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???
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.
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.
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.