What is the difference between a circularly polarized and a linearly polarized antenna?
Polarization Selection
The choice between linear and circular polarization depends on the propagation environment and system requirements. Linear polarization is the default for most terrestrial systems because it is simpler and avoids the 3 dB loss that occurs when a circularly polarized signal is received by a linearly polarized antenna (or vice versa).
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
Frequently Asked Questions
How do I generate circular polarization?
Method 1: dual-feed with 90° phase shift (two orthogonal feeds with a 90° hybrid coupler). Method 2: single-feed with geometric perturbation (truncated corners on a square patch, or slightly elliptic patch). Method 3: sequential rotation of linearly polarized elements in an array (each element rotated 90° with 90° feed phase offset).
What axial ratio is acceptable?
AR < 1 dB: excellent circular polarization. AR < 3 dB: acceptable for most applications. AR = 3 dB: the polarization is between circular and linear (45° elliptical). AR > 6 dB: essentially linear polarization. Higher AR increases the sensitivity to orientation mismatch.
Does circular polarization affect gain?
No. The antenna gain is the same regardless of polarization type. However, a circularly polarized antenna receives only half the power from a linearly polarized signal (or an unpolarized source), which appears as a 3 dB loss in the link budget. Between two matched circularly polarized antennas: no loss.