High gain omnidirectional LoRa 868mhz antenna

This antenna design took me a while to get right, but it tunes up beautifully on a 3 half wave stack, according to my litevna64.

Using the dielectric spacer you can create a simple half wave dipole, or you can stack the elements with the delay coils to make a high gain antenna. The three element stack pictured should be somewhere around 5.8dbi.

Materials required are:

ASA filament. ASA has a low dielectric constant, and any lengths quoted in this design are specifically designed to work with ASA on a 25% infill with 4 outer walls.

4mm x 1mm brass tubing.

10mm x 1mm brass tubing.

Rg316 coax.

some super glue, and some acetone.

N-type male UHF plugs and a crimper, and finally some soldering equipment.

The sleeve: measurements are 74mm for a stacked dipole or 75 for a simple dipole. Two of the small spacers must be printed to space the coax from touching the inside of the sleeve. One sited half way down the length of the 10mm tube, one at the end where the coax leaves the tube. the elements are bonded in place with a small amount of superglue. Take care as the CA glue can throw the tuning off if too much is used.

The first quarter wave element is 73mm for the stacked dipole, or 76mm for a simple dipole, as the delay coils cause dielectric loading and slow the velocity factor. 

Andrew McNeil has very good info on how to solder a sleeve dipole type antenna, I have included a link to the timestamp in this video here: 

My model depends on a 2mm gap between the sleeve element and the first quarter wave section, with the dielectric still intact.

Print as many radome sections and the guy section as you need, ie; 3 sections for the 5.8 version. If building the 5.8dbi version, you would print two delay coils, one right handed and one left handed. The phasing is achieved by cutting a piece of rg316 to 127mm, which is one half wavelength, plus 6mm. 3mm is exposed at each end and coiled round and soldered to the centre of the opening on the delay coil form. One coil must turn clockwise, and one anticlockwise for the antenna to work. I wrap the coils with a cutting of 18650 pvc battery wrap to keep them in place, it is fiddly, so I used a small vice to hold coax in position. The radome parts are solvent welded together using asa slurry, and the whole ting was sprayed with, or painted several times with acetone to weather proof and help structural integrity.

The bottom connector is designed to fit very tightly over a male N-type UHF connector, and is fitted over the coax before crimping the fitting. It is then epoxied in place and the whole assembly is slurried together.