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post #1 of 30 (permalink) Old 2017-05-24, 08:18 AM Thread Starter
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NEC/4NEC2: TR-lines as Wire structures

Hello guys. Lots of nice antenna models. Good job!

Wonder if NEC/4NEC2 is a good tool to evaluate, develop or optimize antenna, if it has symmerical lines, build as Wire-structures, not as TR-Lines.
Many antennas of this kind in holl_ands album (vertical stack Dipoles, BowTies etc)

I did test model of 2xfolded dipols in vertical stack (the simpliest model to test symmetrical wires), and 2-Bay BowTie.

If I feed model with 2 voltage-sources, or with Transmission-Lines - everything works perfect.

But when I build TR-Line as Wire-structure, behaviuor is enexpected.

Is it fault in my model, or is this a limitation of NEC-engine?

2 x "Voltage sources, SWR=1


2 x "TR-Lines" 400Ω, SWR=1.26


2 x "Wire-Lines" 400Ω, SWR>30

Code:
CM 
CE
SY vibrWireRad=0.00859
SY scrWireRad=0.00287
SY feedWireRad=0.00356	'0.00358
SY whiskerL=0.4443
SY gap=0.1
SY angle=33
SY Ly=cos(angle/2)
SY Lz=sin(angle/2)
SY dH=0.05
SY dX=0.2455
SY dW=1
SY LipsL=0.25
SY LipsA=30
SY LipsX=sin(LipsA)*LipsL
SY LipsY=cos(LipsA)*LipsL
SY vStack=0.6
GW	1	1	0	gap/2	0	0	-gap/2	0	feedWireRad/2
GW	2	7	0	gap/2	vStack/2	0	whiskerL*Ly	whiskerL*Lz+vStack/2	vibrWireRad
GW	3	7	0	gap/2	vStack/2	0	whiskerL*Ly	-whiskerL*Lz+vStack/2	vibrWireRad
GW	4	7	0	-gap/2	vStack/2	0	-whiskerL*Ly	whiskerL*Lz+vStack/2	vibrWireRad
GW	5	7	0	-gap/2	vStack/2	0	-whiskerL*Ly	-whiskerL*Lz+vStack/2	vibrWireRad
GW	6	7	0	gap/2	-vStack/2	0	whiskerL*Ly	whiskerL*Lz-vStack/2	vibrWireRad
GW	7	7	0	gap/2	-vStack/2	0	whiskerL*Ly	-whiskerL*Lz-vStack/2	vibrWireRad
GW	8	7	0	-gap/2	-vStack/2	0	-whiskerL*Ly	whiskerL*Lz-vStack/2	vibrWireRad
GW	9	7	0	-gap/2	-vStack/2	0	-whiskerL*Ly	-whiskerL*Lz-vStack/2	vibrWireRad
GW	17	5	0	-gap/2	0	0	-gap/2	-vStack/2	feedWireRad
GW	18	5	0	gap/2	0	0	gap/2	-vStack/2	feedWireRad
GW	19	5	0	-gap/2	0	0	-gap/2	vStack/2	feedWireRad
GW	20	5	0	gap/2	0	0	gap/2	vStack/2	feedWireRad
GW	100	13	-dX	-dW/2	10*dH	-dX	dW/2	10*dH	scrWireRad
GW	101	13	-dX	-dW/2	9*dH	-dX	dW/2	9*dH	scrWireRad
GW	102	13	-dX	-dW/2	8*dH	-dX	dW/2	8*dH	scrWireRad
GW	103	13	-dX	-dW/2	7*dH	-dX	dW/2	7*dH	scrWireRad
GW	104	13	-dX	-dW/2	6*dH	-dX	dW/2	6*dH	scrWireRad
GW	105	13	-dX	-dW/2	5*dH	-dX	dW/2	5*dH	scrWireRad
GW	106	13	-dX	-dW/2	4*dH	-dX	dW/2	4*dH	scrWireRad
GW	107	13	-dX	-dW/2	3*dH	-dX	dW/2	3*dH	scrWireRad
GW	108	13	-dX	-dW/2	2*dH	-dX	dW/2	2*dH	scrWireRad
GW	109	13	-dX	-dW/2	dH	-dX	dW/2	dH	scrWireRad
GW	110	13	-dX	-dW/2	0	-dX	dW/2	0	scrWireRad
GW	111	13	-dX	-dW/2	-dH	-dX	dW/2	-dH	scrWireRad
GW	112	13	-dX	-dW/2	-2*dH	-dX	dW/2	-2*dH	scrWireRad
GW	113	13	-dX	-dW/2	-3*dH	-dX	dW/2	-3*dH	scrWireRad
GW	114	13	-dX	-dW/2	-4*dH	-dX	dW/2	-4*dH	scrWireRad
GW	115	13	-dX	-dW/2	-5*dH	-dX	dW/2	-5*dH	scrWireRad
GW	116	13	-dX	-dW/2	-6*dH	-dX	dW/2	-6*dH	scrWireRad
GW	117	13	-dX	-dW/2	-7*dH	-dX	dW/2	-7*dH	scrWireRad
GW	118	13	-dX	-dW/2	-8*dH	-dX	dW/2	-8*dH	scrWireRad
GW	119	13	-dX	-dW/2	-9*dH	-dX	dW/2	-9*dH	scrWireRad
GW	120	13	-dX	-dW/2	-10*dH	-dX	dW/2	-10*dH	scrWireRad
GS	0	0	0.349417
GE	0
GN	-1
EK
EX	0	1	1	0	1	0	0
FR	0	10	0	0	858	0.1
EN
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post #2 of 30 (permalink) Old 2017-05-24, 02:31 PM Thread Starter
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Folded dipols stack
Code:
CE
SY vibrW=0.4380
SY vibrWireRad=0.005
SY vibrH=0.08
SY gap=0.072
SY vStack=0.6
GW  1   3   0   -gap/2  0   0   gap/2   0   vibrWireRad
GW  2   5   0   vibrW/2 -vibrH/2+vStack/2   0   gap/2   -vibrH/2+vStack/2   vibrWireRad
GW  3   5   0   -vibrW/2    -vibrH/2+vStack/2   0   -gap/2  -vibrH/2+vStack/2   vibrWireRad
GW  4   7   0   -vibrW/2    vibrH/2+vStack/2    0   vibrW/2 vibrH/2+vStack/2    vibrWireRad
GW  5   3   0   -vibrW/2    -vibrH/2+vStack/2   0   -vibrW/2    vibrH/2+vStack/2    vibrWireRad
GW  6   3   0   vibrW/2 vibrH/2+vStack/2    0   vibrW/2 -vibrH/2+vStack/2   vibrWireRad
GW  12  5   0   vibrW/2 vibrH/2-vStack/2    0   gap/2   vibrH/2-vStack/2    vibrWireRad
GW  13  5   0   -vibrW/2    vibrH/2-vStack/2    0   -gap/2  vibrH/2-vStack/2    vibrWireRad
GW  14  7   0   -vibrW/2    -vibrH/2-vStack/2   0   vibrW/2 -vibrH/2-vStack/2   vibrWireRad
GW  15  3   0   -vibrW/2    -vibrH/2-vStack/2   0   -vibrW/2    vibrH/2-vStack/2    vibrWireRad
GW  16  3   0   vibrW/2 vibrH/2-vStack/2    0   vibrW/2 -vibrH/2-vStack/2   vibrWireRad
GW  20  7   0   -gap/2  -vibrH/2+vStack/2   0   -gap/2  0   vibrWireRad
GW  21  7   0   gap/2   -vibrH/2+vStack/2   0   gap/2   0   vibrWireRad
GW  22  7   0   -gap/2  vibrH/2-vStack/2    0   -gap/2  0   vibrWireRad
GW  23  7   0   gap/2   vibrH/2-vStack/2    0   gap/2   0   vibrWireRad
 
