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I am reading about antenna design and have a few questions which I could not get clarified.

I read about "Stubs". I got to know that Stubs are used for impedance matching of an Antenna either by leaving it as an open circuit in one end or as an short circuit.

Question - How to find the input impedance of an Antenna of a particular length? Is there any method and how to calculate the stub length? Is there any formula?

Would really help me if someone could provide an example for calculating the input impedance of the antenna and the stub length for impedance matching

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Question - How to find the input impedance of an Antenna of a particular length?

This is for a monopole but there are equivalent diagrams to be found for other antennas such as dipoles etc..

enter image description here

You've seen this before in a question I answered here.

Is there any method and how to calculate the stub length? Is there any formula?

This is the formula that folk use: -

enter image description here

  • \$V_P\$ is velocity of propagation and is around 0.7c for your average coax cable.

Picture taken from my answer here.

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  • \$\begingroup\$ Thank you for your answer and the formula. If you could provide an example with numbers & calculation relating to the signal frequency, wavelength and finally to match the impedance,your stub length calculation, it would be really helpful for my understanding \$\endgroup\$
    – Newbie
    May 16 '20 at 15:45
  • \$\begingroup\$ I fully recommend that you use something like excel and try it out for yourself. This can be compared with many instances of calculations like this to be found on-line. \$\endgroup\$
    – Andy aka
    May 16 '20 at 15:48
  • \$\begingroup\$ There is this spreadsheet you can download. \$\endgroup\$
    – Andy aka
    May 16 '20 at 15:54
  • \$\begingroup\$ Thank you for the answer. But just I realized that, suppose, I want to design a custom made antenna say, for transmitting a wavelength of a signal, how to find the impedance of the antenna then? \$\endgroup\$
    – Newbie
    May 16 '20 at 17:06
  • \$\begingroup\$ You need to match the antenna's design with a standard antenna type and hope that you can find the impedance on-line somewhere. Deriving the impedance of a bespoke antenna is not that easy. \$\endgroup\$
    – Andy aka
    May 16 '20 at 17:19

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