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Thread: 1.2GHz / 2.4GHz Circular Polarized Patch Antenna - 8.5dB gain - less than 15$

  1. #11
    Engineer for Jesus Christ IBCrazy's Avatar
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    Drill a big hole in the middle (or even better a rectangular slot) in the middle. This will help axial ratio by driving the signal around the low current point in the middle of the patch.

    -Alex
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    videoaerialsystems.com - Performance video piloting

  2. #12
    Pilot Dionysos's Avatar
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    Ib thanks for your pointer, most appreciated. I m afraid I would not know where to place it how large it should be and how it would influence the axial ratio plot.

    A simulation would be nice.

    dio
    Latest Crafts: The Anti-Gravity-Machine, Carbonator, Guava 2m, Wunderwaffe I, Wunderwaffe II, Uberwaffe, Plankton v2, TBS discovery

  3. #13
    Engineer for Jesus Christ IBCrazy's Avatar
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    Quote Originally Posted by Dionysos View Post
    Ib thanks for your pointer, most appreciated. I m afraid I would not know where to place it how large it should be and how it would influence the axial ratio plot.

    A simulation would be nice.

    dio
    In general it doesn't really matter since the outside edge of the patch is resonant. The middle acts as a microstrip line. The middle of the patch is low impedance. The impedance increases as you get closer to the edge of the patch. Any holes or slots should go dead center in the middle of the patch. The hole should be 10-15% of the main element area. A double slot (horizontal) is also very effective. The double slot should be 3-4% of the height of the patch and 25-30% of the width. Space them ~10% of the patch height apart. The truth is that cutting a guide slot (or drilling a hole) is not critical. It simply changes the electrical path around the low impedance point, that's all. This is a small optimization, nothing more

    The patch you have here is similar to the K5OE patch which makes a really good satellite dish feed antenna. The main difference is that yours is fed from the bottom and the K5OE is fed from behind like the Circular Wireless unit. In fact, the only difference between the K5OE and the CW is that CW cut a waveguide in the middle. It should also be noted that the K5OE patch was discovered years ago by Thomas Black (DPCAV) well before we ever had any CP omnis for FPV. He called his tutorial the "Goof Proof Patch": http://www.rc-cam.com/gp_patch.htm
    If it is broken, fix it. if it isn't broken, I'll soon fix that.

    videoaerialsystems.com - Performance video piloting

  4. #14
    Pilot Dionysos's Avatar
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    That's some great pointers IB! Thank you very much, I didn't know about the "goof proof patch". Looks like a good read.


    That's for elaborating on the center cut-out. By simulating these things I usually get a good feel for how things work, so I'm a bit reluctant to try because I'm not sure what I'll be destroying by doing so.


    I updated the first posts...


    Gonna look what my printer says in the meantime with regards to my cover.


    Cheers,
    Dio
    Latest Crafts: The Anti-Gravity-Machine, Carbonator, Guava 2m, Wunderwaffe I, Wunderwaffe II, Uberwaffe, Plankton v2, TBS discovery

  5. #15
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    Hi dionysos!

    First of all, thanks for all the information! I did a crosshair antenna few days ago and i want to give a try to your dio-patch but my transmitter is a lawmate and has up to 1180mhz.

    Can you tell me how can i scale it to my frequency??

    Regards,

  6. #16
    Pilot Dionysos's Avatar
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    sure, I have uploaded a file @ google docs. It's in the 2nd or 3rd post...


    Enjoy.


    The cover looks and fits quite nice. Can't complain... I'm curious to fly it now


    Dio
    Latest Crafts: The Anti-Gravity-Machine, Carbonator, Guava 2m, Wunderwaffe I, Wunderwaffe II, Uberwaffe, Plankton v2, TBS discovery

  7. #17
    Pilot Dionysos's Avatar
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    posts are now updated...
    Latest Crafts: The Anti-Gravity-Machine, Carbonator, Guava 2m, Wunderwaffe I, Wunderwaffe II, Uberwaffe, Plankton v2, TBS discovery

  8. #18
    Navigator Pegru's Avatar
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    Hi Dio,
    to be continued:
    found some time to play with side-fed air-dielectric patches. Built one and found that resonance frequency is too high compared to simulation.
    Stumbled on your thread and [URL="https://www.cst.com/Applications/ArticlePDF?id=245" [/URL]
    You used W = 139mm on 900MHz as reference, looking at figure "parameter sweep control variable =patch size S11/frequency" W = 142mm corresponds to 900MHz.

    Click image for larger version. 

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    (http://www.cst-korea.co.kr/Applicati...0c82c204b453b8)

    No big difference but is explaining my offset.

    Click image for larger version. 

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    S11 = -17dB, f(res) = 1320MHz. Design frequency is 1300MHz => offset is 20 MHz (6,5MHz/delta W in mm)
    Really no problem as swr is about 1.4:1 (S11 -15dB) at design frequency.
    May help designing CPs for 2G4 and 5G8 and hit the frequency.
    Will reprint some more patches and change W step by step to confirm my statement.

    Bye Dio

    PS: very nice VNA!

  9. #19
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    Wow! This looks great! Going to give it a go.
    Thanks for posting! :-)

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