GS  0   0   0.499667
GE  0
GN  -1
EK
EX  0   1   2   0   1   0   0
FR  0   10  0   0   600 0.1
EN
Wire structures:


TR-Lines:


HFSS, wire structures:


NEC+Wire: Z=127 +j126
NEC+TLine: Z=247 -j40.8
HFSS: Z=132 -j35
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post #3 of 30 (permalink) Old 2017-05-25, 08:21 PM
 
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I looked at your first model:
The engine does not like (at least) the segmentation:
Code:
Freq sweeps: [(858, 0.1, 10)]
Autosegmentation: NO


         --- Gain ---              -- Ratios -- -- Impedance --
   Freq    Raw    Net   SWR BeamW    F/R    F/B    Real    Imag  AGT  corr
==========================================================================
  858.0  11.19   2.92 24.77  52.4  17.30  17.30   45.17 -494.1436.08 15.57
  858.1  11.18   2.93 24.70  52.4  17.30  17.30   45.13 -492.8136.08 15.57
  858.2  11.18   2.95 24.62  52.4  17.29  17.29   45.10 -491.4935.85 15.55
  858.3  11.17   2.95 24.54  52.4  17.30  17.30   45.06 -490.1735.85 15.55
  858.4  11.19   2.98 24.46  52.4  17.30  17.30   45.03 -488.8635.62 15.52
  858.5  11.17   2.97 24.39  52.4  17.29  17.29   44.99 -487.5535.62 15.52
  858.6  11.16   2.98 24.31  52.4  17.29  17.29   44.96 -486.2435.62 15.52
  858.7  11.19   3.02 24.23  52.4  17.30  17.30   44.93 -484.9535.28 15.48
  858.8  11.18   3.02 24.16  52.4  17.30  17.30   44.90 -483.6535.28 15.48
  858.9  11.16   3.02 24.08  52.4  17.29  17.29   44.87 -482.3635.28 15.48
Ideally the last column corr-ection should be 0, and AGT should be 1

with autosegmentation set to 10 the result is:
Code:
Freq sweeps: [(858, 0.1, 10)]
Autosegmentation: 10 per 0.174825


