Simulation Fun: Rotary 5-Band Antennas - Let's Compare Them

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by SP3L, Jan 25, 2016.

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  1. UA3TW

    UA3TW Ham Member QRZ Page

    This one is based on 4 el for 20m band

    *
    24.94
    ***Wires***
    50
    0.0, -0.01, 0.0, 0.0, -5.37, 0.0, -0.003, -1
    -1.65, 3.675, 0.0, -1.65, -3.675, 0.0, -0.002, -1
    0.45, 0.01, 0.0, 0.45, 3.5, 0.0, -0.004, -1
    1.4, 3.495, 0.0, 1.4, -3.495, 0.0, -0.002, -1
    3.42, 3.38, 0.0, 3.42, -3.38, 0.0, -0.002, -1
    6.2, 3.465, 0.0, 6.2, -3.465, 0.0, -0.002, -1
    -3.65, -5.5, 0.0, -3.65, 5.5, 0.0, -0.001, -1
    1.85, 5.075, 0.0, 1.85, -5.075, 0.0, -0.001, -1
    5.8, 4.775, 0.0, 5.8, -4.775, 0.0, -0.001, -1
    0.45, -0.01, 0.0, 0.45, -3.5, 0.0, -0.004, -1
    0.0, 0.01, 0.0, 0.0, 5.37, 0.0, -0.003, -1
    0.0, 0.01, 0.0, 0.45, 0.01, 0.0, 0.005, -1
    0.0, -0.01, 0.0, 0.45, -0.01, 0.0, 0.005, -1
    0.0, 0.01, 0.0, 0.0, -0.01, 0.0, 0.002, -1
    0.0, 0.01, 0.0, -0.43, 0.01, 0.0, 0.005, -1
    0.0, -0.01, 0.0, -0.43, -0.01, 0.0, 0.005, -1
    -0.43, 0.01, 0.0, -0.43, 2.54, 0.0, -0.006, -1
    -0.43, -0.01, 0.0, -0.43, -2.54, 0.0, -0.006, -1
    -2.075, 2.66, 0.0, -2.075, -2.66, 0.0, -0.005, -1
    0.89, 2.54, 0.0, 0.89, -2.54, 0.0, -0.005, -1
    2.53, 2.535, 0.0, 2.53, -2.535, 0.0, -0.005, -1
    5.14, 2.5, 0.0, 5.14, -2.5, 0.0, -0.005, -1
    6.82, 2.42, 0.0, 6.82, -2.42, 0.0, -0.005, -1
    0.0, -0.01, 0.0, 0.0, -0.2, -0.35, 0.001, -1
    0.0, 0.01, 0.0, 0.0, 0.2, -0.35, 0.001, -1
    0.0, -0.01, 0.0, 0.0, -0.3, 0.6, 0.001, -1
    0.0, 0.01, 0.0, 0.0, 0.3, 0.6, 0.001, -1
    0.0, 3.763, 0.1, 0.0, 0.3, 0.6, 0.001, -1
    0.0, -3.763, 0.1, 0.0, -0.3, 0.6, 0.001, -1
    0.0, 2.75823, -0.09947, 0.0, 0.2, -0.35, 0.001, -1
    0.0, -2.75823, -0.09947, 0.0, -0.2, -0.35, 0.001, -1
    -3.65, -4.04, 0.1, -3.65, 0.0, 0.4, 0.001, -1
    -3.65, 4.04, 0.1, -3.65, 0.0, 0.4, 0.001, -1
    1.85, -3.91, 0.1, 1.85, 0.0, 0.4, 0.001, -1
    1.85, 3.91, 0.1, 1.85, 0.0, 0.4, 0.001, -1
    6.2, 2.82, -0.1, 6.2, 0.0, -0.35, 0.001, -1
    6.2, -2.82, -0.1, 6.2, 0.0, -0.35, 0.001, -1
    3.42, 2.81, -0.1, 3.42, 0.0, -0.35, 0.001, -1
    3.42, -2.81, -0.1, 3.42, 0.0, -0.35, 0.001, -1
    6.2, 2.326, 0.1, 6.2, 0.0, 0.35, 0.001, -1
    6.2, -2.326, 0.1, 6.2, 0.0, 0.35, 0.001, -1
    3.42, 2.362, 0.1, 3.42, 0.0, 0.35, 0.001, -1
    3.42, -2.362, 0.1, 3.42, 0.0, 0.35, 0.001, -1
    1.4, 2.76, -0.1, 1.4, 0.0, -0.35, 0.001, -1
    1.4, -2.76, -0.1, 1.4, 0.0, -0.35, 0.001, -1
    1.4, 2.492, 0.1, 1.4, 0.0, 0.35, 0.001, -1
    1.4, -2.492, 0.1, 1.4, 0.0, 0.35, 0.001, -1
    -2.4, 2.964, 0.0, -2.4, -2.964, 0.0, 0.006, -1
    5.8, 3.83, 0.1, 5.8, 0.0, 0.4, 0.001, -1
    5.8, -3.83, 0.1, 5.8, 0.0, 0.4, 0.001, -1
    ***Source***
    1, 0
    w14c, 0.0, 1.0
    ***Load***
    1, 0
    w15c, 0, 0.0, 120.0, 0.0
    ***Segmentation***
    400, 40, 2.0, 2
    ***G/H/M/R/AzEl/X***
    0, 15.0, 4, 50.0, 120, 60, 0.0
    $$$Taper wire set$$$
    6
    -0.001, 2, 2.0, 0.015, 0.88, 0.0125, 1.4, 0.01, 0.925, 0.008, 99999.9, 0.006
    -0.002, 2, 1.0, 0.0125, 0.91, 0.01, 0.91, 0.008, 99999.9, 0.006
    -0.003, 3, 1.0, 0.015, 0.88, 0.0125, 1.4, 0.01, 0.925, 0.008, 99999.9, 0.006
    -0.004, 3, 0.5, 0.0125, 0.91, 0.01, 0.91, 0.008, 99999.9, 0.006
    -0.005, 2, 3.0, 0.009, 99999.9, 0.007
    -0.006, 3, 1.5, 0.009, 99999.9, 0.007
    ###Comment###
    Mod by Nick, ua3tw 2/24/2011 8:20:07 PM
    Mod by , 24.02.2011 16:20:19
    Mod by ;))) 23.10.2010 22:30:47
     
