Antenna Polarization

Antenna polarization refers to the orientation of the electromagnetic field vector radiated by an antenna. It determines how a wave propagates and interacts with receiving antennas and environmental objects. Matching polarizations is essential for maximizing signal transmission efficiency and minimizing losses in wireless systems.

Definition and Concept

Polarization describes the trajectory of the electric field vector as the electromagnetic wave travels through space. It can be linear, circular, or elliptical, depending on how the field rotates or oscillates. Correct polarization alignment between transmitter and receiver improves signal strength and reduces interference.

Types of Polarization

• Linear Polarization:
  The electric field oscillates along a single axis.

  • Vertical Polarization: Field is perpendicular to the Earth’s surface; common in mobile and land communication.

  • Horizontal Polarization: Field is parallel to the Earth’s surface; used in terrestrial broadcasting.

• Circular Polarization:
  The electric field rotates in a helical pattern as the wave propagates.

  • Right-Hand Circular Polarization (RHCP): Clockwise rotation when viewed from behind the antenna.

  • Left-Hand Circular Polarization (LHCP): Counterclockwise rotation when viewed from behind the antenna.
    Used in satellite communication to minimize orientation-related losses.

• Elliptical Polarization:
  A general case combining linear and circular components. Applied in systems needing resilience to multipath or varying propagation conditions.

Polarization Loss Factor (PLF)

Polarization mismatch between transmitting and receiving antennas causes signal degradation. This loss is quantified using the Polarization Loss Factor (PLF):

PLF = |cos(θ)|²

Where θ is the angle between the polarization vectors of the two antennas.

• Perfect alignment (θ = 0°): PLF = 1 (no loss)

• Orthogonal polarizations (θ = 90°): PLF = 0 (theoretical infinite loss)

In practice, multipath propagation limits real-world losses to around 20–30 dB, even in severe mismatch cases.

Example: Polarization Mismatch

A vertically polarized mobile phone antenna aligned with a vertically polarized base station achieves optimal signal transmission. If the device is rotated 90°, creating a horizontal polarization, the theoretical loss is maximal. However, due to environmental reflections, the actual loss is usually limited to 20–30 dB.

Importance in Wireless Systems

Polarization impacts link quality, interference rejection, and spatial signal separation. It is a key parameter in:

• Mobile and land-based radio systems

• Satellite communications

• Radar and navigation systems

• Wireless infrastructure in multipath environments

Polarization diversity improves robustness by using multiple polarization orientations to mitigate fading. Cross-polarization discrimination enables better spectrum reuse in dense urban networks.

Typical use cases by polarization:

• Vertical Polarization: Mobile phones, handheld radios

• Horizontal Polarization: TV and FM radio broadcasting

• Circular Polarization: Satellite and GNSS systems