         --- Gain ---              -- Ratios -- -- Impedance --
   Freq    Raw    Net   SWR BeamW    F/R    F/B    Real    Imag  AGT  corr
==========================================================================
  858.0  11.34  10.79  2.05  51.2  15.34  15.34  157.01   70.84 0.77 -1.14
  858.1  11.34  10.79  2.05  51.2  15.34  15.34  157.00   70.94 0.77 -1.14
  858.2  11.34  10.79  2.05  51.2  15.34  15.34  157.00   71.04 0.77 -1.14
  858.3  11.34  10.79  2.06  51.2  15.34  15.34  156.99   71.14 0.77 -1.14
  858.4  11.34  10.79  2.06  51.2  15.34  15.34  156.99   71.24 0.77 -1.14
  858.5  11.35  10.80  2.06  51.1  15.34  15.34  156.99   71.34 0.77 -1.14
  858.6  11.35  10.80  2.06  51.1  15.34  15.34  156.98   71.44 0.77 -1.14
  858.7  11.35  10.80  2.06  51.1  15.34  15.34  156.98   71.54 0.77 -1.14
  858.8  11.35  10.80  2.06  51.1  15.34  15.34  156.97   71.64 0.77 -1.14
  858.9  11.35  10.80  2.06  51.1  15.34  15.34  156.97   71.74 0.77 -1.14
still not good, but better. with AGT outside the range [0.95, 1.05] the model prediction should be considered incorrect.

4nec2 has structure validation that may help you. Also search for AGT correction in the forum
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post #4 of 30 (permalink) Old 2017-05-25, 11:19 PM
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858 MHz 2-Bay Bowtie with Hard-Wired Feedline Pair and NO Reflector:

I took a different tack....I added my usual FR/RP and CMD-EVAL Statements and ran it under 4nec2. Geometry and Segment Checks were OKAY, but AGT was WAY OFF....EXCEEDINGLY HIGH by about 15 dB. I adjusted Radius of the Simulated Balun SOURCE (GW1) until I succeeded in getting AGT=1.0 on desired 858 MHz.

Running the File with my FR/RP Statements [for 758-958 MHz Freq Sweep] shows that the "Impedance Resonance" [i.e. PHASE = 0] was at about 784 MHz, corresponding to MIN SWR with approximate Zc=100-ohms [look at 4nec2 Impedance Chart]...which would be require an unusual 2:1 Balun to match to 50-ohm Load. Raw Gain increased linearly from lowest to highest Frequencies, as is typical for a Simple Dipole and many other Antennas [LPDA is a rare exception to this "Rule"]. As shown in the fol. EVAL RESULTS, SWR=1.67 at 858 MHz was a very acceptable operating point, presuming Zc=100-ohms, which would be compatible with Transmitters limited to SWR<2.0, allowing for somewhat higher final SWR due to effects of the Transmission Line, etc.....and 0.5 dB higher Raw Gain at 858 MHz than if it were Re-Scaled to move SWR Min to 858 MHz.

If you intended to design a 2-Bay Bowtie with a DIFFERENT Characteristic Impedance (Zc)....and Balun, please let us know....that would require DIFFERENT Dimensions to the Feedline Spacing and perhaps also the Feedline Radius....and perhaps even changes to other Dimensions.....which is what nikiml's Python Optimization Scripts are good at determining......

I can not comment re the Separate SOURCE, nor the Transmission Line alternatives, since OP did not provide those 4nec2 Files.

EVAL RESULTS for 858 MHz 2-Bay Bowtie with Hard-Wired Feedline Pair:

Code:
Input file : Z:\4nec2\U\U - 2-Bay Bowtie - Pylypenko\
2-Bay Bowtie 2IndSRC - Pylypenko\858MHz_2-Bay_Bowtie_2FL_Pylypenko.nec
Freq sweeps: [(758, 2, 101)]
Autosegmentation: NO

         --- Gain ---              -- Ratios -- -- Impedance --
   Freq    Raw    Net   SWR BeamW    F/R    F/B    Real    Imag  AGT  corr
==========================================================================
  758.0  10.52  10.42  1.35  55.6  15.82  15.82  106.39  -30.70 1.00 -0.00
  762.0  10.55  10.47  1.31  55.4  15.79  15.79  104.68  -27.47 1.00 -0.00
  766.0  10.59  10.53  1.27  55.2  15.78  15.78  103.06  -24.26 1.00 -0.00
  770.0  10.62  10.57  1.23  55.0  15.75  15.75  101.52  -21.08 1.00 -0.00
  774.0  10.65  10.62  1.20  54.9  15.72  15.72  100.06  -17.92 1.00 -0.00
  778.0  10.69  10.67  1.16  54.7  15.70  15.70   98.67  -14.79 1.00 -0.00
  782.0  10.72  10.71  1.13  54.5  15.67  15.67   97.36  -11.68 1.00 -0.00
  786.0  10.76  10.75  1.10  54.3  15.65  15.65   96.12   -8.60 1.00 -0.00
  790.0  10.79  10.79  1.08  54.1  15.62  15.62   94.95   -5.53 1.00 -0.00

  794.0  10.82  10.82  1.07  53.9  15.58  15.58   93.84   -2.49 1.00 -0.00  MIN SWR(100-ohms)