  2. SP3L

    SP3L Ham Member QRZ Page

    Dear Nick and Dear All,

    I have collected the results of antenna model simulation in the attached file: UA3TW Yagi 2017-03-17.pdf. This is the first time I did such a booklet. I hope you will find it useful. All the simulations were done in the MMANA-GAL.

    It is another excellent design of Nick. The Yagi has very decent gain and bandwidth on all 5 bands. The only thing you need to pay attention to is: it radiates backwards on 17 m.

    upload_2017-4-6_15-19-46.png

    upload_2017-4-6_15-20-49.png

    As you can see in the views above, the antenna has 13 elements. As Nick noted, it has short boom: 6.65 m what, I believe, was a challenge. AFAIK, the shorter the boom the harder it is to achieve high gain.

    Nick succeeded in achieving high gain and wide bandwidth at the same time. The detailed results could be found in the attached file.

    How this antenna compares with the other high gain models presented in this thread? See below.

    upload_2017-4-6_15-27-12.png

    upload_2017-4-6_15-27-36.png

    As you can see, the previous Nick's designs had higher gain. But they had longer booms. Taking this into account, everybody must admit that Nick has done very well again.
    F/B also looks very well. Good job!

    As always, I am attaching the comparison table updated with this Yagi results and the complete model pack. I left the model in its original form in the MMANA-GAL format. As noted in the previous posts, you can convert it either to NEC or to EZNEC format with AC6LA's tool. But remember that the MMANA-GAL produces more credible results when the antenna uses stepped diameter Alu pipes.

