which steps to be cared on designing the inside antenna ?

which steps to be cared on designing the inside antenna of mobile phone? How to measure the peformance for inside antenna , is it the same way as the outside antenna?

Today there are four leading antenna architectures that are commonly used in embedded applications (internal to the mobile): microstrip, patch, Planar Inverted 'F' Antenna (PIFA) and Meander Line Antenna (MLA).

For a while I am using PIFA for multi-band mobile system.

PIFAs make good embedded antennas in that they exhibit a somewhat omnidirectional pattern and can be made to radiate in more than one frequency band. The omnidirectional pattern is not as good as a top-placed Helix for example, but is a good compromise.

Is no difference in measuring radiated performances, between internal or external antennas.

These are some Antenna-Designer issues.
From a System-Engineer point of view, internal (embedded) antennas can give more troubles.
Definitely you will get more receiver desens using embedded antenna compare to external.
Radiated harmonics could be higher and also some parameters like phase-error could be affected (VCO interaction). To minimize all of this you have to have a good ground shield between antenna and main board, but this will affect somehow the omnidirectionality

In the file attached there is an example for designing a microstrip patch antenna for a mobil phone.