AR
Axial Ratio
The ratio of the major to minor axes of the polarization ellipse, expressed in dB, describing how close a circularly polarized wave is to perfect circular polarization
Understanding Axial Ratio
An axial ratio of 0 dB indicates perfect circular polarization, while an infinite axial ratio indicates linear polarization. Practical circularly polarized antennas achieve axial ratios of 1-3 dB across their operating bandwidth.
| Antenna Type | Gain (dBi) | Beamwidth | Bandwidth |
|---|---|---|---|
| Dipole | 2.1 | 360° (H) | Moderate (~10%) |
| Patch | 5-8 | 60-90° | Narrow (2-5%) |
| Horn | 10-25 | 10-60° | Wide (>50%) |
| Parabolic | 25-45 | 1-10° | Wide |
Axial ratio varies with frequency, observation angle, and antenna design. It is measured by rotating a linearly polarized probe antenna and recording the maximum and minimum received signal levels.
Common Questions
Frequently Asked Questions
What is a good axial ratio?
An axial ratio below 3 dB is generally considered acceptable for circularly polarized systems, with precision applications requiring below 1 dB.
How does axial ratio affect system performance?
Poor axial ratio causes polarization mismatch loss when communicating with a circularly polarized counterpart, reducing link margin.
See Also