**4. Practical implementation of polarization agile antenna**

In this section, practical implementations of polarization agile antennas employing microstrip antenna elements and planar microwave circuits are introduced.

#### **4.1 Linear polarization switchable antenna**

**Figure 4** shows a practical implementation of a polarization agile antenna which switches two orthogonal linear polarizations. The configuration is similar to the antenna shown in **Figure 3a**, and it consists of a dual-polarized microstrip array antenna and single-pole double-throw (SPDT) switch [3, 4].

**61**

excites the +45°

**Figure 4.**

the same feed structure.

also demonstrated in [6].

*Polarization Modulation*

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

When the signal is fed to the antenna from A1, the signal propagates along the microstrip line as shown by the red line. Here, the signal from A1 is divided into two inphase signals on the slot line. Each signal on the slot line is divided again into two antiphase signals on the microstrip line. Therefore, the signal fed from A1

input impedance of the array is the same as the input impedance of each microstrip antenna element as the feed network is constructed with a parallel branch and series branch. Therefore, larger array antennas can be easily achieved by simply repeating

The SPDT switch is constructed with a two-wavelength slot ring, four switching diodes D1–D4, and two half-wavelength open-end microstrip lines. Three microstrip lines are coupled for input and output. The switching diodes are placed over the slot ring with a quarter-wavelength interval. When a positive voltage is applied to the inner conductor of the slot ring, the diodes D1 and D2 become *off*, and D3 and D4 become *on*. Then the signal fed from Port S1 propagates to Port S2 because the *on*-state diodes make short circuits on the slot ring. The half-wavelength open-end microstrip lines also make short circuits on the slot ring. The slot lines from output ports to the open-end microstrip lines act as open circuits because the distance from the diode D1 or D2 to the open-end microstrip line is a quarter wavelength. Similarly, when a negative voltage is applied to the inner conductor of the slot ring, the signal fed from Port S1 emerges at Port S3. Hence, the polarization can be switched by changing the polarity of the voltage applied to the inner conductor of the slot ring. A circular polarization switchable antenna shown in **Figure 3b** can be realized by placing a 90-degree hybrid between the antenna and switch [5]. A polarization agile antenna which switches four polarizations using phase shifters and magic-T is

elements. Similarly, the signal fed from A2 excites the −45°

*Structure of a linear polarization switchable antenna [3].*



The dual-polarized array antenna has four microstrip antenna elements and employs a feed network using a combination of microstrip lines and slot lines.

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

*Modulation in Electronics and Telecommunications*

**Figure 3c** shows a basic configuration of a polarization agile antenna which

*Basic configurations of polarization agile antenna. (a) Linear polarization switchable antenna; (b) circular* 

antenna consists of a phase shifter and dual-polarized antenna. When the phase

In this section, practical implementations of polarization agile antennas employ-

**Figure 4** shows a practical implementation of a polarization agile antenna which switches two orthogonal linear polarizations. The configuration is similar to the antenna shown in **Figure 3a**, and it consists of a dual-polarized microstrip array

The dual-polarized array antenna has four microstrip antenna elements and employs a feed network using a combination of microstrip lines and slot lines.

ing microstrip antenna elements and planar microwave circuits are introduced.

linear polarizations, RHCP and LHCP. The

linear polarizations. Furthermore,

switches four polarizations of ±45°

**Figure 3.**

shift value φ = 0 or *π*, the antenna excites ±45°

**4.1 Linear polarization switchable antenna**

when φ = ±*π*/2, the antenna excites circular polarizations.

antenna and single-pole double-throw (SPDT) switch [3, 4].

**4. Practical implementation of polarization agile antenna**

*polarization switchable antenna and (c) linear/circular polarization switchable antenna.*

**60**

**Figure 4.** *Structure of a linear polarization switchable antenna [3].*

When the signal is fed to the antenna from A1, the signal propagates along the microstrip line as shown by the red line. Here, the signal from A1 is divided into two inphase signals on the slot line. Each signal on the slot line is divided again into two antiphase signals on the microstrip line. Therefore, the signal fed from A1 excites the +45° -polarized wave as shown by the arrows on the microstrip antenna elements. Similarly, the signal fed from A2 excites the −45° -polarized wave. The input impedance of the array is the same as the input impedance of each microstrip antenna element as the feed network is constructed with a parallel branch and series branch. Therefore, larger array antennas can be easily achieved by simply repeating the same feed structure.

The SPDT switch is constructed with a two-wavelength slot ring, four switching diodes D1–D4, and two half-wavelength open-end microstrip lines. Three microstrip lines are coupled for input and output. The switching diodes are placed over the slot ring with a quarter-wavelength interval. When a positive voltage is applied to the inner conductor of the slot ring, the diodes D1 and D2 become *off*, and D3 and D4 become *on*. Then the signal fed from Port S1 propagates to Port S2 because the *on*-state diodes make short circuits on the slot ring. The half-wavelength open-end microstrip lines also make short circuits on the slot ring. The slot lines from output ports to the open-end microstrip lines act as open circuits because the distance from the diode D1 or D2 to the open-end microstrip line is a quarter wavelength. Similarly, when a negative voltage is applied to the inner conductor of the slot ring, the signal fed from Port S1 emerges at Port S3. Hence, the polarization can be switched by changing the polarity of the voltage applied to the inner conductor of the slot ring.

A circular polarization switchable antenna shown in **Figure 3b** can be realized by placing a 90-degree hybrid between the antenna and switch [5]. A polarization agile antenna which switches four polarizations using phase shifters and magic-T is also demonstrated in [6].

