144 MHz Omnidirectional Horizontal Antennas - Part 3

NEC Model Comparisons of Stacked Halo, Turnstile and Eggbeater Omnidirectional Horizontally Polarized Antennas for 144 MHz

by Dr. Carol F. Milazzo, KP4MD (posted 05 January 2013)
E-mail: kp4md@arrl.net

INTRODUCTION

The halo, turnstile, eggbeater and Big Wheel are omnidirectional horizontally polarized antennas used for weak signal VHF terrestrial communications.  Cebik3 duly described the benefits and problems of each of these antenna designs.  These antennas can be stacked to increase gain at low elevation angles and to decrease sensitivity to noise from high elevation angles.

This study uses NEC modeling to compare the expected performance of stacked pairs of each of these antenna designs. The antennas were modeled with 4nec2 at 0.5λ and 1λ above a simulated ground with spacing optimized for minimum gain at 90º elevation and maximum gain at 15º elevation.

  1. Single Halo, Turnstile and Eggbeater at 0.5λ NEC Models
  2. Single Halo, Turnstile and Eggbeater at 1.0λ NEC Models
  3. Stacked Halo, Turnstile and Eggbeater Antenna NEC Models
  4. Single Turnstile, Triangle and Wheel at 0.5λ NEC Models
  5. Single Turnstile, Triangle and Wheel at 1.0λ NEC Models
  6. Stacked Turnstile, Triangle and Wheel Antenna NEC Models

144 MHz 2 stacked Halo Antennas horizontal
                      polarization radiation pattern calculated by NEC
                      Model.

1. 144 MHz 2 stacked Halo Antennas horizontal polarization radiation pattern calculated by NEC Model.

144 MHz 2 stacked Turnstile Antennas
                      horizontal polarization radiation pattern
                      calculated by NEC Model.

2. 144 MHz 2 stacked Turnstile Antennas horizontal polarization radiation pattern calculated by NEC Model.

144 MHz 2 stacked Eggbeater Antennas
                      horizontal polarization radiation pattern
                      calculated by NEC Model.

3. 144 MHz 2 stacked Eggbeater Antennas horizontal polarization radiation pattern calculated by NEC Model.

144 MHz 2 stacked Halo Antennas vertical
                      polarization radiation pattern calculated by NEC
                      Model.

4. 144 MHz 2 stacked Halo Antennas vertical polarization radiation pattern calculated by NEC Model.

144 MHz 2 stacked Turnstile Antennas vertical
                      polarization radiation pattern calculated by NEC
                      Model.

5. 144 MHz 2 stacked Turnstile Antennas vertical polarization radiation pattern calculated by NEC Model.

144 MHz 2 stacked Eggbeater Antennas vertical
                      polarization radiation pattern calculated by NEC
                      Model.

6. 144 MHz 2 stacked Eggbeater Antennas vertical polarization radiation pattern calculated by NEC Model.

144 MHz 2 stacked Halo Antennas azimuth
                      pattern calculated by NEC Model.

7. 144 MHz 2 stacked Halo Antennas azimuth pattern calculated by NEC Model.

144 MHz 2 stacked Turnstile Antennas azimuth
                      pattern calculatedby NEC Model.

8. 144 MHz 2 stacked Turnstile Antennas azimuth pattern calculated by NEC Model.

144 MHz 2 stacked Eggbeater Antennas azimuth
                      pattern calculatedby NEC Model.

9. 144 MHz 2 stacked Eggbeater Antennas azimuth pattern calculated by NEC Model.

144 MHz 2 stacked Halo Antennas elevation
                      pattern calculated by NEC Model.

10. 144 MHz 2 stacked Halo Antennas elevation pattern calculated by NEC Model.

144 MHz 2 stacked Turnstile Antennas
                      elevation pattern calculatedby NEC Model.

11. 144 MHz 2 stacked Turnstile Antennas elevation pattern calculated by NEC Model.

144 MHz 2 stacked Eggbeater Antennas
                      elevation pattern calculated by NEC Model.

12. 144 MHz 2 stacked Eggbeater Antennas elevation pattern calculated by NEC Model.

144MHz 2 stacked Halo Antennas
                    4nec2Calculations.

13. 144 MHz 2 stacked Halo Antennas 4nec2 Calculations.

