Using Dual Linear Polarization Antennas in Mobile Communication

Key Takeaways

• The combination of vertical and horizontal polarization introduces orthogonality, which forms a vertically/horizontally dual linear polarization antenna. 

• Vertical/horizontal dual-polarized antennas achieve the required beamwidth in the azimuthal plane, which is impractical when employing vertically polarized or horizontally polarized antennas. 

• Dual linear polarization antennas are used in mobile communication systems due to their wide bandwidth, low cross-polarization, high port isolation, low output correlation, increased channel capacity, and high polarization diversity.

The performance of a mobile communication system is heavily dependent on the antennas in its base station. The system’s performance can be improved by matching the polarization of its antennas. Dual linear polarization antennas are effective at utilizing polarization diversity and are often used in mobile communication base stations to enhance communication. In this article, we will explore the unique characteristics of these antennas and what makes them so valuable.

Dual Linear Polarization Antennas   

Dual linear polarization antennas constitute two orthogonal linear polarization. Orthogonal linear polarization indicates polarization fields that are 90° apart. Dual linear polarization antennas possess two linear polarization modes that are perpendicular to each other. The two linear polarization modes can be excited using two ports of the same antenna.

The type of polarization in dual linear polarization antennas can be either vertical, horizontal, or slant polarization. The combination of vertical and horizontal polarization introduces orthogonality and forms a vertically/horizontally dual linear polarization antenna. The other linear polarization that can be designed as dual linear polarization is slant polarization of +45° and -45°.

Compared to dipole antennas, dual linear polarized antennas offer low output correlation and high diversity gain. The other properties that make them appropriate for cellular base station applications are:

• Wide bandwidth
• Low cross-polarization 
• High port isolation 
• Increased channel capacity
• High polarization diversity

Vertically/Horizontally Dual Linear-Polarized Antennas

Vertically/horizontally dual linear-polarized antennas are commonly used in mobile communication base stations located in rural areas. Such antennas give higher isolation compared to +45°/-45° slant polarized antennas. Vertical/horizontal dual linear-polarized antennas can achieve the required beamwidth in the azimuthal plane, which is impractical when employing vertically polarized or horizontally polarized antennas. 

Construction

Most vertically/horizontally dual linear polarized antennas consist of two dipoles. The polarization of the dipoles gives the duality or orthogonality in dual-polarized antennas. One dipole supports vertical polarization and the other supports horizontal polarization. A reflector can be used to shape the half-power beamwidths for both vertical and horizontal polarization. Any desired angle can be achieved in the azimuthal plane by using the dual linear polarization antenna and its reflector. 

Dual Linear Polarized Antennas for Multiple-Input Multiple-Output

Dual linear polarized antennas are suitable for the concept of multiple-input multiple-output (MIMO), where several antennas are used within a system for transmitting and receiving signals. The combination of polarization plays a major role in implementing the MIMO concept.

Orthogonality helps by sending two sets of information over a long distance using a dual linear polarization antenna. The 90° separation in dual linear polarized antennas prevents the two information sequences from getting mixed up. Dual linear polarization is constructive in increasing the channel capacity and multiplexing gain in MIMO systems.

Dual Polarized Antenna Arrays in Radar Applications

In radar applications, data ambiguity during the post-processing period is not accepted; avoiding ambiguity antennas with high port isolation and low cross-polarization characteristics is essential. Dual polarization antennas can increase the performance and efficiency of radar communications, as they can be designed to have a low profile and be lightweight while still being cost-effective. Dual polarization antenna arrays fabricated from microstrip antennas are recommended for radar applications.

Dual linear polarization antennas operate in two modes in radar applications. The first mode is an alternate single polarized operation. Say, for example, the vertically/horizontally polarized dual polarized antenna is made to operate alternatively as a vertically polarized antenna and horizontally polarized antenna. In the second mode, it operates as a hybrid antenna where both the vertical and horizontal polarization are used together.  The cross-polarization levels of the dual linear polarized antennas are kept low to minimize errors.

Dual linear polarization antennas are used for mobile communication systems due to their wide bandwidth, low cross-polarization, high port isolation, low output correlation, increased channel capacity, and high polarization diversity. Cadence software helps engineers design and optimize antennas or arrays with single or dual polarization.

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