Current flows through a closed conductor whose perimeter is close to one wavelength. Current distribution and radiation pattern depend on geometry, height and feed position.
Antennas · F1SYH
Delta Loop
The Delta Loop is a triangular full-wave loop. It may provide horizontal or vertical polarization depending on the feed-point position.
HF
1 λ
Boucle fermée
Operating principle
Main characteristics
Typical gain
≈ 2 à 4 dBi
Impedance
≈ 100 à 130 Ω selon alimentation
Polarization
Horizontale ou verticale
Difficulty
Intermédiaire
Dimensions and design
A common starting perimeter is approximately 300 to 306 divided by frequency in MHz. Each side of an equilateral triangle is roughly one third of the perimeter.
Construction and tuning
Step 1
Calculate a perimeter slightly longer than one wavelength.
Step 2
Install three strong insulators.
Step 3
Select the feed point according to the required polarization.
Step 4
Use a matching system appropriate to the measured impedance.
Step 5
Tune the loop in its final position.
Advantages
- Closed loop often less sensitive to some local noise.
- Good efficiency with low-resistance conductor.
- Polarization selected through feed position.
- Only three main support points are required.
Limitations
- Large perimeter on lower bands.
- Feed impedance is rarely exactly 50 Ω.
- Pattern strongly affected by installation height.
- Multiband operation is more complex.
History and origin
Full-wave loops have been used since the early years of radio. The triangular form became popular because it requires only three support points.
Safety
High RF voltage may occur at parts of the loop. Keep the wire and insulators out of reach.