144MHz 2 stacked Turnstile Antennas 4nec2
                    Calculations.

14. 144 MHz 2 stacked Turnstile Antennas 4nec2 Calculations.

144MHz 2 stacked Eggbeater Antennas 4nec2
                    Calculations.

15. 144 MHz 2 stacked Eggbeater Antennas 4nec2 Calculations.

CM 144 MHz 2 Stacked Halo Antennas at 0.5 and 1.0 lambda NEC model by Carol F. Milazzo, KP4MD
CM Horizontal orientation (using GH command)
CM Frequency = 145.000 MHz
CM 26-side polygon (40 inch loop with 1.5 inch gap)
CM Simulated good ground
CM http://www.qsl.net/kp4md/omnihoriz.htm
CE
SY frq=145    'Input frequency MHz
SY cir=40.21493    'Input loop circumference inches (loop + gap)
SY r=0.5*cir/3.1415926    'Calculate loop radius
SY dia=0.25    'Input loop wire dia. inches
SY rad=0.5*dia    'Calculate loop wire radius
SY n=26    'Input n-side polygon of loop + gap
SY h=40.87    'Input height inches to 0.5 lambda
SY g=1.5    'Input gap size in inches
SY gseg=int(n*g/cir+0.5)    'Calculate gap length in segments
GH    1    n-gseg    1e-300    1e-300*(n-gseg)/n    r    r    r    r    rad    'First loop
GM    0    0    0    0    gseg*180/n    0    0    h    1    'Raise loop to 0.5 lambda
GM    1    1    0    0    0    0    0    h    1    'Copy to second loop at 1 lambda
GS    0    0    0.0254
GE    1
LD    5    0    0    0    58000000    '0.25 inch copper tubing
GN    2    0    0    0    4    0.01
EK
EX    0    1    (n-gseg)/2    0    0.5    0    0    'Feed point
EX    0    2    (n-gseg)/2    0    0.5    0    0    'Feed point
FR    0    0    0    0    frq    0
EN

16. 144 MHz 2 stacked Halo Antennas NEC model.

CM 144 MHz Stacked Turnstile Antenna NEC model by Carol F. Milazzo, KP4MD
CM Horizontal orientation
CM Frequency = 145.000 MHz
CM 21 segments per dipole
CM Simulated good ground
CM http://www.qsl.net/kp4md/omnihoriz.htm
CE
SY frq=145    'Input frequency MHz
SY len=39.815    'Input dipole length inches
SY dia=0.25    'Input dipole dia. inches
SY rad=0.5*dia    'Calculate dipole radius
SY n=21    'Input segments per dipole (must be odd)
SY nc=0.5*(n+1)    'Calculate feed point segment
SY h=40.87    'Input height inches to 0.5 lambda
SY s=0.25    'Input separation between each dipole in pair inches
GW    1    n    0    -len/2    h    0    len/2    h    rad    'First dipole at 0.5 lambda
GM    1    1    0    0    90    0    0    s    1    'Rotate to form second dipole at right angle
GM    2    1    0    0    0    0    0    h    1    'Copy dipole pair to 1.0 lambda
GS    0    0    0.0254
GE    1
LD    5    0    0    0    58000000    '0.25 inch copper tubing
GN    2    0    0    0    4    0.01
EK
EX    0    1    nc    0    0    1    0    'Feed point
EX    0    2    nc    0    -1    0    0    'Feed point
EX    0    3    nc    0    0    1    0    'Feed point
EX    0    4    nc    0    -1    0    0    'Feed point
FR    0    0    0    0    frq    0
RP    0    1    361    1000    76.    0.    0.    1.    0.   
EN

17. 144 MHz 2 stacked Turnstile Antennas NEC model.