    There is still another Nick's design in the backlog. Be patient, please. It takes time to prepare a new post. I share my time between family, work and hobby. And not always the hobby is priority one. ;-)

    73
    Jacek
     

    Attached Files:

  3. SP3L

    SP3L Ham Member QRZ Page

    I have not posted anything here for some time. That's because I am still busy with my Cat's Whiskers Beam. The antenna is 4.5 m above the ground now. I hope I will be able to hoist it full way up in the next weekened.

    upload_2017-5-23_9-31-28.png

    With all these directors and reflectors, it looks like a sailing boat. doesn't it?

    Jacek, SP3L
     
  4. SP3L

    SP3L Ham Member QRZ Page

    Finally, I found enough time to analyze UA3TW Yagi he shared with us on March 31.
    This is a big antenna. Boom length is 10.47 m (ca. 34.3'). The number of elements is 16. Some of them are more complex than a simple straight tube – as you can see in the picture.
    upload_2017-5-31_10-12-50.png
    As Nick noted, he had used 4 elements for the 20 m band. The effect of his decision can be clearly seen in the graph below (red ink line). This Yagi has the highest gain in the 20 m band of all models covered in this thread - almost 7 dBd.

    upload_2017-5-31_10-17-3.png

    This antenna has excellent gain not only in 20 m band. As you can see in the graph, its gain peaks to almost 8 dBd at 21.45 MHz and 28.5 MHz. If we take into account all test frequencies, this Yagi is the leader in 60% of them.

    Except for the gain, this Yagi has very low SWR in 4 bands. SWR stays also very low for the range 28.0-28.6 MHz and the antenna is still usable up to about 28.8 MHz. I am presenting all SWR graphs in the attached UA3TW_Yagi_2017-03-31.pdf file.

    The F/B ratio is good though not as extremely good as the gain. See the comparison graph below.

    upload_2017-5-31_10-33-11.png

    To sum it up: this is a very high gain antenna with excellent SWR but rather large and complex. I think you should be a really experienced constructor to build and tune such a thing. Well, there no free lunches. But the model itself is a well done job! Congratulations to Nick.

    73
    Jacek, SP3L
     

    Attached Files:

  5. UA3TW

    UA3TW Ham Member QRZ Page

    Thank you very much for your contribution Jacek! Good luck to you with your 'sailing boat' antenna!
    Unfortunately my antenna picture #206 is now disassembled and will hardly be assembled again, since nobody finds a place for it.
    UA3TL couldn't afford to hoist it because of it's scaring look for the neibours - he hoisted an easier one of 2-3-3 config.
    There is some hope still - the antenna model you have just described was made by the request of RA7G. He had made a trybander
    that I had helped to model, and now, after a few years of run, he is going to rebuild it and turn it a pentabander. Shall see if he succeeds.
    73
    Nick, UA3TW
     
    SP3L likes this.
  6. SP3L

    SP3L Ham Member QRZ Page

    This is an update on the Cat's Whiskers Beam prototype antenna.
    The very first Cat's Whiskers (basic, not the beam version) survived several months. But on a very strong windy day its top wire broke. It happened in the spot where it was soldered to another wire. When spring came and finally I was able to take it down, I had two options: either to just repair the basic antenna or to turn it into the beam version. I chose the second option.

    The damage that happened to my first Whiskers taught me two lessons:
    - use thicker wire (stranded copper 2 mm dia)
    - give up soldering and join the wire with screws
    To make the antenna even more robust, I decided to parallel almost every wire with a sailing line (2 mm thick). In the beam version, every reflector or director is attached to a sailing line and this is the line that is subjected to mechanical stress - not the stranded copper wire. Also the external frame of the driven element is strengthen with a sailing line. Wires and sailing lines are taped together and secured with zippers every half a meter or so.

    upload_2017-6-7_21-35-19.png

    I took the first SWR measurements when the antenna was 6 m above the ground. Then, we hoisted it to its final height 9 m a.g.l. I took the measurements again - this time with two different antenna analyzers. There was practically no difference between the results of the two meters. And the difference between 6 m and 9 m height was very small.

