LPDA using ON4AA model - Canadian TV, Computing and Home Theatre Forums

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post #1 of 13 (permalink) Old 2018-03-16, 06:52 AM Thread Starter
 
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LPDA using ON4AA model

Using this calculator: Log?Periodic*Dipole*Array Calculator

modeled 470-860 and 470-690 MHz LPDA in HFSS


Here is 470-690 version: https://ypylypenko.livejournal.com/20233.html

ON4AA model predict "Required characteristic impedance of the feeder connecting the elements Z₀f = 114.2 Ω" (132Ω for 860 MHz version)
With this boom impedance, antenna R is close to 95 Ω, not 75
I changed boom to 89.3 Ω (13х13 mm square boom, spaced 6 mm) and matching is very good, R~75, SWR<1.25

Two things I don't like:
1) 1.7 dB gain drop @ 690 MHz vs 620 MHz
2) antenna is not working during rain. I have a dozen of industrial antennas of this kind with 13x13 mm boom spaced 8 mm. Had to replace all of them, because during rain (and frost) waterfalls along boom degrade signal at least -6 dB

Here is industrial antenna of similar kind (more compact, but still 2x10 dipols): https://ypylypenko.livejournal.com/6070.html

ON4AA calculate impedance from shortest dipol diameter. More diameter -> Lower impedance -> higher boom Zo needed -> more waterproof.

Will try further simulations with thicker dipoles.

Last edited by Yurii Pylypenko; 2018-03-16 at 09:27 AM.
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post #2 of 13 (permalink) Old 2018-03-16, 05:34 PM
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To eliminate water/snow/ice degradation, you could insert Plastic (or whatever) in-between the Twin-Booms and treat it as an Insulating Dielectric Material.

LPDA inherently has more Gain on Low Freqs...cuz the Active Region is in the Rear of the Antenna...with LOTS of Directors in front of that area....and on High Freqs it doesn't. So to minimize this effect, you'll need to increase the Max Operating Freq so that MORE, smaller Elements are added to the Front of the Antenna.

OTOH, I rely on nikiml's Optimizer to FLATTEN out the Freq. Response, as shown in fol. 8-El Pair LPDA example with Zig-Zag Feedline [Raw Gain = 8.6 dBi +/- 0.2 dB], which searches for the "best" set of Sigma-Tau Parameters. Note that I also included a "Fudge" factor which can be used to avoid droop on the Lowest Freqs:
UHF 8-El VEE LPDA + Shorting Stub - Opt
PS: In the early days, nikiml required a separate *.bat file instead of the embedded CMD-OPT commands.

I've SEEN that LPDA "Design" Chart for picking a suitable SIGMA-TAU pair....but it doesn't TELL you how MANY Elements are needed to get you there....so it's pretty much a useless starting point for a REAL Design. BTW: It originated in R.L. Carrel's extensive 1961 Report on LPDA Design...using then-new computer modeling...see pg 132 out of 221 (paper pg118) for Fig 65....and be sure to read back a few pages:
http://www.dtic.mil/dtic/tr/fulltext/u2/264558.pdf
Note that is assumes a particular value for h/a=177 (so Element Diameter is TAPERED) and Zo=100-ohms....and I didn't immediately see what BANDWIDTH was assumed...which obviously drives UP the Number of Element Pairs....hence there is a tradeoff of Gain vs Bandwidth (DUH!!!)....which may or may NOT impact R.L. Carrel's Chart....I'm guessing it DOES....

You should also look at my Downloadable Excel Spread Sheet found at the fol. weblink, where I did a [UHF Band] Twin-Boom LPDA SIGMA-TAU Optimization Search for [nearly ALL] Odd number of Element Pairs from 3 to 23. The Charts illustrate various relationships....and the SIGMA-TAU numbers are found in the Spread Sheet....hmm, someone [Me? In WHAT spare time???] SHOULD do some [3D with Gain] Charts showing THAT as well:
http://imageevent.com/holl_ands/zigz...dawedgelayered








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Last edited by holl_ands; 2018-03-16 at 07:01 PM.
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post #3 of 13 (permalink) Old 2018-03-16, 06:49 PM
 
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Yurii Pylypenko if you look some more on that site you will find the transmission line cal also ,make your own 300 ohm lines
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post #4 of 13 (permalink) Old 2018-03-16, 07:34 PM Thread Starter
 
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It's easy to do 300 Ohm line (though 85 mm spacing for 13x13 mm tubing is quite big), but not easy to do 300 Ohm LPDA.

