Antenna Measurements

Discussion in 'Wireless & RF Design' started by ihaveaquestion, Jan 20, 2011.

  1. ihaveaquestion

    Thread Starter Active Member

    May 1, 2009
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    Hi guys,

    How would an interested individual go about learning how to do various basic measurements on a given antenna? What type of equipment would be needed and do you recommend any sources in particular to learn from?

    Thanks a bunch in advance guys (this certainly isn't a one-post thread)...
     
  2. Kermit2

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    SWR and RF power meters. Minimum.

    Ham and other radio club sites would be the best place to park and listen and read and learn.
     
  3. CDRIVE

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    Jul 1, 2008
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    Many years ago the ARRL published a Directional Coupler (made from 3/4 inch copper plumbing), in the Amateur Radio Handbook. It was an excellent design which I built and tested to well over 1GHz. These devices require a transmitter in use. There is also a method using a Noise Bridge that doesn't require a transmitter. As I recall, it was one of the first products that Palomar Engineers marketed.

    http://kv5r.com/articles/ham/noisebridge.asp

    http://www.qsl.net/m0pmb/noisebridge.html

    http://www.spirat.com.au/vk5zvs/pic21.htm

    http://blog.marxy.org/2008/12/noise-bridge-for-cheap-antenna-analysis.html

    http://jandek.co.uk/Assets/JD031.PDF

    http://newenglandqrp.org/files/noise-bridge-schematic.gif

    There's also the lab method, which uses a sweep generator, scope, 50 Ohm detector and gazinta.
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I merged the posts and deleted double posts.
    One time postsing is enough to avoid confusion.

    A lot of information can be found on this page:
    http://ac6v.com/antprojects.htm

    Bertus
     
    Last edited: Jan 21, 2011
  5. ihaveaquestion

    Thread Starter Active Member

    May 1, 2009
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    Thanks Bertus and sorry for the double post...

    I'll be looking through that page for now, but in the meantime, let me rephrase my initial question:

    If I have an antenna, say from a handheld radio or a given device, how do I measure the basic parameters of it like gain, radiation pattern, beamwidth, polarization, and impedance?

    Thanks in advance
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
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    Except for impedance all the other measurements you listed are done with a Field Strength Meter that can have a measurement scale in Decibels or uVolts or both. Antenna radiation measurements are a relative process, which is why a dB scale is most important.

    It's been quite some time since I've done these measurements but I believe the Field Strength Meter should be at least one wave length from the antenna. Whatever the rule of thumb actually is, ... the idea here is for you and the meter to not become part of the antenna proper. ;)
     
  7. Kermit2

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    The 'near field' radiation is influenced by objects nearby. And this interaction also reflects back into the transmission output.

    Near field is defined as << than a wavelength
    Far field is >> than a wavelength.

    Leaving the range from 2 to 8 times the wavelength as undesirable for radiation output readings due to variations in the electric and magnetic fields that occur throughout that distance.

    If you need a guesstimate then use 50-100 times the antenna length as a minimum distance to start any RF field strength readings.

    With low power outputs you should still stay at least 10 wavelengths away to insure an acceptable level of accuracy in the field strength readings.
     
  8. thatoneguy

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    Feb 19, 2009
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    A bit of it is frequency dependent, once you get into the "microwave" areas, anyway, antennas and transmission lines are quite a bit different, closer to what you'd use to transmit light instead of radio.

    If you stay below that range, there is a lifetime or three in learning all the possible facets of RF Transmission. It's actually quite amazing how far the early radio pioneers got things going.

    Use caution when near high power RF, lethal voltages are usually everywhere in the area.

    Since I don' know what frequencies you are working with, NEVER look into the feedhorn of a satellite dish, if it happens to be a K-Band uplink, you'll be blind.
     
  9. ihaveaquestion

    Thread Starter Active Member

    May 1, 2009
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    Hi guys,

    I'm working in the 2.4GHz band... would access to things like a spectrum analyzer etc be useful for measurements?

    Also, is there anywhere that layouts out typical device antenna parameters/specifications?

    Thanks
     
  10. thatoneguy

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    That is a crowded band, Phones, Wi-Fi, toys, and more all use it.

    You'll need a big equipment budget if planning on making a breakthrough there.
     
  11. ihaveaquestion

    Thread Starter Active Member

    May 1, 2009
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    Could you elaborate more on what you mean regarding the equipment please?
     
  12. CDRIVE

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    And let's not forget FCC certification.;)
     
  13. ihaveaquestion

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    What kind of equipment 'thatoneguy'?
     
  14. ihaveaquestion

    Thread Starter Active Member

    May 1, 2009
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    Any help, guys?
     
  15. thatoneguy

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    Depending on what you want to do, the equipment varies.

    An oscilloscope for that range is near $20,000 or more.

    Network Analyzers, such as the Agilent E5070B are in the realm where rental is preferred over the 6 digit price tag. These are used to match impedances and generally know what is going on between transmitter and antenna.

    Spectrum Analyzers for that same band are also in the 5 digit range.

    That's what I meant by "Spendy". I guess if you are Verizon, it's not that bad and the cost of doing business. Most smaller companies try to get by on guessing and math, and rent in the final test phase.
     
  16. bertus

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  17. ihaveaquestion

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    May 1, 2009
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    thanks bertus... I did a 30-second scan of that page since I won't have time to read it carefully later today, but it certainly looks helpful!

    note to all: equipment is not an issue as I have access to all the things 'thatoneguy' mentioned
     
  18. Kermit2

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