Dipole Antenna Polarization

Key Takeaways

• Dipole antenna polarization influences the transmission of RF signals. Co-polarized antennas, with matched polarizations, ensure optimal power transmission, while cross-polarized antennas, with opposite polarizations, result in signal loss.

• Antenna polarization can mainly be linear, circular, or elliptical. Linear polarization is the most common, while circular and elliptical polarizations offer advantages in maintaining signal reception regardless of alignment.

• A dipole antenna can be made with different polarizations through its construction. Linear polarization is inherent in a standard dipole antenna, while circular polarization is achieved with crossed dipole structures like the turnstile antenna.  

The polarization of an antenna is the orientation of the electric field it propagates or receives. In this case, it’s linearly polarized.

In all antennas including dipole antennas, polarization is a determining factor in the optimal transmission of power across an RF signal. The polarization of an antenna is the orientation of the electric field plane generated by the antenna as energy propagates from it.  Antennas that are cross-polarized, meaning the polarization of the transmitting antenna is the opposite polarization relative to the receiving antenna, won't receive any of the incoming signal. Inversely, antennas that are co-polarized, meaning the polarization of the antennas is matched, will receive the full power transmission of a RF signal. 

Among antenna varieties, the dipole antenna is the most basic and widely used. Dipole antenna polarization can be achieved in three main ways: linear, circular and elliptical polarization. 

Types of Dipole Antenna Polarization

*Axial ratio is the ratio of the orthogonal components in a polarized wave. 

Dipole Antenna Construction for Polarization Types

A standard dipole antenna is constructed with two identical conductive elements, such as metal wires or rods, parallel to each other. These elements are fed by a current source that oscillates on the rods, creating an electromagnetic field that is propagated through space. Variations of dipole antennas are constructed in different ways to achieve different kinds of polarization. 

Linear Polarization

A dipole antenna is inherently linearly polarized. The mounting of the antenna will determine the orientation of the polarization. A dipole antenna radiates broadside, meaning that the energy is transmitted along the direction perpendicular to the rods of the dipole. In the diagram below that is the direction facing into the plane of the screen. 

Dipole antenna diagram showing the rods and source. Radiates into the screen (broadside).

Linearly polarized antennas are preferred for applications in point-to-point transmission because of their straightforward functionality and ease of fabrication for devices. 

• Orientation is dependent on the environment where the antenna will be mounted; for example, a vertically polarized antenna is more favorable for radio towers
• Horizontal polarization is favorable to multi-element array antennas. 
• Vertically polarized antennas tend to be more favorable for ground wave propagation, because their radiation angle — the deviation from the initial height where the signal is transmitted,  is lower than that of horizontally polarized waves. 

Circular and Elliptical Dipole Antenna Polarization

The most basic construction of circularly polarized dipole antennas is made with a crossed dipole structure or turnstile antenna. It consists of two identical dipole antennas mounted on top of each other perpendicularly. In the axial mode of operation, currents feeding each singular dipole antenna are 90° out of phase with respect to each other, giving the quadrature rotation that characterizes CP.  

In the axial mode, signals are radiated from the axis perpendicular to the plane formed by both dipole antennas, as opposed to the normal mode where each dipole antenna individually radiates broadside. This functionality means that the antenna is dual polarized. The antenna propagates in RHCP in one direction perpendicular to the plane of the turnstile antenna and propagates in LHCP in the opposite direction

Crossed dipole antennas can emit and receive both CP and LP signals.

Circular and elliptically polarized antennas are advantageous over linearly polarized antennas in their ability to maintain a relatively constant reception, regardless of alignment. This favors applications for transmitting data to moving targets, which is why satellite stations that are in constant motion make use of CP antennas.  

Design Tools for Dipole Antennas

Proper polarization is crucial to antenna’s data transfer performance. Dipole antenna polarization techniques are the basis for more complex antenna designs. Tools like Cadence AWR software provide the functionality to design, analyze, simulate and optimize RF antennas. The Cadence AWR Design Environment platform provides RF/microwave engineers with integrated technologies to create and simulate antennas that address all aspects of RF behavior for optimal and reliable results for first-pass success.

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