What if I don’t have enough room on my board for the recommended antenna ground plane?
Quarter-wave antennas are only half of the antenna structure. The ground plane, PCB layout and implementation are all critical to proper antenna performance, especially for embedded antennas.
If the ground plane is smaller than what the antenna was designed with, the resonant frequency will shift higher. The frequency can be shifted down using a PI network between the radio and the antenna, but only to a certain extent.  These are generally used for fine tuning an antenna to the board.  If the shift is very large, it may be possible to use an antenna at a lower frequency and have it get pulled into the correct band.
Depending on the application, it could also be possible to design a custom antenna that works with the specific product.
Both of these options are not ideal solutions.  It is best to pay close attention to the layout and implementation requirements of the desired antenna.