CM 144 MHz Stacked Eggbeater Antenna NEC model by Carol F. Milazzo, KP4MD
CM Vertical orientation (using GH command)
CM Frequency = 145.000 MHz
CM 42-side polygon loops
CM Simulated good ground
CM http://www.qsl.net/kp4md/omnihoriz.htm
CE
SY frq=145    'Input frequency MHz
SY d=29.01591    'Input loop diameter inches
SY r=0.5*d    'Calculate loop radius
SY dia=0.5    'Input loop wire dia. inches
SY rad=0.5*dia    'Calculate loop wire radius
SY n=42    'Input n-polygon loop
SY h=40.66136    'Input height inches to 0.5 lambda
GH    1    n    1e-300    1e-300    r    r    r    r    rad    'Form first loop in ground
GM    0    0    90    90-180/n    0    0    0    h    0    'Raise loop center to 0.5 lambda and rotate to orient vertically
GM    1    1    0    0    90    0    0    .25    1    'Rotate loop 90 degrees to form second loop
GM    2    1    0    0    0    0    0    h    1    'Copy to second set of loops at 1.0 lambda
GS    0    0    0.0254
GE    1
LD    5    0    0    0    58000000    '0.5 inch copper tubing
GN    2    0    0    0    4    0.01
EK
EX    0    1    n    0    0    1    0    'Feed point
EX    0    2    n    0    -1    0    0    'Feed point
EX    0    3    n    0    0    1    0    'Feed point
EX    0    4    n    0    -1    0    0    'Feed point
FR    0    0    0    0    frq    0
EN

18. 144 MHz 2 stacked Eggbeater Antennas NEC model.

RESULTS

  1. All antennas had maximum lobe gains between 6.8 and 7.9 dBi of each other at 15º elevation.
  2. The turnstile and eggbeater antennas more closely approximated an omnidirectional pattern with 0.7-1.0 dB variation in azimuth radiation while the halo antenna exhibited a 3.1 dB differential in gain between its major and minor axes.
  3. All antenna types showed similar elevation radiation patterns with nulls of -20 dBi or lower toward the zenith.
  4. The turnstile antenna exhibited the least suppression of vertically polarized noise.

CONCLUSION

Although the overall expected performance of each of the models is similar, the following differences should be considered: 

  1. The difference in performance may not warrant incurring the greater construction complexity of any particular antenna design. 
  2. The losses incurred in the additional stacking and phasing harnesses may diminish or negate the expected gain in any particular antenna design.
  3. Deviations in the antenna and phasing harness dimensions can significantly skew the radiation patterns.3

Composite of all 144 MHz 2 stacked Antennas
                      azimuth patterns - horizontal polarization
                      component only.

19. Composite of all 144 MHz 2 stacked Antennas azimuth patterns - horizontal polarization component only.

Composite of all 144 MHz 2 stacked Antennas
                      azimuth patterns - vertical polarization component
                      only.

20. Composite of all 144 MHz 2 stacked Antennas azimuth patterns - vertical polarization component only.

REFERENCES

  1. The HO Collinear, A Horizontal Omni, Anderson R, W1HBQ
  2. The Double Turnstile Antenna, Beech J, G8SEQ
  3. Horizontally Polarized Omni-Directional Antennas: Some Compact Choices, Part 1, Cebik, LB, W4RNL
  4. Horizontally Polarized Omni-Directional Antennas: Some Compact Choices, Part 2, Cebik, LB, W4RNL
  5. Experimental Omnidirectional Antennas for 6-Meters, Cebik, LB, W4RNL
  6. 144 MHz Halo Antenna, Milazzo C, KP4MD

APPENDIX: NEC MODEL FILES

  1. 144 MHz 2 Stacked Halo Antennas NEC Model
  2. 144 MHz 2 Stacked Turnstile Antennas NEC Model
  3. 144 MHz 2 Stacked Eggbeater Antennas NEC Model

LINKS

  1. Single Halo, Turnstile and Eggbeater at 0.5λ NEC Models
  2. Single Halo, Turnstile and Eggbeater at 1.0λ NEC Models
  3. Stacked Halo, Turnstile and Eggbeater Antenna NEC Models
  4. Single Turnstile, Triangle and Wheel at 0.5λ NEC Models
  5. Single Turnstile, Triangle and Wheel at 1.0λ NEC Models
  6. Stacked Turnstile, Triangle and Wheel Antenna NEC Models
  7. Omnidirectional Horizontal Antenna Photo Album

Composite of all 144 MHz 2 stacked Antennas
                      elevation patterns - horizontal polarization
                      component only.

21. Composite of all 144 MHz 2 stacked Antennas elevation patterns - horizontal polarization component only.

Composite of all 144 MHz 2 stacked Antennas
                      elevation patterns - vertical polarization
                      component only.

22. Composite of all 144 MHz 2 stacked Antennas elevation patterns - vertical polarization component only.

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