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Testing of Helical Antenna

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ping-pong

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I have designed and implemented 2 helical antennas. Now I wanted to test it in the labortary. The testing equipments I have is signal generator and spectrum analyzer. How can I find the gain of helical antenna with these equipments if one helical is used for transmission purpose and the other for receiving purpose. No anehoic chamber available for testing purpose. Are the results accurate in loabortary if the frequency is in 200-300 MHz. Reply as early as possible.
Thanks in advance

:(
 

VSWR

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Forget indoor measurements. There are too much reflections affecting your results 20 dB or so.

But outdoor measurements are better. Requires access to a large field, far from buildings, lamp posts, parked cars, etc. But ground wave reflections will still affect your result. Can be reduced by placing the transmit and receive antennas each on a high mast, at least 10 wavelengths above ground.

I have successfully measured gain of Yagi antennas for 144 and 432 MHz this way. Using simple dipoles as reference and for calibration. Gain measurements were surprisingly accurate - within 2 dB from antenna gain simulations performed in NEC-2 and Mininec (where ground reflections were simulated as well). I only used a borrowed signal generator and spectrum analyzer for the field tests.
 

sergio mariotti

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If you don't have any standard antenna, you may assume that the 2 helicals (i hope same polarizzation, right?) have the same gain because they have the same geometry.
Then, knowing the TX power, the VSWR, distance, ands RX power, you may calculate the gain from the Friis formula.
I agree with VSWR. Go outdoor !, and "far" from reflective targets.
"far" means ... every metal you may see (with your eyes) as "little" solid angle, looking on every directions.
Also the ground do some reflections. try to be tall enough.
 

scoppulal

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hi,
since gain depends on the pattern you could have an idea of it pointing your antenna toward the sun and make it turn.
You need only forward gain so you should turn your system a few degrees,
pointing at the sun the reflections should be negligible.

With a sensitive system you should be able to get how much wide is the first lobe... and then obtain the gain.

Try and let know

Ciao
 

jyfx

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you have test them?can yougive something
 

ping-pong

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Thx all of you for the useful tips and techniques shared, I will provide the results of the test as soon as possible :)
 

ping-pong

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testing of helical antenna was conducted and the results achieved with it is very good. The antenna were placed 20 meters above the ground surface. Gain of helical antenna comes out to be 10.5 dBi as compared to the theoritical gain of 12 dBi whereas a half power beamwidth of 42 degrees is achieved. Once again I appreciate your help in this regard.
:eek:
 

springf2000

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it is difficult to believe the result that your gain is much higher than the theretoical result; so you had better to check your measurement ways,for example your transmitter antenna and receiver antenna are on the same plane..........
 

scoppulal

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to my experience,
the teoretical gain (the one from the Krauss formulas) is about 3dB optimistic.
So your result could be right.

Ciao
 

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