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dkumar
Joined: 04 Jan 2008
Posts: 26
Helped: 1
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 11 May 2008 14:05 Gain and Diractivity of Antenna |
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Hi every one!!
I am stuck up with a petty problem of measuring the gain,and directivity of my micro strip antenna.I have the antenna fabricated and i have to test its specifications.
Please if someone can tell me how can i test these specs,I have VNA with which i have already tested S11 plot for my antenna.
Please reply soon
Thanks in advance.
-dk
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balaguru thavamani
Joined: 08 Nov 2006
Posts: 230
Helped: 25
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| 12 May 2008 6:09 Re: Gain and Diractivity of Antenna |
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Hi dKumar,
For Antenna Gain Measurement you need two antennas,one is standard antenna of which gain(Gstd) is known and another one is Antenna under test(AUT).
Attached here is Test Setup for Gain Measurement.
Gain(AUT)=Total Loss -RSL- Gstd.
where,
RSL=Recieving signal level of AUT
Total Loss = PathLoss + Cableloss.
regards,
balaguru.
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Kohi_boy
Joined: 20 Apr 2008
Posts: 48
Helped: 4
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| 12 May 2008 15:41 Gain and Diractivity of Antenna |
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Hi,
I'm just wondering what is it that you are measuring in the gain test setup.jpg. Doesnt make sense to me.
Added after 3 minutes:
Do you have any access to any Test Chamber ?
You might wan to download from IEEE "Standard Test Procedure for Antennas"
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biff44
Joined: 24 Dec 2004
Posts: 1175
Helped: 149
Location: New England, USA
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| 12 May 2008 16:03 Gain and Diractivity of Antenna |
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| In the drawing, he is measuring S21 (total loss) between the antenna under test and a known good antenna. You rotate around the antenna under test and get a relative gain pattern. THEN you substitute a standard gain antenna (one that you know what its gain is) for the antenna under test, aim the two antennas together, and can "calibrate" the absolute antenna gain of the first test.
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balaguru thavamani
Joined: 08 Nov 2006
Posts: 230
Helped: 25
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| 13 May 2008 6:11 Re: Gain and Diractivity of Antenna |
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| Kohi_boy wrote: |
Hi,
I'm just wondering what is it that you are measuring in the gain test setup.jpg. Doesnt make sense to me.
Added after 3 minutes:
Do you have any access to any Test Chamber ?
You might wan to download from IEEE "Standard Test Procedure for Antennas" |
Antenna Gain and Pattern Measurement must be done in Anechoic Chamber otherwise it'll lead to errors due to reflection.Distance between two Antennas should be greater than or equal to 2Dē/λ. D is the largest dimension of the Antenna.RSL should be maximum RSL.
eg for Gain Measurement at 1795MHz
Considering
Distance between two Antennas = 7m.
0dBm transmit power from VNA,
Gstd=12 dBi (Standard Antenna Gain)
RSL=-28dB (Maximum Recieving signal Level of Antenna under test with respect to Standard Gain Antenna).
Cable Loss can be normalized.
Pathloss = 54.42dB
then gain of AUT= 54.42-28-12=14.42dBi.
regards,
Balaguru.
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farin
Joined: 04 May 2006
Posts: 17
Location: Czech republic
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| 14 May 2008 10:19 Re: Gain and Diractivity of Antenna |
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| Gain of an antenna could be measured with any 3 antennas, cos there are 3 unknow variables, gains of these antennas. You have to measure every kombination of antennas 1-2, 1-3 and 2-3 and you have system of 3 equations with 3 unknow variables. Every equation is in form: Ptx + Gtx - AIR LOSS + Grx = Prx.
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balaguru thavamani
Joined: 08 Nov 2006
Posts: 230
Helped: 25
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| 14 May 2008 10:27 Re: Gain and Diractivity of Antenna |
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| farin wrote: |
| Gain of an antenna could be measured with any 3 antennas, cos there are 3 unknow variables, gains of these antennas. You have to measure every kombination of antennas 1-2, 1-3 and 2-3 and you have system of 3 equations with 3 unknow variables. Every equation is in form: Ptx + Gtx - AIR LOSS + Grx = Prx. |
Yes three antenna method will give accurate results when compared to Standard Gain Antenna Measurement.
Regards,
Balaguru.
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pankajdudulwar
Joined: 30 Mar 2006
Posts: 131
Helped: 2
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| 14 May 2008 14:03 Gain and Diractivity of Antenna |
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I agreee with farin and balaguru. I would like to know if reflection causes gain degradation or up gradation i.e gain will increase or decrease. As the chamber facility will not be available in many of the places and the testing will be done at terrace or free space. Please let me know your views on this guys.
Regards,
Pankaj
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balaguru thavamani
Joined: 08 Nov 2006
Posts: 230
Helped: 25
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| 14 May 2008 14:33 Re: Gain and Diractivity of Antenna |
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| pankajdudulwar wrote: |
I agreee with farin and balaguru. I would like to know if reflection causes gain degradation or up gradation i.e gain will increase or decrease. As the chamber facility will not be available in many of the places and the testing will be done at terrace or free space. Please let me know your views on this guys.
Regards,
Pankaj |
It depends upon reflection of the signal, Gain will increase if orginal and reflection signal are in Phase and decrease if both are out of phase.
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Kohi_boy
Joined: 20 Apr 2008
Posts: 48
Helped: 4
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| 14 May 2008 14:47 Gain and Diractivity of Antenna |
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On top of that,
Polarisation of the reflected wave also plays a part in the gain.
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pankajdudulwar
Joined: 30 Mar 2006
Posts: 131
Helped: 2
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| 14 May 2008 18:22 Re: Gain and Diractivity of Antenna |
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| How I can tolerate this if I don't have RF shielded chamber. Also as the reflected waves will come after a delay and if at all it is phase it will act as a destructive only if I am wrong please correct me.
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balaguru thavamani
Joined: 08 Nov 2006
Posts: 230
Helped: 25
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| 15 May 2008 5:57 Re: Gain and Diractivity of Antenna |
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| Better test in freespace area.
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pankajdudulwar
Joined: 30 Mar 2006
Posts: 131
Helped: 2
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| 15 May 2008 6:08 Gain and Diractivity of Antenna |
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IF I am testing on the terrace of the building but I have tall building surrounded in all direction then it will affect lot or less. But in LOS no interruption as buildings are 2-3 mts away.
Please let me know
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