Wavelength and matching components.

[Rajinder]

Hi all,
I was trying to find the difference of wavelength of 868MHz compared to 928MHz.
Using a online calculator i found that the wavelength if 868MHz is 34.5cm and 928MHz is 33cm.
If i wanted to use a printed antenna, would i simply make the length of the track 33cm? What hapoens to matching components for 50R matchibg, will they change for a 928MHz compared to 868MHz? Finally, please could you explain what quarter wavelength means with resoect to 33cm, is it 33cm/4? Why is this important?
Thanks in advance.

 

[davenn]

868MHz is 34.5cm and 928MHz is 33cm.

34.5 yes 33 no should be 32.3

would i simply make the length of the track 33cm?

no. you never use a full wave antenna plus those figures above don't take into account the velocity factor of the antenna on the board

What hapoens to matching components for 50R matchibg

matching at the feedpoint is another whole different ball game

Finally, please could you explain what quarter wavelength means with resoect to 33cm, is it 33cm/4? Why is this important?

A 3/4 way is the usual length .... yes 34.5 /4 or 32.3 / 4 BUT as I previously said, you still have to find out what the velocity factor will be

so for an example the Vf = .65 then you will have

34.5 / 4 = 8.625cm
then
8.625 x .65 = 5.60cm as a final tuned length

Why is this important?

because if you do di it like that, it will never tune up on the correct frequency


time for you to go do some searching and study of PCB antennas


Dave

 

[Harald Kapp]

do some searching and study of PCB antenna

e.g. these:

• Cypress
• Freescale
• ...