#### **4.2 Active integrated array antenna for polarization modulation**

Active integrated antennas integrate active devices such as transistors or Gunn diodes to build in RF signal processing capabilities in an antenna [7, 8]. There are several types of the active integrated antennas. For example, antennas integrating a power amplifier, oscillator, voltage-controlled oscillator (VCO), or injectionlocked oscillator have been successfully demonstrated. Furthermore, a frequencyswitchable antenna and radiation pattern-switchable antenna have been also proposed.

In this section, an active integrated array antenna which has oscillation and polarization modulation functionalities is introduced. The active integrated array antennas are suitable for the polarization modulation because polarization switching can be realized by simply inverting the phase of one of the two orthogonal polarizations. The active integrated array antenna using an RF signal processing technique achieves a simple transmitter module.

**Figure 5** shows a basic block diagram of the active integrated array antenna [9]. In this configuration, an oscillator and two PSK modulators are integrated with two pairs of antenna elements for horizontal and vertical polarization. The oscillator has four output ports and feeds RF signals to the antenna elements. The PSK modulators invert the phase of the RF signals for the vertical polarization. Hence, ±45° linear polarization switching can be realized.

**Figure 6** shows a practical implementation of the active integrated array antenna [10]. A four-port Gunn oscillator with slog-ring resonator is located at the center of the array antenna. Two PSK modulators using a slot ring and PIN diodes are inserted in the feed line for the vertical polarization. The array antenna consists of 12 antenna elements and feed network using microstrip lines and slot lines.

The Gunn oscillator consists of two Gunn diodes mounted on a two-wavelength slot ring. Four microstrip lines are coupled to the resonator with a half-wavelength interval. Therefore, the output ports O1 and O2 (O3 and O4) generate inphase signals, and the phases of O1 and O3 (O2 and O4) become antiphase with each other.

**63**

**Figure 6.**

result, polarization switching is achieved.

*Structure of the active integrated array antenna [10].*

*Polarization Modulation*

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

The half-wavelength open-end microstrip lines just above the Gunn diodes stabilize the resonant field in the slot-ring resonator. The bias voltage of the Gunn diodes is

The PSK modulator consists of a half-wavelength slot ring and two PIN diodes. A microstrip line and slot line are connected to the slot ring for input and output. The two PIN diodes are mounted at the junction of the slot ring and slot line, and the directions of the PIN diodes are opposite to each other. When positive voltage is applied to the inner conductor of the slot ring, diode D1 becomes *off* and D2 becomes *on*. Therefore, a signal fed to Port M1 propagates along the left half of the slot ring and goes to Port M2. Similarly, when negative voltage is applied, the signal fed to Port M1 propagates along the right half of the slot ring. With this operation, the phase of the signal appeared at Port M2 is inverted by the applied voltage. As a

applied between the inner and outer conductors of the slot-ring resonator.

**Figure 5.** *Basic block diagram of the active integrated array antenna [9].*

*Modulation in Electronics and Telecommunications*

technique achieves a simple transmitter module.

linear polarization switching can be realized.

*Basic block diagram of the active integrated array antenna [9].*

proposed.

**4.2 Active integrated array antenna for polarization modulation**

Active integrated antennas integrate active devices such as transistors or Gunn diodes to build in RF signal processing capabilities in an antenna [7, 8]. There are several types of the active integrated antennas. For example, antennas integrating a power amplifier, oscillator, voltage-controlled oscillator (VCO), or injectionlocked oscillator have been successfully demonstrated. Furthermore, a frequencyswitchable antenna and radiation pattern-switchable antenna have been also

In this section, an active integrated array antenna which has oscillation and polarization modulation functionalities is introduced. The active integrated array antennas are suitable for the polarization modulation because polarization switching can be realized by simply inverting the phase of one of the two orthogonal polarizations. The active integrated array antenna using an RF signal processing

**Figure 5** shows a basic block diagram of the active integrated array antenna [9]. In this configuration, an oscillator and two PSK modulators are integrated with two pairs of antenna elements for horizontal and vertical polarization. The oscillator has four output ports and feeds RF signals to the antenna elements. The PSK modulators invert the phase of the RF signals for the vertical polarization. Hence, ±45°

The Gunn oscillator consists of two Gunn diodes mounted on a two-wavelength slot ring. Four microstrip lines are coupled to the resonator with a half-wavelength interval. Therefore, the output ports O1 and O2 (O3 and O4) generate inphase signals, and the phases of O1 and O3 (O2 and O4) become antiphase with each other.

**Figure 6** shows a practical implementation of the active integrated array antenna [10]. A four-port Gunn oscillator with slog-ring resonator is located at the center of the array antenna. Two PSK modulators using a slot ring and PIN diodes are inserted in the feed line for the vertical polarization. The array antenna consists of 12 antenna elements and feed network using microstrip lines and slot lines.

**62**

**Figure 5.**

**Figure 6.** *Structure of the active integrated array antenna [10].*

The half-wavelength open-end microstrip lines just above the Gunn diodes stabilize the resonant field in the slot-ring resonator. The bias voltage of the Gunn diodes is applied between the inner and outer conductors of the slot-ring resonator.

The PSK modulator consists of a half-wavelength slot ring and two PIN diodes. A microstrip line and slot line are connected to the slot ring for input and output. The two PIN diodes are mounted at the junction of the slot ring and slot line, and the directions of the PIN diodes are opposite to each other. When positive voltage is applied to the inner conductor of the slot ring, diode D1 becomes *off* and D2 becomes *on*. Therefore, a signal fed to Port M1 propagates along the left half of the slot ring and goes to Port M2. Similarly, when negative voltage is applied, the signal fed to Port M1 propagates along the right half of the slot ring. With this operation, the phase of the signal appeared at Port M2 is inverted by the applied voltage. As a result, polarization switching is achieved.