  798.0  10.86  10.86  1.08  53.7  15.56  15.56   92.80    0.54 1.00 -0.00
  802.0  10.89  10.88  1.10  53.6  15.52  15.52   91.81    3.55 1.00 -0.00
  806.0  10.92  10.91  1.12  53.4  15.48  15.48   90.88    6.54 1.00 -0.00
  810.0  10.96  10.94  1.16  53.1  15.46  15.46   90.01    9.52 1.00 -0.00
  814.0  10.99  10.96  1.19  53.0  15.42  15.42   89.20   12.48 1.00 -0.00
  818.0  11.02  10.98  1.23  52.8  15.38  15.38   88.43   15.44 1.00 -0.00
  822.0  11.05  10.99  1.27  52.7  15.34  15.34   87.72   18.38 1.00 -0.00
  826.0  11.09  11.02  1.31  52.4  15.31  15.31   87.06   21.31 1.00 -0.00
  830.0  11.12  11.03  1.35  52.3  15.27  15.27   86.45   24.23 1.00 -0.00
  834.0  11.15  11.04  1.39  52.1  15.22  15.22   85.88   27.14 1.00 -0.00
  838.0  11.18  11.04  1.43  51.9  15.18  15.18   85.37   30.04 1.00 -0.00
  842.0  11.21  11.05  1.48  51.7  15.14  15.14   84.90   32.94 1.00 -0.00
  846.0  11.25  11.06  1.52  51.5  15.11  15.11   84.47   35.84 1.00 -0.00
  850.0  11.28  11.06  1.57  51.3  15.06  15.06   84.09   38.73 1.00 -0.00
  854.0  11.31  11.06  1.62  51.1  15.02  15.02   83.76   41.62 1.00 -0.00

  858.0  11.34  11.06  1.67  51.0  14.97  14.97   83.47   44.50 1.00 -0.00  CENTER FREQ

  862.0  11.37  11.05  1.72  50.8  14.93  14.93   83.23   47.39 1.00 -0.00
  866.0  11.40  11.05  1.78  50.5  14.89  14.89   83.03   50.28 1.00 -0.00
  870.0  11.42  11.03  1.83  50.5  14.83  14.83   82.87   53.16 1.00 -0.00
  874.0  11.45  11.02  1.89  50.3  14.79  14.79   82.76   56.05 1.00 -0.00
  878.0  11.48  11.01  1.94  50.1  14.74  14.74   82.69   58.95 1.00 -0.00
  882.0  11.51  11.00  2.00  49.8  14.70  14.70   82.67   61.85 1.00 -0.00
  886.0  11.54  10.99  2.06  49.6  14.65  14.65   82.69   64.75 1.00 -0.00
  890.0  11.56  10.97  2.12  49.5  14.59  14.59   82.76   67.66 1.00 -0.00
  894.0  11.59  10.95  2.18  49.2  14.55  14.55   82.88   70.57 1.00 -0.00
  898.0  11.62  10.94  2.24  48.9  14.50  14.50   83.04   73.50 1.00 -0.00
  902.0  11.64  10.91  2.30  48.8  14.45  14.45   83.25   76.43 1.00 -0.00
  906.0  11.67  10.89  2.36  48.4  14.41  14.41   83.51   79.37 1.00 -0.00
  910.0  11.69  10.86  2.43  48.3  14.35  14.35   83.82   82.32 1.00 -0.00
  914.0  11.71  10.84  2.49  48.1  14.30  14.30   84.19   85.29 1.00 -0.00
  918.0  11.74  10.82  2.56  47.8  14.25  14.25   84.60   88.27 1.00 -0.00
  922.0  11.76  10.79  2.62  47.6  14.20  14.20   85.07   91.25 1.00 -0.00
  926.0  11.78  10.76  2.69  47.4  14.15  14.15   85.59   94.26 1.00 -0.00
  930.0  11.80  10.73  2.76  47.2  14.09  14.09   86.17   97.27 1.00 -0.00
  934.0  11.82  10.70  2.83  47.0  14.04  14.04   86.80  100.30 1.00 -0.00
  938.0  11.84  10.67  2.89  46.7  13.99  13.99   87.50  103.35 1.00 -0.00
  942.0  11.87  10.65  2.96  46.5  13.94  13.94   88.26  106.41 1.00 -0.01
  946.0  11.89  10.62  3.03  46.3  13.89  13.89   89.09  109.49 1.00 -0.01
  950.0  11.91  10.59  3.10  46.1  13.84  13.84   89.98  112.59 1.00 -0.01
  954.0  11.92  10.55  3.16  45.9  13.78  13.78   90.94  115.70 1.00 -0.01
  958.0  11.94  10.52  3.23  45.6  13.73  13.73   91.97  118.83 1.00 -0.01  MAX GAIN

REVISED 4NEC2 FILE:

