This White Paper is about printed quarter wavelength printed monopole antenna for 2.45GHz. Printed Antennas are low cost and easy to fabricate in devices for short-range 2.4GHz applications.
The quarter wavelength printed monopole antenna can be tuned simply by slight changes in length of antenna PCB trace.
The length of the antenna trace which is presented in this paper for 2.4GHz is about 23 mm with 1.5 mm width using FR4 PCB.
λ/4 printed monopole antenna in a nRF24L01 module
See the full paper on Nordic Semiconductor website.