ON4AA model rely on assumption that LPDA impedance is mostly defined by diameter of 1st director. My HFSS simulations find almost no relation of LPDA impedance to diameter.

This white paper analyzes impedance of LPDA http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf
But I don't understand how to apply this knowledge and what to change in LPDA (sigma? tau? diameter?) for target Zo
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post #5 of 13 (permalink) Old 2018-03-16, 09:05 PM
 
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well I look at the square tubing cal , not sure if its in M or I , so I did with I , for 0.50 square inch tubing and it claims for a

Zc=300
space between the square conductors S = 3.267 inches
centre to centre distance D = 3.767 inches
can you model that ?
that should leave room for 1/4 inch elements
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post #6 of 13 (permalink) Old 2018-03-16, 10:35 PM
 
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Yurii Pylypenko in post one were you went to that cal scroll down to reference 12 it shows forumal
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post #7 of 13 (permalink) Old 2018-03-17, 05:38 AM Thread Starter
 
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𝑍0𝑁 = average characteristic impedance of the shortest element N

I changed diameter ⌀𝑁 (influence formula 12 directly) and HFSS simulation found no influence on total antenna impedance
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post #8 of 13 (permalink) Old 2018-03-17, 06:33 AM
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Although other Parameters likely make a difference, Char. Impedance is primarily determined by the Separation between the Twin-Booms [which shouldn't be a surprise....it's a Transmission Line....so also Cross-section of the Boom]. For the fol. UHF 7-El Twin-Boom LPDA with Optimized TAU-SIGMA, I ran a 4nec2 Parameter Sweep, where for 584 MHz I varied "Zboom" = Center-To-Center Boom Separation. Although it might be a bit difficult to see, 4nec2 "Impedance" Chart shows that Char Imped ~ 50-ohm at 0.25-in, ~ 75-ohm at 0.5-in and reaches Max of just over ~ 150-ohm at 1.5-in thru at least 4.25-in. DO NOT try to draw any conclusions re how Char. Imped affects Performance. I'm running a Re-Optimization with an Impedance TARGET = 300-ohms, also 50 and 150-ohms....and we'll see what happens:

Code:
PARAMETER SWEEP OF "Zboom" AT 584 MHz:

Run     SWR     Gain    F/B     F/R     R-a     X-a     Eff.    Zboom   

3-0     1.7026  9.84    14.88   14.88   46.696  -14.64  99.55   0.25    
3-1     1.4176  8.91    31.38   29.59   95.701  -21.32  99.73   0.5     
3-2     1.7953  8.72    36.32   30.81   122.53  -31.28  99.76   0.75    
3-3     2.0064  8.69    33.16   30.75   136.36  -37.39  99.77   1       
3-4     2.1168  8.7     31.57   30.6    144.57  -39.35  99.78   1.25    
3-5     2.1715  8.73    30.87   30.58   150.18  -38.3   99.78   1.5     
3-6     2.1948  8.77    30.67   30.67   154.37  -35.07  99.78   1.75    
3-7     2.2012  8.79    30.76   30.76   157.69  -30.24  99.78   2       
3-8     2.2003  8.82    31.1    31.1    160.41  -24.13  99.78   2.25    
3-9     2.1993  8.83    31.63   31.63   162.71  -16.98  99.78   2.5     
3-10    2.2041  8.84    32.37   32.03   164.69  -8.928  99.78   2.75    
3-11    2.2195  8.84    33.32   31.98   166.46  -0.078  99.78   3       
3-12    2.2501  8.84    34.56   31.72   168.09  9.4965  99.78   3.25    
3-13    2.2997  8.82    36.16   31.39   169.64  19.736  99.79   3.5     
3-14    2.3718  8.8     38.32   31      171.17  30.6    99.79   3.75    
3-15    2.4686  8.77    41.48   30.56   172.74  42.028  99.79   4       
3-16    2.5921  8.74    46.97   30.08   174.37  53.985  99.79   4.25

