using eznec to compare antennas part 1 - naØtc] 2017. 1. 18. · •band coverage •height...
TRANSCRIPT
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Using EZNEC To Compare AntennasPart 1
Bill Leonard N0CU
1/5/2013
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What is the “Best” antenna?
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There is no “Best” antenna!
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For a given set of goals andconstraints, there may be a“Best” antenna!
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Typical Goals & Constraints
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•Directive vs. Omni Directional•Gain•Beam takeoff angle•Beamwidth (Azimuth & Elevation)•Front to Back Ratio•Front to Side Ratio•Efficiency•Bandwidth•Band coverage•Height required•Support structure required•Rotator required•Governmental & HOA restrictions•Obstructions (buildings, mountains, etc)•Cost•Spouse’s restrictions
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Typical Goals & Constraints
•Directive vs. Omni Directional•Gain•Beam takeoff angle•Beamwidth (Azimuth & Elevation)•Front to Back Ratio•Front to Side Ratio•Efficiency•Bandwidth•Band coverage•Height required•Support structure required•Rotator required•Governmental & HOA restrictions•Obstructions (buildings, mountains, etc)•Cost•Spouse’s restrictions
EZNEC can help
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What Criteria to Use for Comparing Antennas?
•Distance:•DX: >2000 miles•USA: 200-2000 miles•NVIS: <200 miles•Ground Wave: <50 miles
•Takeoff Angle:•DX: 1o-20o (ARRL propagation charts)•USA: 11o-63o (single hop for F2 layer at 200 miles)•NVIS: >63o
•Ground Wave: N/A
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•Distance:•DX: >2000 miles•USA: 200-2000 miles•NVIS: <200 miles•Ground Wave: <50 miles
•Takeoff Angle:•DX: 1o-20o (ARRL propagation charts)•USA: 11o-63o (single hop for F2 layer at 200 miles)•NVIS: >63o
•Ground Wave: N/A
What Criteria to Use for Comparing Antennas?
I like to compare gains above real ground at 10o & 30o
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Example 1: 48’ Shunt Fed Tower as 40M Vertical
Floating HF Beam
48’Rohn 25
40MVertical
40M Trap Dipole @ 45 ft
MatchNet
50 ohmcoax
~20 radials + chicken wire
BALUN
50 ohmcoax
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Floating HF Beam
48’Rohn 25
40MVertical
MatchNet
50 ohmcoax
~20 radials + chicken wire
BALUN
50 ohmcoax
Signals on the dipole are:•1-2 S units stronger than from the tower
95% of the time
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Example 1: 48’ Shunt Fed Tower as 40M Vertical
40M Trap Dipole @ 45 ft
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Example 1: 48’ Shunt Fed Tower as 40M Vertical
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-0.44 dBi
Tower pattern from EZNEC (mountain gnd)
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Example 1: 48’ Shunt Fed Tower as 40M Vertical
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5.79 dBi
Dipole pattern from EZNEC (45 ft above mountain gnd)
Example 1: 48’ Shunt Fed Tower as 40M Vertical
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6.23 dB
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Example 1: 48’ Shunt Fed Tower as 40M Vertical
Dipole
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Isotropic Radiator in Free Space
ELEVATION
AZIMUTH
0 dBi
0 dBi
Note: Elevation & Azimuth haveno meaning in Free Space
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Isotropic Radiator in Free Space
ELEVATION
AZIMUTH
0 dBi
0 dBi
Isotropic Radiators:•Only exist in theory
•“Hertzian Dipole” => 1.76 dBi•Radiate 0 dBi in all directions•Assumes matched linear polarization•Are always in free space
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Dipole in Free Space
ELEVATION
AZIMUTH
2.15 dBi
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2.15 dBi for Az = 0o
Fo: 14.15 MHzGain: 2.15 dBiEL Angle: n/ao
EL BW: n/ao
AZ BW: 78.2o
R: 72.1 WSWR: 1.44 Length (#12): 33.719 ft
Note: Elevation & Azimuth haveno meaning in Free Space
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Dipole in Free Space
ELEVATION
AZIMUTH
0 dBd
Fo: 14.15 MHzGain: 2.15 dBiEL Angle: n/ao
EL BW: n/ao
AZ BW: 78.2o
R: 72.1 WSWR: 1.44 Length (#12): 33.719 ft
0 dBd = 2.15 dBi for Az = 0o
Isotropic (0 dBi)
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Note: Elevation & Azimuth haveno meaning in Free Space
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2.15 dBi
Horizontal Dipole Above Infinite Loss Ground
x ftELEVATION
AZIMUTH
2.15 dBi
Fo: 14.15 MHzGain: 2.15 dBiEL Angle: n/ao
EL BW: n/ao
AZ BW: 78.2o
R: 72.1 WSWR: 1.44 Length (#12): 33.719 ft
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Note: Elevation & Azimuth haveno meaning in Free Space
