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Whats the input impedance of λ/4 whipe antennas ?

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ahmad_abdulghany

ahmad_abdulghany

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Wire antenna problem

Hello all,
I decided to use λ/4 whipe antenna for my Tx/Rx at 100MHz, what's the input impedance of these antennas to consider while matching?
Thanks in advance,
Ahmad,
 

Re: Wire antenna problem

Antenna Impedance
Technically, antenna impedance is the ratio at any given point in the antenna of voltage to current at that point. Depending upon height above ground, the influence of surrounding objects and other factors, our quarter wave antenna with a near perfect ground exhibits a nominal input impedance of around 36 ohms. A half wave dipole antenna is nominally 75 ohms while a half wave folded dipole antenna is nominally 300 ohms. The two previous examples indicate why we have 75 ohm coaxial cable and 300 ohm ribbon line for TV antennas.

A quarter wave antenna with drooping quarter wave radials exhibits a nominal 50 ohms impedance, one reason for the existence of 50 ohm coaxial cable.
Click to expand...

Quoted from:
https://www.electronics-tutorials.com/antennas/antenna-basics.htm

Regards,
IanP
 
Re: Wire antenna problem

Hello IanP :)
Thanks for reply...
I have anothre question, how can i model the infinite ground plane,although the PCB diminsions is very small compared to antenna length?
Also, what are effects of increasing/decreasing the length more than λ/4?

Thanks alot in advance,
Ahmad,
 

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