Because the signal travels through air (or a vacuum) inside the metal guide rather than through a resistive wire, the energy loss is negligible compared to transmission lines. This makes them ideal for applications where signal integrity is critical, such as:
| Use Waveguide Antennas when... | Avoid if... | |--------------------------------|--------------| | Power > 100 W CW | Low cost is critical | | Frequency > 10 GHz | Size/weight must be minimal | | Low loss required (< 0.5 dB) | Integration with planar circuits | | High beam purity needed | Broadband > 20% bandwidth | waveguide antennas
[ G = \frac4\pi A\lambda^2 \eta_a ] where (A) = aperture area, (\eta_a) ≈ 0.5–0.7 for typical horns. Because the signal travels through air (or a