antenna impedance matching
I m designing aan array of patch antenna. I have to match the impedance to 50 ohm for co axial cable. But my patch antenna impedance is 115 ohms!
Can anyone help me to match the impedance to 50 ohms?
add a quarter wave transformer at the input of your antenna with the impedance of 76 ohm.
Quarter wave transformer can match only resistive loads. For reactive loads most probably you need an LC matching network, and use a Smith chart software to find the values.
i aggreed with both replies. try this link
For first reply add 75 Ω quarter wave length coax cable to 50 Ω coax cable.
second :
it ll solve your problem
http://www.ece.osu.edu/~johnson/311/week5.pdf
If you want directly connect the coax to the patch you have to move the probe (i.e. coax) from the patch edge toward patch centre and find the best position to match coaxial to the patch.
Keep in mind that quarter wave matching has a limited bandwidth. How much is your bandwidth (in percentage of the carrier frequency)?
Moving the probe as mentioned in the above post (if possible) is your best bet for high bandwidth patch antennas.
As far as I could read from the question the antenna impedance is 115 ohm, not 115 +jX ohms, hence a real impedance.
So assuming this is a purely real impedance, use of a quarter wave transformer is very easy. For wider BW you can use multiple sections of a quarter wave transformers, but this of course increases the physical size.
you change input impadance matching on Patch. This way can good impadance matching
For most rectangular and circular patch antennas, you can adjust adjust the feed point to match the impedance below 200 Ohms.