**6. Conclusions**

In this chapter, a modulation scheme which effectively utilizes the polarization of the radio wave is introduced. The polarization modulation gives a new degree of freedom in the modulation adding to the phase, amplitude, and frequency. Antenna technology is a key to achieve the polarization modulation communication systems. Basics of the polarization modulation and several examples of the polarization agile antennas are introduced. Furthermore, the detection of polarizations and a polarization discrimination antenna are also explained. The concept utilizing polarizations gives new vistas to the next-generation advanced wireless communication systems.