Code:
CM 2-Bay Bowtie, Two Indep. TX Sources, by Yuril Pylypenko, 24May2017
CM
CMD--EVAL --auto-segmentation=0 --char-impedance=100 --num-cores=12
CMD--EVAL -s(758,4,51) --total-gain --publish
CM
CE
SY vibrWireRad=0.00859
SY scrWireRad=0.00287
'
' SY feedWireRad=0.00356	'0.00358
SY feedWireRad=0.0146		'fm holl_ands: Adjust for AGT=1.0 AT 858 MHz
'
SY whiskerL=0.4443
SY gap=0.1
SY angle=33
SY Ly=cos(angle/2)
SY Lz=sin(angle/2)
SY dH=0.05
SY dX=0.2455
SY dW=1
SY LipsL=0.25
SY LipsA=30
SY LipsX=sin(LipsA)*LipsL
SY LipsY=cos(LipsA)*LipsL
SY vStack=0.6
GW	1	1	0	gap/2	0		0	-gap/2		0	feedWireRad/2
GW	2	7	0	gap/2	vStack/2	0	whiskerL*Ly	whiskerL*Lz+vStack/2	vibrWireRad
GW	3	7	0	gap/2	vStack/2	0	whiskerL*Ly	-whiskerL*Lz+vStack/2	vibrWireRad
GW	4	7	0	-gap/2	vStack/2	0	-whiskerL*Ly	whiskerL*Lz+vStack/2	vibrWireRad
GW	5	7	0	-gap/2	vStack/2	0	-whiskerL*Ly	-whiskerL*Lz+vStack/2	vibrWireRad
GW	6	7	0	gap/2	-vStack/2	0	whiskerL*Ly	whiskerL*Lz-vStack/2	vibrWireRad
GW	7	7	0	gap/2	-vStack/2	0	whiskerL*Ly	-whiskerL*Lz-vStack/2	vibrWireRad
GW	8	7	0	-gap/2	-vStack/2	0	-whiskerL*Ly	whiskerL*Lz-vStack/2	vibrWireRad
GW	9	7	0	-gap/2	-vStack/2	0	-whiskerL*Ly	-whiskerL*Lz-vStack/2	vibrWireRad
GW	17	5	0	-gap/2	0	0	-gap/2	-vStack/2	feedWireRad
GW	18	5	0	gap/2	0	0	gap/2	-vStack/2	feedWireRad
GW	19	5	0	-gap/2	0	0	-gap/2	vStack/2	feedWireRad
GW	20	5	0	gap/2	0	0	gap/2	vStack/2	feedWireRad
GW	100	13	-dX	-dW/2	10*dH	-dX	dW/2	10*dH	scrWireRad
GW	101	13	-dX	-dW/2	9*dH	-dX	dW/2	9*dH	scrWireRad
GW	102	13	-dX	-dW/2	8*dH	-dX	dW/2	8*dH	scrWireRad
GW	103	13	-dX	-dW/2	7*dH	-dX	dW/2	7*dH	scrWireRad
GW	104	13	-dX	-dW/2	6*dH	-dX	dW/2	6*dH	scrWireRad
GW	105	13	-dX	-dW/2	5*dH	-dX	dW/2	5*dH	scrWireRad
GW	106	13	-dX	-dW/2	4*dH	-dX	dW/2	4*dH	scrWireRad
GW	107	13	-dX	-dW/2	3*dH	-dX	dW/2	3*dH	scrWireRad
GW	108	13	-dX	-dW/2	2*dH	-dX	dW/2	2*dH	scrWireRad
GW	109	13	-dX	-dW/2	dH	-dX	dW/2	dH	scrWireRad
GW	110	13	-dX	-dW/2	0	-dX	dW/2	0	scrWireRad
GW	111	13	-dX	-dW/2	-dH	-dX	dW/2	-dH	scrWireRad
GW	112	13	-dX	-dW/2	-2*dH	-dX	dW/2	-2*dH	scrWireRad
GW	113	13	-dX	-dW/2	-3*dH	-dX	dW/2	-3*dH	scrWireRad
GW	114	13	-dX	-dW/2	-4*dH	-dX	dW/2	-4*dH	scrWireRad
GW	115	13	-dX	-dW/2	-5*dH	-dX	dW/2	-5*dH	scrWireRad
GW	116	13	-dX	-dW/2	-6*dH	-dX	dW/2	-6*dH	scrWireRad
GW	117	13	-dX	-dW/2	-7*dH	-dX	dW/2	-7*dH	scrWireRad
GW	118	13	-dX	-dW/2	-8*dH	-dX	dW/2	-8*dH	scrWireRad
GW	119	13	-dX	-dW/2	-9*dH	-dX	dW/2	-9*dH	scrWireRad
GW	120	13	-dX	-dW/2	-10*dH	-dX	dW/2	-10*dH	scrWireRad
GS	0	0	0.349417
GE	0
GN	-1
EK
EX	0	1	1	0	1	0	0
'
' FR	0	10	0	0	858	0.1		' fm PyLypenko
'
' FR/RP From holl_ands:
FR 0 51 0 0 758 4		' Freq Sweep 758-958 MHz every 4 MHz
RP 0 1 73 1510 90 0 1 5 0 0	' 2D Azimuthal Gain Slice - PREFERRED
EN

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands

Last edited by holl_ands; 2017-05-26 at 12:05 AM.
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post #5 of 30 (permalink) Old 2017-05-25, 11:59 PM
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600 MHz 2-Bay Folded Dipole with Hard-Wired Feedline Pair and NO Reflector:

Using same procedure as above [AGT wasn't off by much but did add Variable SYmbol for adjusting Simulated Balun SOURCE Radius so AGT=1.0], I ran revised 4nec2 File and found that SWR Min was at 644 MHz with Characteristic Impedance of about Zc=200-ohms and Raw Gain close to MAX Gain, which would be compatible with the usual 4:1 Balun. A Re-Scale from 644 to 600 MHz should be all it needs [Increase ALL Dimensions by F = 644/600 = 1.073.