    The next logical step was to compare the real SWR with the simulated SWR. And that's what I got:
    upload_2017-6-7_21-36-9.png
    I am presenting the SWR simulation as produced by 4nec2 and MMANA-GAL and real SWR at two heights.

    I expected that the real SWR measured at the TRX end of the coax would be smaller than the simulated one at the antenna feed point. But why the peaks and dips were shifted in the real SWR? They were shifted down for F < 24 MHz and shifted up for F >24 MHz. I could not create that big and regular errors when cutting reflectors and directors to length. It took me more than a week to figure out what has happened. I simulated various things and checked how they impact SWR. Like common mode current or ground parameters.

    In my opinion this is what happened. By adding a sailing line close to antenna wire, I changed the latter into something between a bare copper and insulated copper. Here is a simulation in which I added a distributed inductance to all wires (except the few that do not had sailing line companions). It was 0.05 uH/m (1/3 of what you should normally use for a completely insulated wire).
    upload_2017-6-7_21-39-15.png
    OK, much better for the 14-24 MHz range. Still serious disagreement for the higher frequencies. Before I was able to figure out what to do with the higher frequencies disagreement, it started to rain. I measured the SWR again when the sailing lines were wet after rain. And that's what I got:
    upload_2017-6-7_21-39-56.png
    In wet conditions, everything was shifted down in frequency spectrum even more. In my opinion this is a very strong evidence that using sailing line in close proximity to antenna wires is a total disaster. To correct the antenna, every reflector and director should be shortened. But during the rain you should shorten them even more. If not, the optimal gain and F/B will will no longer be inside amateur bands. Of course that is not possible. So, I will have to get rid of the sailing line and use stronger unisolated copper wires instead.

    It is not so painful in the driven element. Simulations show that leaving or removing the sailing line from the external frame of the driven element has no visible effect on SWR and most likely on gain and F/B.

    So the very last problem left was the shift to higher frequencies for F > 24 MHz. The only explanation I could confirm with simulations was the effect of the balun. Ferrite core material 61 has the following complex permeability graph:
    upload_2017-6-7_21-42-40.png
    It shows that losses in the core rise when you increase frequency from 10 to 30 MHz. When I added 1 kohm resistance in parallel with the antenna to simulate power loss, I got almost what I needed. In the final model, I additionally added 15 pF in parallel with 1 kohm, and a series inductance of 1 uH in series.

    In the graph below you can see how the final model compares with reality. Note that for frequencies below 24 MHz, 1 kohm resistor is removed (losses are small enough to neglect them) but 15 pF and 1 uH are left. The wires that have sailing line companions have distributed inductance of 0.05 uH/m as before. The model is compared with the real antenna in dry conditions.
    upload_2017-6-7_21-45-9.png

    As you can see the model is not completely perfect. For example, for some frequencies, simulated SWR is smaller than the real one. That can not be right. But to improve the model further one would have to take lab measurements of the balun itself. And even then, I am not sure if NEC-2 simulator will enable me to create the right model. Perhaps one day we will have simulators combining NEC-4 and SPICE?

    Final conclusion.
    In my opinion to make this antenna work as intended, I will have to remove the sailing line from reflectors and directors. I think I do not have to do anything to the balun. The shift in the peaks and dips of SWR it produces should impact only antenna impedance but not gain and F/B on amateur bands. And if I am right about the loss (1 kohm in the equivalent circuit), about 10% of the delivered power is dissipated in the balun. It is a loss of 0.5 dB. I can live with it.

    If you think my reasoning presented above has a flaw, let me know. Perhaps I am still missing something important.

