The sleeve acts as the second dipole leg and helps isolate the feed line from the main radiation.
Antennas · F1SYH
Sleeve Dipole
A Sleeve Dipole is a vertical dipole whose lower half is formed by a conductive sleeve surrounding the coaxial feed line.
VHF
UHF
Sans radians
Operating principle
Main characteristics
Typical gain
≈ 2,15 dBi
Impedance
Proche de 50 à 75 Ω
Polarization
Verticale
Difficulty
Intermédiaire
Dimensions and design
Upper radiator and sleeve are each near one quarter wavelength, corrected for diameter and surroundings.
Construction and tuning
Step 1
Cut the upper radiator.
Step 2
Build a conductive sleeve.
Step 3
Insulate the sleeve from the coax.
Step 4
Connect the sleeve to the shield at the feed point.
Step 5
Measure and tune both parts.
Advantages
- No horizontal radials.
- In-line coaxial feed.
- Good vertical symmetry.
- Compact construction.
Limitations
- Accurate mechanical dimensions.
- Sleeve construction can be difficult.
- Some common-mode current may remain.
- Bandwidth depends on diameter.
History and origin
Sleeve antennas were developed to create compact coaxially fed vertical dipoles.
Safety
Weatherproof the sleeve while allowing moisture drainage.