Does a 1/4 wave antenna need a ground plane? Answer: Yes.
All 1/4 wave antennas work best if they are installed in the center of a metal ground plane with at least 1/4 wave length radius (1/2 wave length diameter: ~6 inches for 900Mhz and ~3 inches for 2.4Ghz); larger is better.
The antenna can still work on a smaller ground plane but the efficiency will be reduced.
Note that the 1/4 wave wire antenna available on the RF modules is not perfectly efficient because it uses the ground plane of the Printed Circuit Board (PCB) which extends only in one direction. However, any testing should indicate that it works quite well in many applications.
The antenna should be perpendicular to the ground plane (pointing straight up). Bending the antenna over will attenuate the signal and could reduce the range of the radio by more than half.
Aug 23, 2017