You only provided information about the feedline. The basic idea is your antenna impedance has to match the impedance of the CPW. It's not possible to help with this without information about the type of antenna you're designing.
You can also try with ESPAR antenna. Its passive antenna can be terminated by variable reactance also try with reducing the distance between two antenna elements more than half wavelength. During designing understand the correlation concept as well. I hope you will get better results which will be able to get the desired results