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I try to design bowtie antenna in CST simulation. This design include that substrate FR4 not with ground and top side is antenna(copper). This design's measurement is calculated online sites. Problem is impedance does not matching 50 ohm. I used CPW waveguide feed for port. What can I do for this situation?

  • Parameters

    frequency range: 150-650 MHZ substrate thickness FR4: 1.6mm trace thickness: 0.035 mm gap: 1 mm Length: 271 mm Weight: 136 mm

https://3g-aerial.biz/en/online-calculations/antenna-calculations/bowtie-antenna-online-calculator

dimension

port dimension - left: + , right: -

S parameter

left:line impedance, right: wave impedance

realized Gain

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  • \$\begingroup\$ This design's measurement is calculated online sites <-- please provide a link and also tell us what the impedance is? \$\endgroup\$
    – Andy aka
    Jan 4 at 10:29
  • \$\begingroup\$ @Andyaka <3g-aerial.biz/en/online-calculations/antenna-calculations/…> and also impedance doesnt match because s11 so bad \$\endgroup\$ Jan 4 at 10:49
  • \$\begingroup\$ You should show the impedance graph indicating real and imaginary parts over the band of interest. \$\endgroup\$
    – Andy aka
    Jan 4 at 10:57
  • \$\begingroup\$ @Andyaka ı cant setup solver so ı cant show it \$\endgroup\$ Jan 4 at 11:05
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    \$\begingroup\$ I agree with @Jason that a CPW does not seem right in this application. A bowtie element is just a broadband dipole, isn't it? And a dipole needs a balanced feed? \$\endgroup\$
    – SteveSh
    Jan 5 at 13:15

1 Answer 1

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I have some reasonable experience designing bowtie antennas and transmission lines, also in CST (though it's been a while since I've used CST specifically).

What it looks like is that the feed impedance for the coplanar stripline you're using to feed the antenna is too high. The impedance graph you're showing appears to be just the line impedance for the coplanar stripline feed, and not the antenna itself. This is calculated at the waveguide port, and is governed by the stripline geometry.

Probably a better way to design this is to break up the design into 3 steps.

  1. Simulate and design the bowtie antenna, with the port defined at the bowtie elements. This will likely be a lumped port. Then modify the bowtie geometry as necessary to get your desired center frequency, bandwidth, and impedance.

  2. Simulate and design the feed network. Most likely, you'll have to make the gap between your copper traces smaller to make the feed network also match 50 ohms.

  3. Create a new simulation with the entire structure based on the previous two steps, to make sure it works together.

Also, the bowtie design calculator you linked has no details about the substrate. Based on this, you can only really use it as a starting point for your own design, since it's not going to be accurate for a bowtie on FR-4 substrate.

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  • \$\begingroup\$ Hi thanks for replying, I will apply the steps. what else can I use instead of FR4? I am reviewing other articles. Sometimes uses rogers for high frequencies. But my frequency range is 150-650 MHZ. \$\endgroup\$ Jan 6 at 9:05
  • \$\begingroup\$ FR4 is fine for your frequency range. The bigger issue is that your bandwidth 150-650 MHz is much larger than you can typically get from a bowtie antenna. You probably need to choose some other antenna that can accommodate that sort of bandwidth. \$\endgroup\$
    – David
    Jan 8 at 14:16
  • \$\begingroup\$ maybe there is no need such a bandwidth but ı have to use bowtie. ı need a better s11. how can ı do better? I am changing port measurement or bowties measurement. I checked antenna magus and ı saw similar design. But when I from there to CST export result is so bad. there is not same results. \$\endgroup\$ Jan 8 at 15:12
  • \$\begingroup\$ What do you mean by "better" S11? Until you define a desired level of return loss, required bandwidth, and center frequency, it's unclear what makes your S11 better or worse. \$\endgroup\$
    – David
    Jan 8 at 16:40
  • \$\begingroup\$ @AhmetEnesYILDIRIM the new images you uploaded look correct and match what I'd expect for a dipole. David is right, the bandwidth you're seeking (150-650 MHz, 125%) is way to broad for even a bowtie. \$\endgroup\$
    – Jason
    Jan 8 at 17:39

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