4NEC2 FILE:
Code:
CM UHF 7-Element Wedge LPDA, OPT: Tau-Sigma, 4nec2 by holl_ands, 26Apr2015
CM All elements 0.4-in O.D. Aluminum.  ALL IN INCHES.     FOUR OPT. VARIABLES.
CM Impedance = 75-ohm.  PYTHONSEG(15), NO Errors, Ignore FAT Wire Warnings, AGT=1.0.
CM
CMD--OPT -s(470,12,20) -t(9,9) --swr-target=2.7 --f2r-target=20 --f2b-target=20
CMD--OPT --target-function=(4*max_ml+8*max_gain_diff+4*max_f2r_diff+max_f2b_diff)/17
CMD--OPT --de-np=50 -r restart.log
CMD--OPT --auto-segmentation=15 --char-impedance=75 --num-cores=7
CMD--EVAL --auto-segmentation=0 --char-impedance=75 --num-cores=7
CMD--EVAL -s(470,12,29)
CE
' SOURCE Wire Radius, Adjust for AGT=1.0: UHF=0.1985
SY Rsrc=0.1985
'
SY Relem=0.2		' Element Radius (Equivalent)
SY Rboom=0.2		' Boom Radius (Equivalent)
SY Cond=2.0e7	   	' Conductivity (Copper=3.0e7, Alum=2.0e7, StainlessSteel=1.67e7)
SY C=11803		' Speed of Light (inches/microsec)
'
SY Flow=470
' Below Lowest Frequency Design Factor:
SY Below=1.0
' Element Spacing Ratio = Tau = Li/Li+1 = Dij/Djk
SY Tau=0.8653501' 0.8, 0.995
' Relative Spacing Constant = Sigma = Dij/2*Lj
SY Sigma=0.1719487' 0.1, 0.35
'
' Angle of Boom Relative to Horizon at Apex: [About Half of Total Angle]
SY HalfAngle=0.32781' 0, 25
' Center-Center Separation between Two Boom Lines at Apex:
SY Zboom=0.5004509' 0.5, 2
SY Zb=Zboom/2
SY Zb=Zboom/2
'
' Element Half-Lengths, Longest to Shortest:
SY Y1=0.25*C/(Below*Flow)	' 6.278-in
SY Y2=Tau*Y1			' 5.433-in
SY Y3=Tau*Y2			' 4.701-in
SY Y4=Tau*Y3			' 4.068-in
SY Y5=Tau*Y4			' 3.520-in
SY Y6=Tau*Y5			' 3.046-in
SY Y7=Tau*Y6			' 2.636-in
'
' Spacing between Elements, Longest to Shortest:
SY S12=4*Y1*Sigma		' 4.318-in
SY S23=Tau*S12			' 3.737-in
SY S34=Tau*S23			' 3.234-in
SY S45=Tau*S34			' 2.798-in
SY S56=Tau*S45			' 2.421-in
SY S67=Tau*S56			' 2.095-in
'
' Hypoteneuse Locations, NEGATIVE, Shortest to Longest:
SY Hy7=0			'   0.000-in
SY Hy6=Hy7-S67			'  -2.095-in
SY Hy5=Hy6-S56			'  -4.517-in
SY Hy4=Hy5-S45			'  -7.315-in
SY Hy3=Hy4-S34			' -10.548-in
SY Hy2=Hy3-S23			' -14.285-in
SY Hy1=Hy2-S12			' -18.603-in
'
' Projection to X-Axis Locations, Shortest to Longest:
SY X7=Hy7*cos(HalfAngle)
SY X6=Hy6*cos(HalfAngle)
SY X5=Hy5*cos(HalfAngle)
SY X4=Hy4*cos(HalfAngle)
SY X3=Hy3*cos(HalfAngle)
SY X2=Hy2*cos(HalfAngle)
SY X1=Hy1*cos(HalfAngle)
'
' Projection to Z-Axis Locations, Shortest to Longest
SY Z7=Zb
SY Z6=Z7+S67*sin(HalfAngle)
SY Z5=Z6+S56*sin(HalfAngle)
SY Z4=Z5+S45*sin(HalfAngle)
SY Z3=Z4+S34*sin(HalfAngle)
SY Z2=Z3+S23*sin(HalfAngle)
SY Z1=Z2+S12*sin(HalfAngle)
'
GW 1  1  X7 0 -Z7 X7  0   Z7 Rsrc  ' SOURCE BETWEEN SHORTEST
'
GW 2  7  X1 0  Z1 X1 -Y1  Z1 Relem
GW 3  7  X1 0 -Z1 X1  Y1 -Z1 Relem
GW 4  5  X2 0 -Z2 X1  0  -Z1 Rboom
GW 5  5  X2 0  Z2 X1  0   Z1 Rboom
GW 6  6  X2 0 -Z2 X2 -Y2 -Z2 Relem
GW 7  6  X2 0  Z2 X2  Y2  Z2 Relem
GW 8  4  X3 0 -Z3 X2  0  -Z2 Rboom