EVAL RESULTS for 600 MHz 2-Bay Folded Dipole with Hard-Wired Feedline Pair:

Code:
Input file : Z:\4nec2\U\U - 2-Bay Bowtie vs FD - Pylypenko\
2-Bay Foldeed Dipole 2FL - Pylypenko\600MHz_2-Bay_Dipole_2FL_Pylypenko.nec
Freq sweeps: [(500, 4, 51)]
Autosegmentation: NO

         --- Gain ---              -- Ratios -- -- Impedance --
   Freq    Raw    Net   SWR BeamW    F/R    F/B    Real    Imag  AGT  corr
==========================================================================
  500.0   5.84   3.42  4.79  82.2   0.00   0.00   44.58   50.50 1.01  0.05
  504.0   5.88   3.55  4.63  82.1   0.00   0.00   46.57   54.77 1.01  0.05
  508.0   5.91   3.67  4.48  82.0   0.00   0.00   48.72   59.07 1.01  0.05
  512.0   5.95   3.80  4.34  81.7   0.00   0.00   51.02   63.38 1.01  0.05
  516.0   5.99   3.93  4.19  81.7   0.00   0.00   53.51   67.70 1.01  0.04
  520.0   6.03   4.06  4.05  81.5   0.00   0.00   56.20   72.04 1.01  0.04
  524.0   6.06   4.18  3.92  81.3   0.00   0.00   59.10   76.39 1.01  0.04
  528.0   6.10   4.31  3.78  81.1   0.00   0.00   62.25   80.74 1.01  0.04
  532.0   6.14   4.43  3.65  81.0   0.00   0.00   65.65   85.08 1.01  0.03
  536.0   6.18   4.56  3.52  80.8   0.00   0.00   69.35   89.40 1.01  0.03
  540.0   6.21   4.68  3.40  80.7   0.00   0.00   73.36   93.68 1.01  0.03
  544.0   6.25   4.81  3.27  80.5   0.00   0.00   77.72   97.89 1.01  0.03
  548.0   6.29   4.93  3.15  80.4   0.00   0.00   82.46  102.03 1.00  0.02
  552.0   6.32   5.05  3.03  80.2   0.00   0.00   87.60  106.03 1.00  0.02
  556.0   6.36   5.17  2.92  79.9   0.00   0.00   93.20  109.88 1.00  0.02
  560.0   6.39   5.28  2.80  79.7   0.00   0.00   99.27  113.49 1.00  0.02
  564.0   6.43   5.41  2.69  79.6   0.00   0.00  105.86  116.83 1.00  0.01
  568.0   6.46   5.52  2.58  79.3   0.00   0.00  112.98  119.79 1.00  0.01
  572.0   6.50   5.64  2.48  79.1   0.00   0.00  120.66  122.29 1.00  0.01
  576.0   6.53   5.74  2.37  78.8   0.00   0.00  128.90  124.21 1.00  0.01
  580.0   6.57   5.86  2.27  78.6   0.00   0.00  137.70  125.42 1.00 -0.00
  584.0   6.60   5.96  2.17  78.4   0.00   0.00  147.02  125.77 1.00 -0.00
  588.0   6.62   6.05  2.08  78.3   0.00   0.00  156.78  125.10 1.00 -0.00
  592.0   6.65   6.15  1.98  78.0   0.00   0.00  166.88  123.24 1.00 -0.00
  596.0   6.69   6.26  1.89  77.8   0.00   0.00  177.14  120.03 1.00 -0.01

  600.0   6.71   6.34  1.81  77.5   0.00   0.00  187.35  115.31 1.00 -0.01  CENTER FREQ

  604.0   6.74   6.43  1.72  77.3   0.00   0.00  197.22  108.99 1.00 -0.01
  608.0   6.76   6.50  1.64  77.1   0.00   0.00  206.41  101.02 1.00 -0.01
  612.0   6.81   6.60  1.56  76.8   0.00   0.00  214.56   91.44 0.99 -0.03
  616.0   6.83   6.66  1.48  76.5   0.00   0.00  221.28   80.41 0.99 -0.03
  620.0   6.85   6.72  1.41  76.3   0.00   0.00  226.20   68.19 0.99 -0.03
  624.0   6.87   6.78  1.34  76.0   0.00   0.00  229.05   55.16 0.99 -0.03
  628.0   6.89   6.83  1.27  75.9   0.00   0.00  229.66   41.78 0.99 -0.04
  632.0   6.91   6.87  1.21  75.5   0.00   0.00  227.98   28.55 0.99 -0.04
  636.0   6.92   6.90  1.15  75.3   0.00   0.00  224.13   15.95 0.99 -0.04
  640.0   6.93   6.92  1.09  75.1   0.00   0.00  218.34    4.40 0.99 -0.04
  644.0   6.95   6.95  1.06  74.9   0.00   0.00  210.93   -5.76 0.99 -0.05  MIN SWR

