**1. Introduction**

Nowadays, consumer wireless communication systems like a cell phone and wireless local area network (WLAN) are widely used in the world, and they have become an indispensable part of our daily lives. Much higher data rate and higher capacity are strongly required as well as high-frequency utilization efficiency. To meet the requirements, many advanced technologies such as multiple-input, multiple-output (MIMO) and orthogonal frequency-division multiple access (OFDMA) have been developed.

In the classical wireless communication systems, only the time domain parameters such as amplitude, frequency, and phase are used to modulate the carrier wave. However, actual radio waves are vector quantity, and they have spatial parameters like a polarization and direction of propagation. In the next-generation wireless communication systems, utilization of the spatial parameters is essential to achieve higher data rates, larger capacity, and higher-frequency utilization efficiency since the spatial parameters have not been effectively used in traditional wireless communication systems. Recent advanced wireless communication systems utilize a part of these spatial parameters. MIMO and polarimetric radar as well as the traditional polarization diversity are the examples. The massive MIMO technology, which is expected to be employed in the fifth-generation (5G) mobile communication system, is another example. However, these systems require power-consuming digital signal processing. Therefore, RF signal processing technology utilizing the characteristics of the radio wave is expected to realize advanced transceiver module for many wireless applications. To achieve wireless communication systems which effectively utilize the spatial parameters, antenna technology based on the RF signal processing is one of the most important technologies.

In this chapter, the basic concept of the wireless communication system employing a polarization modulation scheme and antenna technology based on the RF signal processing is introduced.

#### **2. Polarization modulation communication**

As classic wireless communication systems use the amplitude, frequency, and phase of the carrier wave to carry information, the radio wave is treated as a scalar signal as follows:

$$s(t) = A \sin\left(2\pi ft + \varphi\right) \tag{1}$$

where *A*, *f*, and φ are the amplitude, frequency, and phase of the carrier wave, respectively. However, the actual radio wave is a vector signal. For example, the electric field of the radio wave is given by

$$E(r,t) = E\_0 \sin\left(2\pi ft - k \cdot r + \Phi\right) \tag{2}$$

where *E*0 is the vector amplitude that shows the direction of the electric field, i.e., the polarization, and *k* is the wave number vector specifying the direction of propagation. Even though the spatial parameters have not been effectively used in classic wireless communication systems, these spatial vector parameters have the potential to realize new wireless systems.

**Figure 1** shows the basic concept of the wireless communications using the polarization modulation. The transmitter (TX) antenna radiates radio wave while changing its polarizations between +45° and −45° according to the input binary data. At the receiver (RX), the polarization of the radio wave is detected, and the binary data are recovered. As the binary data can be transferred using the orthogonal polarizations as shown in this figure, the polarization can be used as an additional modulation parameter.

**Figure 2** shows a vector diagram of the polarization modulated signal. The ±45° polarizations can be decomposed into the *x* and *y* components as shown by the red and blue arrows, respectively. As only the *y* component is changed according to the data, the ±45° polarization modulated signal is equivalent to the composition of a binary phase shift keying (BPSK) signal and carrier wave. Therefore, the polarization modulated signals can be generated by simply inverting one of the orthogonal polarizations. As the phase inversion of the signal is easily achieved in RF, the polarization modulation scheme is suitable for RF signal processing and realizing a simple transmitter. The polarization modulation also provides great benefits to receivers. As the carrier wave component is included in the polarization modulated signal and it is transmitted to the receiver, the receiver does not require

**59**

*Polarization Modulation*

*DOI: http://dx.doi.org/10.5772/intechopen.87985*

receiver configuration is also applicable.