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2.15 dBi
Horizontal Dipole Above Infinite Loss Ground
x ftELEVATION
AZIMUTH
2.15 dBi
Fo: 14.15 MHzGain: 2.15 dBiEL Angle: n/ao
EL BW: n/ao
AZ BW: 78.2o
R: 72.1 WSWR: 1.44 Length (#12): 33.719 ft
Ground reflection gain = 0 dB
Note: Elevation & Azimuth haveno meaning in Free Space
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Real Antennas
•Any real antenna is always above a Real Ground:•Pattern, Gain and Impedance vary with:
•Height above ground•Type of ground•Polarization•Construction:
•Size of elements•Material used for elements•Mounting hardware and technique•Insulators
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x
Reflections From Real Ground (Ray Tracing)
Antenna
Ground
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x
Reflections From Real Ground (Ray Tracing)
AntennaHorizontal Polarization => 180o phase shiftVertical Polarization => no phase shift
Ground
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Reflections From Real Ground (Ray Tracing)
x
x
Antenna
VirtualAntenna
Ground
Differential Phase
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x
Reflections From Real Ground (Ray Tracing)
Direct Ray
Reflected Ray
AntennaHorizontal Polarization => 180o phase shiftVertical Polarization => no phase shift
Ground
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Reflections From Real Ground (Impedance)
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Ground Reflection Gain
Horizontal Polarization:•Peak gain can be 4.5 – 7.0 dB higher than Free Space gain depending on:
•Ground type•Height above ground•Elevation angle•Azimuth angle
•Vertical Polarization: <3dB over real ground
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When comparing different antennas:•Do not compare a Free Space pattern to a
pattern over ground•Use identical ground conditions•Use identical polarizations•Be careful when using dBd
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Example 2: 20M 5 Element Wide Spaced Yagi
9.84 dBi
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Free Space Pattern
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“Our beam has 12 dB more gain than a dipole”
Free Space Pattern
9.84 dBi
Example 2: 20M 5 Element Wide Spaced Yagi
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Dipole (2.15 dBi)
9.84 dBi
Free Space Patterns
7.69 dB
Example 2: 20M 5 Element Wide Spaced Yagi
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14.09 dBi
Pattern for Beam 5/8 l Above Perfect Ground
Ground reflection gain = 14.09 – 9.84 = 4.25 dB
Example 2: 20M 5 Element Wide Spaced Yagi
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Both Beam & Dipole 5/8 l Above Perfect Ground
7.69 dB
Beam 5/8 lAbove Perfect
Ground
Example 2: 20M 5 Element Wide Spaced Yagi
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Beam 5/8 lAbove Perfect
Ground
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11.94 dB
Dipole in Free Space
Example 2: 20M 5 Element Wide Spaced Yagi
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•Dipole 5/8 l Above Real Ground•Beam 10’ Above Real Ground
Beam 10 ft Above Real
Ground
Dipole 50 ft AboveReal Ground
Example 2: 20M 5 Element Wide Spaced Yagi
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The gain of this antenna “...is only0.25 dB less than if the antenna were in Free Space.”
The theoretical maximum gain (free space) = +2.96 dBi = +0.81 dBd
EZNEC Free Space pattern:2.85 dBi @ 30o
Full wave delta loop for 15M
0.1 ft
11.1 ft
Example 3: January 2013 QST
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Antennas that don’t work off ofground, don’t work well close to a
lossy ground
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2.41 dBi
35o
K1QW Pattern in QST article
Example 3: January 2013 QST
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0.03 dBi
Example 3: January 2013 QST
33o
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show both patterns
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Example 3: January 2013 QST
Dipole @ 30 ft6.15 dBi/33o
Dipole @ 15 ft6.12 dBi/90o
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Delta Loop_Gnd Level
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Example 3: January 2013 QST
Dipole @ 30 ft6.15 dBi/33o
Dipole @ 15 ft6.12 dBi/90o
12/27/2012
Delta Loop_Gnd Level
Vertical antennas radiateequally poorly in all directions!
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Example 3: January 2013 QST
Dipole @ 30 ft6.15 dBi/33o
Dipole @ 15 ft6.12 dBi/90o
12/27/2012
Delta Loop_Gnd Level
Vertically polarized antennas radiateequally poorly in all directions!
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show both vert & horiz patterns for beam
Example 3: January 2013 QST