  648.0   6.96   6.96  1.07  74.6   0.00   0.00  202.28  -14.32 0.99 -0.05
  652.0   6.97   6.96  1.12  74.3   0.00   0.00  192.79  -21.19 0.99 -0.05
  656.0   6.97   6.94  1.18  74.1   0.00   0.00  182.81  -26.36 0.99 -0.05
  660.0   6.97   6.92  1.24  73.9   0.00   0.00  172.68  -29.93 0.99 -0.05
  664.0   6.99   6.91  1.31  73.6   0.00   0.00  162.64  -32.01 0.98 -0.07
  668.0   6.99   6.87  1.39  73.3   0.00   0.00  152.89  -32.79 0.98 -0.07
  672.0   6.99   6.83  1.46  72.9   0.00   0.00  143.58  -32.42 0.98 -0.07
  676.0   6.98   6.77  1.55  72.8   0.00   0.00  134.79  -31.08 0.98 -0.07
  680.0   6.97   6.71  1.63  72.5   0.00   0.00  126.57  -28.94 0.98 -0.07
  684.0   6.97   6.65  1.73  72.2   0.00   0.00  118.95  -26.13 0.98 -0.08
  688.0   6.95   6.57  1.82  72.0   0.00   0.00  111.93  -22.78 0.98 -0.08
  692.0   6.94   6.49  1.92  71.7   0.00   0.00  105.49  -19.00 0.98 -0.08
  696.0   6.92   6.39  2.02  71.5   0.00   0.00   99.60  -14.87 0.98 -0.08
  700.0   6.90   6.29  2.13  71.1   0.00   0.00   94.23  -10.48 0.98 -0.08  MAX GAIN

4NEC2 FILE:

Code:
CM 2-Bay Folded Dipole, Two Physical Feeddlines, by Yuril Pylypenko, 24May2017
CM
CMD--EVAL --auto-segmentation=0 --char-impedance=200 --num-cores=12
CMD--EVAL -s(500,4,51) --total-gain --publish
CM
CE
'
SY vfeedWireRad=0.006		'fm holl_ands: Adjust GW1 for AGT=1.0 AT 600 MHz
'
SY vibrW=0.4380
SY vibrWireRad=0.005
SY vibrH=0.08
SY gap=0.072
SY vStack=0.6
GW  1   3   0   -gap/2  0   0   gap/2   0   vfeedWireRad  ' holl_ands mod to Adjust AGT	
GW  2   5   0   vibrW/2 -vibrH/2+vStack/2   0   gap/2   -vibrH/2+vStack/2   vibrWireRad
GW  3   5   0   -vibrW/2    -vibrH/2+vStack/2   0   -gap/2  -vibrH/2+vStack/2   vibrWireRad
GW  4   7   0   -vibrW/2    vibrH/2+vStack/2    0   vibrW/2 vibrH/2+vStack/2    vibrWireRad
GW  5   3   0   -vibrW/2    -vibrH/2+vStack/2   0   -vibrW/2    vibrH/2+vStack/2    vibrWireRad
GW  6   3   0   vibrW/2 vibrH/2+vStack/2    0   vibrW/2 -vibrH/2+vStack/2   vibrWireRad
GW  12  5   0   vibrW/2 vibrH/2-vStack/2    0   gap/2   vibrH/2-vStack/2    vibrWireRad
GW  13  5   0   -vibrW/2    vibrH/2-vStack/2    0   -gap/2  vibrH/2-vStack/2    vibrWireRad
GW  14  7   0   -vibrW/2    -vibrH/2-vStack/2   0   vibrW/2 -vibrH/2-vStack/2   vibrWireRad
GW  15  3   0   -vibrW/2    -vibrH/2-vStack/2   0   -vibrW/2    vibrH/2-vStack/2    vibrWireRad
GW  16  3   0   vibrW/2 vibrH/2-vStack/2    0   vibrW/2 -vibrH/2-vStack/2   vibrWireRad
GW  20  7   0   -gap/2  -vibrH/2+vStack/2   0   -gap/2  0   vibrWireRad
GW  21  7   0   gap/2   -vibrH/2+vStack/2   0   gap/2   0   vibrWireRad
GW  22  7   0   -gap/2  vibrH/2-vStack/2    0   -gap/2  0   vibrWireRad
GW  23  7   0   gap/2   vibrH/2-vStack/2    0   gap/2   0   vibrWireRad
 
GS  0   0   0.499667
GE  0
GN  -1
EK
EX  0   1   2   0   1   0   0
' FR  0   10  0   0   600 0.1		' fm PyLypenko
' EN	0	858	0.1		' fm PyLypenko
'
' FR/RP From holl_ands:
FR 0 51 0 0 500 4		' Freq Sweep 500-700 MHz every 4 MHz
RP 0 1 73 1510 90 0 1 5 0 0	' 2D Azimuthal Gain Slice - PREFERRED
EN

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #6 of 30 (permalink) Old 2017-05-26, 07:23 AM Thread Starter
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I have no intention to build actual 858-Mhz (CDMA 800) antenna.
I was looking at TV antennas (stack dipoles, BowTies etc)


I had in-depth look how each part of antenna influence final impedance, including R of symmetrical lines, and their L (do they work as matched line, or as transformators. What is trans-ratio etc)

To test NEC2 behaviour I created 2 simple test models: 2xfolded and 2xbowtie (600 Mhz, whatever impedance (preferably at X=0, Z=R), not with practical concern)

Then tried to rescale it to 858 and decrase bowtie R from ~600 to ~400 with thicker wire and more screen offset.

