I have dual stacked crossed yagi antenna. How can I practically measure the gain of the antenna combination? I know that this can be done in an anechoic chamber. But this is not feasible for me (transportation and cost). Please guide me.

The antenna is designed to work in the 430-440 MHz band. I have a spectrum analyzer and network analyzer with me. If I wish to maintain a weekly of of the antenna gain, what can I do? Also while testing how much does the position of reference antenna matter? For testing at the same position, won't the yagi antenna cause interference in power received by reference antenna?

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    Please add to your question what band the antenna is built for. The types of propagation in effect, availability of known transmitters, and so on will affect the best answer. – Kevin Reid AG6YO Mar 17 '15 at 15:48
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    Without such details, the obvious answer is that you set up a receiver and measure the received power, then compare that to the received power from an antenna with known gain at a similar distance. – Phil Frost - W8II Mar 17 '15 at 15:58
  • Please also add the expected gain of the antenna, and/or its length in m. What test equipment do you have access to? Network analyser? Spectrum analyser? Power meter? Test receiver? Attenuators? – tomnexus Mar 19 '15 at 13:50
  • I have access to spectrum analyzer and signal generator. I also have a vector network analyzer. – Vaibhav Rekhate Mar 19 '15 at 13:52
  • @VaibhavRekhate with that equipment you should have no problem measuring gain. Can you edit the question to more specifically ask about the part of the process that you don't understand? – Phil Frost - W8II Mar 19 '15 at 13:56

Measuring received power is pretty straightforward. Set up a receiving antenna some distance away. Make it at least 10 wavelengths, but even farther is better. Make sure the receive antenna has the same polarization. Transmit a carrier at a fixed power. Read the received power at the receive antenna with your spectrum analyzer.

If it's more convenient, you can also run this test in the other direction, transmitting with some other antenna, and receiving with the Yagi. Due to reciprocity, the results you obtain will be identical.

This doesn't tell you gain unless your spectrum analyzer is calibrated and you know the gain of your receiving antenna. Without the tightly controlled conditions of an anechoic chamber you probably can't know the receiving antenna's gain.

However, what you can do is perform the same test again and compare the results. If you are testing modifications to the Yagi you can compare the received power before and after the modification and quantity the change. You can also replace the Yagi with a reference antenna like a dipole for comparison.

If you receive twice the power with your Yagi versus the reference dipole, then you know the Yagi has 3 dB more gain than the dipole. While this isn't exactly a carefully calibrated, quantitative measurement of antenna gain, it is an objective way to validate that you have indeed constructed an effective antenna, that your Yagi is better than a $1 dipole, or that some modification or adjustment you've made to the Yagi has made a measurable improvement.

  • Based on the last part of the question, I think some clarification is in order: when you test again with the reference antenna, you remove the tested antenna and replace it with the reference antenna (or vice versa). – Kevin Reid AG6YO Mar 20 '15 at 14:37
  • Also, is there an advantage to transmitting using the test antenna rather than receiving with it? – Kevin Reid AG6YO Mar 20 '15 at 14:38
  • One small thing to consider is that when you switch antennas to do this sort of test, you need to make sure that the impedance match between the antenna and transmitter (or receiver) is either the same or taken into account for the test evaluation. Another ham operator (not on this forum I don't think) does a lot of lab quality antenna tests in the field: Ward Silver, N0AX, who is the editor of the ARRL Handbook as well as author of the QST "Hands On Radio" column. You (the OP) might consider sending him an e-mail asking for advice. – K7PEH Mar 20 '15 at 15:55
  • @KevinReidAG6YO: To test with the reference antenna (a dipole in my case), I cannot remove the antenna under test (it is fixed) so I place the reference antenna in front of the antenna under test. So will the bigger Yagi antenna behind, will it interfere with the power received by the reference antenna? And as Phil said I am using a spectrum analyzer at the antenna end, and use a constant transmitter at a distance of about 50m. Is this setup and method correct? – Vaibhav Rekhate Apr 7 '15 at 19:07

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