Sleeve dipole antenna for Meshtastic at 868MHz
Sleeve dipole antenna for Meshtastic operation at 868MHz, started as proof of concept design, gone through 3D modeling and optimization and final measurements on a prototype built.
![Final prototype](/img/2024/03/868MHz_Dipole_Final.jpg)
Theory #
Concept, initial design and simulation in CST.
![3D model.](/img/2024/03/868MHz_Dipole_Sim_3D.png)
![3D Gain pattern.](/img/2024/03/868MHz_Dipole_Gain_3D.png)
![Polar pattern.](/img/2024/03/868MHz_Dipole_Sim_1D.png)
![S1 return loss.](/img/2024/03/868MHz_Dipole_Sim_S1.png)
Reality #
Final build dimensions
- Sleeve length: 79 mm
- Sleeve outer diameter: 15 mm
- Sleeve inner diameter: 13 mm
- Sleeve material: Copper
- Semi-Rigid Coax type: UT-141C / SR141CUTP
- Semi-Rigid outer diameter: 3.6 mm
- Semi-Rigid conductor diameter: 0.92 mm
- Semi-Rigid total length: 249 mm
- Radiator length: 78 mm
- Distance feed socket collar to sleeve: 92mm
- Feed socked: SMA type flange mount for UT-141C
- Protection pipe outer diameter: 25 mm
- Protection pipe inner diameter: 23 mm
- Protection pipe length: 260 mm
- Protection pipe material: PCV
![Final build.](/img/2024/03/868MHz_Dipole_Build.jpg)
![Semi-Rigid coax feed with flange type SMA socket for UT-141C coax.](/img/2024/03/868MHz_Dipole_Feed1.jpg)
![Radiator as part of the coax. A 3mm brass flange is used to fix and solder the coax inside the sleeve pipe.](/img/2024/03/868MHz_Dipole_Radiator.jpg)
![4mm foam spacer keeps the dipole centered inside the protection pipe.](/img/2024/03/868MHz_Dipole_Spacer.jpg)
![Dipole inside the protection pipe.](/img/2024/03/868MHz_Dipole_Inside.jpg)
![SMA socket feed.](/img/2024/03/868MHz_Dipole_Feed2.jpg)
Impedance measurement results #
![Tuned to -27dB @ 869 MHz inside protection pipe.](/img/2024/03/868MHz_Dipole_Tuned.jpg)
![Detuned to -24dB @ 876 MHz when protection pipe is removed.](/img/2024/03/868MHz_Dipole_Detuned.jpg)
👈 Home