Antenna polarization refers to the orientation of the electric field of the radiated electromagnetic wave. This field determines how antennas transmit and receive signals. The polarization can be linear, circular, or elliptical depending on the antenna design.
First, linear polarization has a constant electric field direction. It can be vertical or horizontal relative to the Earth’s surface. Antennas with mismatched polarization lose signal strength. Therefore, matching the transmitter and receiver polarization is essential. Next, circular polarization rotates the electric field as the wave travels. It can be right-hand or left-hand circular, depending on the rotation direction. This type resists signal degradation from reflections or multipath effects. GNSS satellites, for example, use right-hand circular polarization. Then, elliptical polarization combines linear and circular characteristics. The electric field traces an ellipse rather than a circle or straight line. It results from unequal signal amplitudes in two perpendicular components.
Polarization affects signal strength, quality, and reliability. Proper polarization ensures efficient energy transfer between transmitting and receiving antennas. When polarization differs, losses called polarization mismatch occur. These losses can reach several decibels in severe cases. Additionally, environmental factors influence polarization. Reflections from buildings or surfaces can alter the wave’s orientation. As a result, signal reception may degrade or fluctuate. Circular polarization helps reduce such effects in mobile or dynamic environments. Moreover, antenna orientation determines polarization. Rotating it changes its polarization plane. This tools must be aligned properly during installation. This alignment is crucial for communication systems, radars, and navigation receivers.
Polarization diversity can improve system performance. It uses multiple antennas with different polarizations. This setup increases signal reliability in challenging conditions.
What is the optimal choice for GNSS systems?
GNSS systems typically use right-hand circular polarization (RHCP) antennas. The main reason is that circular polarization better tolerates physical orientation mismatches. For example, if we transmit with a vertically oriented whip antenna (vertical polarization) and receive with the same type, the signal is strong when both antennas align vertically. However, if the receive antenna rotates 90 degrees to horizontal polarization, signal strength drops by 20 decibels or more. This happens because a horizontally polarized antenna poorly receives a vertically polarized signal.
A circularly polarized antenna combines two antennas: one horizontally polarized and one vertically polarized. Their outputs are combined with a 90-degree phase shift. The direction of this phase shift determines whether the antenna produces right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP).