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dong86
Joined: 22 Jun 2009
Posts: 11
Location: malaysia
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 30 Jul 2009 8:02 rectangular microstrip antenna |
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CAn any1 pls help me figure out what is my problem??
I've design a 886Mhz rect. microstrip antenna and stimulate by using microwave cst!
W(patch)= 10.52cm
L(patch)=8.4cm
h=1.6mm
w(feedline)=3mm
l(feedline)=4.75cm
Substrate=(20cm*17.8cm)
relative permitivity=4.4
from the graph that i attached! return loss how come wont goes up to 10db or more?
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mauloftin
Joined: 29 Oct 2008
Posts: 262
Helped: 22
Location: CZ
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31 Jul 2009 11:01 [Need Help] Rectangular Microstrip Antenna |
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Hi,
of course. You have problem with matching.
follow
http://www.edaboard.com/viewtopic.php?t=346292&highlight=patch+antenna
Added after 5 minutes:
If you use quarter-wave transformer, do not forgot draw 50 Ohm feedline before quarter-wave transformer (http://www.edaboard.com/files-eboard/need_quarter-wave_transformer___50onfeedline_1233.png)
I hope, that I helped you.
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tyassin
Joined: 22 Jul 2004
Posts: 340
Helped: 44
Location: Northern Hemisphere
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31 Jul 2009 12:12 Re: [Need Help] Rectangular Microstrip Antenna |
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Hi
Dont you have another problem like S11 greater than 0 dB. It could be that some seup in CST is not correct.
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mauloftin
Joined: 29 Oct 2008
Posts: 262
Helped: 22
Location: CZ
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31 Jul 2009 12:42 Re: [Need Help] Rectangular Microstrip Antenna |
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| tyassin wrote: |
Hi
Dont you have another problem like S11 greater than 0 dB. It could be that some seup in CST is not correct. |
Hi,
i think, that it is normal problem, it is about accuracy. It will be better use adaptive meshing or Frequency domain solver.
may be, dong86 you can see at the attachment.
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dong86
Joined: 22 Jun 2009
Posts: 11
Location: malaysia
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31 Jul 2009 12:52 Re: [Need Help] Rectangular Microstrip Antenna |
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Hi mauloftin,
I'd like to say "tq very much".. hehe
ya.. its about matching problem! anyway, i m not really know how to calculate L1, how long it should be?? and the distance between substrate and patch must greater than lamda over 4??
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mauloftin
Joined: 29 Oct 2008
Posts: 262
Helped: 22
Location: CZ
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31 Jul 2009 13:42 Re: [Need Help] Rectangular Microstrip Antenna |
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| dong86 wrote: |
Hi mauloftin,
I'd like to say "tq very much".. hehe
ya.. its about matching problem! anyway, i m not really know how to calculate L1, how long it should be?? and the distance between substrate and patch must greater than lamda over 4?? |
Hi,
you can use:
1) λ/4 transformer: http://www.edaboard.com/files-eboard/need_quarter-wave_transformer___50onfeedline_1233.png
2) another type of matching: http://www.edaboard.com/files-eboard/patch_1886.jpg - The L1 you must find it experimentally.
ad 1) - length of λ/4 transformer is λ/4  . You can see at the http://www.edaboard.com/viewtopic.php?t=346292&highlight=patch+antenna, there is all about λ/4 transformer
I wrote:
You must use software TXLine
1) find impedance your microstrip antenna - easy, set right colum "Physical Cahrakteristic" and click left arrow - you have impedance Zm
2) calculate Zx = √(Zm*50), this is impedance λ/4 transformer
3) in left colum set Zx, electical length is 90 deg - click right arrow and you have design λ/4 transformer
4) set left colum 50 Ω and you have feedline. In this case the length of feedline is
not important, you can have it 50 mm or 50 cm or 4.35 km (if you have loss free material)
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