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**56**

Conventional wireless communication systems use amplitude, frequency, and phase of the carrier wave to carry information. However, actual radio waves also have vector parameters, such as polarization and propagation direction. In this chapter, a modulation scheme using polarizations is explained. The polarization modulation provides an additional degree of freedom for the modulation of the carrier waves. Furthermore, the polarization modulation is suitable to realize simple transceivers using RF signal processing. Antennas are the most important key parts of the polarization modulation systems. Polarization agile antennas, active integrated array antenna which integrates an oscillator and modulators, and polarization discrimination antenna are also introduced.

**Keywords:** polarization, antenna, polarization modulation communication, polarization discrimination, active integrated array antenna, RF signal processing
