT HF, LOW VHF TO HIGH VHF, ANTENNA GAIN IS MOSTLY A THEORETICAL APPROXIMATION AND NOT MEASURABLE

18. MORE INFORMATION or COPY OF PRESENTATION
SEND AN TO THE FOLLOWING URL:
CONTACT ME AT:
AL TORRES
KP4AQI
P. O. BOX 24283
DAYTON, OH