My only question is: can we trust to 4NEC2 analysis for UHF antennas with thick wires, wire lines etc

HFSS vs 4NEC2 analysis of the same structure are going to be the same?

I did know about AGT concern, great thanks for clarification. Will read more about that and do more tests
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post #7 of 30 (permalink) Old 2017-05-27, 08:30 AM Thread Starter
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Quote:
Originally Posted by holl_ands
600.0 6.71 6.34 1.81 77.5 0.00 0.00 187.35 115.31 1.00 -0.01 CENTER FREQ
NEC: Z=187 +j 115
HFSS: Z=131.77 -j 34.78
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post #8 of 30 (permalink) Old 2017-05-27, 08:11 PM
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I don't normally deal with Impedance at one particular spot frequency...so I don't really have a "feel" for how much a small Dimensional difference changes those values.

What are Raw Gain and SWR vs Freq Charts look like using HFSS???? [And where can I download at a User Guide for HFSS????]

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #9 of 30 (permalink) Old 2017-08-11, 08:21 AM Thread Starter
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I started learning HFSS.

For training purpose I tried to copy UHF 7-El FD-Yagi - Opt. by Nikiml design as close as possible.

Here is my *.HFSS file: https://goo.gl/R1n3Tv

Here is comparison of Gain, SWR, Real and imaginary impedance: 11 August 2017: ypylypenko
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post #10 of 30 (permalink) Old 2017-08-12, 10:18 AM Thread Starter
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Tried more complex Yagi design: UHF 18-El FD-Yagi (2ReflRods) - OPT
Here is my *.HFSS file: https://goo.gl/HvHwCU

Here is comparison: 18EL Uda-Yagi, 4NEC2 vs HFSS model: ypylypenko
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post #11 of 30 (permalink) Old 2017-08-16, 04:32 AM Thread Starter
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UHF Bi-Quad + 11RR - OPT

In this case, HFSS and 4NEC2 are identical

*.HFSS project: https://goo.gl/EDz8TK


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post #12 of 30 (permalink) Old 2017-08-16, 05:26 PM Thread Starter
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UHF H2 (11x12) 2-Bay Bowtie - NO Refl

*.HFSS file: https://goo.gl/3eRFvn

First model with TR line as wire structure.
Very similar simulation data!
Gain sweep is +-0.02 dB identical to 4NEC2.
Impedances are a bit different (HFSS Real part is lower a bit), but in general behaviour is good.
For very wide band and modest-SWR solutions, NEC2 precision is quite enough.
For low-SWR and narrow band antenna (e.g. transmitting antennas), NEC2 can be used to develop draft, but need more accurate tool to verify design






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post #13 of 30 (permalink) Old 2017-08-17, 03:12 AM
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Don't know what hfss is. But if it requires wasting lots of money on some expensive license or software, not gonna happen here.
Thanks.

DB4E/VHF Yagi rotor FM Bandstop ap-8700 preamp 4way split LG lcd.
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post #14 of 30 (permalink) Old 2017-08-17, 04:05 AM Thread Starter
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HFSS is one of many competitive software, which employs "finite element method" (CST Microwave, FEKO - other popular)
NEC engine uses Method of Moments.

FEM method is extremely expensive in all ways:
- software is very complex and costly
- geometry/material model is very complex, it allow to draw any shape and use any combinations of materials. One can trace waveguides, cabling, PCB, radome etc
- simulation uses enormous amount of RAM and CPU power (BiQuad and 2-bay bowtie with 11 rods took ~5.5 Gb and 1 hour CPU time to proceed simulation + "Fast" freq sweep). Usually people use Xeon clusters for work or at least decent Workstation with 16...64 Gb RAM)

I asked experts theoretical questions about expected impedances of TR lines. They answered both theoretically and confirmed calculations using HFSS. I decided to learn HFSS as a hobby, and model some industrial antennas (already did a bunch) and verify some TV antennas developed at this forum.

From what I see by now, Far-Field is always almost identical (within error margin).

Impedances sometimes are very close, sometimes are quite different. Problematic cases are folded dipole (if it is low height and thick wire!) and TR lines as wire structures.

Good practice of antenna development is manufacturing prototype and measuring it's actual perfomance to confirm modeling.
With modern software and hardware it is possible to verify model without instrumental data. Experts said prototypes has never contradicted to CST or HFSS solutions.

If there is interest, I can convert more models to HFSS (and share *.hfss file) and provide solutions data.

Last edited by Yurii Pylypenko; 2017-08-17 at 06:00 AM.
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post #15 of 30 (permalink) Old 2017-08-17, 08:03 AM Thread Starter
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