The design of antennas matching most of the requirements listed in Table I, is quite challenging as a number of
specifications on the near-field properties are added to conventional requirements for far-field antennas (gain, back
radiation, input impedance, far-field pattern and polarization). For example, travelling wave antennas are a natural
choice to get an almost uniform field on the antenna surface but it is not easy to satisfy requirements on field
polarization and antenna gain.
3. Modular