*Vector diagram of the polarization modulation.*

**3. Basics of polarization agile antennas**

polarized wave when φ = ±*π*/2 and *Ex* = *Ey*.

circular polarizations (RHCP and LHCP).

switching the horizontal and vertical polarizations.

expressed as follows:

**Figure 2.**

carrier recovery circuits, and the phase noise of the local oscillator does not affect the performance of the communication system. The detection in RF with simple

Antennas are one of the key elements to achieve polarization modulation systems because polarizations are generated in antennas. The antennas used in the polarization modulation systems have to switch their polarizations according to the

Basically, any polarizations can be expressed in the sum of two orthogonal polarizations. For example, the electric field propagating along the *z*-axis can be

*E*(*z*,*t*) = *ixEx* sin(2*ft* − *kz*) + *iyEy* sin(2*ft* − *kz* + φ) (3)

where *ix*, *iy*, *Ex*, *Ey*, and φ are the unit vectors of the *x* and *y* direction, the amplitude of *x* and *y* component of the electric field, and the phase difference between the components, respectively. Eq. (3) expresses elliptical circularly polarized waves in general. When the electric field has only the *x* or *y* component, the radio wave becomes a linearly polarized wave. When φ = 0 or *π*, the radio wave also becomes a linearly polarized wave. On the other hand, the radio wave becomes a circularly

**Figure 3** shows basic configurations of several types of polarization agile antennas. The antenna shown in **Figure 3a** is a linear polarization switchable antenna, and it consists of a switch and dual-polarized antenna which radiates horizontal and vertical polarizations. The polarization modulated signals can be excited by simply

The antenna shown in **Figure 3b** is a circular polarization switchable antenna. A 90-degree hybrid is placed between a switch and dual-polarized antenna. As the input signal fed to one of the input ports of the hybrid is divided into two signals with the phase difference of *π*/2, a circularly polarized wave is excited. By switching the input ports of the hybrid, the antenna switches right-handed and left-handed

input data. Therefore, polarization agile antennas are required [1, 2].

**Figure 1.** *Basic concept of the polarization modulation communications.*

*Modulation in Electronics and Telecommunications*

**2. Polarization modulation communication**

electric field of the radio wave is given by

potential to realize new wireless systems.

changing its polarizations between +45°

*Basic concept of the polarization modulation communications.*

tional modulation parameter.

to the data, the ±45°

signal processing is introduced.

signal as follows:

In this chapter, the basic concept of the wireless communication system employ-

As classic wireless communication systems use the amplitude, frequency, and phase of the carrier wave to carry information, the radio wave is treated as a scalar

*s*(*t*) = *A* sin(2*ft* + φ) (1)

where *A*, *f*, and φ are the amplitude, frequency, and phase of the carrier wave, respectively. However, the actual radio wave is a vector signal. For example, the

*E*(*r*, *t*) = *E*<sup>0</sup> sin(2*ft* − *k* ∙ *r* + φ) (2)

where *E*0 is the vector amplitude that shows the direction of the electric field, i.e., the polarization, and *k* is the wave number vector specifying the direction of propagation. Even though the spatial parameters have not been effectively used in classic wireless communication systems, these spatial vector parameters have the

**Figure 1** shows the basic concept of the wireless communications using the polarization modulation. The transmitter (TX) antenna radiates radio wave while

data. At the receiver (RX), the polarization of the radio wave is detected, and the binary data are recovered. As the binary data can be transferred using the orthogonal polarizations as shown in this figure, the polarization can be used as an addi-

**Figure 2** shows a vector diagram of the polarization modulated signal. The

tion of a binary phase shift keying (BPSK) signal and carrier wave. Therefore, the polarization modulated signals can be generated by simply inverting one of the orthogonal polarizations. As the phase inversion of the signal is easily achieved in RF, the polarization modulation scheme is suitable for RF signal processing and realizing a simple transmitter. The polarization modulation also provides great benefits to receivers. As the carrier wave component is included in the polarization modulated signal and it is transmitted to the receiver, the receiver does not require

 polarizations can be decomposed into the *x* and *y* components as shown by the red and blue arrows, respectively. As only the *y* component is changed according

polarization modulated signal is equivalent to the composi-

and −45°

according to the input binary

ing a polarization modulation scheme and antenna technology based on the RF

**58**

**Figure 1.**

±45°

**Figure 2.** *Vector diagram of the polarization modulation.*

carrier recovery circuits, and the phase noise of the local oscillator does not affect the performance of the communication system. The detection in RF with simple receiver configuration is also applicable.

Antennas are one of the key elements to achieve polarization modulation systems because polarizations are generated in antennas. The antennas used in the polarization modulation systems have to switch their polarizations according to the input data. Therefore, polarization agile antennas are required [1, 2].