    73
    Jacek, SP3L

    P.S. This antenna even de-tuned by sailing lines still works better than my multiband GP. But most likely it does not offer me 4dB gain over a basic Cat's Whiskers as intended.
     
  7. AC6LA

    AC6LA Ham Member QRZ Page

    AI6KX and SP3L like this.
  8. UA3TW

    UA3TW Ham Member QRZ Page

    My congratulations, Jacek! Well done!
     
    SP3L likes this.
  9. SP3L

    SP3L Ham Member QRZ Page

    Thanks, Guys!
    According to Steve, WB8IMY, the Editor-in-Chief of QST, the article about the Cat's Whiskers will appear in early 2018. This will be about the basic version of the Whiskers without directors and reflectors. But you - the readers of this thread - already know everything about this antenna. As a matter of fact, without this forum and this thread in particular, the Cat's Whiskers would not have been created. Your feedback was essential. Thank you very much.
    :)
    Jacek, SP3L
     
    UA3TW likes this.
  10. SP3L

    SP3L Ham Member QRZ Page

    Cubical Quad without relays for band switching

    The Cubical Quads presented in this thread required either relays to switch bands or a window line and an ATU to handle high SWR. Although such antennas are built and used, I always considered them as a bit imperfect. My initial attempts to design a 5-band Cubical Quad not requiring relays and having low SWR failed. The main reason for that is the fact that a square loop has a harmonic resonance at about 2F. The 14 MHz band loop resonates also at about 27.45 MHz what interferes with the 12 m and 10 m band loops. At the second harmonic resonance, the loop radiates up and down, left and right, but not forward and backward as it does at the fundamental harmonic. I had tried various antenna geometries but nothing helped. I was convinced it was impossible. But never say never!

    Let's compare the classic square loop with a loop that is fed in the centers of the top and bottom sides.

    upload_2018-5-17_10-52-17.png
    I call the second antenna a split feed point square loop. Two transmission lines connect the feed point located in the center of the antenna with the centers of its top and bottom wires.

    Let’s compare Z/Phase plots of both antennas.

    The classic square loop (5.58 x 5.58 m) has the fundamental resonance at 14.175 MHz and the second harmonic resonance at 27.45 MHz. See below.
    upload_2018-5-17_10-55-7.png

    The split feed point loop (5.58 x 5.58 m, TL characteristic impedance = 300 ohms) does not have a second harmonic resonance but third harmonic resonance. 1F = ca. 11.8 MHz, 3F = ca. 26.9 MHz.
    upload_2018-5-17_10-57-36.png

    Why such difference? The currents flowing in the two antennas differ in phase.
    upload_2018-5-17_11-0-6.png
    As a matter of fact, you can regard the SPF loop as a stack of two dipoles with bent ends. If you break the antenna in the centers of the vertical sides and move the upper and lower halves slightly away from one another, the antenna performance will remain unchanged. It will look then as shown below.
    upload_2018-5-17_11-2-44.png
    SPF loop and the stack of two dipoles with bent ends nearly touching one another are electrically identical.

    But that’s not all.

    If you change the transmission lines characteristic impedance (e.g. 25, 50, 300, 450, 600 ohms) and their length, you can impact Z/Phase plots and change antenna resonance impedance.

    Another interesting fact is you can try to use either the low impedance resonance at 11.8 MHz or the high impedance resonance at 16.1 MHz (see the Z/Phase plot of the SPF). Three reasons back the choice of the high R resonance:
    - impedance magnitude and phase change more gently around it what should make achieving wide bandwidth easier
    - the high R value is relatively low (about 760 ohm) and there are prospects of bringing it even more down by choosing transmission lines characteristic impedance and adjusting their length
    - antenna gain is greater at the high R resonance than at the low R resonance (3.75 dBi vs. 2.82 dBi)

    And there is one obvious drawback of the high R resonance choice. For the same operational frequency, the loop needs to be larger. Nevertheless, I opted for the high R resonance and succeeded in designing the 5-band SPF Cubical Quad.

    To be continued.
     
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