_{The ground plane of the GSM antenna plays a significant role in its operation.}

Excitation of currents in the PIFA causes excitation of currents in the ground plane. The resulting electromagnetic field is formed by the interaction of the PIFA and an ‘image’ of itself below the ground plane.
Its behaviour as a perfect energy reflector is consistent only when the ground plane is infinite or very much arger in its dimensions than the monopole itself. In practice the ground plane area is of comparable dimensions
to the monopole and forms the ‘image antenna’ which is one half of the dipole.

The antenna/ground plane combination will behave as an asymmetric dipole, the differences in current distribution on the two-dipole arms being responsible for some distortion of the radiation pattern

GSM antenna Ground Plane Size

In general, the required PCB ground plane length should be at least one quarter (λ/4) of the operating wavelength.

• If the ground plane is much longer than λ/4, the radiation patterns will become increasingly ‘multilobed’.
• On the other hand, if the ground plane is significantly smaller than λ/4, then tuning becomes increasingly difficult and the overall performance degrades.
• The optimum location of the PIFA in order to achieve an omni-directional far-field pattern and 50Ω impedance match was found to be close to the edge of the Printed Circuit Board