hi,
i am new to Microwave engineering, but i can tell you this much about microstips
microstip line is just planar microwave transmission line, it can be easily integrated with other passive and active microwave devices. they are widely used in microwave or Antenna applications. i have seen N-element Linear array Antenna for using microstip configuration for RADIATION. you can also realize Directional couplers/ Filters using this, but power handling will be less.
I think PIFA type of antenna are used in mobile phones.