GW 9  4  X3 0  Z3 X2  0   Z2 Rboom
GW 10 6  X3 0  Z3 X3 -Y3  Z3 Relem
GW 11 6  X3 0 -Z3 X3  Y3 -Z3 Relem
GW 12 4  X4 0 -Z4 X3  0  -Z3 Rboom
GW 13 4  X4 0  Z4 X3  0   Z3 Rboom
GW 14 5  X4 0 -Z4 X4 -Y4 -Z4 Relem
GW 15 5  X4 0  Z4 X4  Y4  Z4 Relem
GW 16 3  X5 0 -Z5 X4  0  -Z4 Rboom
GW 17 3  X5 0  Z5 X4  0   Z4 Rboom
GW 18 4  X5 0  Z5 X5 -Y5  Z5 Relem
GW 19 4  X5 0 -Z5 X5  Y5 -Z5 Relem
GW 20 3  X6 0 -Z6 X5  0  -Z5 Rboom
GW 21 3  X6 0  Z6 X5  0   Z5 Rboom
GW 22 4  X6 0 -Z6 X6 -Y6 -Z6 Relem
GW 23 4  X6 0  Z6 X6  Y6  Z6 Relem
GW 24 3  X7 0 -Z7 X6  0  -Z6 Rboom
GW 25 3  X7 0  Z7 X6  0   Z6 Rboom
GW 26 3  X7 0  Z7 X7 -Y7  Z7 Relem
GW 27 3  X7 0 -Z7 X7  Y7 -Z7 Relem
'
GS 0 0 0.0254			' All of above in inches.
GE 0
GN -1
EK
LD 5 0 0 0 Cond			' Element Conductivity
EX 0 1 1 0 1 0			' Simulated SOURCE on SHORTEST
'
' FR Freq Sweep choices in order of increasing calculation time (fm holl_ands):
' FR 0 0 0 0 470 0		' Fixed Freq
FR 0 29 0 0 470 12		' Freq Sweep 470-806 every 12 MHz - OLD UHF BAND
' FR 0 34 0 0 410 12		' Freq Sweep 410-806 every 12 MHz - Even Wider Sweep
' FR 0 39 0 0 470 6		' Freq Sweep 470-698 every 6 MHz - PREFERRED FOR UHF
' FR 0 77 0 0 470 3		' Freq Sweep 470-698 every 3 MHz
' FR 0 153 0 0 470 1.5		' Freq Sweep 470-698 every 1.5 MHz
' FR 0 61 0 0 400 10		' Freq Sweep 400-1000 every 10 MHz - WIDEBAND SWEEP
' FR 0 71 0 0 300 10		' Freq Sweep 300-1000 every 10 MHz - WIDEBAND SWEEP
' FR Hi-VHF choices:
' FR 0 15 0 0 174 3		' Freq Sweep 174-216 every 3 MHz
' FR 0 29 0 0 174 1.5		' Freq Sweep 174-216 every 1.5 MHz - PREFERRED
' FR 0 43 0 0 174 1		' Freq Sweep 174-216 every 1 MHz - Hi-Rez
' FR 0 26 0 0 150 6		' Freq Sweep 150-300 every 6 MHz - WIDEBAND SWEEP
' FR Lo-VHF choices:
' FR 0 35 0 0 54 1		' Frequency Sweep every 1 MHz for Ch2-6
' FR 0 36 0 0 75 1		' Frequency Sweep every 1 MHz for Ch5 + Ch6 + FM
' FR 0 28 0 0 54 6		' Wide Freq Sweep every 6 MHz for Ch2-13
' FR 0 64 0 0 54 12			' Super Wide Freq Sweep 54-810 every 12 MHz
' RP choices in order of increasing calculation time:
' RP 0 1 1 1510 90 90 1 1 0 0	' 1D Gain toward 0-deg Azimuth - SIDE GAIN
' RP 0 1 1 1510 90 0 1 1 0 0	' 1D Gain toward 90-deg Azimuth - FORWARD GAIN
' RP 0 1 1 1510 90 180 1 1 0 0	' 1D Gain toward 270-deg Azimuth - REVERSE GAIN
' RP 0 1 37 1510 90 0 1 5 0 0 	' 2D (Left only) Azimuthal Gain Slice
RP 0 1 73 1510 90 0 1 5 0 0	' 2D Azimuthal Gain Slice - PREFERRED
' RP 0 73 1 1510 90 0 5 1 0 0 	' 2D Elevation Gain Slice
' RP 0 73 73 1510 90 0 5 5 0 0 	' 3D Lower Hemisphere reveals antenna (Fixed Freq)
' RP 0 285 73 1510 90 0 5 5 0 0	' 3D Full Coverage obscures antenna (Fixed Freq)
EN
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Last edited by holl_ands; 2018-03-17 at 06:49 AM.
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post #9 of 13 (permalink) Old 2018-03-17, 11:43 PM
 
