questions of atenna test thanks

[aaronwlee]

oscilloscope bad attenuation

I want to test the radiation situation (strength and pattern) of some certain antenna which is bought from didikey. All the antenna i want to test is commercial product. In my school, there is a testing chamber and I have several questions:

1) How can I feed the signal to antenna? Do I have to build a RF system on PC board myself or can I just simply feed the signal from function generator to antenna

2) I also want to study the transmission situation of the isotropic point source in different paths, but how can i implement a isotropic source, is this a standard cell in the testing chamber?

Thanks

Aaron

 

[GVVIN]

Hi,

If you have signal generators which work up to your desired frequency and power , you can directly feed from signal generator.

Usually for measurements you need 2 antennas one your DUT( under test antenna, Digikey one) and the other an isotropic antenna which is used to receive the signal from your antenna. If you have a lab this antenna will be available there.

Regards
GV

 

[vfone]

Feed direct the antenna from the generator using a 50 ohm coaxial cable, and for substitution use a λ/2 dipole antenna (resonating at the same frequency as the Digikey antenna).

To find the gain in dBi (isotropic antenna) from the Dipole gain in dBd:

Gain of λ/2 Dipole dBd = 2.15 dBi

 

[aaronwlee]

Thanks to these two gentlemen

So I can find a isotropic antenna as standard cell in testing facility and even if I can not, I can still use dipole and calculate the equivalent result

 

[RF-OM]

Usually receiving antenna is fixed in such a test. This means you can use any antenna with known gain. Signal generator is preferable excitation source, but even in this case it is better to connect it through 3 or even 6 dB attenuator. It will ensure that you may not count mismatch loss. With RL=10 dB mismatch loss is about 0.46 dB, so even with 5dB attenuator you are safe enough.

 

[aaronwlee]

thanks a lot and I checked the equipment list of the chamber at my school:

Screen Room Station with the following equipment
(1) Lundren 7ft x 7ft screen room, tested to 90dB attenuation at 915 MHz
(2) Digital Oscilloscope, 500MHz, 2 Channel, IEEE488-GPIB interface, Tektronix Model 3052
(3) Spectrum Analyzer, 9K-1800MHz, IEEE488-GPIB interface, HP8591E
(4) Vector RF Network Analyzer, 300K-3000MHz, IEEE488-GPIB interface, HP8714ES
(5) Arbitrary Function Generator, IEEE488-GPIB interface, HP33120A
(6) Pulse Generator, 50MHz, 0.1uS, Data Dynamics Model 5708
(7) Signal Generator, 250K-1000MHz, IEEE488-GPIB interface, HP8647A


Is the screen room only working at 915MHz or lower frequency? I think I need to test the antenna at different frequency.

Is this list enough for my test

Thanks

Aaron

 

[GVVIN]

Hi,

Screen room - Gives 90dB attenuation at 915 MHz . It doesnt mean it is limited to that frequency alone. only the attenuation will be different at other frequencies. You can use this facility for all your measurements , say 500 MHz to 1 GHz. no issues.

You have signal generator which works upto 1 Ghz , you can use that to feed your antenna.
Antenna is not there in this equipment list, may be you have another accessories/component list, check if an isotropic antenna is there for your desired frequency of operation.

regards
GV

 

[jallem]

Hold it...!!!!!
Did you say screen room?....Lindgren screen room
as like a faraday cage and you want to use
it for antenna measurement?.....something is wrong
in that picture or I am mistaken.....

 

[GVVIN]

Hi Jallam,

I think you are right, its just an RF sheild room, No absorbers...

**broken link removed**

Aaron do check whether your facility is only sheild room or Anechoic chamber before proceeding.

**broken link removed**
https://www.ets-lindgren.com/pdf/AMS-8200.pdf

 

[RF-OM]

90 dB attenuation is not bad. Your screen room is probably good. But this is a number stated on the paper. If you want to check it, try to use your cell phone inside the chamber. This is easy and good practical test.

I remember the case when I and my boss (the CTO of the company) were sitting in the cage and do the tests when my wife called me. I talked to her and then realized what was happened. All the test results were abandoned and we started from scratch after examining the cage and removing the reason for so bad attenuation.

Best regards,
RF-OM

 

[Azulykit]

I want to test the radiation situation (strength and pattern) of some certain antenna which is bought from didikey. All the antenna i want to test is commercial product.

***** My first thought is what are you trying to test? What characteristics? What frequency (very important as it sets the stage for how you test)? What is the antenna supposed to do in the first place? From all I can see at this point the testing might be size and weight characteristics. Think about describing your starting point and final objectives in your question. The answers you gut are likely to be more helpful.


***** You might also want to get familiar with generic antenna test measurements. ETS Lingren has an excellent brochure on the subject although it is pointed towards EMI/RFI rather than antennas specifically. Kraus is another useful reference to get started.



***** Once you have an idea of thge test objectives then it makes sense to go on and see if you have the right equipment.

In my school, there is a testing chamber and I have several questions:

1) How can I feed the signal to antenna? Do I have to build a RF system on PC board myself or can I just simply feed the signal from function generator to antenna

***** Probably not. Get one of your professors or a lab technician to help you get started. You probably do not have to start from ground zero.

2) I also want to study the transmission situation of the isotropic point source in different paths, but how can i implement a isotropic source, is this a standard cell in the testing chamber?

***** A perfect omni directional antenna is a fiction. People usually use dipoles to approximate an omni. You really need to get a handle on what you want to test first and then you will be more likely to get meaningful advice from this forum.

***** By the way a screen room is probably not what you are looking for to test an antenna. What you probably need is an anechoic chamber or a far field range. Just a guess so far as I do not know the objective of this testing.