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Yurii Pylypenko looking at that antenna the mounting area , does that not change the feed booms impedance ? the plates.
from your drawing
how much of the boom and model,
is the plate past the end of feed boom in model
or is it the plates covering over the feed booms impedance area
https://ypylypenko.livejournal.com/6070.html
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post #10 of 13 (permalink) Old 2018-03-18, 06:31 PM
 
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holl_ands to search for optium spacing for 300 ohms feed gap
you choose . lets say one inch
But let the script find feed length

element __________feed
element __feed
element________________________________ feed

do you see what I mean
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post #11 of 13 (permalink) Old 2018-03-18, 07:27 PM Thread Starter
 
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Quote:
, does that not change the feed booms impedance ?
It does. In fact there is no matching stub if you don't remove mounting plate.
At f<520 MHz no-stub (short circuit) degrades matching significantly. I don't care about it, since in my region I need 566-646 MHz only
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post #12 of 13 (permalink) Old 2018-03-18, 09:02 PM
 
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Yurii Pylypenko in post one we all can see your drawing .
is there no matching stub ?
and how does one place a matching stub ?
I think I understand how
but some may need a visual to help them understand
how the shorting stub is connected to the boom feed line.


Yurii Pylypenko by lenghting the feed point of the boom from the element
that should move the impedance upward
same as we use element spacing for gain and SWR
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post #13 of 13 (permalink) Old 2018-03-19, 06:37 AM Thread Starter
 
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drawings for ON4AA include 80 mm stub, as recommended by ON4AA calc.

In industrial antenna, 2 aluminum booms are screwed to PCB holder with F-connector. Lead short between screws act as stub shorting.
If mounting plate is present, this stub is excluded and antenna performs poor at f<520 MHz




Quote:
that should move the impedance upward
that should make reactance non-zero. If tr-line length is not multiple of 1/4 lambda, reactance is <>0
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